Femur and Stifle Joint

Editor’s Note – The reader is encouraged to review other sections of this text regarding more recent options for the repair of femoral fractures: Chapter 50 – Interlocking Nailing; Chapter 51 – SOP Locking Plates; Chapter 52 – Plate-Rod Fixation; and Chapter 53 – Hybrid External Skeletal Fixation.

Fractures of the Femoral Head and Neck

Pelvic limb lameness with vehicular trauma often is caused by a fracture of the acetabulum or proximal femur. In the immature animal, fracture through the physis of the femoral head is encountered most commonly. This fracture is due to the weak area at the zone of hypertrophy at the growth plate. Other, less common fractures involve the base of the neck or the trochanteric region (Figure 61-1).

When examination of a dog less than 12 months of age reveals pain on manipulation of the hip joint, one should suspect either a fracture of the proximal femur or acetabulum or a coxofemoral luxation. The exact diagnosis requires radiographic evaluation including ventrodorsal (normal hip dysplasia position) and lateral views. Occasionally, a “frog leg” view assists in the diagnosis. This view requires the animal to be in dorsal recumbency with the pelvic limbs held in a flexed and slightly abducted position. An awake animal is more likely to cooperate for this view than for the normal ventrodorsal view.
 

Anatomic Considerations

In the extremely young animal, the proximal growth plate extends from the greater trochanter to the femoral head. As the animal matures, separation into a capital femoral growth plate and a greater trochanteric growth plate occurs. Investigators have estimated that the capital physeal growth plate contributes up to 25% of the femoral length, whereas the greater trochanteric physis contributes little to the length. The ligament of the femoral head, which extends from the femoral fovea to the acetabular fossa, provides significant support to the hip joint.

The vascular supply to the femoral head continues to be of concern to most veterinary surgeons. If precise, delicate surgical intervention with appropriate stabilization is practiced, few complications should be encountered. Important aspects of the vascular supply include the lateral and medial circumflex femoral arteries, which are branches of the femoral and deep femoral arteries. The lateral branch provides most of the supply to the femoral head and the dorsal aspect of the femoral neck. The medial branch supplies the ventral aspect of the joint capsule, and a branch of the caudal gluteal artery supplies a small portion of the dorsal aspect. Dorsal and ventral ascending branches from the lateral and medial circumflex femoral arteries anastomose and form a rich interosseous arch within the epiphysis. Metaphyseal branches of the lateral and medial circumflex vessels do not communicate with the epiphyseal branches in the immature animal. No evidence suggests that a blood supply enters the epiphysis from the ligament of the femoral head.

Presurgical Considerations

Avascular necrosis of the femoral head secondary to a fracture is not a significant problem if appropriate surgical treatment is followed. Most reports of repair list few cases of avascular necrosis. Although the femoral head completely loses its vascular supply at the time of the initial trauma, revascularization is rapid after stabilization. The time interval to surgery is important because more damage is sustained if the repair is delayed. Attempts by the animal to walk on the affected limb may damage the soft metaphyseal bone of the neck as it rubs on the acetabular rim. Loss of bone results in the inability to reduce and stabilize the fracture components correctly. The degree of damage is most often ascertained at the time of surgery. Occasionally, radiographic evaluation reveals the damage.

Surgical Approach

The craniolateral approach is most often recommended for femoral head and neck fractures because of the preservation of vascular supply. The dorsal approach, including greater trochanteric osteotomy, may be used if increased exposure is required, but it damages the branches of the lateral circumflex femoral artery. In addition, damage to the physis of the greater trochanter may lead to a valgus deformity in a young animal. Successful use of the dorsal approach has been reported, but research also shows that the vascular damage may not be significant.

In the craniolateral approach, the skin incision is curved in a cranial direction starting 3 to 4 cm proximal to the greater trochanter and extending distally to include the proximal one-quarter of the femoral shaft. An incision is made into the fascia lata just cranial to the greater trochanter and is extended to allow retraction of the biceps femoris muscle caudally and the fascia cranially. The muscular tensor fasciae latae is then dissected from the fascia of the vastus lateralis and the middle gluteal muscles. The gluteal muscles are retracted dorsally and the tensor fasciae latae cranially to allow visualization of the cranial aspect of the joint capsule. The joint capsule is incised perpendicular to the acetabular rim, extending to the origin of the vastus intermedius and lateralis. The exposure can be increased by performing a partial tenotomy of the deep gluteal muscle. If difficulty is encountered in visualization and reduction of the fracture, trochanteric osteotomy may be performed. With either approach, the location of the sciatic nerve should be noted.

Fixation Techniques

Capital Physeal Fractures

Reduction of a capital physeal fracture may be difficult. Handling of the femoral head with a retractor or bone-holding forceps should be minimized to lessen damage to the articular cartilage. One or several Kirschner wires are placed to stabilize the fracture after reduction. These pins are placed in retrograde fashion from the fracture site laterally or in a normograde manner from the lateral surface of the proximal femur (Figure 61-2A). After fracture reduction, the pins are seated in the femoral head.

If a lag screw is to be used, the gliding hole through the proximal femur may be drilled before reduction to ensure placement into the center of the neck. A small threaded hole is drilled into the femoral head before measuring and tapping the hole (Figure 61-2B). As the head is encountered, tapping becomes more difficult. Care is taken to ensure that the articular surface is not penetrated. A screw that is 2 to 4 mm shorter than the measured length should be used because of the shortening obtained during lag screw fixation (Figure 61-2C).

Use of measurements taken from the radiographs can help to ensure that implants of appropriate size are used. The articular surface should be inspected after implant placement to check for implant penetration. Areas not visualized may be inspected using a curved instrument to check for any irregularities. Any articular damage fills with fibrocartilage, which permits satisfactory recovery of most animals.

Interfragmentary compression alone should be adequate for most animals. Kirschner wires may be left in place to increase rotational stability if necessary. After the joint is flushed, the joint capsule is closed with a nonreactive suture material before anatomic closure of the other layers.

Other Articular Fractures

Occasionally, an avulsion fracture of the ligament of the femoral head occurs in association with a coxofem-oral luxation. Removal of this fragment and the ligament is recommended if surgical intervention is necessary for stabilization of the hip joint. Closed reduction of this type of coxofemoral luxation may result in degenerative joint disease because the interposed avulsed fragment produces cartilaginous damage.
 

Fractures involving the dorsal articular surface require stabilization to lessen degenerative joint disease. Femoral head and neck excision is an alternative if the articular cartilage is severely damaged or if reduction is too difficult. Fracture fragments involving the non-articular surfaces may be removed.

Extracapsular Fractures

Fractures through the base of the femoral neck are most often encountered in mature animals. Repair is performed as described previously for femoral head fractures (See Figure 61-2). Osteonecrosis is not a problem because of the extracapsular nature of the fracture. Fractures through the apophysis of the greater trochanter sometimes occur in association with a capital physis fracture. Careful evaluation of the radiographs may be necessary because of the superimposition of the greater trochanter on the femoral shaft. Stabilization is performed through a craniolateral approach with retraction of the greater trochanter. After stabilization of the femoral head with a Kirschner wire and lag screw, the greater trochanter is reattached by tension band fixation (Figure 61-3). Care is necessary to ensure complete reduction and realignment before stabilization.
 

Proximal Femoral Fractures

Greater Trochanteric Fractures

Fractures of the greater trochanter are commonly associated with fractures involving the femoral head in young animals and with comminuted proximal femoral fractures in mature animals. The traction physis associated with the greater trochanter is believed to provide no significant contribution to longitudinal bone growth.

Repair of a greater trochanteric fracture is necessary because the distraction forces applied by the gluteal muscles do not allow for normal union. Approach is made just cranial to the greater trochanter, allowing separation of the fascia lata from the biceps femoris muscle. Incision into the origin of the vastus lateralis may be necessary to allow visualization of the fracture.

Of the repair methods available, tension band fixation is probably the easiest and most satisfactory. This method converts distracting forces into compressive forces at the fracture site. Two Kirschner wires are inserted at right angles to the fracture line (See Figure 61-3). Care is taken to gain maximum purchase prox-imally in the greater trochanter and to ensure purchase into the medial cortex at or below the lesser trochanter. Orthopedic wire (18 to 20 gauge) is placed through a hole drilled in a craniocaudal direction 3 to 4 cm distal to the fracture line. This wire is placed around the proximal ends of the Kirschner wires in a figure-of-eight configuration and then is tightened to counteract the distracting forces of the gluteal muscles.

Intertrochanteric and Subtrochanteric Fractures

Either stack-pinning or plate fixation can be used to neutralize both bending and rotational forces acting on the intertrochanteric and subtrochanteric fractures. Approach to the area requires transection of the origins of both the vastus lateralis and intermedius muscles. Pin placement should originate from the proximal point of the greater trochanter and should extend distally, gaining maximal purchase in the femur. A common mistake is to exit the pins within 3 to 4 cm of the fracture line. This technique provides less than satisfactory stabilization. A figure-of-eight wire may be placed in association with the pins to provide increased rotational stability for subtrochanteric fractures (Figure 61-4).
 

Application of a bone plate to the lateral surface is indicated in large dog breeds for repair of these fractures. Careful contouring of the bone plate allows for the placement of at least two screws in the short proximal segment in most cases. One screw (usually cancellous) should extend into the femoral neck for increased purchase, and at least four screws should be placed in the distal segment (Figure 61-5).

Comminuted Fractures

Highly comminuted fractures of the proximal femur require aggressive fixation, usually with a bone plate and lag screws. Care must be taken to ensure adequate stabilization of the calcar region (lesser trochanter) because it is an important medial buttress. Early fixation failure can be expected if stabilization is inadequate. The fracture segments are reduced and stabilized with both lag screws and Kirschner wires. The plate is then contoured and is attached to the proximal segment with one screw placed through the second hole into the femoral neck and head. The proximal screw is placed into the greater trochanter. Use of a dynamic compression plate permits angling of the screws up to 30° from center. The plate acts as a neutralization or buttress plate for this type of fracture. The plate should be attached to the distal segment with at least three screws penetrating six cortices (Figure 61-6A). A cancellous bone graft should be placed into any areas that lack cortical bone.

Intramedullary fixation of comminuted proximal fractures is more applicable to small and medium-sized dogs than to large ones, especially if the fracture has only three or four segments. By use of hemicerclage wire and transcortical pins, a comminuted fracture can be reduced to a two-piece fracture, which then is fixed by normograde or retrograde stack-pinning (Figure 61-6B). Care must be taken to ensure that the transcortical pins do not enter to the medullary canal to allow for the introduction of a maximum number of stack pins. Lag screws are more difficult to incorporate into fractures stabilized with intramedullary pins.
 

Diaphyseal Fractures of the Femur

Transverse Fractures

Transverse diaphyseal fractures are most commonly repaired with one intramedullary pin. Although success is often reported with this method, so too is failure, mainly because of the lack of rotational stability provided by one pin. This method is most likely to succeed with immature animals in which healing is rapid and with small to medium-sized adult animals in which the single pin tends to fill a significant part of the medullary canal. Failure occurs most often in large dogs, when a small pin that does not fill a significant portion of the canal is used. Use of a Kirschner-Ehmer external fixation device (two-pin half-pin splint) in association with the intramedullary pin increases rotational stability.

Stack-pinning of transverse fracture is an easy procedure that results in few complications in most cases. The curved skin incision should be just cranial to the femoral shaft. The biceps femoris muscle belly is encountered if the incision is directly over the shaft; incision through this muscle belly is not the approach of choice. After approaching the fracture by incising the fascia lata cranial to the biceps muscle, the vastus lateralis muscle is retracted cranially, and the biceps femoris muscle is retracted caudally to allow visualization of the fracture site. Minimal stripping of the periosteum is done to check for any fissure lines in the fracture segments. The pins are placed in retrograde fashion, exiting proximally through the trochanteric fossa (Figure 61-7A). The surgeon must extend the animal’s hip joint and adduct the femur when passing the pin proximally to avoid the sciatic nerve as it passes over the greater trochanteric notch. All pins are placed proximally before reduction of the fracture segment. Enough pins are used to fill the medullary canal at its narrowest point. The pins are then driven distally into cortical bone. Because of the cranial curvature of the femoral shaft, the pins usually seat distally in the cranial metaphyseal area near the proximal end of the trochlea (Figure 61-7B). Overreduction of the distal segment allows seating of the pins further distally, but usually this leads to malalignment and instability. Because the feline femur has less curvature, the pins can be seated farther distally in the intercondylar region in cats (Figure 61-7C).
 

Several methods are available to add rotational support to pin fixation of transverse diaphyseal fractures. A two-pin half-pin Kirschner-Ehmer splint in association with a single intramedullary pin is one method. Use of hemicerclage or figure-of-eight orthopedic wire also can increase rotational stability. The figure-of-eight wire can be passed through holes drilled proximal and distal to the fracture line, or two can be placed around transverse Kirschner wires and tightened to form a cruciate pattern (Figure 61-8). The distance from the holes or Kirschner wires to the fracture should be at least equal to the width of the femur at the fracture site.
 

Application of a bone plate to the lateral or cranial surface is indicated for stabilization of transverse fractures in large breeds or in any animal requiring rigid internal fixation. Compression of the fracture line allows for rapid primary bone healing. Screw fixation in at least six cortices above and below the fracture should be obtained.

Oblique and Spiral Fractures

Oblique and spiral fractures are most successfully repaired with intramedullary pins, with additional stability provided by transcortical pins and hemicerclage wire or by full-cerclage orthopedic wire. The fracture is first stabilized with intramedullary pins, as discussed in the section on transverse fractures. Wire can be placed around transcortical pins in a figure-of-eight pattern to provide increased rotational stability (Figure 61-9A). Alternatively, full-cerclage wires can be used (Figure 61-9B).
 

Although investigators initially thought that full-cerclage wires interfered with the new periosteal blood supply needed for fracture healing, more recent studies have shown that this may not occur. Problems only arise when the wire is improperly applied. Common mistakes include inappropriate wire diameter (18 to 20 gauge is appropriate for most animals), placement too close to the fracture ends (a minimum of 5 mm is appropriate), and use of insufficient number of wires (a minimum of two wires placed 1 cm apart is appropriate). As with any technique, failure is more likely to occur when wires are applied in less than ideal fashion. Most complications occur when the wire slips into the fracture site, producing a nonunion.

Comminuted Fractures

Reduction of the fracture segments into two main segments before primary fixation with intramedullary pins provides successful stabilization of most comminuted fractures. Pin fixation is less effective with highly comminuted fractures because of the inability to neutralize compressive forces. Collapse of the fracture is more likely in these cases. Midshaft fractures with one or two butterfly fragments can be stabilized with techniques similar to those discussed in the section on oblique fractures.

Application of a bone plate to the lateral or cranial surface as a neutralization plate (no compression at the fracture site) or a buttress plate (a cortical gap is present) can stabilize most comminuted diaphyseal fractures. The large fragments are attached with Kirschner wires, orthopedic wire, or lag screws before plate attachment. Care must be taken to ensure that these implants do not interfere with placement of the plate. If possible, the plate is positioned to allow for placement of screws in all holes. Occasionally, the number of fissure lines necessitates leaving one or more holes vacant. This situation is to be avoided, especially with a buttress plate, because fatigue failure is more likely to occur at this site. Use of a leg-lengthening plate that lacks holes in the central one-third of the plate may be indicated in these cases (Figure 61-10). Contouring of the plate is made easier if a radiograph of the contralateral femur is available for comparison. By using the greater trochanter, stifle, and linea aspera (the caudal rough surface where the adductor magnus muscle attaches) as reference points, normal anatomic alignment can be obtained in these comminuted fractures.
 

Occasionally, highly comminuted diaphyseal fractures cannot be pieced together with pins or lag screws. Both removing these fragments and leaving them in place while spanning the gap with a bone plate have been reported. The gap is filled with autogenous cancellous bone to stimulate healing. Leg-lengthening plates are ideally suited, because they allow the closer placement of screws in the proximal and distal fragments without leaving several vacant holes over the gap. Success has been reported with the use of dynamic or standard plates with vacant holes. The plate used must be as large as possible in such cases.

Distal Femoral Fractures

Metaphyseal (Supracondylar) Fractures

Although encountered infrequently, distal metaphyseal fractures provide a challenge for repair. Fortunately, the rich blood supply to this trabecular bone promotes rapid bone healing in most cases. This type of fracture occurs most often in mature animals and is often associated with comminution.

The approach to this region is an extension of the approach used for stifle arthrotomy. The incision in the fascia lata cranial to the biceps femoris muscle is extended distally to include the lateral fascia of the stifle. Incision into the joint capsule is extended proximally, lateral to the vastus lateralis muscle to allow medial retraction of the quadriceps group and the patella. A large muscular branch of the popliteal artery must be ligated as this incision is made. Flexion of the stifle with medial retraction of the muscles allows visualization of the medial surface of the distal femur.

Bone plating of the lateral surface is recommended for stabilization of metaphyseal fractures in larger dogs, especially if comminution is present. Use of cancellous screws in the distal segment increases holding power, which is often needed because of the short length of the distal segment. Intramedullary pinning is more appropriate for stabilization in small and medium-sized animals (Figure 61-11). The techniques discussed in the following sections on physeal and epiphyseal fractures are used.
 

Physeal Fractures

Most distal physeal fractures occur in immature animals (4 to 12 months old) because the zone of hypertrophy is structurally much weaker than the surrounding bone, tendons, and ligaments. The most common fractures are Salter I (involvement of the growth plate only) and Salter II (involvement of the growth plate and metaphysis), which fortunately do not involve the germinative or growth layer of the physis. Few complications associated with premature closure of the physis have been noted. Rapid healing can be expected because of the adjacent rich blood supply.

External support alone infrequently allows for normal reduction and bone union and subsequent normal functional use. As with any joint, immobilization of the stifle may lead to adhesion formation and loss of joint motion. Most distal physeal fractures, however, require internal fixation by some type of pinning procedure.

Antegrade introduction of a single Steinmann pin from the trochlea just cranial to the origin of the cruciate ligaments provides maximum purchase in the small distal segment. Reduction of the fracture before pin placement is ideal. Careful handling of the distal segment is important because of the softness of the bone and the presence of articular cartilage. Over-zealous use of bone forceps may result in significant damage. Placement of the pin in the distal segment before reduction, using the pin as a lever, is possible if done carefully (Figure 61-12A). The pin may pull out of the bone, resulting in enlargement of the hole, if the veterinary surgeon is not careful. The pin is driven proximally, exiting through the trochanteric fossa (Figure 61-12B). After the distal end is cut, the pin is retracted proximally until the blunt end is seated just below the cartilaginous surface of the trochlea (Figure 61-12C). Stabilization of these fractures is aided by the interlocking of metaphyseal protuberances in epiphyseal fossae, providing rotational stability.
 

Retrograde placement of the pin avoids damage to the articular cartilage, but it may not always provide adequate purchase in the distal segment. If this method is used, the pin is placed along the caudal aspect of the femur to allow for maximum purchase in the distal segment.

Other methods of fixation include double pinning, modified Rush pinning, and cross-pinning (See Figure 61-11). With all methods, the pins are started just lateral and medial to the trochlear ridges and cranial to the collateral ligaments (Figure 61-13). Larger, less flexible pins are used with cross-pinning fixation. The pins must cross above the fracture line. Exiting of the pins too close to the fracture may lead to failure with weightbearing. Placement of the pins in retrograde fashion results in less than maximum purchase in the distal segment.
 

Epiphyseal Fractures

Excellent radiographic technique is required to demonstrate distal epiphyseal fractures because displacement is often minimal. If not stabilized, these fractures result in degenerative joint disease because of the articular involvement.

The medial condyle is most often involved. Exploration of the joint is required to remove any cartilage and bone fragments and to inspect the menisci and cruciate ligaments. Lag screw fixation, the recommended repair technique, achieves accurate realignment of the articular surfaces and compresses the fracture. In small dogs and cats, multiple Kirschner wires or a single wire and lag screw can provide good fixation (Figure 61-14).
 

Postoperative Management and Complications

Physical therapy is an important part of the total treatment regimen in all animals with femoral fractures.

The soft tissue structures around a fracture also sustain trauma, and the bruised and swollen muscles require appropriate therapy after fracture fixation.

Fractures of the Femoral Head and Neck

All animals require strict confinement for the first 4 to 6 weeks after repair of a femoral head and neck fracture. The owner should be instructed on the method of physical therapy of the hip joint to help to restore early limb function.

Radiographic evaluation at 4 to 6 weeks usually reveals thinning of the femoral neck. In most cases, this thinning is normal, but if pronounced lameness is still apparent at this time, these findings suggest avascular necrosis and possible failure of the fixation. If the animal is recovering use of the limb, radiographic evaluation usually is delayed until 6 to 8 weeks after stabilization. Radiographic evaluation after complete healing has occurred usually reveals a thickening of the femoral neck and some evidence of degenerative joint disease. Removal of the implants is not recommended unless complications occur.

Other Femoral Fractures

Physical therapy should be instituted within 2 to 3 days of the surgical procedure. Gentle flexion and extension of the hip and stifle joints for 3 to 5 minutes, a minimum of three times daily, assist in the early return of limb function. This is especially important in an immature dog with a fractured femur, which is prone to quadriceps muscle contraction and tie-down. If this syndrome is allowed to progress to the stage of severe stifle hyperextension, the prognosis for return of limb function is poor. Walking the animal on a leash during the first 4 weeks postoperatively also encourages use of the limb and a return of the normal range of motion in all joints.

Pin migration into the stifle results in damage to the trochlear groove and the patella and, ultimately, in degenerative joint disease. Migration proximally may cause open wounds and possibly osteomyelitis. Sciatic nerve entrapment may result from pin migration or formation of fibrous tissue at the proximal end of adequately seated pins. Clinical signs include acute onset of lameness, pain in the hip region, and eventual knuckling of the paw and hypalgesia over the area of nerve distribution. Exploration and freeing of the nerve from the fibrous tissue are required to allow recovery; in addition, the pins should be shortened or removed if complete fracture healing has occurred. Return of normal limb function depends on the degree of nerve damage sustained in such cases.

Suggested Readings

Aron DN, et al. A review of reduction and internal fixation of proximal femoral fractures in the dog and man. J Am Anim Hosp Assoc 1979;15:455.

Daly WR. Femoral head and neck fractures in the dog and cat: a review of 115 cases. Vet Surg 1978;7:29.

Frey AJ, Olds R. A new technique for repair of comminuted diaphyseal fractures. Vet Surg 1981; 10:51.

Gambardella PC. Full cerclage wires for fixation of long bone fractures. Compend Contin Educ Pract Vet 1980,11:665.

Gilmore DR. Application of the lag screw. Compend Contin Educ Pract Vet 1983;5:217.

Grauer GF, Banks WJ, Ellison GW, et al. Incidence and mechanisms of distal femoral physeal fractures in the dog and cat. J Am Anim Hosp Assoc 1981; 17:579.

Hauptman J, Butler HC. Effect of osteotomy of the greater trochanter with tension band fixation on femoral conformation in beagle dogs. Vet Surg 1979;8:13.

Hulse DA, Abdelbaki YZ, Wilson J. Revascularization of femoral capital physeal fractures following surgical fixation. J Vet Or-thop 1981,2:50.

Hulse DA, et al. Use of the lag screw principle for stabilization of femoral neck and femoral capital epiphyseal fractures. J Am Anim Hosp Assoc 1974; 10:29.

Kaderly RE, Anderson WD, Anderson BG. Extraosseous vascular supply to the mature dog’s coxofemoral joint. Am J Vet Res 1982;43:1208.

Kagan KG. Multiple intramedullary pin fixation of the femur of dogs and cats. J Am Vet Med Assoc, 182:1251, 1983.

Milton JL, Home RD, Goldstein GM. Crosspinning: a simple technique fortreatmentofcertainmetaphysealandphysealfracturesofthelong bones. J Am Anim Hosp Assoc 1980; 16:891.

Milton JL, Newman ME. Fractures of the femur. In : Slatter DH, ed. Textbook of small animal surgery. Philadelphia: WB Saunders, 1985.

Nunamaker DM. Repair of femoral head and neck fractures by interfragmentary compression. J Am Vet Med Assoc 1973,162:569.

Renegar WR, Leeds EB, Olds RB. The use of the Kirschner-Ehmer splint in clinical orthopedics. Compend Contin Educ Pract Vet 1982,4:381.

Rhinelander FW, Wilson JW. The blood supply of developing mature and healing bone. In: Sumner-Smith G, ed. Bone in clinical orthopedics. Philadelphia: WB Saunders, 1982.

Rivera LA, Aldelbaki YZ, Hulse DA. Arterial supply to the canine hip joint. J Vet Orthop 1979; 1:20.

Shires PK, Hulse DA. Internal fixation of physeal fractures using the distal femur as an example. Compend Contin Educ Pract Vet 1980; 11:854.

Stone EA, Betts CW, Rowland GN. Effect of Rush pins on the distal femoral growth plate of young dogs. Am J Vet Res 1981 ;42:261.
 

Pathophysiology

The patella is a large sesamoid bone which is responsible for redirecting the forces generated from the contraction of the quadriceps muscle group to the patellar ligament and tibia. As such, it is under continuous tension during pelvic limb weight bearing. Fractures of the patella are uncommon and constitute less than 1% of all fractured bones in the small animal. It is thought that patellar fractures occur by one of two injury mechanisms: either through hard falls during which the animal lands on its feet, thus causing a sudden overload of tensile forces across the patella, or from direct impact such as vehicular trauma. The mechanism of the injury often dictates the mode of failure of the patella and subsequent fracture type. Patellar fractures can be transverse, longitudinal or comminuted with varying degrees of displacement. Overloading injuries from high falls typically fracture the patella in a transverse fashion whereas direct trauma from impacts can lead to comminuted fractures.

Acutely, patellar fractures result in a non-weight bearing lameness of the affected limb. Swelling and crepitus is palpable over the distal quadriceps tendon, patella and patellar ligament. Animals with patellar fractures are usually unable to extend the stifle for some time following the injury. If left untreated, organizing fibrous tissue will eventually form within the fracture allowing the animal to minimally bear weight on the limb, however the swelling on the cranial surface of the stifle will persist. Direct palpation of the fractures is not possible due to abundant inflammation of the overlying soft tissues. Definitive diagnosis of patellar fractures can be achieved with standard radiography. In addition to orthogonal views, oblique positioning can be useful in tangentially highlighting subtle fissure fractures. In addition, the appearance of non-displaced fractures can be enhanced by stressing the patella by flexing the stifle while taking the radiograph.

Treatment

There are three objectives for patellar fracture repair: 1) re-establish the function of the quadriceps mechanism, 2) anatomically reduce the articular chondral surface of the patella to minimize secondary osteoarthritis and 3) apply appropriate fixation to the fracture to optimize osseous union.

Surgical Repair

Prior to surgical reduction of the fracture, the stifle must be examined either arthroscopically or via arthrotomy for evaluation of the articular surface of the patella as well as for additional injury, including cruciate or meniscal damage. Arthrotomies can be completed either medially or laterally without risk of patellar vascular impairment as the patella possesses a complex interior vascular network instead of being supplied through a single nutrient vessel. Because of the large tensile forces constantly applied to the patella, most fractures are displaced to some degree. Repair strategies must be directed at countering the distracting pull of the quadriceps. For most transverse and some comminuted fractures, this can be accomplished with a variety of tension band configurations (Figure 61-15). In each case, the wire must be placed on the cranial, or tension surface, of the patella. Placement of the tension band on either the medial or lateral surface will result in malreduction of the fracture. The extensiveness of the repair is often dictated by the size of the animal and the complexity of the fracture. Non-displaced transverse fractures in medium to smaller-sized animals can be treated with single cerclage wires placed through the quadriceps tendon and patellar ligament (Figure 61-15A and B). Larger and less compliant animals will benefit from the addition of Kirschner wires and the application of the orthopedic wire in a pin and tension band fashion (Figure 61-15C-F). Passage of orthopedic wire through the quadriceps tendon and patellar tendon should be kept as close to the patella as possible. This can most easily be accomplished by placing a hypodermic needle just proximal and distal to the patella through which the orthopedic wire can be passed. The tension band should be tightened sufficiently to provide compression across the fracture lines.

To combat individual bone segment rotation around a single wire (Figure 61-15C), the Kirschner wires can be applied in pairs in both parallel and crossed fashion. Kirschner wires can also be used to align separate fragments encountered with comminuted fractures (Figure 61-15E). When applying Kirschner wires to the patella, pre-drilling is necessary as the bone is very dense. Retrograde application allows greater placement accuracy. Fragment reduction is most optimally accomplished with the leg in extension and a bone holding forceps placed longitudinally across the patella. Although uncommon, pure longitudinal patellar fractures can occur and can be treated with modifications of the aforementioned techniques in addition to lag screwing.

Post-operative care for a standard repair includes keeping the limb immobilized and in extension within a soft padded-bandage for several days following surgery. The animal should have restricted activity for the ensuing 4 to 6 weeks to minimize repetitive cyclic tensile load on the repair. Gentle physical therapy, such as passive range of motion, is appropriate to help combat severe quadriceps muscle atrophy during the post-operative convalescent period. Additional radiographs should be completed to document healing and to examine for implant migration which is not uncommon. Implants can be removed following radiographic union if they are the source of pain or are unstable.
 

Patellectomy

If small chondral or osteochondral fragments are not able to be incorporated into the repair, or appear unstable following fracture reduction, they may be removed. In certain cases, there exist highly comminuted, irreparable fractures of the distal apical third of the patella only. In this situation, the proximal patella is salvaged while removing the distal fragments constituting a partial patellectomy. This is completed from the articular surface of the patella with ronguers or forceps and scalpel. Because this may weaken the junction of the patellar ligament and potentially lengthen the quadriceps mechanism, surgical reinforcement and imbrication of the ligament may be indicated with 4-0 stainless steel or heavy gauge non-absorbable suture following partial distal patellectomy (Figure 61-16). Occasionally, partial patellectomy will result in the surgical transection of the patellar ligament which will require primary repair. Patellar ligament repair techniques can be reinforced with the placement of a temporary patello-tibial cerclage wire which protects the ligament from tensile forces during healing (Figure 61-17).

For large, highly comminuted and irreparable patellar fractures, total patellectomy can be completed. However with the propagation of degenerative joint disease and altered quadriceps function, the prognosis for return of normal function of the limb is very poor. Therefore, preservation and, if possible, reconstruction of the larger fragments of the fractured patella is advantageous over total patellectomy.
 

Non-surgical Treatment

If financial constraints prohibit surgical treatment of patellar fractures, conservative management may be considered. Non-surgical care consists of keeping the limb immobilized in extension for 4 to 6 weeks. Complications associated with this technique include advanced osteoarthritis associated with the non-anatomic reduction of chondral fractures on the articular surface of the patella and prolonged joint immobilization. In addition, non-unions and delayed unions may occur with the development of fibrous interpositional tissue within the fractures. These complications necessitate the need for diligent and aggressive physical therapy following the period of immobilization. The prognosis for non-surgically treated displaced patellar fractures is guarded.

Suggested Readings

Arnoczky SP, Tarvin GB: Surgery of the stifle: the patella. Compend Contin Educ Pract Vet 2:200, 1980.

Betts CW, Walker M: Lag screw fixation of a patellar fracture. J Small Anim Pract. 16:21, 1975.

Howard PE, Wilson JW, Robbins TA et al.: Normal blood supply of the canine patella. Am J Vet Res 47:401, 1986.

McLaughlin R: Intra-articular stifle fractures and arthrodesis. Vet Clin North Am Small Anim Pract 23:877, 1993.

Piermattei DL, Flo GL: Fractures of the Femur and Patella In Brinker WO, Piermattei DL, Flo GL, eds.: Handbook of Small Animal Orthopedics and Fracture Repair, Third edition. Philadelphia: W.B. Saunders, 1997, p 469.
 

Introduction

Problems involving the patella are frequent causes of lameness in small animals. The most common problem is patellar luxation. Medial luxation is the most frequent type occurring over 75% of the time and is the most prevalent type in small dogs and cats. Lateral luxation occurs most frequently in larger breed dogs and is much less common than medial luxation.¹ Although traumatic patellar luxations may occur, in the authors’ experience they are very rare. There is strong evidence that the majority of patellar luxations are heritable in nature² and appropriate recommendations such as neutering/OHE and a removal of affected individuals from breeding stock should be part of the treatment regimen encouraged by the Veterinarian.

Functional Anatomy

The patella can be described as the ossified portion of the quadriceps tendon. Although the patella itself is a passive structure in the body, it plays an important role in a dynamic system referred to as the extensor mechanism of the stifle. Movement of the patella is under direct influence of this mechanism, and knowledge of the mechanics of this system is essential in the treatment of patellar dysfunctions.

The primary extensor group of muscles of the stifle is the quadriceps femoris. Three of the four muscles in this group, the vastus lateralis, the vastus medialis, and vastus intermedius, originate from the proximal femur, whereas the fourth, the rectus femoris, originates from the ilium; all four converge to form the quadriceps tendon.³ This tendon primarily attaches to the proximal portion of the patella; however, a thin portion crosses over the cranial surface of the patella to blend with the patellar ligament.

The patellar ligament is a strong band of fibrous connective tissue that courses from the patella to the tibial tuberosity. When the quadriceps muscle group contracts, the resulting force pulls on the patella, the patellar ligament, and the tibial tuberosity, causing extension of the stifle. During this motion, the patella rides in the trochlear groove. A cross section of the patella reveals a convex articular surface. The corresponding trochlear groove is concave and therefore allows for an intimate articulation between the femur and patella. On both sides of the patella and attached to the joint capsule are the parapatellar fibrocartilages. These structures articulate with the trochlear ridges and increase the surface area and thus disperse the force of the quadriceps muscles.

Normal alignment of the extensor mechanism is necessary for stability of the stifle joint. Dysfunction of this mechanism results in abnormal joint mechanics and joint instability.⁵ Such instability not only causes degenerative joint disease but also places increased stress on other supporting structures, such as the cranial cruciate ligament, the collateral ligaments, and the menisci.³

Pathogenesis and Diagnosis

Medial patellar luxation is one of the most common patellar problems presented to the veterinary practitioner.^1,5-7 This disorder can be either congenital or traumatic. The congenital form, which is more common, usually is observed in small breed dogs^1,8 and may cause minimal to severe gait abnormalities. The clinical picture often is one of an obese animal with varus (bow-legged) deformity of the rear limbs. The animal often crouches, owing to the inability to extend the stifles fully, with its toes pointed inward. Often, the owner describes a skipping or hopping type of gait in which the animal skips one or more steps on the involved limb. This gait, which is generally transient, is caused by the patella’s riding up and over the medial trochlear ridge and being “trapped” on the medial aspect of the joint. Bilateral limb involvement is not unusual. Medial patellar luxations, unless traumatic, rarely cause acute lameness. Although medial patellar luxations sometimes coexist with acute lameness, these luxations usually are chronic; thus, other causes of acute lameness should be pursued. Those dogs with a history of patellar luxation and a sudden onset of pain in the stifle should be examined carefully to rule out cruciate ligament injury.

The incidence of medial patellar luxations in cats is much lower than that of dogs. Abyssinians and Devon Rex breeds may be predisposed to congenital medial patellar luxations.¹ The authors find that many of the same diagnostic and treatment protocols can be applied to cats suffering from medial patellar luxations.

Various causes of congenital medial patellar luxation have been proposed.^7,9-11 Its pathogenesis, however, probably involves a combination of underlying bony abnormalities, any of which may be a cause or an effect of the disorder. Any of the following abnormalities can result in congenital medial patellar luxation, coxa vara, medial displacement of the quadriceps tendon, external femoral torsion, medial deviation of the distal femur, shallow trochlear groove, internal rotation and medial deviation of the proximal tibia.^7,11 Some degree of each deformity may be present in all cases.

Diagnosis is primarily based on palpation. After observing the patient ambulate and assessing conformation, a thorough general and orthopedic evaluation of the patient is performed. To evaluate the patellar mechanism, the authors prefer to have the pet stand on the ground and approach it from the rear. Both stifles are palpated to assess the position of the patella. With one hand over the patella, the other hand gently flexes and extends the stifle. Internal and external rotation of the tibia can also be incorporated during this maneuver. Spontaneous luxation may occur. If no luxation occurs, gentle medial and then lateral pressure is applied to the patella to determine if it will luxate. In the normal stifle the patella may ride up on the trochlear ridge but should not easily luxate. In immature or young patients, some degree of joint laxity is normal. In the young patient, if the patella remains in place but can be luxated only with digital pressure, the authors recommend to follow that patient. In our experience, many of these patients will stabilize once mature. The surgeon should not forget to assess other structures of the stifle such as the cranial cruciate ligament for integrity.

Radiographs to include the hips and stifles are useful to assess for concurrent problems such as aseptic necrosis of the femoral head in young small breed dogs and hip dysplasia in larger breeds. They are also useful in assessing the amount of coxa vara, coxa valga, and femoral and tibial torsion.

Repair of Patellar Luxations

Because the presenting symptoms and signs of medial patellar luxation vary in severity, each patient should be handled individually. Numerous methods exist for the repair of medial patellar luxation,^5-7,12-16 and a single technique may not work or may not be indicated for all degrees of medial patellar luxations. The following discussion presents our treatment approach, which is based on the grading system of Putnam.¹¹

Grade I Luxations

In a grade I medial patellar luxation, the stifle joint is almost normal, and the patella luxates only when the joint is extended and digital pressure is applied. Animals with grade I medial patellar luxation often have no clinical signs when presented. Indications for surgical treatment should be weighed carefully because it is difficult to suggest operating on a clinically normal animal. That these asymptomatic animals may be prone to future ligamentous or bony abnormalities,¹⁷ owing to the abnormal pull across the joint, may justify them as surgical candidates. We recommend, however, that these animals not be operated on until they become clinically symptomatic for the disease.

The bony structures of the joint in grade I luxation are nearly normal; that is, the tibial tuberosity and the femoral trochlea are properly formed and have proper anatomic relationships within the joint. When surgical treatment is considered necessary, these two structures should be checked at the time of operation.

Surgical Approach and Assessment

For most medial patellar luxations( regardless of grade) a lateral parapatellar incision is made, and the extensor mechanism is visualized. Before opening the joint capsule, one should examine the alignment of the tibial tuberosity and the patella. These structures should be in a straight line and be parallel to the long axis of the limb when viewed from a craniocaudal direction. In grade I medial patellar luxation, these structures usually line up well. The lateral joint capsule is then opened, and the patella is retracted medially to permit visualization of the trochlear groove. The groove is examined for depth and any degenerative changes. If the groove is normal in appearance, no reconstructive procedures are needed for the trochlea.

Creation of Lateral Restraint

In most cases of grade I medial patellar luxation, the only repair required is the creation of a lateral restraint to prevent medial displacement of the patella. This can be accomplished by imbricating the lateral joint capsule with an interrupted Lembert suture pattern. In smaller animals (15 kg or less), 2-0 monofilament synthetic absorbable suture is used; in larger animals, 1-0 monofilament synthetic absorbable suture usually suffices. Another technique that has worked well is the use of a single suture of 1-0 or 2-0 nylon passed around the lateral fabella and through the quadriceps tendon just proximal to the patella. The suture is then directed distally along the medial border of the patella and is passed through the patellar ligament immediately distal to the patella. The suture is tied on the lateral aspect of the joint and restricts medial displacement of the patella. This technique works especially well in large dogs.⁴

The patella is now examined by placing a varus stress on the stifle and by internally rotating the tibia. If the patella does not luxate through a range of motion with the limb in this position and with digital pressure applied to the patella, the repair is sufficient. If the patella still has a tendency to luxate, a medial releasing incision is created by making a longitudinal parapatellar incision through the fibrous portion of the joint capsule; this incision is not closed. These procedures work well if the tibial tuberosity and femoral trochlea are normal. If these structures are abnormal, soft tissue procedures alone are not capable of overcoming the problem.

Grade II Luxations

The patella usually lies in its normal position in grade II luxation, but luxates with flexion of the joint and remains luxated until relocated by manual pressure or extension of the joint. Animals with grade II medial patellar luxation usually have some form of gait disturbance. They are also more likely to develop degenerative changes than are animals with grade I luxation because of the greater degree of malarticulation.

Trochleoplasty

The tibial tuberosity and trochlear groove are evaluated as described for grade I luxations. If the trochlear groove is shallow, it is corrected first. There are several options to deepen the trochlea. One is to perform a trochleoplasty. This is performed by first making two parallel incisions into the trochlear cartilage with a scalpel blade. These incisions delineate the medial and lateral boundaries of the new trochlear groove. The groove should be wide enough to permit proper seating of the patella while maintaining an adequate lateral and, especially, medial trochlear ridge. The cartilage between the incisions is removed with a bone rongeur or a high-speed drill.⁷ In younger dogs, the cartilage can easily be removed with a No. 15 scalpel blade. The groove must be deepened uniformly to the level of bleeding subchondral bone to ensure the regeneration of fibrocartilage.¹⁶ The new groove should be of sufficient width to accommodate the patella, it should have a well-developed medial ridge, and it should be of sufficient depth to discourage luxation (Figure 61-18).

After this type of trochleoplasty, fibrocartilaginous tissue forms over the articulating surface of the deepened trochlear groove.¹⁶ Although this newly generated fibrocartilage surface does not possess the same physical properties of articular (hyaline) cartilage, it was thought to be sufficiently similar to be clinically effective, and indeed this technique has given good results over the years. Nonetheless, preservation of the normal hyaline cartilage surface of the trochlear groove would be expected to enhance the results of the deepening procedure.¹⁸ To that end, a newer procedure, the trochlear wedge recession technique, was developed to deepen the trochlear groove without destroying the cartilage present.^18,19
 

Trochlear Wedge Recession Technique

In this technique, an osteochondral wedge is removed from the trochlear groove with a fine-tooth bone saw. As in the previously described trochleoplasty, an adequate trochlear ridge must be maintained on the medial and lateral aspect of the trochlear groove. To accomplish this, the saw cuts are started at the highest point on the medial and lateral trochlear ridges (Figure 61-19A). The cuts are then directed to intersect at a point just proximal to the femoral origin of the caudal cruciate ligament. Care is taken not to extend the osteochondral wedge into the intercondylar notch. The osteochondral wedge is then removed to reveal a V-shaped trochlear bed (Figure 61-19B). Owing to the width of the saw blade used to remove the wedge, the wedge of bone is actually smaller than the created bed, therefore, when the osteochondral wedge is replaced into the groove, the wedge is naturally recessed, resulting in a deepened trochlear groove. If additional depth is required (at least 50% of the patellar depth should be seated in the groove), approximately 1 to 1.5 mm of additional bone can be removed by making another set of saw cuts parallel to the first (Figure 61-19C). The wedge is then replaced in the bed, so the original cartilage surface is recessed (Figure 61-19D). The friction of the cancellous bone surfaces (plus the compressive force of the articulating patella) keeps the wedge in place, and no fixation appliances are needed. Even more recently, a third option (Figure 61-20) the rectangular recession trochleoplasty has been suggested as an improvement on the trochlear wedge recession.²⁰ An experimental in vitro study indicates that the rectangular recession has increased patellar articular surface contact, less subchondral bone exposure, recesses a larger percentage of the trochlea, and results in greater resistance to patellar luxation with the stifle extended as compared to the trochlear wedge recession.²¹ However the rectangular recession is more technically difficult to perform. To date no clinical studies comparing the two have been performed.
 

Transposition of Tibial Tuberosity, Lateral Imbrication, and Medial Releasing Incision

If the tibial tuberosity is deviated medially, this deviation is corrected by transplanting the attachment of the patellar ligament to a more lateral position. This transplantation is done by osteotomy of the tibial tuberosity. Care is taken to preserve the distal fascial attachment of the osteotomized portion of the tibial tuberosity to the distal tibia as this enhances stability to the repair. The osteotomized portion of tibial tuberosity is placed more lateral under the cranial tibialis muscle.^5,6,12,14,15 The tibial tuberosity is then fixed in place by one or two small Kirchner wires (Figure 61-21). The patella is then tested in the previously described manner for stability. Little, if any, tendency for luxation should be noted. If some tendency for medial luxation still exists, the tibial tuberosity can be moved farther laterally, or the joint capsule can be imbricated laterally. A medial releasing incision can be added if necessary (Figure 61-22).

Transposing the tibial tuberosity with the aforementioned technique, does result in rotation of the patellar ligament and caudalization of the insertion of the ligament on the tibia (Figure 61-23A). It has been proposed that this rotation and caudalization may predispose the patellar articular cartilage to abnormal wear with subsequent degenerative joint disease. A modification of the tibial tuberosity transplant has therefore been proposed by L’Eplattenier and Montavon² in which the osteotomy is created further caudally and is angled rostrally from medial to lateral in a transverse plane (Figure 61-23B). This allows the osteotomized portion of the tibial tuberosity to be “slid” laterally to realign the patella within the trochlear groove(See Figure 61-23B). If performed correctly, it also allows for cranialization of the patellar ligament insertion. This cranialization may actually relieve stress on the articular surface of the patella.² Tibial tuberosity transposition has worked well in our hands. L’Eplattenier and Montavon report good success with this technique but admit that at this time there is no comparative data to demonstrate any superiority of this technique over the first technique described in this chapter for tibial transposition. At this time, we recommend using either technique as good results can be expected from both. Perhaps future scientific data may become available to determine if one is superior to the other.
 

Grade III Luxations

The patella is luxated most of the time, but it may be reduced with the limb in the extended position in grade III medial patellar luxation. All the techniques used in treating grade II medial patellar luxations will probably be needed to correct grade III luxations. The same format for examining the structures should be followed to assess the necessity of each procedure.

If the tendency for luxation remains after correction with these techniques, the medial releasing incision may be inadequate or medial rotary instability of the tibia may be present. The medial releasing incision can be extended proximally to incise a portion of the vastus medialis muscles. If rotational instability is present, it can be corrected with a lateral suture of heavy nonabsorbable material placed around the lateral fabella and though a drill hole in the tibial crest (Figure 61-24). This suture is tightened to externally rotate the tibia and thus help realign the extensor mechanism. Usually, a combination of the aforementioned techniques are sufficient to correct a grade III medial patellar luxation.
 

Grade IV Luxations

The patella is dislocated and cannot be reduced without surgical intervention in grade IV medial patellar luxation. If diagnosed early, this least common type of luxation should be corrected at an early age to prevent the resulting bony deformities of the femur and tibia. In most cases; however, the patients already have severe bony deformities and the previously discussed techniques are inadequate to correct the disorder. These patients usually require osteotomies (derotational, cuneiform) of the tibia or femur to correct the anatomic structures and thereby the mechanics of the patella.^5,6

Lateral Patellar Luxations

Lateral patellar luxations, which are not as common as medial patellar luxations, occur most often in large breed dogs.^1,5,6 The disorder can be congenital of traumatic. In the congenital form, this condition is often associated with hip dysplasia, and thus simple correction of the resulting patellar alignment may eliminate the signs and symptoms but may not correct the underlying problem. Isolated deformities, such as genu valgum, also may cause lateral patellar luxations. The deformities causing lateral malalignment of the extensor mechanism are coxa valga, increased anteversion angles, lateral displacement of the quadriceps tendon, internal femoral torsion, laxity of medial fascia and contraction of lateral fascia, and external rotation and lateral deviation of the proximal tibia. These disorders are, for the most part, the opposite of those causing medial luxations.

As in medial patellar luxations, the severity of the lesion varies widely. Affected animals usually have a valgus (knock-knee) deformity of the rear limbs and are first seen in a crouched stance with the toes pointing outward. Correction of this disorder is based on the grading system described for medial luxations. In each case, the structures of the stifle are assessed and are corrected in the same stepwise manner as for medial patellar luxation with the following obvious modifications to the procedures: 1) medial (not lateral) imbrication; 2) lateral (not medial) releasing incision; 3) medial (not lateral) transposition of the tibial tuberosity; and 4) medial (not lateral) derotational suture.

The prognosis for grades I to III medial and lateral patellar luxations is good and success has been reported as high 90%.² Most patients improve clinically but degenerative joint disease does progress in a majority of cases. In our experience, grade IV luxations offer a poor prognosis, may require several surgeries including osteotomies, and still remain lame.

Postoperative Care

After surgical repair of both medial and lateral patellar luxations, patients should be fitted with a soft, padded bandage for 2 weeks and have restricted exercise for a minimum of 6 to 8 weeks. In the case of bilateral patellar luxations, the most severely affected limb is usually operated on first, and at least a 4 week healing period is observed before the second limb is treated. In the authors’ opinion, simultaneous bilateral repairs have a higher degree of failure and are seldom recommended.

References

1. L’Eplattenier H, Montavon P: Patellar luxation in dogs and cats: pathogenesis and Diagnosis. Compend Contin Educ Prac Vet 24:234, 2002.
2. L’Eplattenier H, Montavon P: Patellar luxation in dogs and cats: management and prevention. Compend Contin Educ Prac Vet 24:292, 2002.
3. Evans HE: Miller’s anatomy of the dog. 2nd ed. Philadelphia: WB Saunders, 1993.
4. Arnoczky SP, Tarvin GB: Surgery of the stifle: patella. Compend Contin Educ Pract Vet 2:20001980.
5. Rudy RL: Stifle joint. In: Archibald J, ed.: Canine surgery. 2nd ed. Santa Barbara, Ca: American Veterinary Publications, 1974.
6. Harrison JW: Patellar dislocation. In: Bojrab MJ, ed.: Current techniques in small animal surgery. Philadelphia: Lea & Febiger, 1975, 714.
7. Trotter E: Medical Patellar luxation in the dog. Compend Contin Educ Pract Vet 2:58, 1980.
8. Priester WA: Sex, size, and breed as risk factors in canine patellar dislocation. J Am Vet Med Assoc 160:740, 1973.
9. Hobday F: Congenital malformation and displacement of the patella. Vet J 60:216, 1905.
10. Lacroix JV: Recurrent luxation of the patella in dogs. North Am Vet 2:47, 1930.
11. Putman RW: Patellar luxation in the dog. Master’s thesis, University of Guelph, Ontario, Canada, 1968
12. Brinker WO, Keller WE: Rotation of the tibial tuberosity for correction of luxation of the patella. Mich State Univ Vet 22:92, 1962.
13. DeAngelis MP: Patellar luxations in dogs. Vet Clin North Am 1:403, 1971.
14. Flo G, Brinker WO: Fascia lata overlap procedure for surgical correction of recurrent medial luxation of the patella in the dog. J Am Vet Med Assoc 156:595, 1970.
15. Singleton WB: Transplantation of the tibial crest for treatment of congenital patellar luxation. In: Proceedings of the 27th Annual Meeting of the American Animal Hospital Association.: American Animal Hospital Association, 1967.
16. Vierheller, RC: Grooving the femoral trochlea. In: Proceedings of the 34th Annual Meeting of the American Animal Hospital Association.: American Animal Hospital Association, 1970.
17. O’Brian TR: Developmental deformities due to arrested epiphyseal growth. Vet Clin North Am 1:441, 1971.
18. Slocum B, Slocum DB, Devine T, et al.: Wedge recession for treatment of recurrent luxations of the patella. Clin Orthop 164:48, 1982.
19. Boone EG Jr, Hohn RB, Weisbrode SE: Trochlear recession wedge technique for patellar luxation: an experimental study. J Am Anim Hosp Assoc 19:735, 1983.
20. Talcott KW, Goring RL, de Haan JJ: Rectangular recession trochleoplasty for treatment of patellar luxation in dogs and cats. Vet Comp Orthop Traumatol 13:39, 2000.
21. Johnson AL, Probst CW, DeCamp, et al.: Comparison of trochlear block recession and trochlear wedge recession for canine patellar luxation using a cadaver model. Vet Surg 30:140, 2001.
     

Introduction

The purpose of the Fabellar Suture Stabilization Technique is to provide extracapsular stabilization of the stifle following partial or complete rupture of the cranial cruciate ligament. The technique described here is a modification of Flo’s original modified retinacular imbrication technique¹ as the fabellarpatella stabilizing suture is no longer incorporated and the location of the tibial suture hole has been revised. The overall objective is to place stabilizing sutures from the lateral and medial fabella to the tibial tuberosity. The intention is for these sutures to mimic the activity of the cranial cruciate ligament in the sagittal plane, eliminating cranial drawer movement when tightened. The lateral suture alone should eliminate most drawer movement. The medial suture plays a more secondary role in stifle stabilization. While these sutures stabilize the stifle acutely, it is theorized that fibrous tissue laid along the suture track maintains long term stability. Suture size and the number of sutures used vary on a per case basis and will be reviewed in the discussion.

Surgical Technique

Prior to extra-articular stabilization of the stifle an arthrotomy should always be performed and the joint thoroughly examined. A medial or lateral arthrotomy may be used. A medial arthrotomy generally allows for easier access to the medial meniscus if a menisectomy is indicated. Any remaining tags of the cranial cruciate ligament are removed and both menisci are examined. Damage to the medial meniscus is seen in over 50% of cases with cranial cruciate ligament rupture.² Damage to the lateral meniscus has also been reported but is more commonly limited to small radial tears in the cranial horn.³ The damaged portion of affected menisci should be removed. The joint capsule is then closed with a synthetic absorbable suture in a simple interrupted pattern.

The fabellar suture stabilization technique is begun by identifying both fabellae. The fabellae are located along the caudomedial and caudolateral aspect of the distal femur. In surgery, their position can be approximated by moving either medially or laterally at the level of the distal third of the patella. An incision is made through the insertions of the sartorius medially and the biceps femoris laterally for fabella identification and suture placement. Medially, a longitudinal incision is made in the fibrous insertion of the caudal head of the sartorius muscle at the level of the patella (Figure 61-25). With the caudal sartorius muscle retracted caudally, the medial fabella should be palpable under the medial head of the gastrocnemius muscle (Figure 61-26). Laterally, a slightly curved longitudinal incision is made in the fibrous insertion of the biceps femoris muscle (Figure 61-27). With this muscle retracted caudally, the lateral fabella should be palpable under the lateral head of the gastrocnemius muscle (Figure 61-28). On the lateral aspect of the stifle joint the peroneal nerve should then be identified. This nerve lies underneath the biceps femoris muscle and runs in a caudoproximal - craniodistal direction. Locating this nerve is essential to avoid damaging it during suture placement.
 

To place the fabellar sutures, the stifle is held in moderate flexion with the overlying muscle (sartorius or biceps femoris) retracted. The fabellar-femoral junction is identified by placing a curved hemostat around the caudal aspect of the fabella and rocking the sesmoid up or outward, away from the femur. Once the junction is identified the needle is passed around the proximal third of the fabella in a cranial to caudal direction (See Figure 61-27 and 61-28). Care must be taken on the lateral side to avoid the peroneal nerve. Correct suture placement is confirmed by lifting up on both ends of the suture and palpating the fabella to insure that the suture is well locked behind the bone. If two sutures are to be placed on a side, a double length of the suture material is threaded through the needle to the midpoint. Heavy, non-absorbable suture should be used. Ethylene oxide sterilized, monofilament nylon fishing leader (20-80# test, Hard Nylon leader, Mason Tackle Co, Otisville, MI) with a heavy, half curved Martin’s uterine needle is commonly used.
 

A hole is then drilled in the tibial tuberosity for fabellar suture anchoring. This hole is placed just caudal to the patella tendon insertion and in line with (distal to) the cranial edge of the extensor groove (Figure 61-29). This is a more isometric point than previously described distal locations.⁴ This should place the tibial hole just below the tibial attachment of the cranial cruciate ligament. With the tibial suture hole at the approximate isometric point, slacking of the suture during either flexion or extension should be minimal (Figure 61-30). The caudal strand of each suture is then passed through this hole with either the Martin’s uterine needle or threaded through a 14 or 16 gauge needle. All sutures can be passed through the same hole. Once a suture is brought through the tibia it is then passed back under the patella tendon. For example, the caudal strand of a lateral fabellar suture is first passed through the tibia from lateral to medial and then passed under the patellar tendon from medial to lateral. To confirm correct tibial hole placement, the sutures are threaded into position and the matching ends can be wrapped lightly around one another and held under tension. The stifle is then gently put through a range of motion. The sutures should move less than 2 mm relative to one another with correct tibial placement.⁵ The lateral sutures are tied or secured with a crimp tube first as they alone should eliminate most drawer movement. To tie the lateral suture, the limb is held at the angle of flexion which produces the most “cranial drawer” with an assistant externally rotating the tibia and pushing it in “caudal drawer”. This manipulation removes any instability while the sutures are being secured. Following lateral stabilization the medial sutures are secured with the stifle held in mild flexion (Figure 61-31).
 

The suture can be secured by using either two interlocking slip knots, a surgeons throw or a crimp tube. If monofilament nylon is used with a knot, a smooth faced needle holder may be applied to lightly hold the first throw while the second throw is being prepared. No less than four throws should be used. Alternatively, an aluminum crimp tube can be used to secure monofilament nylon sutures (Securos, Charlton, MA.) The advantage of the crimp tube is that it has a low profile and is less likely to produce a seroma than a large suture knot. In addition, the position of the crimp tube can be monitored radiographically. If crimp tubes are used postoperative radiographs should be taken to confirm post-op location of each tube. Following suture placement both the sartorius fascia and biceps femoris fascia are closed in an imbricating fashion. The subcuticular tissue and skin are closed in a routine fashion.

Postoperative Care

The incision should be iced 3x/day for 10 to 15 min for the first 3 to 5 days. This can begin as the animal is recovering from anesthesia. The animal’s activity should be restricted for 6 to 8 weeks with no running or jumping and short leash walks only. Animals will benefit from specific physical therapy of the limb during this 6 to 8 week period 6. (See Table 61-1 for a recommended postoperative activity regime.) Following this 6 to 8 week period the dog is slowly reintroduced to normal levels of activity over a 4 week period. If animals are overactive during the recovery period immature fibrotic tissue can be stretched resulting in joint instability. Adequate exercise restriction is essential for clinical success. Weight loss should be recommended if indicated and owners should also be advised that contralateral cranial cruciate ligament rupture may occur in 30 to 40% of cases.
 

Discussion

Although some surgeons reserve this technique for smaller dogs, consistent success has been reported over a wide range of weights. The number of sutures placed is determined by the weight of the animal, body condition, activity level and the degree of joint instability. The following are only general guide lines for the number of sutures placed. Dogs weighing under 40 pounds receive two fabellar sutures (two lateral). Dogs weighing 40 to 80 pounds receive three sutures (two lateral, one medial). In dogs weighing greater than 80 pounds or in those with severe instability four sutures are placed (two lateral, two medial). Dogs with chronic cruciate ligament rupture and minimal instability may only receive one or two sutures (one lateral or one lateral and one medial). If monofilament nylon (fishing leader) is used, the strength of the material selected should roughly correspond to the weight of the animal (40 pound test for a 40 pound animal, 80 pound test for an 80 pound animal). On rare occasions, in cases of chronic cruciate injury with no “drawer” movement present, fabellar stabilization sutures are unnecessary following arthrotomy. The primary causes of lameness in these animals is often chronic inflammation, meniscal damage or osteophyte formation.

Complications are uncommon (less than 10%) but include suture rupture, meniscal damage and seroma formation due to suture irritation. Suture rupture and meniscal damage are the most common causes of poor recovery. Clinically these patients may show either lack of full recovery or full recovery followed by a return of lameness. Meniscal damage should be suspected if a popping or clicking noise is heard on ambulation or palpated on examination. If a meniscectomy has already been adequately performed suture rupture should be suspected. If poor recovery is seen with the formation of large seromas over the suture knots suture irritation should be suspected. In dealing with animals with poor or inadequate recovery from the Fabellar Suture Technique simple fabellar suture removal should be attempted first if meniscal damage is not suspected or a meniscectomy has been previously performed. Suture removal as early as 12 weeks postoperatively should not increase drawer movement. Lameness usually resolves within two weeks if it was the result of suture problems. Suture replacement is rarely required and only in cases of gross stifle instability. If lameness persists following suture removal and a meniscectomy has not been previously performed, a repeat arthrotomy and medial meniscectomy are advised.

References

1. Flo G: Modification of the lateral retinacular imbrication technique for stabilizing cruciate ligament injuries. J Am Anim Hosp Assoc 11:570, 1975.
2. Flo G: Meniscal Injuries. Vet Clin North Am Small Anim Prac 23:831, 1993.
3. Ralphs SC, Whitney WO: Arthroscopic evaluation of menisci in dogs with cranial cruciate ligament injuries: 100 cases (1999-2000). J Am Vet Med Assoc 221:1602, 2002.
4. Roe SC: Optimizing the attachment sites of an extracapsular suture used for stabilizing a cruciate deficient stifle. Proceedings of the 10th Annual American College of Veterinary Surgeons Symposium, Washington DC,:19, 2000.
5. Roe SC: Personal Communication, July 2005.
6. Marsolais GS, Dvorak G, Conzemius MG: Effects of Postoperative Rehabilitation on Limb Function after Cranial Cruciate Ligament Repair in Dogs. J Am Vet Med Assoc 220:1325, 2002.
    

Introduction

Cranial cruciate ligament incompetence is a leading cause of lameness in the dog. Many surgical treatments have been described that aim to restore stifle joint stability and minimize the progression of subsequent osteoarthritis. Historically, most surgical techniques were designed to replace the function of the pathologic cranial cruciate ligament through some means of substitution using autologous tissues or synthetic materials and these methods have been described exhaustively elsewhere. More recently, tibial plateau leveling osteotomy (TPLO) was described by Dr. Barclay Slocum utilizing techniques that alter the mechanical forces acting upon the stifle in order to render the cranial cruciate ligament unnecessary.¹ The biomechanics of the TPLO have been discussed elsewhere.^2-5 The purpose of this chapter is to provide a detailed description of the TPLO procedure and its preoperative planning.

Preoperative Planning

Precise patient positioning is required when making radiographs for accurate measurement of tibial plateau angle (TPA) and other aspects of preoperative planning.^6-8 These mediolateral and caudocranial radiographs are most commonly performed with the patient under general anesthesia immediately prior to the TPLO surgery. TPA is measured on a mediolateral radiograph of the stifle with the tibia parallel to the radiographic film (Figure 61-32). The dog is placed in lateral recumbency with the affected limb down. The lateral surface of the hip, stifle, and hock are placed on the same surface. When using table-top radiographic technique, all these structures can be placed upon a large radiographic cassette or upon a smaller cassette with an adjacent spacer. The “up” leg is pulled cranially (rather than abducted at the hip) in order to keep all three structures in contact with the cassette. The “down” leg is positioned with the stifle and hock flexed to approximately 90 degrees. It is essential to center the beam upon the center of the tibial plateau while collimating the beam to include the tarsus. A cranial or proximal shift of the stifle from the center of the beam erroneously increases the measured TPA.⁷ A caudal or distal shift of the stifle from the center of the radiographic beam erroneously decreases the measured TPA. Properly positioned radiographs display superimposition of the medial and lateral femoral condyles (unless there is a significant varus/valgus and/or torsional deformity of the femur) and distinct visualization of the medial condylar portion of the tibial plateau. The slope of the tibial plateau is defined by a line joining a point at the cranial-most edge of the medial tibial condyle with its caudal-most point (Figure 61-33). The tibial functional axis is defined by a line joining a point at the intersection of the superimposed medial and lateral intercondylar tubercles with a point at the center of the talus. Next, a line is drawn perpendicular to the tibial functional axis. The TPA is defined as the angle formed between the perpendicular and the tibial plateau line. The author has measured TPA’s varying from 10° to 53° in dogs with cranial cruciate ligament incompetence, but the majority of TPA measurements in large breed dogs fall between 18° and 30°.^6,8,9
 

In addition to TPA measurement, the mediolateral radiograph is used for detailed preoperative planning.^3,10-12 Imaging Software or transparent templates are superimposed on the radiograph to evaluate the suitability of the various sizes of TPLO saw blades, jigs and bone plates. The desired point of insertion of the most proximal jig pin into the tibia is along the tibial functional axis immediately distal to the articular surface of the tibia. This critical point is marked on the mediolateral radiograph for intraoperative reference (Figure 61-34). Next, templates of available saw blade sizes (varying radius and circumference) are used to determine appropriate saw blade size. A properly sized blade should allow centering of the osteotomy about the most proximal end of the tibial functional axis, while the proximal end of the osteotomy is positioned midway between the cranial point of the tibial plateau and the tibial tuberosity. The distal end of the proposed osteotomy should be perpendicular to the tibial functional axis. The proposed osteotomy is marked upon the film for intraoperative reference. Next, a template for the appropriate size of bone plate is used to be certain that the planned osteotomy position will permit the desired implant placement (Figure 61-35). The extent of “coving” of the caudal tibial surface (created by the popliteal notch) is noted on the medio-lateral radiograph as the separation of the two cortical lines extending distally from the tibial plateau. This observation helps the surgeon avoid inadvertent laceration of the popliteal vessels during periosteal elevation of the tissues from the caudal surface of the tibia and know how to best position the screws through the bone plate to maximize screw purchase.
 

The caudocranial TPLO radiograph is used to evaluate the alignment of the tibia, the degree of attachment of the fibular head to the proximal tibia, and identify palpable landmarks that can help the surgeon avoid intra-articular placement of screws and jig pins. The stifle is locked in full extension to minimize physiologic rotation in the stifle and the contralateral hip is abducted by suspending the thigh over a rolled towel (or foam block) to position the limb for caudo-cranial radiography (Figure 61-36). When the stifle is properly positioned (patella superimposed in the center of the distal femur and the fabellae are bisected by their respective femoral cortex), the medial margin of the tuber calcis on the superimposition of the center of the distal tibia suggests the absence of internal or external tibial torsion (Figure 61-37). On a properly positioned radiograph, lateral shifting of the medial margin of the talus suggests internal tibial torsion. Conversely, external tibial torsion shifts the medial margin of the tuber calcis medially. These radiographic observations should be correlated with direct visualization of limb alignment because internal rotation of the stifle cannot be definitively distinguished from internal tibial torsion on properly positioned caudocranial radiographs of cranial cruciate ligament deficient stifles.¹³ Fibular head-proximal tibial synostosis is noted, if present, as this can restrict rotation of the tibial plateau and can lead to iatrogenic fibular fracture. The radiographic position and contour of the fibular head with respect to the stifle articular surface is noted and correlated with palpation findings. In some patients the fibular head is very palpable and extends proximal to the stifle joint while in others it is barely palpable at a point a centimeter or more distal to the articular surface. The position of the fibular head relative to the proposed insertion point of the proximal jig pin is noted so that proper jig pin position can be confirmed at the time of placement.
 

Surgical Technique

Patient Preparation

The affected hindquarter is shaved from the dorsal and ventral midlines to the mid-metatarsus. The patient is positioned in dorsal recumbency and the patient’s midline is shifted slightly from the middle of the surgical table toward the affected limb to minimize the need for the surgical assistant to lean across the table. The foot is wrapped routinely being sure to keep the wrap distal to the hock so that the talocrural joint can be fully flexed and extended. The surgeon should closely evaluate limb alignment and correlate palpation observations to radiographs positioned on a radiographic viewer in the operating room. A routine hanging limb preparation is then performed. Draping is performed in a routine manner being sure to leave the hip, stifle and hock freely mobile and palpable.

Surgical Approach

A craniomedial skin incision is made from the suprapatellar joint pouch proximally to a point several centimeters distal to the distal end of the tibial crest. The subcutaneous tissues are gently dissected to reveal the cranial and caudal bellies of the sartorious muscles and the patellar ligament. A fascial incision is made starting between the sartorius muscle bellies proximally and extends through the tendinous insertion of the pes anserinus muscle group (caudal belly of the sartorius, gracilis, and semitendinosus muscles) approximately 6 to 10 mm medial to the tibial crest. Distally, the fascial incision shifts to the cranial midline of the tibia to release the medial border of the cranial tibial muscle. The cranial tibial muscle is elevated from the lateral surface of the proximal tibia. Starting at the distal end of the surgical field, thumb forceps are used to lift the semitendinosus from the medial tibial surface while the back of a scalpel handle is used to bluntly elevate it to reveal the firm insertions of the gracilis and sartorius muscles on the medial aspect of the tibial crest (just cranial to the medial collateral ligament). The shiny white insertion of the medial collateral ligament is visualized. The insertions of the gracilis and sartorius muscles are sharply incised using care to protect the medial collateral ligament. The elevated pes anserinus is preserved as a distinct layer as it is separated from its firm adherence to the underlying fascia of the stifle using sharp dissection (Figure 61-38.).
 

Arthrotomy and Meniscal Procedures

A medial parapatellar arthrotomy is performed routinely (not necessary with diagnostic and therapeutic arthroscopy). Care is taken to avoid incising the cranial belly of the sartorius and vastus medialis as the arthrotomy is extended proximally. The cranial and caudal cruciate ligaments, medial and lateral menisci, long digital extensor tendon and joint cartilage are evaluated. TPLO should be aborted if the caudal cruciate ligament (CdCL) is ruptured because the technique is reliant upon an intact CdCL for stifle stabilization.^4,5 The cranial cruciate ligament is debrided as appropriate. Placement of a small Hohmann retractor between the caudal cruciate ligament and the tibial plateau facilitates visualization of the menisci while protecting the caudal cruciate ligament from inadvertent laceration. Frequently medial meniscal pathology is present and can vary from partial-thickness tearing to a full-thickness “bucket-handle” tear to a severe crushing injury. The pathologic segment of the medial meniscus should be excised with a #11 blade or a Beaver blade using caution to protect the caudal cruciate ligament in the process. Suction is essential and headlight illumination is helpful. Surgical “release” of the caudal body of the medial meniscus has been theorized to decrease the incidence of delayed meniscal injury, but the associated risks and benefits are still debated.^14-16 Release of the medial meniscus is performed by transecting its caudal tibial insertion with a #11 blade. Caution is used to preserve the caudal cruciate ligament during medial meniscal release (Figure 61-39). Alternatively, the medial meniscus can be released via a mid-body transection as described later. The caudal body of the medial meniscus should snap caudally as the release is completed. If the caudal body folds cranially, it should be removed.
 

TPLO Preparation

In preparation for the TPLO, a deep incision is made along the caudal edge of the tibial insertion of the medial collateral ligament effectively separating it from the popliteus and semimembranosus muscles. Next, the muscles are elevated from the caudal surface of the tibia using great care. First, the index finger of one hand is placed between the cranial tibial muscles and the lateral margin of the tibia to identify the caudolateral edge of the tibia. Next, an AO elevator in the opposite hand is used to slowly and deliberately elevate the muscles from the caudal surface of the tibia using care to keep the elevator blade in firm contact with the “coved” caudal surface of the tibia until it reaches the surgeon’s opposite index finger at the tibia’s caudo-lateral edge (Figure 61-40). Laceration of the popliteal vessels may occur if the elevator is not kept in contact with the tibia. Soft tissue elevation adequate to safely perform the osteotomy is confirmed by correlating surgical landmarks with the preoperative planning radiographs. If indicated, release of the medial meniscus can be performed at mid-body at this time by directing a #11 scalpel blade from the caudal margin of the medial collateral ligament toward the tubercle of Gerdy along the craniolateral margin of the tibial plateau. Opening the tips of a small hemostat within the medial meniscal incision confirms that the release incision is complete. Next, radio-opaque marked gauze sponges are packed around the tibia to retract the surrounding soft tissues from the tibia.
 

Jig Placement

Proper insertion point and orientation of the most proximal jig pin are essential because it functions as the axis around which the tibial plateau will rotate and as a visual guide for orientation of the osteotomy. Regional landmarks should be correlated to the radiographs to determine the desired insertion point for the pin. Often, the properly positioned pin must penetrate the fibers of the medial collateral ligament just distal to the articular surface of the tibial plateau. The exact location of the proximal tibial articular surface can be identified by sliding a freer periosteal elevator under the tibial surface of the caudal body of the medial meniscus starting immediately caudal to the medial collateral ligament (Figure 61-41). An assistant holds the limb with stifle and tarsus flexed to approximately 90 degrees and the hip in a neutral position such that the stifle is pointed directly upward. The jig is assembled and a slow-speed, high-torque, power drill is used to insert the proximal jig pin from medial to lateral into the tibia. The jig pin should be perpendicular to the sagittal plane of the stifle in both the craniocaudal direction and proximodistal direction (Figure 61-42). When the jig pin is properly oriented, the proximal joint of the jig will be in the same sagittal (flexion/ extension) plane as the stifle joint. The distal joint of the jig will be ‘out of plane’ with the talocrural joint if there is notable tibial varus/valgus or torsional malalignment. After seating the pin into or through the lateral tibial cortex, it must be cut flush with the surface of the jig to allow for proper passage of the saw blade in later stages of the procedure. Next, a small soft tissue corridor is established for the distal jig pin being sure to avoid the medial saphenous vessels. The distal jig pin is inserted in a similar manner using care to keep it parallel to the proximal pin in all planes. The jig is secured firmly to each of the jig pins by tightening appropriate set screws. The desired position for the osteotomy is determined by comparison of the regional anatomy to the marked radiograph. A small zone of periosteal elevation is used to mark this location and to prepare the tibia for osteotomy. The surgeon temporarily places the bone plate upon the medial tibial cortex to confirm that the plate will fit appropriately with the position of the planned osteotomy.
 

Osteotomy

The limb can either be positioned with the hip in the neutral position and the stifle pointed upward (as for jig placement) or the hip can be abducted to place the limb as flat as possible on the surgical table. The assistant places a small Hohmann retractor under the patellar ligament to retract it away from the saw blade. An appropriately sized TPLO saw blade is positioned in the desired location upon the medial tibial cortex. The surgeon uses one hand to stabilize the saw blade until the kerf of the osteotomy begins to stabilize the blade. At this point, the axis of the saw blade (like the most-proximal jig pin) should be perpendicular to the sagittal plane of the stifle in both the craniocaudal direction and proximodistal directions. Surgical assistant(s) help the surgeon to keep the saw blade properly aligned while cooling it with an irrigation solution. Before completing the osteotomy, the saw blade is temporarily removed and a small, sharp osteotome is used to create reference marks indicating the displacement needed along the osteotomy to accomplish satisfactory tibial plateau leveling (Figure 61-43). This chord length is geometrically derived and has been recorded in chart form for simplicity. Leveling the tibial plateau to an angle of approximately 6.5° eliminates cranial tibial subluxation by converting cranial tibial thrust into caudal tibial thrust that must be constrained by the intact caudal cruciate ligament.⁵ Progressive leveling from 6.5° toward 0° further increases caudal cruciate ligament strain. The currently recommended postoperative TPA is 5°. The preoperative TPA and the radius of the saw blade influence the amount of tibial plateau rotation required to achieve a TPA of 5°. The osteotomy is completed and the gauze sponges are removed. An appropriately sized Steinmann pin is temporarily inserted into the plateau segment from cranio-medial toward the popliteal notch of the tibia with a slight proximal to distal orientation being sure to engage but not penetrate the caudal tibial cortex to minimize risk of popliteal hemorrhage. A Jacob’s chuck is applied to the temporary pin such that the pin can be used as a “handle” and the tibial plateau is slowly rotated about the proximal jig pin until the reference marks are aligned. The surgeon verifies that cranial tibial thrust instability is satisfactorily controlled. No effort is made to keep the medial surface of the tibial segments flush as this will typically create tibial malalignment.⁹ Instead, as the tibial plateau is rotated about the proximal jig pin, the surgeon may slightly translate the distal segment medially or laterally to ensure a normal proximal-to-distal course of the patellar tendon. An appropriately sized Kirschner wire is passed across the osteotomy from the proximal-most end of the tibial tubercle into the tibial plateau to provide temporary stabilization during subsequent bone plate application. It is very important that this K-wire penetrate the tibial tubercle proximal to the insertion of the patellar ligament in order to minimize the risk of tibial tubercle fracture (Figure 61-44). The K-wire must also penetrate the medial tibial cortex to effectively maintain the rotation during plate application. The surgeon should verify proper plateau rotation and secure fixation before removing the temporary Steinmann pin (“rotation handle”). Next, the surgeon should extend and flex the stifle while evaluating the tibia for torsional or varus/valgus mal-alignment. Varus/valgus mal-alignment is corrected by sliding the jig out or in on the distal jig pin. Torsional mal-alignment can be corrected by bending the distal jig pin either cranially or caudally (Figure 61-45). Large tibial alignment adjustments create large osteotomy gaps and/ or medial cortical surface “stair-steps”. Large gaps may require autogenous cancellous bone grafting. The edge of the saw blade can be used to level out any “stair-steps” at the osteotomy site in the region of the proposed plate placement.
 

Bone Plate Application

A variety of TPLO-specific plate designs are commercially available. The following discussion pertains to the original Slocum-style TPLO plate design. The bone plate is contoured for a precise fit against the medial tibial cortex to avoid inducing tibial malalignment. Typically this requires two bends and a twist within the plate. The first bend is placed between the third and fourth screw holes in the plate. A second, more-subtle, bend is often needed through the second hole in the plate. Next, an internal twist of the proximal section of the plate is made between the third and fourth holes. Occasionally, a slight bend and/or twist are needed through the fifth hole to keep the distal end of the plate in contact with the bone. The plate is held in the desired location and a cortical screw is placed in the fourth hole using standard screw insertion techniques. Next, cortical screws are placed in the fifth and sixth holes. Next, cortical or cancellous screws (as appropriate) are placed in the second, third and first holes respectively. The screws in the proximal section of the plate are inserted in compression mode provided no tibial alignment adjustments were made. If, however, tibial alignment corrections were made, the screws in the proximal segment are inserted in neutralization mode to avoid shifting the osteotomy. Occasionally, it is necessary to remove the jig, jig pins, and/or Kirschner wire before inserting a screw into the most proximal hole of the plate. Care must be used to avoid placement of these proximal screws into the stifle joint. An aiming guide can be used if needed, but judicious correlation of palpable landmarks (such as the fibular head) to the preoperative radiographs is usually efffective. Cancellous bone grafting is not necessary for most congruent osteotomies, but may be indicated for incongruent osteotomies. The jig is removed. Stifle stability, limb alignment, and implant placement are assessed (Figure 61-46). The surgical field is lavaged thoroughly with a physiologic irrigation solution. The joint capsule is apposed routinely with a continuous suture pattern. The popliteus muscle is apposed to the medial collateral ligament. The pes anserinus muscle group is apposed to the insertion remnant left on the tibial crest using stifle flexion to ease tension during closure. Subcutaneous tissues may be closed in one or two layers. Skin is apposed routinely.

Postoperative mediolateral and caudocranial radiographs are made using the same patient positioning described previously and the TPA is measured. The radiographs are evaluated for proper jig pin, osteotomy, and implant placement. Some surgeons prefer to apply a soft padded bandage to minimize patient self-mutilation and to reduce swelling and bruising in the region of the surgical site.
 

Postoperative Care

Recovery from TPLO consists of three stages: 1) incisional healing, 2) bone healing, and 3) physical rehabilitation/reconditioning. During the two week incisional healing, self-mutilation must be prevented through the use of a protective bandage and/ or a restraint collar. The duration for bone healing is variable, but typically lasts 8 to 12 weeks. During this time, running, jumping, free access to furniture, stairs, slippery surfaces, other pets, and the yard must be avoided. Confinement to a large crate in a quiet room works nicely when the patient is unsupervised. Short walks at a slow pace on a short leash are encouraged several times per day. Sling support of the hindquarters may be indicated for patients with multi-limb disability, poor strength or balance, and for patients who are required to traverse slippery surfaces or steps. Bone healing is monitored radiographically in 4 to 8 week intervals until healing is documented. As bone healing is progressing, slow and methodical increases in patient activity are encouraged as part of their physical rehabilitation. This begins with increasing lengths of leash walks each week progressing to slow and methodical increases in supervised time off of the leash.

Complications

A wide variety of complications have been reported for the TPLO.^12,18,19 Intra-operative complications including extreme hemorrhage, intra-articular placement of screws and jig pins, and iatrogenic fracture of the tibial crest can be avoided with attentive preoperative planning and surgical technique. Postoperative soft tissue complications include seroma/hematoma, dehiscence, infection, and bandage irritation and can usually be treated routinely.

More severe postoperative complications including tibial crest fracture, fixation failure, and patellar desmitis typically cause a sudden and sustained increase in patient discomfort and lameness. Tibial crest fracture is predisposed by the tension of the patellar ligament on the tibial tubercle. Improper placement of the temporary K-wire distal to the insertion of the patellar ligament on the tibial tubercle creates a stress-riser that increases the risk of tibial crest fracture. Likewise, a shift of the osteotomy too far cranially (not centered appropriately or too large a saw blade) creates a thin tibial crest segment that is at risk of fracture. Placement of a tension band may prevent this complication in “at risk” patients. It has been suggested that tibial plateau rotation should not be performed to such an extent as to leave the tibial tubercle unsupported and that a cranial closing wedge ostectomy should supplement TPLO when patients with excessive tibial plateau angles are encountered.¹¹ This surgical treatment is quite complex and is beyond the scope of this chapter.

TPLO fixation failure may result from catastrophic loading of the limb in excess of fixation strength or from repetitive low-energy loading leading to fatigue failure. Improper orientation of the osteotomy may increase the relative loading on the implants (less load borne by the bone segments). Likewise, iatrogenic fibular fracture during TPLO likely increases mechanical demand on the implants due to loss of the caudolateral buttressing effect of the fibula. Osteomyelitis often causes increased lameness, patient discomfort and draining tracts or incisional drainage. Bacterial culture and antimicrobial sensitivity testing of fluids obtained by deep surgical site aspirate are used to select appropriate antimicrobial therapy. Implant removal may be indicated upon completion of osteotomy healing.

Neoplasia has been reported at the site of previously performed TPLO procedures.^20-22 It is unclear, currently, if this is related to the procedure, the implants, or is an incidental location of the disease. The benefit of elective plate removal following bone healing has not been established.

Technique Variations

Many variations of the surgical technique have been described including minimal dissection around the tibia, no application of surgical sponges, jig-less application, and the use of pre-contoured and locking plate systems.

References

1. Slocum B, Slocum TD. Tibial plateau leveling osteotomy for repair of cranial cruciate ligament rupture in the canine. Vet Clin North Am-Small Anim Pract 23:777, 1993.
2. Dejardin LM. Tibial Plateau Leveling Osteotomy In: Slatter D, ed. Textbook of Small Animal Surgery. 3 ed. Philadelphia: Saunders, 2002; p 2133-2143.
3. Palmer R. Understanding tibial plateau leveling osteotomies in dogs. Vet Med 100:426, 2005.
4. Reif U, Hulse DA, Hauptman JG. Effect of tibial plateau leveling on stability of the canine cranial cruciate-deficient stifle joint: an in vitro study. Vet Surg 31:147, 2002.
5. Warzee CC, Dejardin LM, Arnoczky SP, et al. Effect of tibial plateau leveling on cranial and caudal tibial thrusts in canine cranial cruciate-deficient stifles: an in vitro experimental study. Vet Surg 30:278, 2001.
6. Caylor KB, Zumpano CA, Evans LM, et al. Intra- and interobserver measurement variability of tibial plateau slope from lateral radiographs in dogs. J Am Anim Hosp Assoc 37:263, 2001.
7. Reif U, Dejardin LM, Probst CW, et al. Influence of limb positioning and measurement method on the magnitude of the tibial plateau angle. Vet Surg 33:368, 2004.
8. Reif U, Probst CW. Comparison of tibial plateau angles in normal and cranial cruciate deficient stifles of Labrador retrievers. Vet Surg 32:385, 2003.
9. Wheeler JL, Cross AR, Gingrich W. In vitro effects of osteotomy angle and osteotomy reduction on tibial angulation and rotation during the tibial plateau-leveling osteotomy procedure. Vet Surg 32:371, 2003.
10. Kowaleski MP, McCarthy R.J. Geometric analysis evaluating the effect of tibial plateau leveling osteotomy position on postoperative tibial plateau slope. Vet Comp Orthop Traumatol 17:30, 2004.
11. Kowaleski MP. Technique and indications for TPLO/CCWO. ACVS Veterinary Symposium 449, 2005.
12. Palmer R. Postoperative TPLO Complications. ACVS Veterinary Symposium 2004; p 378.
13. Apelt D, Kowaleski MP, Dyce J. Comparison of computed tomographic and standard radiographic determination of tibial torsion in the dog. Vet Surg 34:457, 2005.
14. Pozzi A, Kowaleski MP, Apelt, D, Johnson KA. Motion of the caudal pole of the medial meniscus after meniscal release. ACVS Veterinary Symposium 2005; p 20.
15. Pozzi A, Litzky AS, Field J, Apelt, D, Meadows C, Johnson KA. In vitro effect of meniscal release on load transmission in stifles with and without tibial plateau leveling osteotomy. ACVS Veterinary Symposium 2005; p 21.
16. Slocum B, Devine-Slocum, T. Meniscal release In: Bojrab M, ed. Current Techniques in Small Animal Surgery. 4th ed. Philadelphia: Lea & Febiger, 1998; p 1197.
17. Slocum B, Devine-Slocum, T. Tibial plateau leveling osteotomy for cranial cruciate ligament rupture In: Bojrab MJ EG, Slocum B, ed. Current techniques in small animal surgery. 4 ed. Baltimore: Williams & Wilkins, 1998; p 1209.
18. Pacchiana PD, Morris E, Gillings SL, et al. Surgical and postoperative complications associated with tibial plateau leveling osteotomy in dogs with cranial cruciate ligament rupture: 397 cases (1998-2001). J Am Vet Med Assoc 222:184, 2003.
19. Priddy NH, 2nd, Tomlinson JL, Dodam JR, et al. Complications with and owner assessment of the outcome of tibial plateau leveling osteotomy for treatment of cranial cruciate ligament rupture in dogs: 193 cases (1997-2001). J Am Vet Med Assoc 222:1726, 2003.
20. Boudrieau RJ. Corrosion of the Slocum TPLO plate. ACVS Veterinary Symposium 2005; p 324.
21. Boudrieau RJ, McCarthy RJ, Sisson RD, Jr. Sarcoma of the proximal portion of the tibia in a dog 5.5 years after tibial plateau leveling osteotomy. J Am Vet Med Assoc 227:1613-1617, 2005.
22. Punke J. Clinical occurence of sarcoma post tibial plateau leveling osteotomy (TPLO). ACVS Veterinary Symposium 2005; p 318.
     

Introduction

The cranial cruciate ligament constrains joint motion. It prevents cranial subluxation of the tibia on the femur (cranial drawer sign), hyperextension of the stifle joint, and, along with the caudal cruciate ligament, excessive internal rotation of the tibia on the femur.¹ Excessive forces during extremes of any of these movements may damage this ligament.² Although excessive trauma causes acute rupture of the cranial cruciate ligament, most cruciate ligament lesions are thought to result from chronic degenerative changes within the ligaments themselves.^2,3 Variations in conformation, valgus (knock-knee) and varus (bowleg) deformities of the stifle, and repeated minor stresses can result in progressive degenerative joint disease. As these joint changes develop, the cruciate ligaments undergo alterations in their microstructure and may be more susceptible to damage from minor trauma.⁴

Because rupture of the cranial cruciate ligament results in progressive degenerative joint changes within the joint,^3,5,6 most such injuries should be repaired. In the authors’ experience, many large breed dogs present with partial cranial cruciate ligament tears. The authors currently recommend repair in these cases even though they may not be grossly unstable (see diagnostics below). The cranial cruciate ligament has poor healing capabilities and eventually will completely tear. During that process, degenerative joint disease will progress leading to a poorer prognosis. We must stress; however, that each patient needs to be assessed individually as other factors may make surgical repair either unnecessary or not in the best interests of the patient. For example in some chronic cases of cranial cruciate ligament rupture, severe degenerative joint changes are present and these patients have an unfavorable prognosis after surgical repair. In these patients, conservative management with anti-inflammatory drugs and somatic pain relievers may provide adequate palliative care and an equal, if not superior, result than surgical intervention. Moreover, concurrent joint diseases such as rheumatoid arthritis and systematic lupus erythematosus, may obviate the repair of the ligament insufficiently. A final exception would be the smaller patients, such as cats and small dogs (less than 15 kg.), with isolated cranial cruciate ligament injuries. One study demonstrated that conservative therapy(nonsurgical) had a high degree of clinical success.⁷

Diagnosis of cranial cruciate ligament insufficiency is based on historical and clinical evidence of rear limb lameness. Palpation of the stifle is the most useful tool to make a diagnosis of cranial cruciate ligament insufficiency. In acute complete ruptures, instability of the stifle is present when applying the cranial drawer test or tibial compression test.⁷ In incomplete tears or chronic complete tears with secondary periarticular fibrosis, these tests will not be as dramatic and may not be conclusive. In many chronic cases, medial collateral ligament hypertrophy secondary to the injury may be palpated. This finding can support the diagnosis of cranial cruciate ligament disease. Radiographs are usually not necessary to establish a diagnosis but can be useful in assessing secondary degenerative joint disease and stifle effusion.⁷ In early partial tears joint effusion is a helpful finding to establish a diagnosis. In the rare case in which all these diagnostic tests fail to establish a diagnosis, nuclear scintigraphy can be used to pinpoint the cause of lameness. The clinician should always evaluate the entire limb for other abnormalities. The contralateral limb should also be evaluated because bilateral cranial cruciate ligament disease is not uncommon.⁷

Many methods of repair have been devised to treat cranial cruciate ligament insufficiency. These can be categorized as either extra-articular or intra-articular repairs. Whereas extra-articular repairs stabilize the joint by tightening or altering the position of extra-articular structures, intra-articular repairs anatomically replace the cranial cruciate ligament with some type of graft. The over-the-top procedure⁸ is an intra-articular repair that uses a patellar tendon graft to replace the cranial cruciate ligament. This procedure was designed for use in dogs weighing more than 15 kg. In our experience, the over-the-top patellar tendon graft provides a functional replacement for the cranial cruciate ligament and thereby limits any abnormal joint motions.

Surgical Technique

The animal is placed in lateral recumbency, and the affected limb is prepared for an aseptic surgical procedure. A lateral parapatellar skin incision is made extending from the midshaft of the femur to the proximal tibia. The subcutaneous and fascial tissues are dissected free, and the patellar ligament is clearly defined. The patellar ligament is incised longitudinally between the junction of the middle and medial thirds of its width. The incision is extended over the patella and into the patellar tendon, where it is directed in a proximo-lateral direction to incorporate the fascia lata (Figure 61-47A). The incision proximal to the patella should be made 1 to 1.5 times the distance from the patella to the tibial tuberosity; this incision ensures an adequate length of graft in dogs of all sizes. The incision into the fascia is also made 1 to 2 centimeters lateral to the medial boundary of the fascia lata with the vastus medialis.

An osteotome is placed in the groove of the patella created by the scalpel blade. A handsaw can also be used to deepen this groove to allow better purchase with the osteotome. A craniomedial wedge of bone is removed with the medial third of the patellar tendon with the ligament attatched (Figure 61-47B). If power equipment is available, use of an oscillating saw can also be employed to make the patellar wedge. Extreme care should be taken during the osteotomy to preserve the entire articular surface of the patella. To complete the harvest of the graft, the surgeon begins at the proximal extent of the incision in the fascia lata. A scissors is used to cut the fascia lata transversely in a medial direction to where it blends into the vastus medialis. The distal portion of the fascia lata is then elevated from the underlying muscle and grasped with a thumb forceps. The scissors is used to cut the medial border of the fascia strip distally in a direction parallel to the first fascial incision. As the incision approaches the suprapatellar joint pouch, the scissors can be directed medially if necessary to incorporate more joint capsule and parapatellar fibrocartilage. This can be employed if the surgeon feels that the graft needs reinforcing in this area. The medial third of the patellar ligament is then dissected free to the level of the tibial tuberosity. In doing so a medial arthrotomy is created. An incision through the infrapatellar fat pad is necessary to mobilize the graft, but the fat pad should not be stripped from its ligamentous attachments because it provides much of the blood supply to the patellar ligament graft. An autogenous graft consisting of fascia, patellar tendon, a patellar bone wedge, and patellar ligament with a distal attachment to the tibial tuberosity is thus created (Figure 61-47C).

The remnants of the ruptured cranial cruciate ligament are then removed through the medial arthrotomy, and the joint is inspected for further pathologic features. The authors find it useful to use a curette to debride the intercondylar notch of osteophytes and cranial cruciate ligament remnants. This aids in graft passage. The patella, joint capsule, and soft tissues are retracted laterally to expose the lateral femoral condyle and fabella (Figure 61-47D). The lateral fabella is located by palpation, and a small vertical incision is made in the femorofabellar ligament. With the joint in extreme flexion, curved hemostatic forceps are inserted into the incision and passed over the top of the lateral femoral condyle and into the intercondylar notch; one must take care to preserve the causal joint structures by staying close to the bone. The tips of the hemostatic forceps are gently manipulated until they can be seen within the joint (Figure 61-47D and E). The surgeon then grasps the free end of the graft directly or grasps a suture that has been placed in the free end of the graft with the hemostat. The graft is pulled through the joint and over the top of the lateral condyle by gentle traction on the hemostat. Flexing and extending the joint during this maneuver facilitates passage of the graft.

After the graft has been pulled though the joint, it is held under gentle traction, and the joint is tested for craniocaudal stability. Once cranial drawer motion has been eliminated, the graft is attached to the lateral femoral condyle. The authors feel that the graft should be tightened and attached to the lateral femoral condyle with the stifle in full extension. Functional studies of the canine cranial cruciate ligament indicate that its maximum length and therefore its most taut state occur at full extension.¹ Since the graft’s attachment sites closely mimic those of the normal cranial cruciate ligament, it is logical to assume that the graft should also be most taut in extension. If the graft would be tightened with the stifle in some degree of flexion, the graft would become more taut as its attachment sites become farther apart in extension. In this scenario, extension would be constrained by the graft or the graft would be stretched and be more prone to fail. Therefore, the authors secure the graft with traction maintained and the stifle in full extension. The graft is sutured to the tissues of the lateral femoral condyle with simple interrupted sutures of nonabsorbable suture material (Figure 61-47F). The authors also find that a small titanium bone staple and belt loop also offers secure and quick fixation of the graft (Figure 61-48). In our experience using bone staples, implant complications (i.e. reaction, irritation, or loosening) are extremely rare.

The arthrotomy is closed in a routine manner. During closure of the medial arthrotomy, care should be taken to avoid excessive tension on the patella and patellar ligament, which may predispose the joint to a medial luxation of the patella. If tension is a problem, loose approximation sutures should be placed in the joint capsule, and the subcutaneous soft tissues should be used to cover the arthrotomy defect.
 

Postoperatively, the limb is placed in a modified Robert Jones dressing for 2 weeks, and the animal’s activity is restricted for a total of 8 to 12 weeks. In larger dogs (over 30 kg) a lateral splint may be added for the first 2 to 4 postoperative weeks.

The biologic fate of the patellar tendon graft within the joint was investigated in an experimental study.⁹ The results of this study demonstrate that the blood supply of the graft is disrupted at the time of surgery, and approximately 20 weeks are needed for the graft to become completely revascularized. During this period, the graft undergoes ischemic necrosis, and its strength may be at risk. In an effort to minimize this revascularization process, one of the authors (SPA.) and his colleagues proposed a modification of the over-the-top technique in which the medial vascular supply of the patellar tendon graft was carefully preserved and maintained.¹⁰ They suggested that if a “vascularized” patellar tendon graft were used to reconstruct the cranial cruciate ligament, the revascularization and remodeling process would be eliminated, or at least minimized. Furthermore, the use of vascularized patellar tendon graft would prevent, or at least minimize, any changes in the material strength of the graft secondary to the ischemic changes or revascularized process. However, a subsequent study evaluating the strength of vascularized and non-vascularized patellar tendon grafts failed to demonstrate any significant differences in any of their biomechanical parameters with time.¹¹ It thus appears that there is no inherent advantage of preserving the blood supply to the graft at the time of surgery.

Several other modifications of the over-the-top graft technique have been proposed and have produced good results^8,10,12 Although these techniques use other tissues for the graft (fascia lata, lateral aspect of the patellar tendon) and may include the addition of other ancillary stabilization procedures (lateral imbrication suture), they all incorporate the over-the-top femoral positioning of the intra-articular graft. The over-the-top positioning allows the most consistent placement of the graft in the most biomechanically and anatomically correct position (Figure 61-49). In our opinion, this positioning may be the most important consideration in intra-articular reconstructions of the cranial cruciate ligament. Indeed, an evaluation of two over-the-top techniques by Denny and Barr suggests that this biomechanically correct placement of the graft, and not the type of graft used, is responsible for the success of this repair technique.¹³
 

In summary, successful repair of insufficiency of the cranial cruciate ligament depends on the reestablishment of joint stability. Although this end can be accomplished by the aforementioned techniques, other components of the stifle (patella, menisci, collateral ligaments) must not be overlooked when evaluating the joint. These structures work in concert to allow normal joint motion, and failure to recognize concurrent patellar malalignment or meniscal injury in cranial cruciate ligament insufficiency may result in less than optimal postoperative function.

References

1. Arnoczky SP, Marshall JL: The cruciate ligaments of the canine stifle: an anatomical and functional analysis. Am J Vet Res 38:1807, 1977.
2. Arnoczky SP, Marshall JL: Pathomechanics of cruciate and meniscal injuries. In Bojrab MJ, ed.: Pathophysiology of small animal surgery. Philadelphia: Lea & Febiger, 1981, p 590.
3. Arnoczky SP: Surgery of the stifle: the cruciate ligaments. Compend Contin Educ Pract Vet 2:106, 1980.
4. Vasseur PB, Pool RR, Arnoczky SP, et al.: Correlative biomechanical and histologic study of the cranial cruciate ligament in dogs. Am J Vet res 46:1842, 1985.
5. Hulse DA, Michaelson F, Johnson C. et al.: A technique for reconstruction of the anterior cruciate ligament in the dog: preliminary report. Vet Surg 9:135, 1980.
6. Strande A.: Repair of the ruptured cranial cruciate ligament in the dog. Baltimore: Williams & Wilkins, 1967.
7. Vasseur PB: Stifle joint. In Textbook of small animal surgery. Philadelphia: W. B. Saunders, 1993, 1817.
8. Arnoczky SP, Tarvin GB, Marshall JL, et al. The over-the-top procedure: a technique for anterior cruciate ligament substitution in the dog. J Am Anim Hosp Assoc 15:283, 1979.
9. Arnoczky SP, Tarvin GB, Marshall JL.: Anterior cruciate ligament replacement using patellar tendon: an evaluation of graft revascularization in the dog. J Bone Joint Surg [Am] 64A:217, 1982.
10. Boudrieau RJ, Kaderly RE, Arnoczky SP, et al.: Vascularized patellar tendon graft technique for cranial cruciate ligament substitution in the dog: vascular evaluation. Vet Surg 14:196, 1985.
11. Butler DL, Grood ES, Noyes FR, et al.: Mechanical properties of primate vascularized vs. nonvascularized patellar tendon grafts: changes over time. J. Orthop Res 7:68-79, 1989.
12. Shires PK, Hulse DA, Liu W: The under-and-over fascial replacement technique for anterior cruciate ligament rupture in dogs: a retrospective study. J Am Anim Hosp Assoc 20:69, 1984.
13. Denny HR, Barr ARS: An evaluation of two “over the top” techniques for anterior cruciate ligament replacement in the dog. J Small Anim Pract 25:759, 1984.
     

Surgical Technique

The primary purpose of these extracapsular procedures is to reduce caudal displacement of the tibial plateau relative to the femoral condyles, and the secondary purpose is to reduce excessive internal tibial rotation.

The animal is placed in dorsal recumbency, and a lateral parapatellar approach is used for a stifle joint arthrotomy. The joint is examined for concurrent ligamentous or meniscal injuries, which are treated accordingly. The remnants of the caudal cruciate ligament (CaCL) are resected, and the joint is lavaged with sterile saline or lactated Ringer’s solution. Joint capsule closure is performed using 2-0 or 3-0 monofilament nylon, polypropylene, or polydioxanone suture material placed in a continuous pattern while a cranially directed force on the tibia is used to reduce caudal drawer motion.

Extracapsular imbrication is performed by placing a single mattress suture of size 1 or 2 nonabsorbable suture (polypropylene or nylon) on the lateral and medial aspects of the joint between the head of the fibula (laterally) or proximal tibial (medially) and just proximal or distal to the patellar (Figure 61-50). The direction of these sutures mimics the orientation of the CaCL to reduce abnormal caudal displacement and internal rotation of the proximal aspect of the tibia. To perform lateral imbrication, the suture is passed into the quadriceps tendon above or below the patella, is directed caudodistally under or through the head of the fibula, and then is directed cranioproximally to be tied along the lateral aspect of the stifle joint while caudal drawer motion and internal tibial rotation are reduced and the normal standing angle of the joint is maintained. To place the medial imbrication suture, the skin incision is displaced medially, and subcutaneous tissues are dissected to reveal the medial retinaculum of the stifle joint. The mattress suture is placed in the quadriceps tendon above or below the patella and is oriented caudodistally through the caudal aspect of the proximal tibia. The suture is then directed cranioproximally and is tied along the medial aspect of the stifle joint. Placement of medial and lateral sutures in the quadriceps tendon prevents unilateral displacement of the patella or tendon.
 

The lateral retinaculum opened during the arthrotomy can be closed with 0 or 2-0 nonabsorbable sutures placed in a mattress pattern resembling the direction of the lateral imbrication suture. The subcutaneous tissues and skin are closed in a routine manner. Postoperatively, a soft, padded limb bandage is used for 2 weeks, and exercise is restricted for 1 month to protect soft tissue healing.

Lateral and medial imbrications are recommended for midsubstance ligamentous tears. Bone avulsion injuries involving the origin or insertion of the CaCL can be repaired by stabilization of bone fragments with a small bone screw or with Kirschner or orthopedic wires (Figure 61-51).¹ Small unattachable fragments can be removed (along with the CaCl), and extracapsular imbrication can be performed. Alternatively, medial collateral ligament and popliteal tendon entrapment with bone screws have been described for midsubstance Ca CL tears.²

Surgical stabilization of a CaCL-deficient stifle joint is variable for human and veterinary patients. In human patients, unidirectional (anteroposterior) instability due to in-continuity tears is treated with physical therapy designed to strengthen the quadriceps muscles while surgical stabilization of avulsion injuries is recommended.³ In animals, persistent caudal drawer motion in experimental and clinical patients after resection with or without surgical stabilization has not been consistently associated with lameness or lack of limb function.^4-6 This finding has been attributed to the lack of importance in stabilization of the canine stifle joint by the CaCL at normal angles of the limb. At our clinic, therefore, surgical stabilization of tears of this ligament is not routinely performed. An arthrotomy or arthroscopy is performed to remove proliferative ends of the damaged ligament and to inspect the joint for concurrent meniscal or cranial cruciate ligament lesion.⁶ Bone avulsions are reattached if technically feasible. A caudomedial stifle joint arthrotomy is necessary to attach or resect avulsion of the CaCL tibial insertion.¹ Long-term, objective clinical evaluations of affected stifle joints, therefore, are warranted to delineate the natural progression of CaCL-deficient canine stifle joints. Recently, a high incidence (88%) of dogs with CrCL injury Synovitis, and concomitant CACL lesions has been described.⁷
 

References

1. Reinke JD. Cruciate ligament avulsion injury in the dog. J Am Anim Hosp Assoc 1982; 18: 257 – 264.
2. Schulz K. Caudal cruciate ligament injury. In Fossum TW, Small Animal Surgery. 4th ed. St. Louis. Mosby/Elsevier, 2013; 1344 – 1345.
3. Abate J. Dislocations and soft tissue injuries of the knee. In: Brouner BD. Sletel Trauma. 4th ed. Philadelphia, PA. Saunders/Elsevier. 2009; 2167 – 2201.
4. Pournaras J, Symeonides PP, Karkavalas G. The significance of the posterior cruciate ligaqment in the stability of the dog’s knee. J Bone Joint Surg Br 1983; 65: 204 – 209.
5. Harari J, Johnson AL, Stein LE, Evaluation of experimental transection of the caudal cruciate ligament in dogs. Vet Surg 1987, 16: 151 – 154.
6. Johnson AL, Olmstead ML. Caudal cruciate ligament rupture: a retrospective analysis of 14 dogs. Vet Surg 1987; 16: 202; 16: 202 – 206.
7. Sumner JP, Markel MD, Muir P. Caudal cruciate ligament damage with cranial cruciate ligament rupture. Vet Surg 2010; 39: 936 – 941.
    

The collateral ligaments are important stabilizing elements in the stifle joint. Injury to the collateral ligaments usually is caused by trauma and often is associated with disruption of either the cranial or caudal cruciate ligament.

Anatomic Features

The medial collateral ligament originates on the medial epicondyle of the femur and passes distally in the joint capsule. It passes over the medial lip of the tibial plateau, where an underlying bursa allows the ligament to slip back and forth as the joint moves. The ligament attaches to the medial shaft of the tibia with a long, narrow insertion.¹ The medial collateral ligament is positioned over the central axis of the stifle to remain tight throughout flexion and extension of the joint.² The lateral collateral ligament originates on the lateral epicondyle of the femur and passes distally in the joint capsule to insert on the fibular head.¹ The lateral collateral ligament is caudal to the central axis of the joint.² This results in a tight ligament in extension, which limits internal rotation and contributes to craniocaudal stability. The ligament loosens as the joint flexes, allowing the tibia to rotate internally.

Diagnosis and Treatment Options

The clinical diagnosis of isolated collateral injuries can be difficult. With the joint held in full extension, varus and valgus forces occasionally result in angulation away from the side with ruptured ligament. However, if both cruciate ligaments are intact, they will greatly reduce or prevent this instability. Some increase in rotational movement may occur. Evidence of a widened joint space on one side on radiographs taken while the joint is stressed may aid in the diagnosis. Collateral rupture in the presence of a cruciate disruption is readily revealed by the presence of varus or valgus angulation of the joint when stress is applied and a dramatic increase in rotational instability with the stifle extended.

Management of collateral ligament injuries varies with the severity of injury and resultant instability. A stretched or isolated torn collateral ligament without gross instability can often be managed with external coaptation. A contoured lateral splint fashioned of plaster or Hexcelite (Hexcel Medical Products, Dublin, CA) in a padded bandage is used to stress the joint toward the injured collateral ligament. This coaptation must be maintained for at least 3 to 4 weeks. Collateral ligament injuries resulting in gross instability are repaired by suturing or other internal fixation procedures.

Surgical Technique

Because the collateral ligaments are extrasynovial, blood supply is adequate to allow simple ruptures to heal if the ends are adequately apposed. A three-loop pulley pattern of monofilament nonabsorbable material such as nylon or polypropylene can be used to suture collateral ligaments³ (Figure 61-52). Each pass of the suture is a different distance from the torn ends and axially at a 120° rotation from the previous passage. In one study, this three-loop pulley pattern tolerated approximately 25% more tensile load and allowed only 34% as much distraction before failure under tension as the locking-loop pattern in canine collateral ligaments.⁴
 

Suturing of severely traumatized ligaments may not provide adequate support. For these cases, a large figure-of-eight suture of nylon or polypropylene can be placed between bone screws seated at the collateral ligament’s attachments to provide additional support while the tissues heal (Figure 61-53).

Care must be taken to tighten a lateral collateral ligament repair only in moderate extension because overtightening of this area prevents normal range of motion. Cases in which the ligament has been torn away from the bone are best managed by fixation with bone screws. A spiked washer (Synthes, Paoli, PA) can be used to trap the ligament without compromising its vascularity (Figure 61-54). Any concurrent injury (e.g., a torn meniscus or cruciate ligament rupture) should be dealt with, and then the joint should be externally supported with a lateral splint for 3 to 4 weeks while the collateral ligament heals.

Avulsion fractures of the ligament’s bony attachments are best handled by surgical reduction and fixation (Figure 61-55). One or two Kirschner wires are driven through the fragment to hold reduction. A figure-of-eight tension band wire is then passed behind the Kirschner wires and through a transverse hole in the bone. This wire is tightened to counteract the pull of the ligament. The Kirschner wires should be cut off and bent back to reduce soft tissue irritation. Alternatively, a bone screw can be used if the avulsion fragment is large enough. Because internal fixation of a fracture should result in a stable repair, extended external coaptation is usually not indicated. However, a soft, padded bandage may be used for several days postoperatively to control soft tissue swelling.
 

References

1. Evans HE, Christensen CG. Miller’s anatomy of the dog. 2nd ed. Philadelphia: WB Saunders, 1979.
2. Arnoczky SP, Tarvin GB, Vasseur P. Surgery of the stifle: the menisci and collateral ligaments. Compend Contin Educ Pract Vet 1980;2:395.
3. Griffiths RC. Collateral ligament injuries. In: Proceedings of the 7th annual surgical forum.: American College of Veterinary Surgeons, 1979.
4. Berg RJ, Egger EL. In vitro comparison of the three loop pulley and locking loop suture patterns for repair of canine weightbearing tendons and collateral ligaments. Vet Surg 1985; 15:107.
    

Overview of OCD of the Stifle

Osteochondritis dissecans (OCD) in dogs occurs most often at the humeral head (~ 75% of OCD cases). OCD of the stifle has been reported to be the second most common location in European dogs, but in the U.S.A. the stifle is a less common site than the elbow or hock. Either frequency of OCD in the stifle differs due to unknown factors at different geographic locations, or OCD of the stifle is underdiagnosed in the U.S.A.

OCD can only occur in dogs with a systemic defect in endochondral osteogenesis called osteochondrosis. Since only juvenile bones grow, OCD necessarily develops in juveniles, although diagnosis may be after osseous maturity. Rapid growth is part of the pathogenesis of OCD. Consequently, OCD almost exclusively affects large breed dogs, and about 75% of the cases are in males. In addition, OCD affects the same joint bilaterally in at least half of the cases, even if the lameness is unilateral. OCD in two different joints of a single patient (stifle and shoulder), however, is uncommon.

Diagnosis

The presenting complaint for dogs with OCD of the stifle is unilateral or bilateral rear leg lameness, usually with an insidious onset. The signalment is almost exclusively a young, large dog (generally one less that 12 months old and greater than 30 pounds). The differential list includes trauma (Salter-Harris fractures, avulsions, luxations, fractures, etc.), and the juvenile bone and joint diseases of the rear limbs of large breed dogs (hip dysplasia, panosteitis, patella luxation, OCD of the stifle or hock, HOD, and Osgood-Schlatter’s disease). Under diagnosis of stifle OCD may occur due to its insidious onset, often mild clinical signs, and/or inappropriately stopping examination once another diagnosis has been made. A complete orthopaedic examination is indicated because multiple orthopaedic problems can, and often do, occur concurrently.

Examination of a canine stifle with OCD may yield pain at full extension or full flexion, have an audible click while going through a range of motion, and have joint effusion palpable on either side of the patellar tendon. Arthrocentesis is a simple procedure that can confirm that the stifle does have pathology based only on the gross characteristics of the synovial fluid (volume > 0.5 ml, yellow color, decreased viscosity). Stifle pathologies such as patella luxation, collateral ligament rupture, avulsion of a cruciate ligament or fracture are readily diagnosed or ruled out. The remaining stifle diagnoses that could present like stifle OCD are rare (e.g. avulsion of long digital extensor origin or popliteus insertion, isolated meniscal tears, etc.).

Confirmation of stifle OCD can usually be accomplished by radiographs (Figure 61-56). However, not visualizing an OCD lesion on radiographs does not rule out the diagnosis, especially if the lesion is small and/or not depicted in skyline view. The lateral view should be oblique to avoid superimposition of the femoral condyles, with the lateral femoral condyle more caudal. OCD lesions have been reported most often on the lateral femoral condyle (94%), but have also been reported on the medial femoral condyle, the patella, and the trochlear ridge. CT is highly reliable in diagnosing or ruling out OCD. Other imaging modalities reported as useful for diagnosis of OCD of the stifle include MRI and ultrasonography. Exploratory arthrotomy, either via arthroscope or open procedure, is also reasonable if some type of pathology of the stifle is indicated by orthopaedic examination and synovial fluid analysis.

Surgical Technique

Arthroscopy involves the lowest morbidity for exploring the stifle and treatment of an OCD lesion. A limited arthrotomy (Figure 61-57) provides much less morbidity than a full arthrotomy of the stifle, if the parapatellar fibrocartilage is not transected and the patella is not dislocated. The parapatellar skin incision extends from the mid-patella level to just distal to the tibial plateau. Incisions through the retinaculum and then the joint capsule are successively slightly shorter to facilitate complete closure. A self retaining retractor (e.g. Gelpi, Wallace) is placed and firmly distracted to provide visibility of the femoral condyle and inter-condylar notch area. Flexion and extension will facilitate visualization of the weight bearing surface of the condyle. Preoperative identification of the OCD location (i.e. medial or lateral condyle) is beneficial when using a limited arthrotomy. If necessary for exploration, the incision can be extended to a standard parapatellar approach to the stifle. OCD flaps are removed in most cases. However, some OCD lesions of the stifle can be quite large, and reports of fixing them in situ with bone pegs, pins, etc. has been reported. Once the OCD flap has been removed, the defect (“bed”) from which it originated should be evaluated. The defect will likely fill with fibrocartilage, if a blood supply is present. If the OCD bed is red, then granulation tissue is present and it should not be significantly disturbed. If the bed is white (e.g. eburnated bone), then forage into the medullary cavity with a 0.062” K-wire (or smaller) at multiple locations will supply blood to the site with considerably less morbidity than curettage.
 

Prognosis

Long term prognosis depends primarily on the amount of preexisting degenerative joint disease, plus the size and location (weight bearing vs. non-weight bearing areas) of the OCD lesion. Short term morbidity is most affected by the surgical technique. Morbidity from arthroscopy is typically only a few days at most. Limited arthrotomy morbidity is only slightly longer than for arthroscopy, if the patella is not destabilized. Deeply curetting the OCD bed rather than forage can extend the postoperative morbidity for weeks.

Suggested Readings

Kramer M, Stengel H, Gerwing M., et al: Sonography of the canine stifle. Vet Rad & Ultrasound 40:282, 1999.

Necas A, Dvorak M, Zatloukal J: Incidence of osteochondrosis in dogs and its late diagnosis. Acta Veterinaria Brno 68:131, 1999.

Montgomery RD, Milton JL, Henderson RA, Hathcock JT: Osteochondritis dissecans of the canine stifle. Compendium on Continuing Education for the Practicing Veterinarian 11:1199, 1989.

Morgan JP, Wind A, Davidson AP: Bone dysplasias in the Labrador retriever: a radiographic study. J Am Animal Hosp Assoc 35:332, 1999.

Shealy PM, Milton JL: Limited arthrotomy of the canine stifle for osteochondritis dissecans. Vet Comp Ortho & Trauma 4:134, 1991.