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Radius and Ulna
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Radial and ulnar fractures are seen frequently in small animal practice. These fractures often, but not always, involve both bones. Most fractures are the result of automobile trauma; however, fractures in toy breeds often result from jumps or falls.
As with all traumatized animals, the first step in managing patients with radial and ulnar fractures is to perform a complete physical examination. The surgeon should pay particular attention to the cardiovascular and respiratory systems. Approximately 40% of animals that have been hit by a car have some type of respiratory system damage; therefore, thoracic radiographs are advisable. One should also carefully assess the patient for the presence of cardiac arrhythmias that may result from traumatic myocarditis. Once the patient’s condition has been stabilized, the surgeon can attend to the fracture.
Radiographs (at least two views) of the radius and ulna are essential to define the fracture properly. The fractured limb should be protected by applying a Robert Jones bandage until definitive treatment can be performed. This bandage should extend from the toes to well above the elbow. Half circumference splints applied distal to the elbow joint are ineffective in immobilizing radial and ulnar fractures.
Fractures of the radius and ulna may be associated with a higher complication rate than fractures of other long bones. Because of the potential complications, which include delayed union, nonunion, joint stiffness, and growth deformities, one should not dismiss these fractures lightly.
I prefer to group radial and ulnar fractures into several categories because of the difference in principles of treatment. These categories include olecranon fractures, Monteggia fractures, isolated ulnar or radial diaphyseal fractures, radial or ulnar styloid fractures, radial head fractures, combined radial-ulnar diaphyseal fractures, and radial physeal fracture-separations.
The olecranon,the proximal portion of the ulna, serves as a fulcrum for the extensor muscles of the elbow joint. Fractures of the olecranon can occur proximal to the trochlear notch (i.e., extra-articular fractures) or through the trochlear notch (i.e., intra- articular fractures). These fractures can be simple two-piece fractures or complex comminuted fractures. Regardless of the type of fracture, the proximal fragment usually is severely displaced because of the pull of the triceps muscle (Figure 57-1). Open reduction and internal fixation of these fractures are required because external coaptation (e.g., a cast or splint) is unable to counteract the distractive force of the triceps muscle.
Generally, olecranon fractures are exposed through a caudal approach in which the extensor carpi ulnaris and flexor carpi ulnaris muscles are subperiosteally elevated, thus exposing the ulnar diaphysis and olecranon. The skin incision is made slightly lateral to rather than directly over the caudal surface of the olecranon.
With an intra-articular fracture, the anconeus muscle and joint capsule must be incised so the surgeon can see the articular surface. Perfect reduction of articular fractures is essential to minimize the development of secondary degenerative joint disease. Extension of the elbow relaxes the triceps pull, thus facilitating fracture reduction. After reduction, olecranon fractures can be stabilized with pins and tension band wire or bone plates and screws.
Tension Band Fixation
The preferred technique for repairing extra-articular olecranon fractures and transverse or short oblique intra-articular fractures involves pinning and placement of a tension band wire. After exposure of the fracture and removal of blood clots and fibrous tissue the elbow is extended, and the fracture fragments are reduced. Reduction usually can be maintained with digital pressure or a bone clamp.
The reduced fracture is initially stabilized by driving two Kirschner wires or Steinmann pins across the fracture. The pins are driven in a normograde fashion through the proximal fragment, across the fracture, and into the distal fragment with a Jacob’s pin chuck. The proximal olecranon is quite dense bone, so it may be helpful to pre-drill pilot holes of a slightly smaller diameter than the pins. The pins should be parallel to each other to allow compression of the fracture with the tension band wire. The pins should be directed so they engage the cranial cortex of the distal ulnar fragment, rather than extending directly down the medullary cavity, because the latter placement may not counteract rotation effectively (Figure 57-1B); similarly, a single pin does not counteract rotation. A hole is then drilled transversely in the caudal aspect of the distal fragment. The hole should be large enough to accept 18-gauge orthopedic wire (20-gauge wire in small dogs and cats) and should be placed roughly the same distance distal to the fracture as the length of the proximal fragment. A single tightening twist is made in the center of an appropriate length of wire, and one end is then passed through the hole. The other end of the wire is then passed underneath the triceps tendon and cranial to the pins (Figure 57-1C). The free ends of the wire are twisted together, thus forming a figure-of-eight (Figure 57-1D). The two twist points on the medial and lateral portions of the figure-of-eight wire are alternately tightened until the fracture is compressed. The wire should not be over-tightened because this may cause a gap to form in the cranial aspect of the fracture. The excess wire is cut, leaving three or four twists, and the two ends of the wire are bent so they lie flat against the bone. The pins are bent in a caudal direction and are cut to leave 4 to 5 mm’s of pin; the ends are then turned cranially so they lie flat against the triceps tendon (Figure 57-1E and F). If the pins are initially bent in a cranial rather than a caudal direction, the cut ends will not lie flat against the triceps tendon.
If properly applied, the tension band wire is strong enough that no postoperative support is needed. The wound is covered with a sterile dressing, and the limb is placed in a light support wrap for 48 hours postoperatively. The animal’s activity should be limited to leash walks for 6 to 8 weeks after surgery. The implants are not removed unless they loosen, break, or cause soft tissue irritation.
I prefer to use a bone plate and screws to repair comminuted olecranon fractures and olecranon fractures in large and giant breed dogs. A plate applied to the caudal aspect of the ulna acts as a tension band, provided no cortical fragments are missing from the cranial cortex. Screws can be applied through the plate using the lag principle, thus achieving interfragmentary compression in comminuted fractures (Figure 57-2A and B). Screws must not be placed through the articular surface of the trochlear notch. With fractures that are sufficiently proximal to require plating up to the most proximal aspect of the ulna, pressure sores frequently develop over the olecranon if the plate is applied caudally. The plate should be applied to the lateral aspect of the ulna and inter-fragmentary lag screws may be used as necessary (Figure 57-2C).
Fractures of the proximal half of the ulna with luxation of the radial head are known as Monteggia fractures. The radial head usually luxates cranially, and the ulna may be fractured anywhere from the middle of the diaphysis to the trochlear notch. The proximal annular and interosseous ligaments may be torn (Figure 57-3A) or may remain intact, as is common when the ulnar fracture is at the base of or into the trochlear notch (Figure 57-3B). Early treatment is helpful for ease of reduction of the luxation and fracture.
A caudal approach usually provides adequate exposure to allow reduction of both the radial head luxation and the ulnar fracture. A craniolateral approach can be used in addition to the caudal approach if the luxation cannot be reduced.
If the proximal annular ligament is torn, as occurs when the ulnar fracture is distal to the annular ligament (See Figure 57-3B), one must not only stabilize the ulnar fracture but also secure the radial head in its normal relationship with the ulna. Although suture repair of the annular ligament has been described, this is seldom possible. I prefer to secure the radial head to the ulna with lag screws alone or in conjunction with a bone plate. If the ulnar fracture is oblique enough, lag screws alone are sufficient to repair the fracture (See Figure 57-3A) (Figure 57-3C). If the ulnar fracture is comminuted, I prefer to use a bone plate and place one or two screws through the plate into the proximal radius (Figure 57-3D).
If the proximal annular ligament is intact, reduction of the ulnar fracture can be accomplished only with concurrent reduction of the radial head luxation. Because the intact annular ligament maintains the normal relationship between the radial head and the ulna, the surgeon only needs to stabilize the ulnar fracture. I prefer to use a bone plate and screws to stabilize this type of ulnar fracture (Figure 57-3E and F), although repair with pin(s) and tension wire has been described.
Postoperatively, the incision is covered with a sterile dressing, and the limb is placed in a modified Robert Jones bandage. The bandage helps to minimize postoperative swelling and is left in place for several days. The animal’s activity should be limited to leash walks only for 10 to 12 weeks after surgery, but early movement of the elbow is encouraged to minimize stiffness.
Isolated Ulnar or Radial Diaphyseal Fractures
Isolated radial or ulnar fractures generally are the result of falls, gunshot wounds, or the patient being kicked by a horse, for example, rather than automobile accidents. Isolated ulnar diaphyseal fractures occur more frequently than isolated radial diaphyseal fractures. These fractures usually are minimally displaced because the intact companion bone acts as an internal splint. Radiographic diagnosis of these fractures may be difficult because of the minimal displacement; therefore, one should obtain two radiographic views of diagnostic quality.
Most isolated radial or ulnar fractures can be stabilized with a properly applied fiberglass cast. The joints proximal and distal to the fracture must be immobilized to stabilize a fracture properly with external coaptation. Half circumference splints, although used frequently, are an unacceptable means of stabilizing radial or ulnar fractures because they do not immobilize the elbow joint adequately.
A cast should be applied with the patient under general anesthesia. The fracture is manually reduced. The reduced fracture should have at least 50% purchase (i.e., contact between fracture ends) before the reduction is considered adequate. One should avoid casting the limb with a varus or valgus angulation at the fracture. This type of angulation can lead to secondary arthritis because of abnormal stresses placed on the joints during weight-bearing. The cast should extend from the midshaft of the humerus to the digits, with only the distal phalanx of the third and fourth digits left exposed distal to the cast.
External coaptation is not without complications, but many problems can be avoided by applying the cast properly. Pressure sores over the accessory carpal bone and olecranon are common. They can be avoided by applying “donuts”,layers of cast padding with a hole cut in the center,over these pressure points (Figure 57-4A). Donut pads placed around a pressure point alleviate the pressure directly on the bone. Simply adding more padding directly over a pressure point actually increases the pressure and should be avoided. The distal end of the cast can cause severe erosions to the dorsal aspect of the protruding toes as the animal walks. Adding extra padding and applying a walking bar (i.e., aluminum rod) to the distal end of the cast helps prevent damage to the dorsum of the protruding toes (Figure 57-4B). The walking bar can be incorporated into the cast or can be secured to the dried cast with adhesive tape. A cast also may not immobilize the elbow joint properly. This problem usually occurs because the cast is not applied as far proximal to the elbow as it should be or because the cast is applied too loosely proximal to the elbow.
Diaphyseal fractures of the radius or ulna that are the result of gunshot wounds may not be amenable to treatment by external coaptation. Because such fractures frequently are severely comminuted, restoration of cortical continuity may be difficult, if not impossible. Fractures involving only the radial diaphysis are best treated with an external fixator (Figure 57-5). The external fixator provides direct skeletal fixation and allows treatment of open wounds. Generally, the major segments of the radius are not severely displaced; therefore, the external fixator can be applied after closed reduction. This technique minimizes further disruptions of the blood supply to the fracture fragments. If the major fracture segments are displaced, or if one chooses to use a cancellous bone graft, then open reduction is required. It is best to use a minimal approach and avoid handling the fracture fragments (i.e., the “look but don’t touch” method) to avoid further iatrogenic disruption of blood supply. The application of external fixators is described later, in the discussion of combined radioulnar diaphyseal fractures.
Isolated ulnar diaphyseal fractures resulting from gunshot wounds can be treated with a cast, provided no extensive open wounds are present. Such fractures usually do not require rigid fixation because the radius is the major weight-bearing bone. The limb can be immobilized temporarily in a Robert Jones bandage until any swelling subsides or the open wounds begin to heal before applying a cast.
Radial and Ulnar Styloid Fractures
The radial and ulnar styloid processes serve as the origins of the medial and lateral collateral ligaments of the antebrachiocarpal joint. The styloid processes also extend distal to the proximal row of carpal bones, thus providing a buttress for medial and lateral stability. Because carpal instability results from fracture of one or both styloid processes, internal fixation of these fractures is required.
The styloid processes are exposed by incising directly over the process taking care to avoid iatrogenic laceration of the collateral ligaments. Fixation of radial styloid fractures usually is accomplished with tension band wire or lag screws (Figure 57-6A-C). It may not be possible to place two pins into the distal ulna in small dogs; therefore, ulnar styloid fractures may not be completely rotationally stable (Figure 57-6D and E).
Because uncomplicated healing of these fractures is necessary to prevent carpal instability, supplemental external coaptation is necessary. A fiberglass half-cast or Mason metasplint provides satisfactory support. External coaptation can be discontinued after 6 to 8 weeks. The animal’s exercise should be restricted until fracture healing is complete.
Radial Head Fractures
Radial head fractures, which are uncommon, may or may not involve the articular surface. If the articular surface is involved, perfect reduction and rigid fixation are required to minimize secondary arthritis and joint stiffness.
The radial head is most easily approached through a lateral skin incision. A fascial incision is made between the common and lateral digital extensor muscles near their origin. These muscles are separated to expose the supinator muscle, deep branch of the radial nerve, branches of the dorsal interosseous artery, and part of the radius. One should protect the radial nerve during the surgical procedure. Incision of the supinator muscle along its insertion on the radius exposes the lateral collateral ligament annular ligament and joint capsule. The annular ligament and joint capsule are incised along the cranial border of the collateral ligament thus exposing the radial head. After the fracture is repaired, the joint capsule and annular ligament are re-apposed. The supinator muscle may be sutured to the radial periosteum. The remainder of the closure is routine.
Extra-articular radial head fractures can be repaired with a T-plate or crossed Kirschner wires (Figure 57-7A and B). The latter method is used in cats and small dogs in which T-plate fixation often is not feasible. Intra-articular radial head fractures can be repaired with lag screws or divergent Kirschner wires, depending on the size of the fragment. Lag screw fixation is ideal because it provides interfragmentary compression. A small Kirschner wire should be used in conjunction with the lag screw to counteract rotation of the fragment around the screw (Figure 57-7C). If the fragment is too small for lag screw fixation, then multiple divergent Kirschner wires can be used. Because interfragmentary compression is not achieved with Kirschner wires, the fracture should be reduced and compressed as much as possible with a bone clamp before the Kirschner wires are placed. At least two, and preferably more, Kirschner wires should be driven at maximally divergent angles across the fracture and through the opposite cortex (Figure 57-7D). The divergence of the wires prevents the fragment from loosening and sliding along the wires.
Preventing the animal from bearing weight on the radial head for several weeks postoperatively may be advisable, depending on the stability of the repair. This goal may be accomplished by placing the limb in a carpal flexion bandage, Velpeau bandage, or cast.
Salvage procedures such as elbow joint arthrodesis or excision of the radial head can be considered for treatment of severely comminuted radial head fractures.
Combined Radioulnar Diaphyseal Fractures
Most fractures of the antebrachium involve both the radius and ulna, and many of these fractures occur in the middle or distal third of the diaphysis. These fractures can be managed in several ways, depending on the fracture type, patient, client cooperation, facilities available, and the surgeon’s capabilities. The methods of managing these fractures include closed reduction and external coaptation, open reduction and bone plating, open reduction and pinning, and closed or open reduction and external skeletal fixation. Each method is described here.
Closed Reduction and External Coaptation
Some combined fractures of the radius and ulna can be managed adequately with external coaptation after closed reduction. This method should be reserved for treatment of incomplete or transverse midshaft fractures in young, medium-sized dogs and in cats. External coaptation of radial and ulnar fractures should be avoided in toy breeds and in large, active dogs. There is a high incidence of delayed union or nonunion in distal radial and ulnar fractures in toy breeds treated with external coaptation. This may be due, in part, to a decreased interosseous blood supply in the distal radius of toy breed dogs compared to large breed dogs. Bone plates and screws should be used to treat radius and ulnar fractures in toy breed dogs.
When performing closed reduction of transverse midshaft radial and ulnar fractures, reduction is considered adequate only when a 50% or more purchase is achieved. The limb should not have a varus or valgus angulation when it is cast. (See the earlier discussion of isolated ulnar or radial diaphyseal fractures for guidelines and complications of external coaptation.)
Open Reduction and Bone Plating
The radius is an ideal bone to plate because the approach to it is straightforward, its cranial surface is the tension side of the bone, and little bending is required to contour the plate properly to the bone. Open reduction and bone plating are the treatments of choice for combined radioulnar fractures in toy breeds, in large or giant breeds, and in animals with multiple limb fractures. In toy breeds, distal radial and ulnar fractures seem to have an unusually high incidence of delayed or nonunion when treated conservatively; plating these fractures provides the rigid fixation necessary for healing. Properly applied bone plates are better than other methods of fracture repair in withstanding the tremendous stresses placed on fracture repairs by active large and giant breed dogs. Similarly, the rigid fixation provided by bone plates permits earlier return to function in the patient with multiple limb fractures than when more conservative treatment methods are used.
Usually, only the radius needs to be plated, although plating both the radius and ulna may be advisable in large or active dogs. The radius is exposed through a craniomedial approach; the ulna can be exposed through a caudal or caudolateral approach if it is to be plated also. The most proximal and distal aspects of the radius are more difficult to expose than the diaphysis because of proximal muscular insertions and tightly adherent extensor tendons distally. The plate is applied to the cranial surface of the radius and, if necessary, the caudolateral surface of the ulna (Figure 57-8A). One must be certain that a plate applied to the radius is beneath the extensor tendons. Failure to do so results in entrapment of the extensor tendons and limited function of the carpus or digits.
With proximal radial fractures, screws can be placed through the radial plate into the ulna. This procedure may increase fracture stability, but it prevents supination and pronation of the antebrachium. Therefore this technique should be used only when there is a short proximal segment and additional screw purchase is warranted. Screws should never be placed through the radius into the ulna in a growing animal because doing so causes the animal to develop an angular limb deformity.
Plating the medial aspect of the radius is advised for treating distal radial and ulnar fractures where three screws cannot be placed into the distal fracture segment using a dorsally applied bone plate (Figure 57-8B). Because the plate can be applied along the radial styloid process, additional screw purchase can be achieved in the distal radial epiphysis. Additionally, the screws engage the thicker medial and lateral radial cortices, and the extensor tendons are avoided. Generally, a narrower plate is chosen for the medial radius compared to the plate that would be chosen for the dorsal radius. The radius is narrower in a craniocaudal direction than it is mediolaterally, therefore accurate aiming of the screws is necessary to capture the entire width of the radius. Care must be used to avoid placing the most distal screw into the antebrachiocarpal joint.
A cancellous bone graft is recommended for comminuted fractures and for fractures in older animals. The proximal humerus is a convenient site to harvest cancellous bone for radial and ulnar fractures. The cancellous graft can be placed around the fracture site as it is removed from the humerus, or the graft can be put into a stainless steel bowl until enough cancellous bone has been harvested. The fracture site should not be lavaged after the graft has been placed.
A padded bandage is applied to the limb after wound closure. The bandage is applied snugly from the toes to the midshaft of the humerus. The bandage minimizes postoperative swelling of the limb and keeps the incision clean. The bandage can be removed in 48 hours. The dog’s activity should be restricted to leash walks only for 10 to 14 weeks postoperatively. Although not routinely done, the plate may be removed 10 to 12 months after the fracture has healed.
Open Reduction and Intramedullary Pinning
The radius is not as amenable to intramedullary pinning as the other major long bones for several reasons. Because the radius is relatively straight and both ends are completely covered with articular cartilage, retrograde pin placement causes the pin to enter either the elbow or the carpal joint. The oval cross-sectional shape of the medullary cavity limits the size of the pin that can be used. Furthermore, many toy breed dogs do not have a distinct medullary cavity in the radius, making it difficult or even impossible to pin. A single medullary pin does not provide stable fixation of a radial fracture even if the ulna is also pinned. Therefore, treating radial fractures with an intramedullary pin is not advised and should be avoided.
Pinning of the ulna may be performed in conjuction with other types of radial fracture fixation (e.g., bone plate and screws, external fixator) to facilitate alignment of the ulna. One may wish to use this auxiliary fixation in large or active dogs. Retrograde placement of the pin is more easily accomplished than normograde placement. It is advisable to insert the pin into the proximal ulnar fragment before stabilizing the radial fracture if one wishes to use retrograde placement. The pin should be aimed toward the caudal ulnar cortex to avoid the pin exiting the ulna through the dorsal aspect of the anconeal process. If normograde placement is chosen, the pin is inserted at the medial aspect of the olecranon and directed slightly laterally to insure the pin enters the medullary canal.
Closed or Open Reduction and External Skeletal Fixation
External skeletal fixation is a versatile and useful method of managing many combined radioulnar fractures. An external fixator can be applied after open or closed fracture reduction. If open reduction is chosen, the approach should be limited in length to what is necessary to see the fracture site. I prefer to use a limited craniomedial approach. The open approach offers the advantages of seeing the fracture during reduction and allowing application of a cancellous bone graft. However, open reduction also has disadvantages of causing further trauma to the blood supply of the fracture fragments and exposing the fracture to the outside environment.
Several different external fixator configurations are applicable to the radius. Stable transverse or short oblique fractures in medium-sized dogs can be treated with a Type 1-a fixator consisting of four half- pins and a single connecting bar (Figure 57-9C). A similar configuration with six pins and a single connecting bar is used for similar fractures in larger dogs (Figure 57-9D). The fixator is applied on the cranial or craniomedial aspect of the radius. Driving the pins in a true medial to lateral direction across the radius is difficult and may result in iatrogenic fracture because of the oval shape of the radius. If one chooses to apply a Type II fixator, smaller diameter pins should be used in the proximal portion of the radius to minimize the risk of iatrogenic fracture.
Depending on the system used, the pins must be inserted in a particular order during application of an external fixator with only one connecting bar. The fracture is reduced, and the most proximal and distal pins are inserted first. These pins should be inserted as far away from the fracture as possible and at a 45 to 60° angle to the long axis of the bone (Figure 57-9A) if smooth pins are used. If positive profile threaded pins are used, they should be applied perpendicular to the long axis of the bone. A connecting bar with four clamps is attached, and the two outermost clamps are tightened on the pins. The middle two pins are placed through the clamps and then are driven into the bone (Figure 57-9B). These pins should be 1 to 2 cm from the fracture. The greatest biomechanical stability is achieved when there is maximal distance between the two pins on each side of the fracture (Figure 57-9C). All clamps are then completely tightened, and postoperative radiographs are obtained. Minor adjustments in fracture reduction can be made if the clamps are loosened. Because use of a single connecting bar precludes major adjustments in fracture reduction once all the pins have been placed, one should reduce the fracture properly before applying the external fixator.
A six-pin, single-connecting bar fixator is applied similarly to a four-pin, single-bar fixator. Six clamps are placed on the bar instead of four. The middle pins on either side of the fracture are placed last (See Figure 57-9D).
A quadrilateral frame (Type I-b) external fixator is useful for unstable comminuted fractures and open fractures with missing bone fragments (Figure 57-10). This configuration is also particularly useful for proximal or distal fractures in which one segment is short. A quadrilateral frame allows pin fixation in two planes, thus providing stable fixation of short fragments that would not be possible with other configurations. A quadrilateral frame, like other external fixators, can be applied after open or closed reduction. If reduction is not possible (i.e., if cortical fragments are missing), the bone is anatomically aligned before the fixator is applied. The first row of pins is applied from the craniomedial aspect of the radius toward the caudolateral aspect in the same way as described for a four-pin, single-bar fixator. Once the first row of pins is placed and the connecting bar is applied, the second row of pins is placed. The second row of pins is placed identically to the first, except it is applied from the craniolateral aspect of the radius toward the caudomedial aspect. The second connecting bar is then applied. The two rows of pins are connected to each other by applying a connecting bar to the two most proximal and another to the two most distal pins (Figure 57-11). Alternatively, a diagonal connection can be made (i.e. from the most proximal pin on the lateral side to the most distal pin on the medial side) which has been shown to be stronger than the proximal and distal connections previously described.
Other fixator configurations may be used depending on the nature of the fracture. Generally, the more unstable the fracture or the longer the expected healing time, the more stable the configuration should be. Positive profile threaded pins provide greater bone holding power and are less likely to loosen prematurely. Pre-drilling technique is recommended with these pins. Some of the newer systems allow placement of threaded pins through the clamps and permit clamps to be tightened on the pins after they have been inserted into the bone. These systems provide the flexibility of adding additional pins after the connecting bar and initial clamps have been applied. Regardless of the configuration chosen, the points of the pins should protrude slightly beyond the second cortex. The pins should be driven by hand or with a low-speed power drill. The clamps should not touch the skin; rather, they should be approximately 1cm above the skin. The pins are cut off near the clamps after any necessary adjustments have been made.
Circular ring fixators may be used to stabilize radius and ulnar fractures. These devices require some preoperative assembly of the rings to facilitate application during surgery, and may require more time to apply than conventional external fixators. Ring fixators offer the advantage of placing small wires (e.g., 1.6 mm diameter) through the fracture fragments. These wires are attached to the rings and tension is applied which dramatically increases the stiffness of the wires. Therefore these small wires can be used instead of larger pins (see Chapter 53 – Circular External Skeletal Fixation). Using small wires allows one to stabilize short bone fragments that occur with distal radial fractures because they do not require as much bone length as larger pins. I believe circular ring fixators offer the greatest advantage when attempting to repair fractures with one main fragment is very short. Hybrid fixators utilizing a ring and wires to capture the short segment and linear fixator elements to immobilize the long segment have also been used successfully (see Chapter 53 – Circular External Skeletal Fixation).
Post-operative placement of a compression bandage is helpful. The bandage helps to minimize postoperative swelling and is left on for 48 hours. The fixator is wrapped with cotton and elastic tape after the compression bandage has been removed. This wrap covers any sharp pins and prevents the fixator from catching on carpet and similar objects. The client should limit the animal’s exercise to leash walks until the fracture has healed.
Fixation pins may loosen before a fracture has healed. The likelihood of this complication depends on the type of fracture, the configuration of the fixator, the number and type of fixation pins used and the techniques used to place them, the animal’s age, and the amount of activity the animal is allowed. One may choose to replace the loose pins or to remove the fixator and use external coaptation for the remainder of fracture healing. In certain cases, one may be able to remove only the loose pins and leave the rest of the fixator undisturbed. This can only be done if at least two pins remain fixed on each side of the fracture.
Generally, an external fixator can be removed without anesthesia or even sedation. The clamps and connecting bars are loosened and removed. Smooth fixation pins can be pulled out by hand or with a pair of pliers. Positive profile threaded fixation pins must be un-screwed from the bone with a hand chuck or power drill. The small amount of hemorrhage that usually occurs from the pin holes can be controlled with a light pressure bandage. The animal’s activity should be restricted for several weeks after removal of the fixator while re- modeling of the holes in the bone begins.
Radial Physeal Fracture-Separations
Fracture-separation through either radial physis is uncommon. Such fractures occur through the zone of hypertrophied cartilage. The animal’s owner should always be warned that premature physeal closure and angular limb deformity may follow such a fracture. If premature physeal closure does occur, it usually happens within 2 weeks of the fracture.
Closed reduction of a radial physeal fracture and external coaptation should be attempted first. If closed reduction fails, open reduction should be performed. The fracture can be stabilized with small Kirschner wires (See Figure 57-11). The wires are driven from the epiphysis across the physis and into the metaphysis. To minimize premature physeal closure, the wires should be as parallel to one another as possible and as perpendicular to the physis as possible. Some form of external coaptation is advisable for 2 weeks, especially for distal physeal fractures. These fractures usually heal within 3 weeks. The pins should be removed if possible.
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Welch JA, Boudrieau RJ, Dejardin LM, Spodnick GJ: The itraosseous blood supply of the canine radius: implications for healing of distal fractures in small dogs. Vet Surg 26:57, 1997.
The most common angular deformities in dogs affect the antebrachium and represent 0.74% of all skeletal diseases in dogs. Among these, angular deformities attributed to crushing injuries (Salter V fractures) of the distal ulnar growth plate have been well described. This type of injury may result in external rotation, radius valgus, cranial bowing of the radius, radio-ulnar incongruence, and limb shortening. Retained cartilage core, hypertrophic osteodystrophy, nutritional disorders, asymmetrical crushing injuries (Salter VI) and other fractures of the growth plates can also result in premature physeal closure of the antebrachium. Scientific documentation of the effects of angular deformity and limb shortening on limb function and secondary degenerative joint disease is limited. However, surgical correction has traditionally been recommended in cases with elbow dysplasia, more than 10 degrees of angulation, and / or more than 20% limb length discrepancy. The management of growth deformities of the antebrachium is based on consideration of the following factors:
- Presence of a unifocal or bifocal (resulting in translation of the limb) deformity
- Three-dimensional (rotation, medio-lateral and craniocaudal planes) assessment of the severity of the angular deformity
- Point of maximum deformation
- Limb length discrepancy (actual and expected)
- Growth potential of the affected limb and the contralateral limb
- Congruence of the elbow joint
Careful patient selection and thorough pre-operative planning are crucial to optimize treatment outcome. Physical examination is essential to evaluate the overall function of the limb and evaluate joints for pain on manipulation, crepitation, effusion and range of motion. Rotational deformity is easier to measure on physical examination than radiographs, by comparing the planes of flexion and extension of adjacent joints. Planning requires a minimum of two orthogonal radiographic views including the elbow and the carpus of the affected limb. Similar radiographs of the contralateral antebrachium are useful as a reference. Additional radiographs and/or computed tomography of the forelimb are indicated to evaluate the elbow for any evidence of dysplasia.
Ulnar Ostectomy in the Immature Dog
The purpose of this technique is to release the constraint created by the ulna on the remaining growth of the radius in immature dogs. Postoperative increase in radial length and correction of the angular deformity correlate with the growth potential in the radial physes. Owners should be warned that any rotational deformity will most likely persist and that additional surgical correction may be warranted at skeletal maturity. Ulnar ostectomy is always coupled with procedures to prevent premature union of the ulnar segments, such as the insertion of a fat graft.
The dog is placed in lateral recumbency, with the affected forelimb and ipsilateral flank prepared for aseptic surgery. A lateral approach to the distal ulna starts with a skin incision extending over the mid to distal ulna. Subcutaneous tissue is incised and the lateral digital extensor muscle is separated from the extensor carpi ulnaris muscle. Fascia and surrounding soft tissues are dissected to expose a segment of ulna carefully insuring that all periosteum, with its osteogenic potential, remains with the segment of bone to be resected. Depending on the size of the dog, a one to three centimeter segment of the ulna is resected using bone cutters or an oscillating bone saw cooled with a saline flush. The segment of bone and associated periosteum are removed (Figure 57-12). If the interosseous artery is disrupted during the ostectomy, effective hemostasis must be achieved.
Bone wax may be applied directly over the proximal and distal ends of the osteotomized bone to prevent premature healing of the ulna. While this procedure effectively inhibits bone formation and development of a synostosis, it is associated with a risk of foreign body reaction. Other surgeons have recommended suturing the periosteum covering the resected segment of ulna over each end of the osteotomized bone. However, the procedure most commonly used to prevent premature healing of the ulna consists of interposing a fat graft in the ulnar defect. A 2 to 3 centimeter skin incision is made in the ipsilateral flank area, exposing the subcutaneous fat. A large single piece of fat is sharply dissected free and placed in the ostectomy gap (See Figure 57-12). Hemostasis is achieved at the donor site and the subcutaneous tissue and skin are sutured. The transplanted fat is secured in the ostectomy gap by suturing adjacent soft tissues. The subcutaneous tissues and skin are closed in a routine fashion.
Post operative radiographs are obtained to document the location and length of the ostectomy gap. A soft padded bandage is placed for 2-4 days after surgery to prevent seroma formation. A splint is recommended to protect the limb for 2 weeks if bilateral procedures are done. The dog is released to the owners with instructions to limit activity. Monthly radiographs are indicated until skeletal maturity, to allow serial evaluation of radial growth, correction of the angular deformity and persistance of the ostectomy gap. Restoration of the normal configuration of the elbow due to the release of the proximal ulna may be noted. Union of the ulna prior to skeletal maturity may require reoperation. A corrective osteotomy of the radius may be indicated if angular deformity remains clinical at maturity.
The ostectomy should be performed in the distal ulna just proximal to the physis to effectively relieve the restraints on the radial growth plate without affecting the stability of the elbow or carpus. Failure to remove all of the periosteum at the ostectomy site will result in premature bone bridging of the ostectomy gap. Meticulous apposition of soft tissues and obliteration of dead space minimizes the risks of herniation of the fat graft (potentially leading to dehiscence and premature union of the ulna) and seroma formation at the donor site. Postoperative splint support for two weeks is important with bilateral ostectomies to prevent motion at the ostectomy gap and displacement of the fat graft. However, splinting an immature dog often leads to laxity of the flexor tendons and hyperextension of the carpus. Therefore careful attention must be paid to removing the splint at the appropriate time.
Radial Ostectomy in the Immature Dog
The goals of treatment are to allow unrestricted growth of the normal physes of the radius and ulna, and to restore and maintain elbow congruity. This procedure is indicated in immature dogs with premature closure of the proximal or distal radial growth plate and active ulnar physes.
The animal is treated with a middiaphyseal ostectomy of the radius coupled with the placement of a free autogenous fat graft in the defect to prevent bone union (Figure 57-13A and B). Release of the tension on the proximal and distal radius will usually allow the adjacent joints to reestablish normal position. A postoperative splint is applied for three to four weeks once surgical swelling has decreased (24 to 48 hours after surgery), as the radius is the primary weight bearing bone in the distal forelimb. The limb should be splinted in a slight flexion and varus, to minimize post-immobilization laxity of the carpus. The dog is released to the owners with instructions to limit activity. Monthly radiographs are indicated until skeletal maturity, to allow serial evaluation of radial growth, correction of the angular deformity and persistance of the ostectomy gap. Thickening and cranial bowing of the ulna commonly occurs in response to the increased mechanical loading of the bone. A second surgical procedure to reunite the radial segments by bridging the ostectomy gap with autogenous cancellous bone graft once the dog has reached skeletal maturity is therefore rarely indicated.
Radial ostectomy can also be considered in dogs with asymmetrical closure of the radial growth plate secondary to retained cartilage core or Salter VI fracture. In these cases, the active portion of the affected growth plate may be stapled to prevent any further deviation of the radial segment and interference with the ostectomy site (Figure 57-13C). Partial closure of the distal radial growth plate has also been treated by resection of the bone bridging the physis and placement of a fat graft. Whereas this option may decrease the risk of postoperative fracture and compensatory changes in the ulna, identifying the margins of diseased growth plate may require advanced imaging and is technically challenging. Complications include incomplete resection of the bone bridge and collateral damage to remaining growth plate resulting in failure to correct the deformity.
Closing Wedge Osteotomy and Plate Fixation in the Mature Dog
A closing wedge osteotomy can be used to treat an angular deformity of a long bone that is not significantly shortened, as this procedure will result in loss of bone length. This procedure results in cortical apposition if no rotational correction is required.
Preoperative planning is based on radiographs of the affected and contralateral control radius and ulna, including the adjacent joints. The radiographs of the affected radius are studied to determine the location of the point of greatest curvature of the radius and to evaluate the anatomy of the adjacent elbow and carpus. The affected limb is compared to the control limb to determine the discrepancy in length. The plane of angulation may be calculated based on the deviations measured on lateral and cranio-caudal projections. It may also be directly determined on a radiograph which best shows the angle of the deformity. Lines are drawn parallel to the proximal and distal joint surfaces to determine the angle of deformity of a radius (Figure 57-14). A line is then drawn perpendicular to the proximal line and centered within the proximal diaphysis. A similar line extends from the distal line, centered within the distal diaphysis. The intersection of these lines identifies the location of the osteotomy. At the osteotomy site, lines are drawn parallel to the proximal and distal joint lines. These lines intersect to form the wedge to be removed. The base of the wedge is at the convex surface of the deformity. The distance between the osteotomy line and the carpal joint, and the width of the wedge to be removed on the convex side of the radius are measured and corrected for radiographic magnification (115%). A template of the selected plate can be used to verify that the bone stock between the osteotomy and the joint will allow screws to purchase six cortices. If necessary, the location of the wedge may be moved slightly proximally to secure a plate. However, moving the osteotomy site away from the area of greatest curvature results in a translational deformity. The dog is placed in dorsal recumbency, with the affected limb prepared for aseptic surgery and hanging from the ceiling. A sterile hook connects the distal extremity of the limb to a hook fixed to the limb, to allow aseptic, intra-operative manipulation of the limb. Draping the contralateral limb (if normal) in the surgical field allows intra-operative comparison, which is especially helpful in chondrodystrophic breeds. Kirschner wires are placed parallel to the proximal joint and parallel to the distal joint. A small needle may be inserted in the carpal joint as a landmark. The proximal and distal osteotomies should be parallel to the proximal and distal Kirschner wires, respectively. The distal osteotomy is located as close as possible to the point of maximum deformation, at the predetermined distance from the carpal joint. The proximal osteotomy should intersect the distal osteotomy at the convex surface of the bone, creating a bone wedge of a similar size to the preoperative plan. (Figure 57-15). The bone wedge is removed and may be morsellised to use as an autogenous graft. An ulnar ostectomy is performed via a separate lateral approach to the bone. Removing a small segment of ulna prevents interference of the ulna during manipulation of the radius and provides additional bone graft. The major segments of the radius are reduced and rotational alignment verified and corrected, if needed. Bone segments are stabilized with a compression plate. Correction of any rotational deformity will affect cortical apposition and complicate plate contouring, since the distal radius is not cylindrical.
Postoperative radiographs are indicated to evaluate correction of the deformity and implant placement. Postoperative care is similar to the management of a plated fracture. Bone healing should occur within 6 to 12 weeks.
Open Corrective Osteotomy and External Fixation (Linear or Hybrid) in the Mature Dog
This procedure combines an oblique osteotomy of the radius and a transverse osteotomy of the distal ulna to correct angular and rotational deformities while preserving pre-existing limb length. This technique is therefore preferred in mature dogs with minor limb length discrepancy, especially if morbidity would result from shortening of the limb secondary to a closed wedge osteotomy. External fixation is a versatile method of stabilization of the osteotomy, which allows additional postoperative correction if necessary. Hybrid fixators add further versatility to this technique, especially when osteotomies are located close to a joint. These advantages facilitate the correction of angular deformities in multiple planes, and avoid the technical difficulties associated with plate contouring. However, the owners must be willing to comply with the post-operative care of external fixators. In addition, type II linear fixators are not very effective at correcting the cranio-caudal component of antebrachial deformities, most likely because this plane is perpendicular to that of the fixator.
The dog is placed in dorsal recumbency with the affected limb prepared for aseptic surgery and securely suspended from the ceiling. A sterile hook connects the distal extremity of the limb to a hook fixed to the limb, to allow aseptic, intra-operative manipulation of the limb. The contralateral limb may be included in the surgical field for comparison. In addition, a donor site for cancellous bone (usually the proximal humerus of the affected forelimb) should be prepared for aseptic surgery and draped off if the surgeon plans to fill the open osteotomy site with an autogenous bone graft.
Small needles may be placed in the carpal and elbow joints as landmarks. The lateral head of the radius is palpated, the skin incised and the bone exposed by blunt dissection of the subcutaneous tissues and grid dissection of the muscle. Small Hohmann retractors may be placed on the cranial and caudal cortices of the radius to facilitate placement of the pin in the center of the bone. Using predrilling technique, a centrally-threaded positive profile fixation pin is placed through the proximal radius from the lateral aspect. The pin should be parallel to the proximal radial articular surface and should be within the lateral transverse plane of the proximal radius. The lateral aspect of the distal radius is palpated and the ulnar styloid process is identified. Using predrilling technique, a centrally-threaded positive profile fixation is placed through the distal radius, starting cranially to the ulnar styloid process, from the lateral aspect. The pin should be parallel to the distal radial articular surface and should be within the lateral transverse plane of the distal radius.(Figure 57-16) A lateral approach is made to the distal ulna (see ulnar ostectomy) and a transverse osteotomy is performed with an osteotome or oscillating saw. Intraoperative radiography or fluoroscopy may be used to verify acceptable placement of the pins in relation to the joints. A skin incision is made over the cranio-medial aspect of the distal radius at its point of greatest curvature. Dissection through the subcutaneous tissues exposes the radial diaphysis. An oblique osteotomy of the radius is made at the point of greatest curvature using an osteotome or an oscillating bone saw. The osteotomy line should be directed parallel to the distal radial articular surface (See Figure 57-16). The operating table is lowered so the weight of the animal is suspended from the ceiling. The weight of the animal distracts the distal radius and helps to align the proximal and distal joint surfaces parallel to each other. The proximal and distal transfixation pins are aligned parallel to each other and in the same transverse plane which should eliminate any angular or rotational deformity. Connecting rods with two to six single fixation clamps on the medial rod are connected to the transfixation pins on the lateral and medial aspect of the limb. Additional fixation half-pins are driven through the unused single clamps and into the medial aspect of the radius, penetrating both cortices. One to two additional pins should be placed in each radial segment (See Figure 57-16). Placing these pins on the medial aspect of the radius allows post-operative destabilization and conversion of the type II external fixator to a type Ia. Autogenous cancellous or allogeneic bone (demineralized bone matrix) is placed at the radial osteotomy site. The wounds are closed by suturing the subcutaneous tissue and skin separately.
A circular ring and fixation wires may be used to secure the distal radial segment instead of threaded pins (Figure 57-17).
Hybrid fixation is especially relevant for adequate fixation of a short segment of bone in dogs with a point of maximum angulation located very distally along the radius. In these cases, the osteotomy site may need to be displaced proximally to allow placement of at least two threaded pins in the distal segment, thereby creating a translation of the radial segments during correction of the deformity. Use of a circular ring and fixation wires to capture the distal segment requires less bone stock and allows optimal placement of the osteotomy. The dog is placed in dorsal recumbency with the affected limb prepared for aseptic surgery and securely suspended from the ceiling. A sterile hook connects the distal extremity of the limb to a hook fixed to the limb, to allow aseptic, intra-operative manipulation of the limb. The procedure starts with the placement of the distal ring around the limb (See Figure 57-17). The most distal wire is inserted parallel to the plane of the distal radial articular surface to serve as a reference. This wire may be used as the most distal element of fixation and fixed to the bottom of the ring.
The second wire is inserted from the proximal aspect of the ring, at a 60 to 90° angle from the first wire. Both wires are secured to the ring and tensioned appropriately. Another wire is placed distal and parallel to the elbow joint to serve as reference. An osteotomy of the radius and ulna are performed as described above. The operating table is lowered so that the weight of the animal distracts the distal radius and helps to align the proximal and distal joint surfaces parallel to each other. The proximal and distal references are aligned parallel to each other and in the same transverse plane to eliminate any angular or rotational deformity. A hybrid rod is attached to the ring with a pair of nuts and an SK single fixation clamp applied to the rod is used to secure a threaded half pin placed in the most proximal, medial or cranio-medial aspect of the radius. Limb alignment and range of motion are checked prior to application of additional fixation pins to the proximal segment to complete the hybrid fixator. The positioning of wires and rod (thereby determining the plane of the most proximal pin) on the distal ring should be planned to allow insertion of a drop wire, providing a third element of fixation in the distal segment (See Figure 57-17). Clamps and fixation pins are added to stabilize the proximal segment and form a Type I-a hybrid construct. A type I-b construct may be preferred, especially in cases with cranio-caudal angulation. In these cases, the hybrid rod placed cranially should be short enough to allow flexion of the elbow. Olive wires may be used for better control of the distal radius, especially if cranio-caudal correction is attempted and/or if only two wires are placed in the short segment of bone.
Postoperative radiographs are obtained to document radial alignment and implant position. The limb is bandaged with gauze sponges wedged between the apparatus and the skin to minimize soft tissue swelling. As postoperative swelling decreases, the limb may be left unbandaged. A light wrap around the rods and rings minimizes the risk of catching the fixation on surrounding objects after discharge from the hospital. Owners are instructed to confine their dog, limit activity to leash walking and clean the pin tracts daily. Weekly rechecks should be scheduled initially, to monitor pin tracts, remove sutures (at 2 weeks) and change the bandage around the frame. Radiogaphic evaluation of healing of the osteotomy is indicated every 4 to 6 weeks. The fixator is removed when the osteotomy site is bridged with bone.
Suspending the limb from the ceiling during the osteotomy aids the surgeon in aligning the limb, and apparently decreases the amount of postoperative swelling because of the minimal manipulation needed to support the limb during correction and fixation. It is important to make the radial osteotomy cut parallel to the distal radial joint surface not only in the lateral to medial plane but also in the cranial to caudal plane to enable correction of a severe cranial bowing deformity. External fixation of the osteotomy is useful for several reasons. The proximal and distal transfixation wires serve as external landmarks to help align the bone after osteotomy. Additional manipulations can be easily made after the surgical procedure if the surgeon is not satisfied with the corrections. The rigidity of the fixator can be altered to fit the animal and the stage of healing of the osteotomy. Finally, removal of the fixation after bone healing is simple and generally requires only sedation. The disadvantages of external fixation lie in the aftercare which the owner must perform, and the damage the external fixator can do to the dog’s surrounding environment.
Correction of Angular Deformity and Continuous Distraction with a Circular External Fixator
Circular fixators are indicated as treatment for adult dogs that have a limb length discrepancy of at least 20%, or immature dogs with anticipated extensive growth. Circular fixators can be effectively used to simultaneously correct angular deformities and length discrepancies. It is also indicated to treat dogs with complex deformities such as 1) bifocal angulations, resulting in a translation of the limb, or 2) significant cranio-caudal and rotational deformities. Although the circular fixator can be used to treat dogs with varus/valgus deformities, there are simpler techniques that are equally as effective using plate or standard external fixation. However, the advantage of the circular fixator in treating angular deformities consists in its flexibility in allowing correction of the deformity and length discrepancies simultaneously. The disadvantages of the circular fixator in correcting deformities are the intensive and sometimes lengthy learning curve for the surgeon, the detailed preoperative planning, and the need for regular postoperative monitoring of the distraction process. Length deficit, rotational, craniocaudal and mediolateral angulations are determined as previously described (see pre-operative planning in closing wedge osteotomy and Figure 57-14).
The simplest method described to treat angular deformities with circular external fixators (CEFs) consists of an acute correction of the angulation and rotation, followed by a linear distraction. The procedure starts by placing the most proximal and distal rings parallel to the plane of the proximal and distal joint surfaces of the radius, respectively. The radial osteotomy is then performed at the point of maximum curvature, parallel to the carpal joint. The periosteum should be incised along with the cortex to allow manipulation of the bone, but care is taken to avoid stripping this layer. The ostectomy of the ulna can be achieved through the same incision, or via a lateral approach to the ulna. The antebrachial deformity is corrected by aligning the proximal and distal rings (Figure 57-18). Additional fixation is added to the short segment using a second ring and fixation wires (preferably) or a drop wire, depending on the bone stock available. Another ring is placed in the proximal segment and connecting rods are added between these rings. Linear motors connect the ring immediately proximal to the osteotomy to the ring immediately distal to the osteotomy to enable postoperative lengthening of the bone.
Limb alignment and implant position are confirmed on postoperative radiographs. The limb is bandaged with gauze sponges wedged between the apparatus and the skin to minimize soft tissue swelling. As postoperative swelling decreases, the limb may be left unbandaged. A light wrap around the rods and rings minimizes the risk of catching the fixation on surrounding objects after discharge from the hospital. A delay, or latency period, is recommended after surgery, before distraction is initiated. This allows local cellular and vascular responses to occur in order to facilitate optimal distraction osteogenesis. The recommended latency period varies from 1 to 3 days for immature animals to 5 to 7 days for adult animals. Early distraction may cause diminished callus production while unduly delayed distraction may allow premature consolidation. For the same reasons, distraction is started at a rate of 1 to 2 mm daily, divided into two to four increments. Physiotherapy and pain medications are indicated until the dog is bearing full weight on the limb. Low-impact exercise is essential to encourage use of the limb and stimulate formation of regenerate bone. Owners are shown how to turn the linear motors in order to provide a rate of distraction adjusted to the age and size of the dog. For example, the distraction rate may be increased to 2 mm daily in large dogs, less than 6 months of age, who have undergone an osteotomy of the radial metaphysis. Daily cleaning of the skin with 0.05 percent chlorhexidine solution and application of a triple antibiotic ointment around the wire-skin interface minimize the risk of wire tract infection.
Use of the limb, range of motion of the carpus and radiographs are re-evaluated every seven to ten days. Because planned and actual adjustments routinely differ by 25%, the distraction regimen is adjusted based on serial radiographs. Contracture of the flexor muscles is a common complication, leading to decreased range of motion of the carpus and reluctance to use the limb. This complication is more likely in dogs requiring more than 10 percent lengthening and is best managed by decreasing the distraction rate (to 0.5 mm daily), pain medications and aggressive physical therapy. When the distraction is complete, the frame is left in place until the gap has completely filled with new bone, typically three to five weeks after distraction has stopped. CEFs are removed under sedation and exercise is limited to low-impact activity for three weeks thereafter.
This standard circular fixator is a relatively simple technique to allow lengthening of the bone if there is no angular deformity, or if the deformity is mild and can be corrected as a one-stage procedure. However, it requires complete transection of the periosteum and limits contact between the proximal and distal radial segments. The resulting gap increases the stress placed on the frame, may slow bone healing, and increases postoperative morbidity. Complications requiring a second surgery have been described in 29 to 67% of cases, with good to excellent results reported in 68% of dogs treated with this method. To address these limitations, another strategy consists of placing hinged external fixators to gradually correct the angular deformity and length deficit. The positioning of the hinges is critical to the outcome and requires careful pre-operative planning to determine the direction and amplitude of the oblique deformity
The frame is assembled before surgery so that the rings are placed at an angle to each other corresponding to the amount of deformity. Hinges are levelled with the origin of the deformity. Their axis (line joining these hinges) should be perpendicular to the direction of the deformity and tangential to the bone at the origin of the angulation. The angular motor is placed on a third connecting bar in the plane of deformity and on the concave side of the deformity. Positioning olive wires against the concave surface of the bone prevents translation of the radius during angular correction. Acute, intra-operative correction of any torsional deformity simplifies the design of the frame. As the angulation is corrected, an opening wedge of regenerate bone is formed, resulting in an overall gain of length equal to half of the length gained on the concave surface of the bone. Hinge fixation is also indicated in the treatment of bifocal deformities, where bone lengthening and correction occur at two osteotomy sites, effectively doubling the rate of distraction.
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