Thoracolumbar and Sacral Spine

Indications

Fenestration of thoracolumbar intervertebral discs is appropriate for dogs of breeds predisposed to disc herniation (such as the dachshund and Pekingese), with clinical signs ranging from lumbar pain to paresis, that are otherwise in good health and are less than 8 years of age. One study indicated that only 5% of dogs with thoracolumbar disc herniations were more than 8 years of age.¹ Whether older dogs are less likely to have recurrent problems is unknown, but in such dogs a conservative approach seems advisable initially.

Fenestration should be considered when signs of disc herniation are first evident; the operation is definitely recommended if signs progress in severity or on the first recurrence. Dogs presented with caudal motor paralysis should undergo spinal cord decompression, because disc fenestration alone is not appropriate treatment for paralysis. If the dog still perceives pain in the rear toes, fenestration should also be accomplished. Fenestration can be performed within a variable period after disc herniation; we prefer to operate within the first 2 to 3 days. The patient can then recuperate from surgery while hospitalized to treat signs produced by that herniation.

Preoperative Preparations

Corticosteroids and antibiotics are administered preoperatively. Anesthesia is induced with a short-acting anesthetic agent and maintained by endotracheal administration of an acceptable volatile agent. Intravenous fluids are administered during surgery and postoperatively. An area of the back extending from the vertebral border of each scapula to the crest of each ilium is clipped and prepared for surgery. The dog is positioned in ventral recumbency on an insulating pad to conserve body heat. It is most convenient for surgeons to operate from the side of the patient opposite that of their dominant hand. Radiographs and a skeleton should be available for reference.

Surgical Technique

A dorsolateral approach2 is used to gain access to eight intervertebral discs between T10 and L5. Discs between T9-10 and L5-6 can also be fenestrated if they are calcified or partially herniated. These discs are not routinely fenestrated because of their low incidence of herniation. They are also technically more difficult to fenestrate because of anatomic differences. Not only is the L5-6 disc more difficult to fenestrate, but also considerable risk of creating a femoral nerve deficit exists if the adjacent ventral nerve branch is damaged.

A skin incision is made from one to two spinous processes rostral to the anticlinal vertebra (T11) to one vertebra rostral to the ilium. This incision may be made directly on the dorsal midline or 1 to 2 cm lateral to the midline on the side from which discs are to be fenestrated. The cutaneous trunci muscle, subcutaneous fat, and superficial fascia are incised in the same plane and are reflected sufficiently to expose lumbodorsal fascia 1 to 2 cm lateral to the dorsal midline (Figure 48-1A). Lumbodorsal fascia and aponeurosis of the longissimus thoracis et lumborum muscle are incised along an imaginary line from a point 5 mm lateral to the spinous process of T9 to a point 1 to 2 cm lateral to the comparable process of L6 (Figure 48-1B). In the rostral portion of the surgical field, the caudal border of the spinalis and semispinalis thoracis muscles, interposed between the lumbodorsal fascia and aponeurosis of the longissimus thoracis muscle, is also incised (Figures 48-1B and 48-2).
 

Access to intervertebral discs is gained by opening the intermuscular septum between multifidus lumborum and thoracis muscles medially and longissimus dorsi and sacrococcygeus dorsalis lateralis muscles laterally (Figures 48-1C, 48-2 and 48-3). This septum is the first one lateral to the dorsal spinous processes; it is easiest to locate in the midlumbar region, where fat is interposed superficially between muscles. Muscles are easily divided by blunt dissection in the lumbar region; however, the septum is less distinct over the ribs. All blunt dissection is done with a curved semisharp Adson, or comparable, periosteal elevator in each hand. As tubercles of the last four ribs are exposed, care should be taken not to disturb small nerves and vessels coursing craniolaterally immediately dorsolateral to each tubercle. Separating muscles is carried to the base of the lumbar transverse processes.

The novice should completely separate muscles to this level taking care to avoid dorsal branches of spinal nerves (See figure 48-1C). This provides good visualization of intervertebral discs and adjacent structures. Experienced surgeons can “tunnel” down to each lumbar transverse process, thereby avoiding considerable tedious dissection and trauma. The short transverse process of L1 lies adjacent to the last rib, assuming the thirteenth rib is present, and is used as an anatomic reference point. All other lumbar transverse processes can be “tunneled” down to by referring to the lateral radiograph and estimating the distance between each process. If judgment is correct, the veterinary surgeon will never see dorsal branches of each rostral spinal nerve or its allied vessels. As the operation proceeds caudally from T13 to L1, succeeding transverse processes are progressively deeper.
 

As the surgeon exposes lumbar transverse processes (L1-5), the lumbar discs are exposed. The lateral anulus of intervertebral discs lies immediately rostral to the base of each transverse process (Figure 48-4). In the caudal thoracic area, discs are rostromedial to the head of each rib. The T10-11 disc is difficult to expose because it is 1 to 2 cm ventromedial to and is partially covered by the rib tubercle. Each disc can be visualized by elevating tissue off the lateral anulus with a periosteal elevator. Use of a small self-retaining retractor (Gelpi or Weitlaner) or hand-held retractors enhances visualization. Care should be taken not to invade intervertebral foramina, which lie immediately dorsal to each disc and contain spinal nerves and allied vessels. The inexperienced surgeon may overcompensate while attempting to avoid intervertebral foramina and work too far ventrally, where one risks injuring ventral branches of spinal nerves. Ventral branches of spinal nerves pass adjacent to the ventrolateral aspect of each disc (See figure 48-4).
 

In the lumbar area, ventral branches of the spinal nerves are located under the intertransverse fascia and are not visible in the surgical field unless an attempt is made to expose them. To ensure that a ventral branch is not traumatized, the tip of a curved mosquito hemostat can be introduced into the intertransverse fascia adjacent to the ventrolateral border of the anulus and the jaws can be spread gently. This exposes the ventral nerve branch occasionally, and creates a landmark for the surgeon to avoid. If the L5-6 disc is fenestrated, the ventral branch of the fifth lumbar nerve should be identified and avoided to ensure it is not damaged.

A disc’s lateral anulus is visualized best for fenestration if adjacent muscle is retracted rostrodorsally with a curved, semisharp periosteal elevator. This instrument also protects dorsal branches of spinal nerves and associated vessels. A pointed scalpel blade is used either to incise or to remove an elliptical section of the anulus fibrosus. The anulus should not be cut where it cannot be visualized. Fenestration is accomplished with a modified dental-claw tartar scraper or the eye portion of a large suture needle held in a needle holder. Modifications to dental tartar scrapers include grinding off the sharp tip and sides of the claw. The nucleus pulposus is removed using a circular motion. The tip of the hook or needle-eye is directed upward, with care taken not to break through the dorsal anulus. A partially herniated disc must he fenestrated cautiously, to avoid forcing additional nucleus pulposus into the spinal canal (Figure 48-5). The surgeon must remove as much disc material as possible.
 

Fenestrating T10-11 disc requires special care to avoid creating pneumothorax; pleura, directly ventral to this disc, rises and falls with respiratory movement. If existence of pneumothorax is in question, irrigating the area with saline solution and expanding the lungs by compressing the ventilation bag should provide an answer; air bubbles will appear in the surgical field if significant pneumothorax exists.

Minimal hemorrhage associated with exposure and fenestration of thoracolumbar discs can usually be controlled by topical pressure on bleeding tissue with a periosteal elevator. Rarely, hemostatic forceps or electrocautery is required to control bleeding.

Every disc fenestrated should be identified to ensure no discs are missed between T10 and L5. If clinical signs merit decompression of the spinal cord, decompression should be performed first, followed by disc fenestration. Fenestration is more compatible with hemilaminectomy than with dorsal decompression. Hemilaminectomy and fenestration can be performed from the same side; although the multifidus muscle is badly traumatized, no adverse clinical signs have been observed. Lateralization of signs often dictates performing a decompressive surgical procedure and fenestration on opposite sides of the spinal column.

Debridement of tissue is not necessary when the “tunnel” technique is used to expose lumbar discs. Performing a hemilaminectomy on the same side, or division of the multifidus and longissimus dorsi muscles down to the level of transverse processes for improved exposure, may necessitate some debridement. Aponeurosis of the longissimus and spinalis et semispinalis muscles in the caudal thoracic area and overlying thoracolumbar fascia are approximated with one suture line of absorbable suture material. Subcutaneous tissues are apposed with similar material, catching underlying fascia occasionally to obliterate dead space. The skin incision is closed with any dermal suture. A light-pressure bandage may he applied around the trunk of the dog and left in place for 4 to 7 days.

Postoperative Care and Prognosis

Corticosteroid and analgesic agents should be administered for 1 to 3 days postoperatively because most dogs experience some discomfort. Thereafter, treatment depends on clinical signs. Because corticosteroids are used in association with this operation, skin sutures should be left for at least 3 weeks to avoid incisional dehiscence. Dogs routinely go home 48 to 72 hours after surgery, or as soon as voluntary urination is evident. In addition to preventing subsequent attacks of disc prolapse, fenestration eliminates the need for prolonged confinement of dogs with functional ambulatory ability. Physical therapy can be initiated within a day or so of surgery in patients with caudal paralysis.

Paresis, if present, remains unchanged in most animals immediately postoperatively. Because clinical signs occasionally are more severe immediately after the procedure, the client must be forewarned of this possibility. Deterioration in neurologic status can be associated with the operation. If pathologic changes in the spinal cord, which may or may not be known, are progressive at the time of surgery, disc fenestration itself will not be responsible for a worsened neurologic state. Such a condition may result from spontaneous herniation of additional nucleus pulposus while the dog is anesthetized for radiographs or surgery. Overzealous fenestration of a partially herniated disc may also force additional material into the spinal canal. Trauma to the spinal cord from the fenestration hook is an unlikely cause of increase in neurologic deficit. The client should be advised that some dogs suddenly deteriorate neurologically without radiographs or operation.

The most likely potential surgical complications are 1) failure to fenestrate a disc, 2) creating a pneumothorax, 3) injury to spinal nerves, 4) damage to the spinal cord, and 5) cutting spinal arteries.

In most dogs, evidence of some degree of spinal nerve injury exists for at least a few days postoperatively. Dogs may have slight scoliosis, with deviation to the operated side, and sag (paralysis) of abdominal muscles ipsilateral to the operated side may be noticeable. If the ventral branch of the fifth lumbar (L5-6) has been damaged, the dog will have at least a temporary femoral nerve deficit. Severity of these signs is directly correlated with the expertise of the veterinary surgeon.

We are aggressive in promoting thoracolumbar disc fenestration because it is impossible to predict severity of a recurrent disc attack. Herniation of a cervical disc has not been observed to cause permanent caudal paralysis or death from diffuse myelomalacia; in the thoracolumbar region, however, such a sequela is not unusual. Fenestration, properly performed, should minimize chances of subsequent disc episodes, and the dog’s locomotion should not be compromised.

The dorsolateral approach is preferred for fenestrating thora- columbar discs because it 1) permits decompression by hemilaminectomy when this procedure is also indicated, 2) results in minimal trauma, and 3) provides easy access to nine discs. Thoracolumbar intervertebral disc fenestration is more difficult than cervical disc fenestration, and the potential for severe and possibly permanent neurologic injury can not be overemphasized. Success with this procedure requires a thorough understanding of anatomy and basic surgical principles. Consequently, the novice should perform this surgical procedure on a cadaver before attempting it on a clinical patient.

References

1. Gage ED: Incidence of clinical disc disease in the dog. J Am Anim Hosp Assoc 11:135, 1975.
2. Yturraspe JD. Lumb WV: A dorsolateral muscle separating approach for thoracolumbar intervertebral disc fenestration in the dog. J Am Vet Med Assoc 162:1037, 1973
3. Bartels KE. Creed JE: Yturraspe DJ. Complications associated with the dorsolateral muscle-separating approach for thoracolumbar disc fenestration in the dog. J. Am Vet Med Assoc 183:1081, 1983
    

Surgical fenestration of the intervertebral space provides a means of prophylaxis in disc disease. If protrusion exists, surgical removal of the nucleus remaining in the intervertebral area will eliminate the pressure causing the protrusion. When all other discs that are potential problems (T9-10 to L5-6) are fenestrated at the same time, complete prophylaxis against future disc protrusions is achieved. The material already extruded into the canal cannot be removed by disc fenestration alone; however, fenestration of other degenerated discs is recommended, so vigorous physical therapy, such as hydrotherapy and cart walking, can be prescribed without fear of causing another protrusion or even extrusion.

The ventral fenestration technique described here facilitates access to all potentially offending discs with a minimum of surgical trauma. Ten discs are fenestrated (T9-10 to L5-6). The thoracic discs are exposed through a left tenth intercostal thoracic approach, and the lumbar discs are exposed through a paracostal abdominal incision (Figure 48-6).
 

Surgical Technique

The patient is medicated preoperatively with corticosteroids (dexamethasone 1 mg/lb) and antibiotics. The patient is placed in right lateral recumbency, and the left lateral side is clipped and prepared aseptically. The skin incision is made over the thirteenth rib from the dorsal to the ventral midline. The subcutaneous tissue is dissected, the incision is slid caudally, and a paracostal incision is made into the abdomen. The left kidney is located and is reflected ventrally with the peritoneum. Frazier laminectomy retractors are positioned (Figure 48-7), and the abdominal viscera are packed off with a laparotomy pad. This retroperitoneal abdominal exposure affords access to the LI-2 through L5-6 intervertebral spaces. The iliopsoas (psoas minor) muscle is hooked with a muscle retractor and is retracted away from the ventral midline (Figure 48-8). The ventral crests can be palpated.
 

The transverse processes are identified and are numbered for orientation. Medial to the first transverse process is the T13-L1 intervertebral space. This space is not easily exposed from the abdominal approach and thus is fenestrated from the thorax. The remaining intervertebral spaces (Ll-2 to L5-6) are fenestrated by first cutting the ventral longitudinal ligament and annular fibers of the ligament of the rib head with a scalpel. The nucleus pulposus is removed with a Miltex scaler B tartar scraper. An inward, upward, and outward motion is used to clear the intervertebral space of as much nucleus as possible. Once this maneuver has been completed, the retractors are removed, and the muscle layers are individually sutured with 2-0 synthetic absorbable suture material.

The skin incision is slid in the cranial direction, and an incision is made into the thorax between the tenth and eleventh ribs. Frazier laminectomy retractors are placed (Figure 48-9), and ventilation is instituted. The T9-10 through T13-L1 intervertebral spaces are located and are dissected free of pleura; the sympathetic trunk and intercostal vessels are carefully avoided. When the dissection is complete, the discs are fenestrated in the same manner as already described (Figure 48-10). The thorax, latissimus dorsi muscle, and skin are closed in a routine manner.
 

Postoperative Care

The animal is monitored closely during the anesthetic recovery period. Antibiotics are given, the bladder is kept evacuated, and intensive physical therapy is instituted. Physical therapy includes hydrotherapy and cart walking.
 

Indications

The most common indication for surgery of the thoracic spinal cord is the removal of extradural masses usually diagnosed by myelography, CT and MRI. Disc herniations in the thoracic spine are rare, and many surgeons ignore the few disc lesions seen there. The intercapital ligaments occupying the floor of the canal between T2-10 help to protect the spinal cord from disc herniation. Neoplasia in the thoracic spine is relatively more common than in other areas of the spine because of the lack of thoracic disc herniation. Therefore, exploration of the thoracic cord is likely to yield a tumor more often than in other areas of the spine.

Thoracic spinal fractures are rare because of the stabilizing influence of the ribs and long dorsal spines that help to prevent rotational deformities as well as flexion extension injuries. The mobile spine anterior and posterior to the thorax suffers more traumatic lesions.

The degenerative changes seen in the cervical and lumbar spine are not so common in the thoracic spine. Disc degeneration occurs as frequently as elsewhere in the spine, but disc herniations into the canal are rare. Redundancy of the ligamentum flavum is rare. Acquired bony stenosis is not often seen. Facet degenerative changes, synovitis, and synovial proliferation seldom cause cord stenosis or cord pressure. Bony stenosis, such as seen in the cervical region of caudal cervical spondylopathies of large dog breeds, has not been reported. Because many of these degenerative changes occur in more mobile segments of the spine, the more rigid thoracic spine is believed to be spared these changes.

Positioning of the Patient

The patient is placed in ventral recumbency. Elevation of the sternum (but not the elbows) by pillows, sandbags, or padding raises the spine in relation to the scapula. Pulling the forelegs forward usually loosens the adduction of the scapula to the spine, thereby allowing lateralization of the scapula. However, positioning the forelimbs posterior or crossing them under the sternum may aid in spinal visualization, so experimentation with foreleg positioning may be helpful.

Surgical Approach and Anatomy

A midline incision is made through the skin, subcutaneous fat, and fascia to the midline over the dorsal thoracic spinous processes. Just off the midline, the approach continues ventral alongside the dorsal spines to the dorsal lamina, which forms the base of the dorsal spines. The cutaneous trunci, trapezium, and cleidocephalicus are the first muscles encountered and are incised along their attachment to the dorsal spine processes on the midline. The latissimus dorsi and rhomboideus muscles are likewise incised, allowing lateralization of the scapula by self-retaining rib, Gelpi, or Weitlaner retractors. The cranial serratus dorsalis insertions are incised, as are the insertions of the thoracic spinalis and semispinalis muscles on the dorsal spines. The spinalis thoracis muscles are elevated by periosteal elevators to expose the lateral dorsal spines. The longissimus muscles are lateralized with retraction and do not require incision. The thoracic multifidus muscles are elevated with periosteal elevators or are incised at their origins. The supraspinatus ligament and interspinales muscles are left intact. The longi and breves rotatores muscles are incised at their origins exposing the dorsal lamina (Figure 48-11). The levator costae muscle can be spared unless rib head exposure is needed.

Once the lamina is exposed, a high-speed drill is needed to remove the dorsal lateral lamina. For right-handed surgeons, a left-sided hemilaminectomy is preferred (Figure 48-12). The dorsal spine can be undercut to the off side of the spinal canal. The ventral 1 to 2 cm of the dorsal spine can be removed, allowing wide lateral exposure to the off side (Figure 48-13). The resultant floating dorsal spine, suspended by interspinous muscles and supraspinous ligament, produces no noticeable effect. Likewise, the rib head, neck, and tubercle can be removed as needed for lateral cord exposure on the near side. The resultant floating rib seldom causes problems because it is supported by adjacent ribs through the intercostal muscles. As the surgeon moves forward in the thoracic spine, the ribs articulate higher in the interdiscal space and may necessitate rib head, neck, and tubercle resection. Resection of the proximal rib head, neck, and tubercle allows adequate spinal cord visualization. Care must be taken to avoid dissection below the rib that could allow penetration into the chest cavity, thereby creating a pneumothorax.

The length of the dorsal spines in some breeds may create a deep surgical field. Proper instrumentation and lighting allow careful cord evaluation. The arteries encountered are the dorsal branches of the intercostal arteries. The spinal branches supply the spinal cord through the foramen just above the rib neck. These vessels can be avoided by staying close to the midline along the dorsal spines. The veins encountered parallel the arteries and join the azygos posterior to the heart and the costocervicalvertebral trunk anterior to the heart.
 

Wound closure is similar to that of lumbar or cervical hemilaminectomy. A free fat graft harvested from the subcutaneous tissue is placed into the hemilaminectomy defect. Careful cord hemostasis lessens the hemorrhage under the fat graft that increases scar invasion of the graft. The more graft that undergoes revascularization, the less restrictive scar forms above the cord.^1-3 The trapezius, rhomboideus, serratus dorsalis, and cranialis muscles should be reattached to preserve scapular function. The rest of the epaxial muscles reattach to the spine without direct suturing.

Postoperative care is similar to that after other spine approaches. Lameness is common for a few days until the scapular sling muscles lose their tenderness.

Benefits

Inclusion of this approach to the thoracic spine with well-known approaches to the neck and lumbar spine allows the surgeon to explore any lesion in the spinal canal from the foramen magnum to the coccygeal vertebrae. Most extradural lesions can be removed from the spinal canal, especially if undercutting the dorsal lamina or removal of the base of the dorsal spine is used to gain access to the far side of the spinal cord.

Limitations

Long, wide laminectomies over many disc spaces entail removal of the bases of many dorsal spines. The need for stabilization of these spines to prevent their ventral collapse into the laminectomy site adds additional hardware, expertise, and complexity to an already challenging approach. In addition, visualization, especially under the spinal cord, is sometimes poor.

The scapula prevents a lateral view of the cord in the cranial thoracic spine. Instruments have to be placed from a dorsal aspect. This necessitates using right-angled instruments that are not used in cervical and lumbar spine operations. Removal of the rib head and neck, especially over many disc spaces, adds complexity.

A surgical headlamp and 2x loop magnification are helpful in visualizing the spine especially in deep surgical fields. Bipolar cautery and fine tip suction are essential in providing hemostasis. The added visual acuity gained by hemostasis is more beneficial than the more obvious benefit of preventing blood loss and shock.

Because of the stabilizing influence of the adjacent dorsal spines and ribs, the destabilizing effects of wide deep laminectomy over the thoracic spine are less than those of the cervical or lumbar spine. Wider exposure of the spinal cord is possible, allowing a greater amount of adjacent tissue excision for biopsy or tumor removal. However, the close proximity to the aorta, azygos vein, and chest cavity makes exposure ventral to the cord or rib head hazardous. Damage to the nerve roots exiting the foramen cause some loss of forelimb function as well as loss of intercostal function affecting respiration.

Variations: First and Second Thoracic Cord Exposure

The first and second thoracic vertebral cord can be approached as a posterior extension of a seventh cervical dorsal laminectomy.^4,5 The thoracic dorsal spines can be exposed anteriorly without disturbing the ligamentum nuchae or supraspinous muscles, which are retracted laterally. The drill is angled from anterior to posterior, with the right-handed surgeon positioned on the right side of the patient that has been placed in sternal recumbency. Removal of the lamina between the base of the dorsal spine and first rib head exposes the spinal cord and canal over one side. Care must be used to leave enough of the base of the first dorsal spine to maintain the strength necessary to support the head and neck through its attachment of the nuchal ligament. This limits the exposure of the first thoracic spinal cord. If complete removal of the base of the first dorsal thoracic spine is needed, then enough of the base of the spine should be removed to prevent downward pressure of the spine stump on the exposed cord. Support of the head by the nuchal ligament, which attaches to the first three dorsal spines, pushes the remaining spine ventrally when its lower base is removed.

Approaching the anterior thoracic cord in this way avoids the disruption of the musculature along the dorsal spine and attachments to the scapula. The scapula influences the approach to the thoracic spine only anterior to T6 or T7. Posterior to these areas, the approach is similar to that of the lumbar spine.

References

1. Biggart JF III. Laminectomy membrane: etiology and prevention. In: Proceedings of the American College of Veterinary Surgeons Annual Meeting. Denver, CO: American College of Veterinary Surgeons, 1981.
2. Biggart JF III. Prevention of laminectomy membrane by free fat grafts after laminectomy in dogs with disc herniations. Vet Surg 1988;17:29.
3. Gill GG, Sakovich L, Thompson E. Pedicle fat grafts for the prevention of scar formation after laminectomy. Spine 1979;4:I76.
4. Piermatei DL, Greeley RG. An atlas of surgical approaches to the bones of the dog and cat. 2nd ed. Philadelphia: WB Saunders, 1979:46-49.
5. Parker AL. Surgical approach to the cervico-thoracic junction. J Am Anim Hosp Assoc 1979;9:374-377.
    

Hemilaminectomy of the Caudal Thoracic and Lumbar Spine

Hemilaminectomy of the caudal thoracic and lumbar spine is used to gain access to the vertebral canal for the removal of offending masses, often impinging on or involving the spinal cord. These masses include intra and extradural tumors, granulomas, bone fragments resulting from vertebral fracture, and (by far most common) intervertebral disk extrusions and protrusions. The term “hemilaminectomy” may be a misnomer, since the lamina of the vertebrae is the boney structure which is dorsal to the vertebral canal, dorsal to the articular facets. The pedicle, or root, is the boney structure lateral to the vertebral canal between the vertebral body and articular facets. It is the pedicle, more than the lamina that is removed during what is commonly referred to as a hemilaminectomy. Some authors do refer to removal of sections of the pedicle as pediculotomy, however the term hemilaminectomy is used to describe the common surgical procedure for removal of part of the vertebral arch on a single side of the spinous process to gain access to the vertebral canal.

The timing of surgical intervention and the urgency of spinal cord decompression has been explored in several clinical studies. Though there is some disagreement in interpretation of the clinical studies, and hospitals have different capabilities for after hours imaging and surgery, a general consensus regarding the triage of patients with spinal cord compression is available. In cases of thoracolumbar spinal cord compression resulting from presumed intervertebral disk extrusions or protrusions the recommendations are as follows:

1. No deep pain less than 12 hours. Emergency operation should be recommended. The prognosis is 50% for ambulating. At present, there are no clinical studies that demonstrate efficacy of any glucocorticosteroid including methylprednisolone sodium succinate, therefore the administration of these medications in not indicated.
2. No deep pain over 24 hours. Operate when practical. “Practical” is defined as in the morning if presented at night, as soon as possible if presented during the day, but do not wait until the next day. There is no reported correlation between duration of paralysis prior to surgery, and clinical outcome.
3. Acute, less than 12 hours with no motor function but deep pain is present. Offer emergency operation contingent on personnel, progression of neurologic signs and how long to morning (e.g. is it 3:00am? Then wait.) These cases may loose deep pain as the pathophysiology is not static. Prognosis is therefore guarded but not poor.
4. Deep pain present, no motor function, over 24 hours. Operate when practical. Prognosis is good with 96% of dogs becoming ambulatory. It will take an average of two weeks for these dogs to walk.
5. Non-ambulatory, purposeful motor movement. If admitted in evening, then operate in am. Perform serial neurologic exams to assure patient’s neurologic status does not worsen. Some facilities will delay day admitted cases if the neurologic examination is static and noninvasive imaging (CT,MR) is available in the morning, therefore avoiding a myelogram. Prognosis is good for ambulating. It will take an average of one week for these dogs to walk.
6. Ambulatory paretic. Operate the next day. Of course sooner if patient is stable and facilities and personnel are available. Prognosis is excellent for ambulating. Cage rest can be considered if cost is a factor, but owners should be warned about worsening of neurologic status including paralysis.

A majority of disk extrusions occur near the thoracolumbar junction; rostral to the lumbar intumescence of the spinal cord and caudal to the thoracic intumescence. Therefore the neurologic signs are normal sensation, proprioception and motor function to the thoracic limbs and loss of proprioception, motor function, and pain sensation (in that order) to the pelvic limbs. The common neurologic localization and clinical diagnosis is a T-3 to L-3 (third thoracic to third lumbar spinal cord segment) myelopathy. Disinhibition from compromise of the upper motor neurons to the femoral and sciatic nerves results in hyper-reflexia or upper motor neuron signs to the patellar and cranial tibial reflexes. The progression of signs from loss of proprioception, to loss of motor function, to loss of superficial then deep pain, is most often a function of compression on the descending and ascending spinal cord axons. The larger axons, such as those that carry proprioceptive information, are affected first. Deep pain sensation, or spinal thalamic pathways are not discrete in domestic animals as they are in humans. Instead they are diffuse, multisynaptic and bilateral within the spinal cord. Loss of deep pain perception reflects a functional transection of the spinal cord. Though a functional transection does not necessarily mean an irreversible condition, the loss of deep pain sensation is a negative prognostic indicator. The alpha motor neurons to the femoral nerve are located above the interbertebral disk between the third and fourth lumbar vertebrae. The alpha motor neurons to the sciatic nerve are located roughly above the fourth and fifth lumbar vertebra. For this reason compressions of the spinal cord in these locations can result in lower motor neuron signs to the segmental reflexes in these areas. Offending masses can impinge on vertebral nerve roots and can result in pain and hyperesthesia due to the radiculopathy. Hyperesthesia in descrete areas as assessed by the paniculus reflex can give a more precise indication of the location of an offending mass.

Because the neurologic examination often does not give an exact localization of the area of compression or side of the mass if it is lateralized, imaging should be performed to define the pathology of the mass (tumor or disk, size) and location (vertebral segment, left, right, midline). Myelography with conventional radiographs has classically been used to localize the lesion. Though sufficient in most cases, a discrete lesion my not be apparent if there is considerable spinal cord swelling. In addition it may be difficult to differentiate disk extrusions from other pathologies. Computed tomography (CT) can be used since many disks are partially calcified. The soft tissue resolution of newer CT scanners is very good and can image most masses. Spiral CT scanners are very fast and can noninvasively localize a lesion in less than 10 minutes in most cases. Magnetic resonance imaging (MRI) scanners provide the best resolution of both soft and boney tissues and are becoming the standard of care for neurologic imaging in veterinary medicine.

Once a lesion is localized with either modality, identifying the proper location for a surgical approach to perform hemilaminectomy can be troubling for inexperienced surgeons. Several strategies can be employed. First, the surgeon should count the number of lumbar vertebrae. This is obvious with myelograms and most CT scans, but a scout image must be taken with MR scans. Though in most cases there are seven lumbar vertebrae, in some patients there are transitional vertebrae. Vestigial ribs may arise from the first lumbar vertebra, or the most caudal rib may be present on one side only. Since ribs are not always imaged with MR, a dorsal plane scout film (dorsal plane localizer) from the sacrum to the twelfth thoracic vertebra will demonstrate rib anatomy. Hemi-vertebra may be present at the lumbosacral junction. These anatomic variations must be noted and kept in mind. With MR, a scout film (sagittal localizer) will image the celiac and cranial mesenteric vessels along with the lumbar vertebrae. The vessels arise below the thirteenth thoracic or first lumbar vertebrae. These vessels serve as land marks for more focal MR images.

Palpation of the spinous processes can usually give the proper location in the lumbar area. The spinous process of the seventh lumbar vertebra may be palpated between the cranial aspects of the wings of the ilium. The spinous processes are usually palpable and the surgeon can count cranially to find the proper surgical site. In some cases where lumbar fat is very thick, the surgeon may need to make an approximate surgical approach through the skin and lumbar fat, then palpate the spinous processes surgically. In the thoracolumbar area, the ribs serve as landmarks for localization. Again, confirm the anatomy of the patient, as transitional vertebrae and small vestigial ribs can confuse localization. After an initial surgical approach through the skin and fat is made, a small incision in the lumbar fascia lateral to the longissimus and iliocostalis muscles is made by the thirteenth rib just large enough to accommodate one’s index finger. The thirteenth rib can be palpated. This rib attaches to the cranial aspect of the thirteenth thoracic vertebra. The spinous process of the thirteen thoracic vertebra is also often the first that can be distinctly palpated as those of the ninth to twelfth tend to be very close to each other. Once the thirteenth thoracic spinous process can be identified with certainty, the location for laminectomy can be accurately determined. Matching the shape of the spinous processes seen during a surgical approach with pre-operative imaging is also helpful.

Some surgeons use other techniques to localize the proper location for the hemilaminectomy. Specifically a hypodermic needle (such as 22 ga.) can be pressed into a spinous process prior to surgery, then a lateral radiograph taken to define which spinous process the needle is in. The hub of the needle is then cut off leaving the shaft of the needle beneath the skin. The needle is then found during the surgical approach, defining the proper surgical location. It is not uncommon, however, for a surgeon to loose the needle and spend some time finding it during the surgical approach. Another similar technique is to use Methylene blue. Instead of leaving the shaft of the needle under the skin, a needle is pressed into a spinous process then a lateral radiograph is taken. A small amount of sterile methylene blue 1% (0.1 ml) is injected into the area of the spinous process then the needle removed. The area of staining is found during the surgical approach defining the proper location. However, the staining may not be as discrete as desired, especially in the lower thoracic area, and therefore the surgeon may not be absolutely certain about anatomic localization.

It is a standard of care in surgery on humans to take an intra-operative radiograph during the surgical approach to confirm localization. Many veterinary surgical hospitals have equipment for intraoperative radiographs such as C-Arms and fluoroscopy. Intraoperative radiographs are probably the best technique to assure and document surgical localization, and should be used when available.

Deciding on Approach

A hemilaminectomy is often chosen over a dorsal laminectomy for several reasons. It is a rapid operation that gives good exposure to the dorsal, lateral and ventral spinal canal on one side. Though a dorsal laminectomy gives exposure to both sides of the vertebral canal, this approach does not allow direct exposure of the ventral floor of the vertebral canal and the intervertebral disk. In the lower lumbar area essential nerve roots are in the area of a hemilaminectomy and can be avoided with a dorsal laminectomy. However, if carefully performed, a hemilaminectomy can be utilized throughout the thoracic and lumbar spine.

Surgical Prep and Positioning

A hemilaminectomy is performed by a dorsal approach close to the midline. The hair should be clipped in the area of the lesion, extending about 5 cm laterally on each side. A more liberal clip should be performed both cranially and caudally to assure that the surgeon has enough flexibility to extend the incision if needed. The skin of the dorsum of dogs and cats is quite movable allowing some flexibility if the skin incision does not exactly match the approach to the vertebrae. The patient is placed on the operating table in ventral recumbency. It is very important to make sure the patient’s spine is straight and placed straight on the table, and also that the patient is not leaning to the left or right. Errors can be easily made during the hemilaminectomy when the orientation of the patient makes anatomic perspective confusing. Patient postitioners such as vacuum bags are very useful to stabilize the patient and keep them steady during the operation. Rolled towels and orthopedic tape are also helpful.

Goals of Surgical Decompression

A hemilaminectomy is simply the approach made by the surgeon to decompress the spinal cord. The overall goal should be to remove the offending mass without manipulation of critical neurologic structures. With this in mind, the principles of proper surgical decompression are as follows:

1. The approach should be made aseptically and atraumatically.
2. The hemilaminectomy should be performed so that the offending mass can be removed without manipulation of the dural sac.
3. The offending mass must be removed completely without residual compression.
4. Hemorrhage must be minimal as postoperative hematoma can act as a compressive mass.

These principles of decompression dictate the instrumentation needed and the surgical techniques employed to properly perform the surgical procedure.

Instrumentation

A surgical pack with basic high quality instruments is needed. In addition, several other instruments are very helpful. Visualization of the surgical field is very important. Proper surgical lights should have at least 5,000, and preferably closer to 10,000 Foot Candles at 36 inches. Two light heads are important to prevent shadowing. Many surgeons use a head light which is very helpful, especially if the surgical lighting is questionable. Surgical loupes are also important for magnification (Figure 48-14). Custom built loupes for inter-pupillary distance, frame size, corrective lenses, and working arm distance (focal distance) should be used so that the surgeon is not distracted by improper fit. Usually 2.5x magnification is sufficient. Higher amounts of magnification give a smaller field of view.

Hemostasis is essential to prevent blood loss, provide better visualization, and prevent postoperative hematoma which can act as a compressive mass (Figure 48-15). A high quality electrocoagulation unit should be available. Usually about 35 watts of power are used for both cutting and coagulation. Bipolar cautery should be available as this tends to localize current and prevent inadvertent stimulation of nervous structures and heat damage. With bipolar cautery the power is reduced to 15 Watts. Bone wax is very helpful in stopping hemorrhage from cancellous bone. Other hemostatic agents such as absorbable gelatin sponge and oxidized cellulose are useful in stopping hemorrhage and encouraging coagulation.

Elevating and retracting the axial muscles are performed with periosteal elevators and retractors (Figure 48-16). Besides either ASIF or Keyes periosteal elevators, Freer elevators are very helpful for fine elevation. Gelpi retractors are used by many veterinary surgeons and several sizes should be available.
 

Historically different instruments have been successfully used to perform the laminectomy including trephines and ronguers. However, a principle of surgical decompression is to remove the offending mass without manipulation of the dural sac and other eloquent neurologic structures. It is difficult, if not impossible to chip away the lamina or pedicle of a vertebra with a rongeur without placing one tip of the rongeur into the vertebral canal and therefore pressing on the dural sac. Currently, most surgeons will use a high speed drill with a variety of burrs to remove bone. Air (nitrogen) powered drills are most useful as they stay cool and are durable (Figure 48-17).

Suction is essential for removal of the bone swarf (particles of bone material produced during drilling), blood and saline. Small Frazier suction tips are best. The area can be lavaged using a 10 cc syringe with a needle or canulla (Figure 48-18).

Removal of the offending mass requires a variety of different instruments depending on the specific situation. These include dental instruments, pituitary curettes, wire loops, nerve root retractors, probes, biopsy forceps, etc. (Figure 48-19). Different surgeons have their own preferences regarding which instruments work best. A very versatile and inexpensive instrument is small gauge wire (24 or 26 ga,) which can be fashioned into many different shapes and held with a mosquito hemostat or small needle holder.
 

Technique

A skin incision about four vertebra in length is made, and the approach advanced to the lumbar fascia. Many surgeons will towel or drape the incision for added sterility. An incision through the lumbar fascia using a scalpel or electroscalpel is made on the dorsal midline between the spinous processes and just to the side of the hemilaminectomy around the spinous processes in a scalloped like shape. Then a periosteal elevator is used to elevate each (usually four) spinous process. In the lumbar area, the elevation is carried to the transverse processes. In the thoracic vertebra the elevation is carried to the costal fovea or articulation with the rib. A scissor is then used to cut the interspinous ligament, lengthwise between the spinous processes, allowing the transversospinalis muscles to be retracted laterally. Gelpi retractors are commonly used with one tip deep in the musclulature and the other in the interspinous ligament over the area of the laminectomy. At this point, many surgeons will remove the tendinous attachments of the lumbar musculature from the articular facets of the vertebrae. This will provide further retraction of the axial musculature, however it will also result in a small arterial hemorrhage which must be controlled. The hemilaminectomy can be performed without this dissection and as the facet is removed with a bur, the muscles will retract laterally and carry the small arteriole laterally as well.

Though some surgeons still use rongeurs to perform laminectomies, the use of a high speed burr allows better exposure with less manipulation of the dural sac. Burring must be performed carefully, but a few simple techniques make this technically simple. The most common mistake in burring is to try to breach the vertebral canal as quickly as possible with a large burr. This results in a limited exposure to the vertebral canal (Figure 48-20). This small hemilaminectomy with sharp bone edges is not helpful as it provides limited exposure, and can make decompression without spinal cord manipulation difficult. In addition, extending a small approach with rougeurs requires one tip of the rongeur to be placed inside the vertebral canal which can result in manipulation of the dural sac. The preferred approach utilizes smaller burr size for more precise bone removal. The compressive lesion can be relieved from the spinal cord without manipulation of the spinal cord. The burring is begun in two separate locations, at the level of the accessory process (dorsolaterally) in the center of the vertebral pedicle on either side of the offending disk space, until cancellous bone is exposed. The key to careful and efficient burring is to locate the layer of cancellous bone (red in appearance) between the outer cortex of the vertebra and inner cortex (white in appearance), beyond which lies the vertebral canal and spinal cord. Burring is continued until the inner cortical bone is exposed, but stopped before the vertebral canal is entered. The bur is directed ventrally and burring continues ventrally removing the lateral cortical wall of the vertebral pedicle. The burr is not directed toward the vertebral canal, but safely in the direction of bone to be removed (Figure 48-21). A sharp, properly sized burr will progress through cancellous bone quickly and safely. The dorsal extent of the hemilaminectomy of the two vertebrae is connected longitudinally across the articular facets (Figure 48-22). Since the facets are cortical bone, it is much more difficult to gauge the appropriate burr depth. That is why burring is begun at the center of a vertebra where outer cortex (white), cancellous bone (red), and inner cortex (white) can be more easily discerned. The surgeon can then extend the bone aperture at the correct depth across the articular facets.
 

Ventrally, bone is removed to the level of the ventral aspect of the vertebral canal. The bur is then directed from either direction toward the vertebral foramen. Removing bone from either side of the ventral aspect of the vertebral foramen is the most difficult aspect of this operation and should be performed most carefully as the arterial and venous supply to the vertebral canal, and nerves or nerve roots can be damaged. However, carefully preformed, the end result is an oval to almost rectangular aperture with dorsal and ventral extents at the levels of the vertebral canal. At this point a smaller bur is chosen to enter the vertebral canal. The smaller bur is then used to remove bone around the perimeter of the hemilaminectomy. The bur should not be directed straight toward the vertebral canal, but rather toward the perimeter of the bone window to prevent inadvertent penetration of the vertebral canal (Figure 48-23). Usually the side of the bur us used to remove bone from the vertebral canal and the bur can be subtly felt to “give way” when the inner cortical bone is removed. If skillfully and carefully performed, the inner cortical bone can be removed without breaching the inner periosteum of the vertebral canal. If the inner periosteum is kept in tact, the vertebral canal can be entered dorsally with a dental or other instrument. This periosteum can be retracted ventrally, exposing the vertebral canal and spinal cord and in addition avoiding and even occluding the ventral vertebral sinuses.

Once the laminectomy is complete, the offending mass can be seen and removed. It is important to relieve the mass without manipulation of the spinal cord. Rounded instruments are used rather than sharp to avoid lacerating the venous sinuses. The spinal cord should be completely decompressed. Hemorrhage should be controlled with collagen sponge or other techniques.

If there is a significant amount of disk material adhered to the dura mater, or in cases of Hanson Type II, it may be impossible to remove the disk material without manipulation of the spinal cord. In these cases the laminectomy is extended under the spinal canal leaving the dorsal annulus of the disk intact. A small bur removes disk and bone until a small cavity exists (Figure 48-24). This can extend well over 50% of the distance to the opposite side. The dorsal annulus and disk material can then be pushed down into this cavity thereby relieving spinal cord compression without manipulation of the spinal cord.
 

Closure

There is some controversy regarding placement of fat or other materials over the laminectomy site. Laminectomy membranes and resultant pain are not as frequent in veterinary medicine as in humans. If a hemilaminectomy is performed as described, the resulting scar and fibrous tissue do not result in compression of the spinal cord or nerve roots. A small amount of fat placed in the laminectomy aperture will prevent some scar tissue from forming. Fat grafts are frequently used in veterinary surgery. However, the surgeon should use a small amount of fat as too much can result in spinal cord compression when the hypaxial musculature swells post operatively. The deep lumbar fascia is closed with a monofilament absorbable suture material in a simple continuous pattern. The subcutaneous tissues and skin are closed routinely.

Post operative Care

Steroids and antibiotics are not used post operatively. If the spinal cord is decompressed, there is no rational for continued administration. Complications associated with steroid use in neurosurgical patients are severe and well reported. Incisional infections are very rare. The main consideration for postoperative care is micturition. If the patient recovers with purposeful motor movement, they can usually urinate on their own. However, if the patient does not have purposeful motor movement, the bladder must be cared for until motor function returns, or the bladder converted into an automatic bladder that the owner can care for at home. An indwelling urinary catheter can be used for several days, but will often result in a urinary tract infection. In many cases the bladder can be expressed several times a day without catheterization. The bladder must never be allowed to overfill, because this results in stretching of the detrusor muscle and an atonic bladder. In male dogs it may be necessary to administer medications that relax the urethral spincters. The internal urethral spincter can be relaxed with phenoxybenzamine and the external urethral sphincter with Diazepam.

Those patients requiring several weeks to recover will require physical therapy. The goal of physical therapy is to frequently move the limbs in physiologic walking motions. Resolution of spinal cord swelling and remyelination of damaged axons will result in complete return of neurologic function if axons are intact. However, more severe spinal cord damage with axonal loss and gliosis will require establishment of new synaptic connections and central plastic reorganization. Physiologic motion enhances the speed and degree of these processes. Swimming is excellent if tolerated, and should be begun as soon after the sutures are moved as possible. The patient’s limbs should be moved in walking motions for at least fifteen minutes three times a day. The patient should be encouraged to stand, support weight, and walk as much as possible.

Suggested Readings

Davis GJ, Brown DC: Prognostic indicators for time to ambulation after surgical decompression in nonambulatory dogs with actue thoracolumbar disk extrusions: 112 cases Veterinary Surgery 31:513-518, 2002.

Kraus KH. Medical managment of acute spinal cord injury. In Kirk RW and Bonagura JD. (eds). Current Veterinary Therapy XIII: Small Animal Practice. W.B. Saunders Co., Philadelphia, 2000. Pp. 186-190.

Moissonnie P, Meheust P, Carozzo C; Thoracolumbar lateral corpectomy for treatment of chronic disk herniation: Technique description and use in 15 dogs. Veterinary Surgery 33:620-628, 2004.

Scott HW, McKee WM: Laminectomy for 34 dogs with thoracolumbar intervertebral disc disease and loss of deep pain perception. J Sm Anim Pract 40: 417-422, 1999.

Slocum B, Slocum Devine T: Pediculotomy in the thoracolumbar vertebra In Bojrab MJ, ed: Current Techniques in Small Animal Surgery, 4th ed, Baltimore: Williams and Wilkins, 1998, p 853.
 

Introduction

A variety of surgical procedures have been described for decompression of the spinal cord in the thoracolumbar region of dogs. The procedures differ in the amount of bone removed, and thus, are referred to as hemilaminectomy, mini-hemilaminectomy, pediculotomy, pediculectomy, dorsal laminectomy, modified dorsal laminectomy, and laminectomy modifications, including laminotomies and laminoplasties. Each technique has its own indications, inherent advantages and disadvantages, and most, if performed properly, satisfy the two basic tenets of spinal cord surgery, i.e., spinal cord decompression and mass removal. There is no one best technique for all patients.

Hemilaminectomy, mini-hemilaminectomy, and pediculectomy are particularly well-suited to the removal of extruded or protruded intervertebral disc material from the vertebral canal without fear of laminectomy membrane formation. Bone removal and resultant exposure of the vertebral canal and spinal cord are minimal in comparison to dorsal decompressive techniques. Vertebral column stability is less compromised with these procedures, even with concurrent prophylactic intervertebral disc fenestration than with dorsal laminectomy techniques which require bilateral exposure and partial facetectomies.

Objective comparison of the many decompressive techniques, at least in intervertebral disc disease, has been clouded by the many variables associated with spontaneous extrusion or protrusion of intervertebral discs in the thoracolumbar region. Personal preference and the individual surgeon’s training have all too frequently determined the type of decompressive procedure utilized. Previously, severely-limited imaging modalities, i.e., flat films and myelography, also made rational, logical selection of the most appropriate technique for the individual patient difficult, if not impossible. With the increased availability of CT and MRI, selection of the most appropriate decompressive technique based on the precise location of the extradural mass became far more objective, and allowed for minimally invasive surgical techniques. For these reasons, although performed for many years with excellent results at this hospital, dorsal or modified dorsal laminectomy are only infrequently performed for uncomplicated thoracolumbar intervertebral disc extrusion or protrusion in chondrodystrophoid or non-chondrodystrophoid dogs. However, in many cases, i.e., vertebral column fractures, luxations, congenital vertebral malformations, synovial cysts, arachnoid cysts, vertebral or spinal cord neoplasms, or syrinxes, and in some cases with intervertebral disc disease, laminectomy will be the procedure of choice to allow for expansive spinal cord exposure, decompression, and mass removal when these other techniques would prove to be inadequate.

Surgical Technique for Modified Dorsal Laminectomy

Following confirmation of the neuroanatomic lesion by either myelography, CT, or MRI, the anesthetized patient is placed in sternal recumbency, without pressure on the abdomen, and prepared for aseptic surgery of the thoracolumbar spine. Prophylactic antibiotics (cefazolin, 22 mg/kg IV at time of surgery, then 22 mg/kg PO BID, G.C. Hanford Manufacturing Co., Syracuse, NY 13201) are administered intravenously at the time of surgical intervention, and may be continued in the early postoperative period. Corticosteroids (methylprednisolone sodium succinate, 30 mg/kg IV, Solu-Medrol, Pharmacia & Upjohn, Kalamazoo, MI 49001) may be administered at the time of surgery in patients who have not already been treated with steroids. Gastric protectants (Pepcid, Famotidine, 0.5-1mg/kg QD or BID, Bedford Laboratories, Bedford, OH 44146; and sucralfate, medium and large dogs 1 gm TID, toy dogs (< 7 kg) 0.5 gm TID, Major Pharmaceuticals, Livonia, MI 48150) are administered preoperatively when possible, and continued postoperatively.

The skin incision, centered over the area of involvement, is made slightly lateral to the dorsal midline. Length of this incision is determined by the specific pathology in the individual patient. Moistened laparotomy tapes or surgical paper towels are clipped to the reflected subcutaneous tissue and/or superficial fascia on each side of the incision to cover any exposed skin. The thoracolumbar fascia is incised bilaterally immediately lateral to the spinous processes. Periosteal elevators are utilized to lever or reflect the epaxial muscles bilaterally to a level just ventral to that of the accessory processes (Figure 48-25). Utilization of self-retaining retractors (Gelpis or Beckmans) allows for relatively atraumatic dissection under tension, which is most easily performed from caudal to cranial. Maceration of the epaxial musculature contributes to delayed wound healing, postoperative pain, and laminectomy membrane formation. Small branches of either the paired lumbar or intercostal arteries are cauterized by means of bipolar cautery as they are exposed both cranially and caudally to the cranial articular processes of each adjacent vertebra. Care must be exercised during both periosteal elevation and the cauterization of small bleeders around the articular processes to avoid exacerbation of spinal cord ischemia by interruption of the, at best, tenuous spinal cord blood supply through the varying intervertebral foramen (dorsal and ventral radicular branches).^1-3
 

For laminectomy at the thoracolumbar junction, the 13th rib and first lumbar transverse process are readily identifiable landmarks to confirm the appropriate site for laminectomy. The 13th rib arcs dorsocaudally and is located far more superficially than the cranioventrally directed first lumbar transverse process. Particularly in obese patients, some surgeons prefer to place a sterile hypodermic needle into one of the dorsal spines during preoperative films to confirm anatomic location, especially in the mid lumbar spine, since localization by palpation of the dorsal spine of the seventh lumbar vertebra may be difficult. The spinous processes of the vertebrae cranial and caudal to the disc space (in a two level laminectomy) are removed by means of bone rongeurs (Figure 48-26). This is preferable to the utilization of a bone cutter which can result in excessive torque being applied to the vertebral column of small breed dogs.

By means of a high-speed air drill with a new 4 mm egg-shaped bur with notched flutes, the remainder of the dorsal spine is removed. Meticulous hemostasis, and irrigation with sterile saline or lactated Ringer’s solution and fluid removal by suction maintains a clear field, removes the bone dust produced by the air drill, and dissipates the minimal amount of heat produced by a new bur. Old dull burs should not be used for this technique because they generate significant heat by sanding rather than cutting away the bone of the laminae. In cases of thoracolumbar disc disease, the laminectomy defect is centered over the area of involvement and most often extends cranially and caudally almost to the adjacent interarcuate ligament unless significant spinal cord compression and edema necessitate extension of the defect until normal amounts of epidural fat are visualized surrounding the spinal cord in the epidural space. Length of the defect in other cases is determined by the specific pathology encountered. Width of the defect is determined by the joint spaces between the cranial and caudal articular processes at the involved interspaces (Figure 48-26, arrow). Complete facetectomy at multiple locations has been shown experimentally to result in some vertebral column instability, although this has not been problematic in clinical cases other than vertebral column fractures/luxations in which this induced instability is compensated for by the vertebral column instrumentation which had been planned.
 

The bone structure and color are reliable indices of the depth of drilling: (1) outer cortical bone is dense and white; (2) middle cancellous bone is spongy and reddish-brown; (3) the inner cortical bone is dense, white, and very thin. Only cortical bone is present at the attachments of the interarcuate ligament. Once the limits of the laminectomy defect have been defined, drilling continues to completely remove the outer layer of cortical bone and then the middle layer of spongy cancellous bone (Figure 48-27). Hemorrhage from the cancellous bone is easily controlled with bone wax.
 

The surgeon must remember that he or she is removing the top of a horizontally-oriented cylinder while maintaining bone at the pedicles at a level dorsal to the dorsal tangent of the spinal cord. The inner layers of the laminar-pedicle junctions are excavated bilaterally to provide complete exposure of the epidural space (Figure 48-28). When the thin layer of inner cortical bone begins to sag under the pressure of the drill, a 2.3 or 1.6 mm round carbide-tip bur is substituted for the large bur (Figure 48-29). A thin plate of inner cortical bone remains in all areas of the defect to protect the spinal cord during the majority of the drilling, or “brushing away” of the bone. This thin plate of inner cortical bone is isolated by drilling around the periphery of the laminectomy defect with a small drill with approximately a 45 degree angle away from the spinal cord (Figure 48-30). The angled drilling into the pedicles avoids drilling directly over the spinal cord and results in smooth, deeply undercut edges of the laminectomy with excellent exposure of the full width of the vertebral canal. Some additional undercutting is necessary to remove portions of the cranial articular processes of the more caudal of the two vertebrae which are located somewhat in the frontal plane, deep to the caudal articular processes of the more cranial of the two vertebrae. Complete excision of the caudal articular processes and undercutting in this region results in impressive exposure of the full width of the spinal cord for resection of intra- or extramedullary mass lesions and sufficient access to the vertebral canal for the removal of extradural mass lesions, even those located ventral to the spinal cord. Excavation of the pedicles, i.e., removal of the inner cortical and middle layers of cancellous bone of the pedicles, while preserving the outer layer of cortical bone of the pedicles, dramatically increases exposure without predisposing to the phenomenon of constrictive fibrosis (Figure 48-31).^4-7 Removal of extruded intervertebral disc material, even if located bilaterally or ventral to the spinal cord is uncomplicated, in spite of the minimal epidural space of chondrodystrophoid dogs with relative vertebral canal stenosis. Minimal spinal cord manipulation is necessary. The spinal cord may be gently retracted by means of a small suture placed in a relatively avascular area of the dura mater. Rhizotomy in appropriate locations releases the dural tube for additional retraction or “rolling”. Fine-tipped suction and various ophthalmic and dental instruments have proven useful for the removal of mass lesions from the vertebral canal. Bleeding from the internal vertebral venous plexus is controlled by means of bipolar cautery, macerated muscle, or absorbable gelatin sponge (Gelfoam, Upjohn Co., Kalamazoo, MI 49008). It is imperative that the bone of the remaining pedicles on both sides of the defect be maintained at a level dorsal to the dorsal tangent of the spinal cord to prevent the occurrence of secondary spinal cord flattening during healing of the laminectomy defect (laminectomy membrane formation, epidural scar, laminectomy scar, postlaminectomy stenosis, or constrictive fibrosis). For the same reason, a hemilaminectomy, with complete excision of the facets, or articular processes, should never be converted to a dorsal laminectomy, nor should facet or laminar fragments be indiscriminately removed in vertebral column fractures unless appropriate (and as yet somewhat unproven) measures are taken to prevent secondary spinal cord compression due to formation of the laminectomy membrane. When the thin remaining layer of inner cortical bone has been completely isolated (See Figure 48-32), it is grasped with a hemostat and “peeled off”, or removed as a complete boney shelf with the periosteum lining the vertebral canal. Because laminectomy scar formation and secondary spinal cord compression increase with an increase in not only defect width, but length, the length of the defect should be limited to only what is necessary to decompress the involved segments of spinal cord or resect the offending mass lesion.
 

Durotomy may be performed for the removal of intradural mass lesions or may be utilized to establish a more definitive prognosis in paraplegic, analgesic cases in which acute focal, segmental spinal cord necrosis, malacia, thrombosis, blanching, or chronic loss of cord substance with glial scarring is suspect. Dorsal midline myelotomy is only performed in paraplegic, analgesic patients in which the prognosis is in question. Continued leakage of cerebrospinal fluid has not been a problem with durotomies. A mild, transient neurologic deficit has been demonstrated in normal dogs following durotomy. The dura mater appears to heal rapidly by neomembrane formation.⁵
 

Durotomy is performed with either Potts-Smith 60 degree angled cardiovascular scissors or a bent disposable 20 to 25 gauge needle. The dura mater is usually incised on the dorsal midline for the full length of the laminectomy defect. Incision of the inelastic, and often opaque (loss of the normal translucent appearance) dural sheath and frequently the underlying pia mater may result in greater intramedullary decompression of the spinal cord and associated vasculature. Neither hypothermic or normothermic perfusion are utilized routinely.

Torn or devitalized epaxial musculature is excised prior to closure. This also appears to limit the infolding or collapse of the epaxial musculature into the laminectomy defect, a factor in the formation of laminectomy membrane. A section of absorbable gelatin sponge, creased on the midline to resemble a tent, and shaped to conform as closely as possible to the margins of the laminectomy defect is carefully placed in direct apposition with the remaining pedicles (marginal fitting). With this particular technique in the thoracolumbar region of dogs, the healing pattern following implantation of absorbable gelatin sponge is predictable and relatively innocuous.⁵ Other implants such as absorbable gelatin film (Gelfilm, Upjohn Co., Kalamazoo, MI 49008), muscle, and free or pedicle fat grafts have met with variable and unsatisfactory or even disastrous results. Although highly successful in other locations, subcutaneous fat grafts in this location, with this laminectomy technique actually increase spinal cord compression postoperatively.^7,8 Cosmetically unacceptable scars, structural defects, or vertebral column instability have not been problems with this technique.

Postoperative Care

Postoperative analgesia, predominantly with opioids, is usually indicated for the first 12 to 24 hours. Corticosteroid therapy is no longer continued in the postoperative period due to the limited benefits confirmed by experimental studies and the possibility of gastrointestinal complications. Nonsteroidal anti-inflammatories are rarely used since most patients have been treated with corti-costeroids either pre- or intraoperatively. Their concurrent or sequential use would increase the risks of catastrophic gastrointestinal bleeding or perforation. Postoperative therapy includes manual expression of the urinary bladder or urinary tract catheterization, tail walking, whirlpool hydrotherapy, exercise carts, and general supportive care. Patients are discharged from the hospital as soon as conscious control of micturition is regained. Early return to familiar surroundings seems to promote enthusiasm on the part of the patient and owner, more rapid return of urinary continence, and an early return to full function.

References

1. Caulkins SE, Purinton PT, Oliver JE. Arterial supply to the spinal cord of dogs and cats. Am J Vet Res 50:425, 1989.
2. Parker AJ. Distribution of spinal branches of the thoracolumbar segmental arteries in dogs. Am J Vet Res 34:1351, 1973.
3. Parker AJ, Park RD, Stowater JL. Traumatic occlusion of lumbar segmental arteries. J Trauma 14:330, 1974.
4. Funkquist B, Schantz B. Influence of extensive laminectomy on the shape of the spinal canal. Acta Orthop Scand Suppl 56:1, 1962.
5. Trotter EJ, Crissman J, Robson D, et al. Influence of nonbiologic implants on laminectomy membrane formation in dogs. Am J Vet Res 49:634, 1988.
6. Trotter EJ. Dorsal laminectomy for treatment of thoracolumbar disc disease. In: Bojrab MJ ed. Current techniques in small animal surgery. 3rd ed. Philadelphia: Lea & Febiger, 608, 1990.
7. Trevor PB, Martin RA, Saunders GK, et al. Healing characteristics of free and pedicle fat grafts after dorsal laminectomy and durotomy in dogs. Vet Surg 20:282, 1991.
8. Trotter EJ. Unpublished data.

Suggested Readings

Biggart JF, III. Prevention of laminectomy membrane by free fat grafts after laminectomy in dogs with disk herniations. Vet Surg 17:28, 1988.

Cook S, Prewett A, Dalton J, et al. Reduction in perineural scar formation after laminectomy with Polyactive membrane sheets. Spine 19:1815, 1994.

Einhaus SL, Robertson JT, Dohan FC, Jr., et al. Reduction of peridural fibrosis after lumbar laminotomy and discectomy in dogs by a resorbable gel (ADCON-L). Spine 22:1440, 1997.

Geisler FH. Prevention of peridural fibrosis: current methodologies. Neurol Res 21;Suppl 1:S9, 1999.

Gill G, Sakovich L, Thompson E. Pedicle fat grafts for the prevention of scar formation after laminectomy. An experimental study in dogs. Spine 4:176, 1979.

LaRocca H, Macnab I. The laminectomy membrane. Studies in its evolution, characteristics, effects and prophylaxis in dogs. The Journal of Bone and Joint Surgery – British volume 56B:545, 1974.

Olby N. Current concepts in the management of acute spinal cord injury. J Vet Int Med 13:399, 1999.

Robertson J, Meric A, Dohan FJ, et al. The reduction of postlaminectomy peridural fibrosis in rabbits by a carbohydrate polymer. J of Neurosurg 79:89, 1993.

Schulz KS, Waldron DR, Grant JW, et al. Biomechanics of the thoracolumbar vertebral column of dogs during lateral bending. Am J Vet Res 57:1228, 1996.

Shires PK, Waldron DR, Hedlund CS, et al. A biomechanical study of rotational instability in unaltered and surgically altered canine thoracolumbar vertebral motion units. Prog Vet Neurol 2:6, 1991.

Smith GD, Walter MC. Spinal decompressive procedures and dorsal compartment injuries: comparative biomechanical study in canine cadavers. Am J Vet Res 49:266, 1988.

Songer MN, Rauschning W, Carson EW, et al. Analysis of peridural scar formation and its prevention after lumbar laminotomy and discectomy in dogs. Spine 20:571, 1995.

Viguier E, Petit-Etienne G, Magnier J, et al. Mobility of T13-L1 after spinal cord decompression procedures in dogs (an in vitro study). Vet Surg 31:297, 2002.

Yovich JC, Read R, Eger C. Modified lateral spinal decompression in 61 dogs with thoracolumbar disc protrusion. J Sm An Pract 35:351, 1994.
 

Introduction

A definitive preoperative diagnosis of cauda equina syndrome can be difficult to make. Not all practitioners have access to magnetic resonance imaging, the best modality for defining problems in the lumbosacral region. Access to computed tomography (CT) is equally limited, and often myelography or epidurography is required in concert with a CT scan to demonstrate soft tissue lesions such as nerve root entrapment. Epidurography alone is difficult both to perform and to interpret if conducted only on occasion. Electrodiagnostic testing and electromyography require special equipment and expertise to perform and to evaluate, and not all dogs with cauda equina syndrome have electrophysiologically demonstrable signs of lower motor neuron disease. Myelography is incapable of defining many pathologic processes involving the nerve roots of the cauda equina in the lumbosacral area of the dog. Stressed radiographs (hyperextension-flexion) of the spine demonstrate hypermobility, but they are not necessarily diagnostic of neurologic involvement even when used in conjunction with myelography. In fact, many animals affected by cauda equina syndrome have normal spinal radiographs. Hence, a veterinarian must use clinical acumen along with one or more of these diagnostic modalities to establish a diagnosis of cauda equine syndrome before recommending surgical intervention. In many cases only an exploratory laminectomy can provide both a diagnosis of and cure for cauda equina syndrome. The purpose of the surgery is to decompress the conus medullaris or those nerve roots of the cauda equina that are causing clinical symptoms. The surgeon should be vigilant to remove only as much bone as needed to accomplish this task, especially when dealing with cauda equina syndrome secondary to lumbosacral instability. The removal of portions of discs or facets progressively destabilizes the spine and may predispose the patient to adverse postoperative sequelae.

Surgical Procedure

The animal is placed in ventral recumbancy with the stifles and hips flexed and the hocks extended. If extensive foraminal exploration is anticipated, then placement of the patient’s hind legs in the forward extended position combined with padding placed under the belly in the lumbosacral region will accentuate lumbosacral kyphosis to more widely open the foramina at the lumbosacral junction.

A dorsal midline approach to the lumbosacral spine is performed. Several large Gelpi or hinged Weitlaner retractors facilitate muscle retraction (Figure 48-33). Suction is essential for good visualization, and most typically a No. 10 or 12 Frazier suction tip is adequate. Electrocautery, surgical sponge (Gelfoam), bone wax and small pieces of epaxial muscle placed on small bleeders are essential for adequate hemostasis in large breed dogs.

A modified dorsal laminectomy is performed over the affected interspaces (generally L7 to S1-2), initially leaving the caudal pedicles of L7 intact. If the compression is due to either midline disc bulging or hypertrophy of the interarcuate ligament, then this surgical approach alone should result in decompression. If the surgeon is unsure of complete decompression, then extradural fat and fibrous connective tissue are removed from the spinal canal as needed to facilitate visualization of the various nerve roots and ganglia of the cauda equina. A nerve hook helps to isolate and trace individual nerves as they enter their respective foramina to exit the spinal canal. Unilateral or bilateral pediculectomy is performed as needed to gain further exposure and decompression of the involved nerves. In some cases, foraminotomy without pediculectomy is possible and preferred. Tethered nerve roots are freed from any fibrous connective tissue constraints. In the case of a Hansen type I disc rupture, the ruptured nuclear material is removed (generally by suction). If a Hansen type II disc rupture is present, the location of the bulging annulus in relation to a compressed nerve determines the surgical procedure. Disc material that is entrapping a nerve root is either cut away or, alternatively, is left alone and the nerve decompressed by facetectomy, pediculectomy, or foraminotomy.

Once decompression has been achieved and hemostasis is complete, an autologous free fat graft is harvested from the subcutaneous region and placed over the laminectomy site to minimize cicatrix formation. Muscle, fascia and subcutaneous layers are closed, respectively, with synthetic absorbable suture material. Inaccurate closure of the muscle results in a palpable midline defect, whereas inattention to subcutaneous closure results in seroma formation. The application of a compression bandage is optimal, yet difficult to apply and maintain, given the location of the operative site, especially in male dogs.
 

Postoperative Care

Postoperative recommendations include strict confinement to house and leash walking activity only for 8 weeks’ time, before a return to moderate function. This confinement allows time for the musculature to adhere to the lamina and for the spine to adjust to the added instability imposed by the surgical procedure.

In most cases, a modified dorsal laminectomy is sufficient to gain good visualization of the problem and to effect decompression. Removal of the dorsal spinous processes and dorsal laminectomy minimally destabilize the lumbosacral motion unit in four point flexion/extension tests in vitro. Hence, one may expect resolution of nerve root symptoms without significant subsequent clinical deterioration if successful mechanical decompression has been achieved (and if mechanical compression alone was the source of the pain). Osteoarthritic symptoms may be expected to persist however (i.e. morning and exercise induced stiffness with occasional episodes of low back pain lasting several days). The addition of discectomy, foraminotomy or facetectomy further destabilizes the spine. Clinically significant sequelae such as facet fracture, lumbosacral subluxation, cicatrix formation and ongoing clinical symptomatology can result. It is therefore important to use a minimalistic approach in one’s decompression technique.

Decompressive laminectomy in a hypermobile lumbosacral segment should be undertaken with caution, particularly if discospondylitis is suspected. In such instances, laminectomy only further destabilizes an already unstable situation and may have orthopedic and neurological sequelae, if the infection is not brought under control quickly.

The literature would indicate that on average 85% of the animals operated on demonstrate initial improvement. However, subsequent deterioration occurs in up to 1/3 of patients resulting in an overall longterm success rate of around 55%. Approximately 25% of cases are improved by surgery but not symptom free, and there is on average a 25% failure rate. Persistent postoperative clinical symptoms most probably relate to ongoing lumbosacral instability, attendant discogenic pain, epidural scarring, arachnoiditis, facet arthritis or fracture, insufficient decompression at the operative site, alternate segment disease, iatrogenic conus or nerve root trauma, infection, etc. Preoperative conditions predisposing to surgical failure seem to include advanced age, chronicity of symptoms, concurrent hind limb problems, and urinary or fecal incontinence. Favorable preoperative conditions include young age and mild clinical symptoms.
 

If there is a recurrence of symptoms in the early postoperative phase, a second exploratory surgery is justified in selected cases.

Bony or soft tissue disease at any of the L5-6 to S1-2-3 vertebral interspaces potentially can result in clinical signs of cauda equina syndrome (sciatic or sacral nerve root involvement) (Figure 48-34). The clinician must attempt to localize the lesion to a specific area of the spinal cord or nerve roots preoperatively. A “routine” dorsal laminectomy at the L7-S1 interspace may miss the underlying disorder entirely, if the signs of the cauda equina syndrome are, for example, due to an intramedullary tumor affecting the L6 segment of the spinal cord.

Suggested Readings

Danielson F, Sjostrom L. Surgical Treatment of Degenerative Lumbosacral Stenosis in Dogs. Vet Surg 28: 91, 1999.

Dr. Risiol, Sharp NJH, Olby NJ, et al. Predictors of outcome after dorsal decompressive laminectomy for degenerative lumbosacral stenosis in dogs: 69 cases (1987-1999). J. Am Vet Med Assoc 219: No5: 624, 2001.

Janssens LAA, Moens Y, Coppens P, et al. Lumbosacral Degenerative Stenosis in the Dog. Vet Comp Orthrop Traumatol 13:97, 2000.

Linn LL, Bartels KE, Rochat MC, et al. Lumbosacral Stenosis in 29 military working dogs: Epidemiologic findings and outcome after surgical intervention (1990-1999). Vet Surg 32:21, 2003.

Moens NMM, Runyun CL. Fracture of L7 vertebral articular facets and pedicles following dorsal laminectomy in the dog. J Am Vet Med Assoc. 221: No 6: 807, 2002.

Smith MEH, Bebchuk TN, Shmon CL, et al. An invitro biomechanical study of the effects of surgical modification upon the canine lumbosacral spine. Vet Comp Orthrop Traumatol 17:17, 2003.
 

Introduction

The thoracolumbar and lumbar spine are relatively common locations for spinal fractures, luxations and subluxations in the dog and cat. As previously mentioned, it appears that the higher incidence of fracture/luxations at certain sites along the vertebral canal may not correlate to differences in muscular or ligamentous attachments, but rather to areas of the vertebral column with a static/kinetic relationship (ie. thoracolumbar and lumbosacral junction).^1,2,3,4 As mentioned also in the previous chapter on cervical spine injury, the history, physical and neurologic examinations are crucial to the determination of prognosis and surgical outcome.

Technique Selection

There are numerous techniques that have been developed to stabilize thoracolumbar and lumbar spinal fractures, luxations and subluxations in dogs and cats.^5-19 As mentioned previously, the technique chosen is dictated by the location of the fracture, size, age, and disposition of the patient, equipment available and experience of the surgeon.

Surgical Techniques

Dorsal spinous process plating requires exposure of the dorsal spinous processes and articular facets.⁵ The supraspinous and interspinous ligaments should be preserved if possible. A minimum of three spinous processes on each side of the fracture/luxation should be exposed. Metal or plastic plates are available for dorsal spinous process plating. When using plastic plates, a plate is used on each side of the exposed dorsal spinous processes (2 plates total)^6,8 (Figure 48-35). The roughened side of the plate is placed against the dorsal spinous processes. The plates are attached with appropriate size nuts and bolts placed between the dorsal spinous processes. It is important to keep the plates as close to the base of the dorsal spinous processes as possible. Grooves can be created in the lamina at the base of the spine using a high speed bone burr or rongeurs to help keep the plates low on the spine. This will allow maximal purchase of the spinal plates to the dorsal spinous processes. Metal plates are used in a similar fashion however the nuts and bolts are placed through the dorsal spinous processes (Figure 48-36).

The advantage of dorsal spinous process plating is preservation of the inherent stability provided by the articular facets, supra-spinous and interspinous ligament. The major limiting factors of dorsal spinous process plating are the age and size of the patient. The dorsal spinous processes must be large enough and the bone compact enough to support the stresses that are encountered by an unstable spine. This technique is commonly used in combination with other stabilization techniques (ie. pins and polymethyl methacrylate, vertebral body plating). The most common postoperative complications are fracture of the spinous processes and plate slippage.
 

Spinal stapling also requires exposure of the dorsal spinous processes and facet joints. An intramedullary pin is placed through a dorsal spinous process, bent 90 degrees, laid along the lamina between the base of the spinous processes and articular processes, and secured to the base of the dorsal spinous processes with orthopedic wire (Figure 48-37). Added security can be accomplished by wiring the pin around the base of the transverse processes in the lumbar spine or around the rib heads in the thoracic spine (Figure 48-38) or by incorporating multiple pins and wires in a modified segmental spinal instrumentation technique (Figure 48-39).⁹ At least two interspaces on each side of the fracture/luxation should be included in the repair.

Vertebral body plating (dorsal body plating) requires dorsolateral exposure of the articular facet, vertebral body and transverse process of the lumbar vertebrae or the articular facet, vertebral body and rib head of the thoracic vertebrae¹⁰ (Figure 48-40). Care should be taken to protect the spinal nerve roots encountered cranial and caudal to the fracture/luxation. The spinal nerve and vessels at the involved space must be severed. The proper length and size plate is selected and placed on the dorsolateral aspect of the vertebral bodies. There should be at least four cortices engaged cranial and caudal to the involved fracture/luxation. Use of locking plates and screws may permit monocortical screw placement. If a luxation, subluxation or fracture close to the interspace exists, stabilization of the two adjacent vertebrae is adequate, however if a mid body fracture exists, three vertebral bodies should be spanned. The holes are drilled and screws are placed in a ventral and medial direction, being careful to avoid entering the spinal canal dorsally or the abdominal cavity ventrally. Placement of the plate on the thoracic vertebrae is more difficult due to the presence of rib heads. The rib heads must be removed and the transverse process contoured so the plate lies flat against the vertebral body. It is recommended that an anatomic specimen be available for visualization during placement of plates and screws. The need for rhizotomy precludes the use of vertebral body plating caudal to the fourth lumbar vertebra.^10,a,b
 

Stabilization techniques utilizing pins (or screws) and polymethyl methacrylate require exposure of the dorsal spinous processes, articular facets and transverse processes bilaterally.^11,12 A minimum of two appropriate sized endthreaded, knurled acrylic pins are placed into the vertebral bodies on each side of the fracture/luxation. In the thoracic vertebrae, the pins are inserted into the pedicle and driven into the vertebral bodies, using the tubercle of the ribs and the base of the accessory processes as landmarks. In the lumbar vertebrae, pins are inserted directly into the vertebral bodies using the accessory processes and transverse processes as landmarks. Because pin placement is critical and landmarks vary considerably, depending on the level of the spine, a skeleton should be available for reference. The pins are directed cranioventral and from lateral to medial in the vertebral body cranial to the fracture/luxation, and caudoventral and from lateral to medial in the vertebral body caudal to the fracture/luxation. The Steinmann pins are power driven so they exit 2 to 3 mm from the ventral aspect of the vertebral body and are cut leaving 1.5 to 2 cm exposed dorsally. The polymethyl methacrylate forms around the knurled shaft of the pin and helps prevent pin migration. The surgical field is lavaged and dried in preparation for application of polymethyl methacrylate. If a laminectomy is not performed, polymethyl methacrylate is simply applied as a spherical mass, incorporating the Acrylic pins as well as the articular facets and adjacent dorsal spinous processes (Figure 48-41A and B). If a laminectomy is performed, the exposed spinal cord is covered with an autogenous fat graft and the polymethyl methacrylate is molded into the shape of a doughnut (Figure 48-42). Care is taken not to allow the polymethyl methacrylate to contact the spinal cord. The polymethyl methacrylate is lavaged with cool saline to dissipate the heat of polymerization. Portions of the epaxial muscles adjacent to the polymethyl methacrylate may have to be excised to facilitate closure. Rarely, relief incisions in the lumbodorsal fascia lateral to the polymethyl methacrylate are necessary to allow closure of the primary incision.^11,12
 

The major disadvantage of this technique is the exposure necessary for pin placement, however, in a series of dogs treated with this technique, there were no failures associated with stress fatigue.¹¹ The technique is relatively straightforward, requires minimal special equipment, though a thorough knowledge of anatomy and constant reference to an appropriate anatomic specimen are recommended.

In some instances (generally T-L fractures or luxations in large breed dogs with hyperactive personalities), a combination of the above described techniques should be considered. Combinations such as pins and polymethyl methacrylate with dorsal spinous process plating, cross pins with dorsal spinous process plating, or body plating with dorsal spinous process plating have proven successful.^a

^a Lubra ̈ plate, Lubra Co, 1905 Mohawk, Fort Collins, CO 80521 
^b Auburn spinal plate, Richard Manufacturing Co, Memphis, TN 38101

Fractures of L6, L7 and S1

Fractures and luxations of the caudal lumbar and sacral vertebrae are relatively common due to the static-kinetic relationship of the sacral and lumbar segments, respectively. Neurologic signs occurring secondary to trauma of the cauda equina, result in varying degrees of femoral, sciatic, and sacral nerve dysfunction. Because the spinal cord ends cranial to L7, patients with 60 to 70% displacement of the spinal canal may still have a favorable prognosis.¹

Due to the increased shearing forces present in the lumbosacral region, caudal lumbar and lumbosacral fracture/luxations are difficult to stabilize. Techniques used to successfully treat L7-S1 fracture/luxations include transilial pinning, transilial pinning with plastic plate support, pins and polymethyl methacrylate, transilial pinning with external skeletal fixation, and spinal stapling.^{6,9,13,14,15,16,17}

Surgical Techniques

In cases of L7-S1 luxations or subluxations, manipulation of L7-S1 during reduction involves grasping towels clamps or bone forceps placed on the wings of the ilium and pulling caudally and slightly dorsal. A non-sterile assistant can place counter traction on the head or front legs and this can help to lever the sacrum against the lamina of L7 while pressing ventrally on L6. Also, a small Hohmann retractor can be used to aid reduction of an L7 fracture or luxation by hooking the jaws of the forceps under the cranial lamina of the sacrum and lower the jaws against the caudal lamina of L7. Transilial pinning requires exposure of the dorsal L7-S1 region.¹⁷ The caudal segment is most often displaced ventrally and cranially. Bone forceps are placed on each ilial wing to help elevate the ilium and sacrum dorsally to align the articular processes of L7 with the cranial articular surface of the sacrum. An appropriate sized trocar tip pin (1/8” or smaller) is driven through the wing of the ilium, across the laminae of L7 and through the opposite wing of the ilium (Figure 48-43). The most common problem associated with this technique is migration of the Steinmann pin. A more stable technique is generally recommended. To help prevent migration of the Steinman pins, bending the ends of each pin at a 90 degree angle can be done, as well as connecting the pins on each side with a double Kirschner clamp (see below) or notching the pins’ ends with a pin cutter and incorporating them with bone cement.

The use of plastic dorsal spinous process plates and transilial pins has been reported^6,13 This requires a similar approach and reduction as previously described. Plastic dorsal spinous process plates are placed on each side of the three dorsal spinous processes cranial to the fracture/luxation and secured with nuts and bolts as previously described for plastic dorsal spinous process plating. The plastic plates extend caudad to S2-3. A 3/32” or 1/8” trocar tip pin is driven through one ilial wing, through the plastic plate at the level of L7-S1, and through the opposite ilial wing. A second pin is placed caudal to the first pin. The ends of the pins are bent craniad at a 90° angle and cut to leave 5 mm protruding (Figure 48-44). Postsurgical complications include fracture of the dorsal spinous processes or migration of the transilial pins. Pin migration may be decreased by application of polymethyl methacrylate to notched pins. Transilial pinning and external skeletal fixation with a Kirschner-Ehmer^c apparatus has been described.^15,16 In this technique the transilial pins are placed percutaneously. In addition, one pin is inserted percutaneously through the vertebral body cranial to the fracture/ luxation. Kirschner clamps attach the pins to a connecting bar on each side of the spine (Figure 48-45).

Pins and polymethyl methacrylate can also be utilized to stabilize lumbosacral fracture/luxations. The approach and reduction is as previously described. Two pins are placed in the vertebral body cranial to the fracture/luxation and two pins are placed in the wings of the ilium. The pins are incorporated with polymethyl methacrylate as previously described. The disadvantage of this technique is the large amount of polymethyl methacrylate needed for adequate stabilization, making closure difficult. Modified segmental spinal instrumentation has been used successfully to stabilize lumbosacral fractures. Pins are prebent 90°, placed through holes drilled in the wings of the ilium, laid alongside the dorsal spinous processes of at least two vertebra cranial to the fracture/luxation, and wired in place to the adjacent articular facets, dorsal spinous processes and lamina (Figure 48-46). Combinations of the above techniques may be utilized in large breed dogs with hyperactive personalities.
 

^c Kirschner-Ehmer apparatus, Kirschner Co

Sacral and Sacrococcygeal Fractures

Special attention to the S2-S3 dermatomes and evaluation of bowel and bladder function should be considered when performing a neurologic examination on patients with sacral and sacrococcygeal fracture/luxations. Fracture of the sacral wings generally occurs through the sacral foramina, damaging the S1, S2 and S3 nerve roots. Sacroiliac luxation however, rarely effects the nerve roots. A dorsal approach to the sacroiliac junction can be utilized to expose fractures of the sacral wing. Careful periosteal elevation of the paraspinal musculature allows visualization of the fracture fragments. Once reduced, the fracture can be stabilized with a lag screw inserted through the ilium and sacral fragment and into the sacral body.¹⁸ A parallel trocar tip pin or wire may be inserted to provide rotational stability (Figure 48-47). If the neurologic examination reveals severe nerve root damage (shearing of the S1-S3 nerve roots), laminectomy and exploration of the cauda equina should be considered. Patients sustaining sacral or sacrococcygeal fracture/luxation may present with an anesthetic tail. If the tail remains anesthetic at 2 to 3 weeks post trauma, an amputation may be necessary to eliminate associated fecal matting, urine scalding (cats), and self-mutilation.¹⁴ Traumatic injury of the sacrococcygeal area frequently occurs in cats.^4,19 Avulsion of the nerve roots of the cauda equina is a frequent sequela to injuries causing sacrococcygeal fracture/luxations. The prognosis is good for return of normal urinary function in cats that have anal tone and perineal sensation at the time of initial examination.¹⁹ Cats that are unable to urinate normally within 4 to 6 weeks after the injury are not expected to recover normal urination habits.¹⁹
 

Coccygeal fractures

Coccygeal fractures may result in various neurologic deficits to the tail. Rarely should they be treated surgically. If anesthesia of the tail persists, amputation may be the only feasible alternative.

New Horizons

One new spinal fixation technique has been described in the literature and involves the use of closed fluoroscopic-assisted spinal arch external skeletal fixation (ESF) for the stabilization of traumatic vertebral column injuries in 5 dogs. In this study, the fixator configuration consisted of pins placed bilaterally in 2 contiguous vertebral bodies cranial and caudal to the fracture. The protruding portion of the pins were incorporated into an external connecting system (IMEX Veterinary Inc., Longview Texas) for spinal stabilization. Results of this study were initially encouraging and this device may prove to be useful in the future.^20,d

^dIMEX Acrylic pins, IMEX Veterinary Inc., Longview, TX

Post-operative Management

Post-operative management of spinal fracture patients is generally divided into ambulatory or non-ambulatory convalescence. Patients with an ambulatory status postoperatively are generally managed in the following manner: cage confinement, brief exercise 2 to 3 times a day for 2 to 3 weeks, serial neurologic and radiographic examinations and home on restricted exercise and/ or passive range of motion exercises until radiographic evidence of healing is present. Non-ambulatory patients are managed in the following manner: elevated padded cage rack or waterbed, turned every 2 to 4 hours, bladder expressions 4 to 5 times a day or intermittent sterile catheterization in the male patient 2 to 3 times daily, passive range of motion exercises 3 to 4 times a day, electrical stimulation (if available), serial neurologic and radiographic evaluations and frequent hydrotherapy until return to an ambulatory status is achieved. Complications as described for the recumbent cervical injury patient have been described and apply to these patients as well. The use of back braces or splints is somewhat controversial. If the brace is comfortable, light weight and tolerated by the patient they are helpful. However, most braces are heavy, nonconforming, result in pressure sores and are not well tolerated by the patient.³ Heavy reliance on a back brace, especially in large breed, hyperactive dogs should be avoided unless surgical intervention is not an option.

References

1. Feeney DA and Oliver JE. Blunt spinal trauma in the dog and cat: neurologic, radiologic and therapeutic correlations. J Am Anim Hosp Assoc 1980;16:664-668.
2. Swaim SF. Biomechanics of cranial fractures, spinal fractures, and luxations, in (ed) Bojrab, Pathophysiology in Small Animal Surgery. 1981:774-778.
3. Carberry CA, Flanders JA, Dietze AE, et al. Nonsurgical management of thoracic and lumbar spinal fractures and fracture/luxations in the dog and cat: a review of 17 cases. J Am Anim Hosp Assoc 1989;25:43-54.
4. Feeney DA and Oliver JE. Blunt spinal trauma in the dog and cat: insight into radiographic lesions. J Am Anim Hosp Assoc 1980;16:885-890.
5. Piermattei DL. An atlas of surgical approaches to the bones and joints of the dog and cat. 3rd ed. WB Saunders, 1993;45-89.
6. Dulisch ML and Nichols JB. A surgical technique for management of lower lumbar fractures: case report. Vet Surgery 1981;10:90-93.
7. Sharp NJ and Wheeler SJ: Trauma. In Small Animal Spinal Disorders. Philadelphia; Elsevier, 2005, 282-305.
8. Lumb WV and Brasmer TH. Improved spinal plates and hypothermia as adjuncts to spinal surgery. J Am Vet Med Assoc 1970;157:338-342.
9. McNaulty JF, Lenehan TM, Maletz LM. Modified segmental spinal instrumentation in repair of spinal fractures and luxations in dogs. Vet Surgery 1986;15:143-149.
10. Swaim SF. Vertebral body plating for spinal stabilization. J Am Vet Med Assoc 1971;158:1653-1695.
11. Blass CE and Seim HB. Spinal fixation in dogs using steinmann pins and methyl methacrylate. Vet Surgery, 1984;13:203-210.
12. Rouse GP and Miller JI. The use of methyl methacrylate for spinal stabilization. J Am Anim Hosp Assoc 1975;11:418-425.
13. Lewis DD, Stampley A, Bellah JR, et al. Repair of sixth lumbar vertebral fracture-luxations, using transilial pins and plastic spinous-process plates in six dogs. J Am Vet Med Assoc 1989;194:538-542.
14. Matthiesen DT. Thoracolumbar spinal fractures/luxations: Surgical management. Comp Cont Ed 1983;5:867-878.
15. Shores A, Nichols C, Koelling HA. Combined Kirschner-Ehmer apparatus and dorsal spinal plate fixation technique of caudal lumbar vertebral fractures in dogs: biomechanical properties. Am J Vet Res 1988;49:1979-1982.
16. Shores A, Nichols C, Rochat M, et al. Combined Kirschner-Ehmer device and dorsal spinal plate fixation technique for caudal lumbar vertebral fractures in dogs. J Am Vet Med Assoc 1989;195:335-339.
17. Slocum B and Rudy RL. Fractures of the seventh lumbar vertebral in the dog. J Am Anim Hosp Assoc 1975;11:167-174.
18. Taylor RA. Treatment of fractures of the sacrum and sacrococcygeal region. Vet Surgery 1981;10:119-124.
19. Smeak DD and Olmstead ML. Fracture/luxations of the sacrococ-cygeal are in the cat: a retrospective study of 51 cases. Vet Surgery 1985;14:319-324.
20. Wheeler JL, Lewis DD, et al. Closed Fluoroscopic-Assisted Arch External Fixation for the Stabilization of Vertebral Column Injuries in 5 Dogs. Vet Surg 2007, 36: 442-448.