Decompressive procedures. Indications and techniques.

Hemilaminectomy and dorsal laminectomy are the surgical techniques most suited for decompression of the thoracic, thoracolumbar, lumbar, and lumbosacral spine. Hemilaminectomy is preferred for decompressing the spinal cord before applying fixation devices for fractures/luxations. Dorsal laminectomy is the method of choice for exploration of the spinal canal and for decompression of the lumbosacral region. Either method is applicable to removal of herniated intervertebral disc material and fenestration of other disc spaces.     

Fractures and luxations of the vertebral column.

External fixation of the vertebral column is indicated to treat fractures of the caudal lumbar spine, open fractures where vertebral osteomyelitis is present or likely to occur, and vertebral fractures not easily stabilized by internal fixation alone (e.g., compression fractures, fractures including spinous processes, and articular facets). Advantages of external fixation of caudal lumbar fractures, especially in combination with dorsal fixation devices, include the following: Fracture fixation does not preclude dorsal decompression; fixation devices need not be applied directly to the fractured vertebrae; and the combined technique provides dorsal and ventral vertebral fixation, which is more stable than dorsal fixation alone. Although external fixation is not applicable to all vertebral fracture/luxations in small animals, it provides additional points of fixation for rigid stability. Animals with vertebral fracture/luxations treated with an external fixation device have tolerated the external portion well. Development of additional applications for this method of vertebral fracture repair seems warranted.     

Biomechanical flexion-extension forces in normal canine lumbosacral cadaver specimens before and after dorsal laminectomy-discectomy and pedicle screw-rod fixation

Objective— To determine biomechanical flexion–extension forces in cadaveric canine lumbosacral specimens, before and after dorsal laminectomy with partial discectomy, and after dorsal pedicle screw–rod fixation of L7 and S1.
Study Design— Biomechanical cadaver study.
Animals— Cadaveric spine specimens without lumbosacral pathology from mature, intact Labrador retrievers (n=12).
Methods— Lumbosacral spine segments were subjected to a constant bending moment from L6 to S1 in a hydraulic 4-point bending materials testing machine. Force and displacement were recorded during each loading cycle constituting 1 complete flexion–extension cycle of the spine. Each spine segment had 3 series of recordings of 5 loading cycles each: (1) intact spine, (2) after surgical destabilization by dorsal laminectomy and partial discectomy, and (3) after surgical stabilization using dorsal pedicle screw–rod fixation.
Results— After dorsal laminectomy and partial discectomy, the neutral zone and range of motion were not different from those in the native spine specimen. After pedicle screw–rod fixation, the neutral zone and range of motion of the instrumented specimen significantly ( P <.0001) decreased compared with the native specimen and the specimen after dorsal laminectomy.
Conclusion— Dorsal laminectomy and partial discectomy does not lead to significant spinal instability in flexion and extension whereas pedicle screw and rod fixation effectively stabilizes the lumbosacral spine.
Clinical Relevance— Dorsal laminectomy and partial discectomy does not lead to significant spinal instability. Pedicle screw–rod fixation of L7 and S1 may be used to stabilize an unstable L7–S1 junction in dogs with degenerative lumbosacral stenosis.     

Thoracolumbar dorsolateral laminectomy with osteotomy of the spinous process in fourteen dogs

Objective— To describe outcome after an alternative unilateral approach to the thoracolumbar spine for dorsal laminectomy.
Study Design— Retrospective clinical study.
Animals— Dogs (n=14) with thoracolumbar spinal cord compression.
Methods— Thoracolumbar spinal cord compression was lateral (6 dogs), dorsal (4), and dorsolateral (4) caused by subarachnoid (7) and synovial cysts (2) and intradural-extramedullary neoplasia (5). All dogs were treated by dorsal laminectomy with osteotomy of the spinous process using a unilateral paramedian approach. The contralateral paraspinal muscles were not stripped from the spinous process and the osteoligamentous complexes were preserved. Retraction of the spinous process and muscles to the contralateral side resulted in complete visualization of the dorsal vertebral arch thereby allowing dorsal laminectomy to be performed.
Results— No technique complications occurred. Approximately 75% exposure of the spinal cord (dorsal and lateral compartments) was achieved providing adequate visualization and treatment of the lesions. Transient deterioration of neurologic state occurred in 5 dogs because of extensive spinal cord manipulation. At long-term follow-up, 6 dogs were normal, 6 had clinical improvement, and 2 were unchanged.
Conclusion— Dorsal laminectomy after osteotomy and retraction of the spinous process may be considered in canine patients with dorsal, dorsolateral, or lateral compression to facilitate adequate decompression of the spinal cord.
Clinical Significance— This surgical technique offers an alternative approach to the thoracolumbar spine and spinal cord by a modified dorsal laminectomy that preserves the paraspinal muscle integrity on the contralateral side.     

Clinical Technique: Myelography in Rabbits

Spinal disease in rabbits is most often the result of trauma; however, other causes have been reported including congenital defects and degenerative spinal diseases. Diagnosis of spinal disease is based on history, physical and neurologic examination findings, and imaging. Fractures and luxations of the spine are often apparent on plain radiographs; however, myelography is used to determine if the lesion is causing spinal cord compression that may be amenable to surgical decompression. Unless intervertebral discs are mineralized, they are not visible when viewing plain radiographic images; therefore, myelography may be useful to diagnose spinal cord compression from a herniated disc. Myelography can also define lesions that do not result in a disruption of the osseous vertebral architecture such as tumors and granulomas. In rabbits, myelography is performed when the animal is under general anesthesia and in lateral recumbency. A nonionic iodinated contrast agent is injected into the subarachnoid space, usually at the level of the lumbar spine, to outline the spinal cord and identify cord compressive or disruptive lesions.     

Imaging findings and surgical treatment of hemivertebrae in three dogs

CASE DESCRIPTION: 3 immature screw-tailed dogs were evaluated because of progressive pelvic limb paraparesis. CLINICAL FINDINGS: Each dog had marked ataxia and paresis of the pelvic limbs and a palpable deformity of the midthoracic portion of the vertebral column. Pain perception in the pelvic limbs was considered normal, and there was no evidence of fecal or urinary incontinence in any of the 3 dogs. Radiography and magnetic resonance imaging revealed hemivertebrae with severe dorsoventral stenosis of the vertebral canal resulting in spinal cord compression in 2 dogs and lateral compression in the other. TREATMENT AND OUTCOME: Each dog underwent decompressive surgery consisting of dorsal laminectomy or hemilaminectomy and vertebral stabilization by use of combinations of Kirschner wires or threaded external fixator pins plus polymethylmethacrylate bone cement. All dogs regained strong locomotor function with minimal residual pelvic limb ataxia. CLINICAL RELEVANCE: Little detailed information regarding surgical treatment of hemivertebrae in dogs is available; results of treatment in these 3 dogs suggest that spinal cord decompression and stabilization of the vertebral column can achieve a satisfactory, functional outcome.     

Laminotomy of the Axis for Surgical Access to the Cervical Spinal Cord A Case Report

A cranially hinged laminotomy of vertebra C2 was used to expose the cervical spinal cord of a dog with a meningioma in the region of the atlantoaxial articulation. By preserving the dorsal atlantoaxial ligament, the technique seemed to result in greater and more physiologic stability between the atlas and axis than dorsal laminectomy and prosthetic replacement of the dorsal atlantoaxial ligament. The procedure allowed a dorsal approach, avoiding injury to the vertebral arteries and limited exposure, which are potential problems with hemilaminectomy of C1-C2. Further investigation is needed to evaluate long-term consequences of this procedure.     

Vertebral stabilization using positively threaded profile pins and polymethylmethacrylate, with or without laminectomy, for spinal canal stenosis and vertebral instability caused by congenital thoracic vertebral anomalies

Objective— To describe diagnostic findings, surgical technique, and outcome in dogs with thoracic spinal canal stenosis and vertebral instability secondary to congenital vertebral anomalies.
Study Design— Retrospective clinical study.
Animals— Dogs (n=9) with thoracic spinal canal stenosis.
Methods— Medical records (1995–1996; 2000–2006) of 9 dogs with a myelographic diagnosis of spinal canal stenosis and/or vertebral instability secondary to congenital vertebral anomaly that were surgically managed by vertebral stabilization with or without laminectomy were reviewed. Data on pre- and postoperative neurologic status, diagnostic findings, surgical techniques, and outcomes were retrieved. Follow-up evaluations were performed at 1, 2, and 6 months. Long-term outcome was assessed by means of clinical examination or owner telephone interviews.
Results— Spinal cord compression was confirmed by myelography, and in 2 dogs, dynamic compression by stress myelography. Eight dogs regained the ability to ambulate postoperatively. One dog with a partial recovery regained voluntary movement but did not become ambulatory.
Conclusions— Spinal cord injury secondary to congenital vertebral anomaly may have a good outcome when treated by vertebral stabilization with or without laminectomy. Adequate stabilization of the vertebrae and improved neurologic outcome were achieved in most dogs.
Clinical Relevance— Vertebral stabilization using positively threaded profile pins and polymethylmethacrylate with or without laminectomy is an effective treatment for spinal canal stenosis and vertebral instability secondary to congenital thoracic vertebral anomalies.     

INTRAOPERATIVE SPINAL ULTRASONOGRAPHY IN DOGS: NORMAL FINDINGS AND CASE-HISTORY REPORTS

Intraoperative spinal ultrasonography was performed in cervical and lumbar spine of 2 and 5 normal dogs, respectively, following ventral slot technique or dorsal or hemilamenectomy. The dura was hyperechoic, while the parenchyma was hypoechoic. The subarachnoid space was anechoic. An echogenic line was present in the center of the spinal cord, as seen in human. Pulsation of the spinal cord was noted during M-mode imaging. Clinical findings of one dog with thoracolumbar disk herniation and one with thoracic vertebral fracture/subluxation confirmed the usefulness of intraoperative spinal ultrasonography for real time evaluation of spinal canal spatial abnormalities (mass lesion and degree of spinal cord compression on scanning planes) and spinal cord motion. Follow-up ultrasound examinations were possible from 6 days postoperatively.     

Lumbosacral intervertebral disk disease in six cats

Medical records of six cats diagnosed with lumbosacral intervertebral disk disease were reviewed. Clinical signs included reluctance to jump, low tail carriage, elimination outside the litter box, reluctance to ambulate, pelvic-limb paresis, urinary incontinence, and constipation. All cats had lumbosacral hyperpathia on palpation. Computed tomography in four cats revealed evidence of extradural spinal cord compression at the seventh lumbar (L(7)) to first sacral (S(1)) vertebral interspace. Compression was confirmed via myelography in three of these four cats, with confirmation in the fourth cat at the time of decompressive laminectomy. Each of the six cats underwent dorsal decompressive laminectomy at the L(7) to S(1) interspace. Postoperative clinical follow-up lasted 3 to 35 months, with most cats having excellent outcomes.     

Dorsal Laminectomy in the Horse III. Results in Horses With Cervical Vertebral Malformation

Subtotal dorsal cervical laminectomy was used to relieve spinal cord compression due to cervical vertebral malformation in 16 horses. The majority were Thoroughbred or Quarter Horse males, 1 to 4 years old. The caudal cervical vertebrae were involved in all but two instances. A Funkquist type B laminectomy was performed and the defect filled with a free autogenous nuchal fat graft. All horses recovered from surgery without complication or deterioration in neurological status. Neurological improvement occurred in 12 cases, including six that became sound. Three horses fractured a vertebral articular process and were euthanized. A modification to the shape of the laminectomy was adopted to reduce this complication.     

Vertebral stabilisation and selective decompression for the management of triple thoracolumbar disc protrusions

Triple adjacent thoracolumbar disc protrusions causing moderate to severe spinal cord compression were diagnosed by magnetic resonance imaging in two German shepherd dogs with marked paraparesis and pelvic limb ataxia. Both cases were managed by selective hemilaminectomy, partial annulectomy and bilateral quadruple vertebral body stabilisation using novel canine locking fixation plates (SOP). The stabilisation of multiple vertebrae in the thoracolumbar spine was possible because the plates could be contoured with six degrees of freedom. Spinal pain resolved and neurological function improved in both dogs. Screw breakage was evident in one dog five months following surgery.     

Asymmetrical, transitional, lumbosacral vertebral segments in six dogs: a characteristic spinal syndrome

Clinical findings in six dogs with asymmetrical, transitional, lumbosacral vertebral segments are reported. All dogs exhibited low back pain and varying degrees of asymmetrical cauda equina dysfunction. Results of myelography, epidurography, and magnetic resonance imaging (MRI) indicated a unilateral disk protrusion in all dogs. In the dogs with MRIs, focal degenerative alterations in the vertebral end plates and adjacent body of the vertebra were detected. All dogs were treated with a dorsal laminectomy or hemilaminectomy. Results following surgery were good or excellent in all six dogs.     

Modified deep dorsal laminectomy in the dog.

Spinal cord compression subsequent to radical laminectomy was investigated. A modified deep dorsal laminectomy technique was devised to allow extensive exposure and decompression of the canine spinal cord without undue hazard of postoperative fibrotic spinal cord compression. A previously described laminectomy technique was modified by the addition of spinal plating to avoid the occurrence of constrictive fibrosis.     

Intraoperative use of ultrasonography during continuous dorsal laminectomy in two dogs with caudal cervical vertebral instability and malformation ("Wobbler syndrome")

OBJECTIVE: To describe an intraoperative ultrasound imaging technique during dorsal laminectomy in 2 dogs with caudal cervical vertebral instability and malformation (CCVIM, "Wobbler syndrome"). STUDY DESIGN: Clinical case report. SAMPLE POPULATION: Two dogs with CCVIM. RESULTS: On neurologic examination there was tetraparesis with upper motor neuron signs in the thoracic limbs and lower motor neuron signs in the pelvic limbs in dog 1, and hyperreflexia of the rear limbs, normoreflexia of the right front limb, and hyporeflexia of the left front limb of dog 2. Both dogs had signs of marked cervical pain and radiographic signs of cervical spinal cord compression. Intraoperative ultrasonography of the spinal cord revealed protruding intervertebral disc at C5-6 (dog 1) and C6-7 (dog 2), and the parallel borders of the spinal cord and central canal after decompression. Continuous dorsal laminectomy (CDL) resulted in improvement over 16 months (dog 1) and 20 months (dog 2). CONCLUSIONS: Intraoperative ultrasonographic imaging of the cervical spinal cord after CDL was helpful in determining adequate decompression (postlaminectomy) of the spinal cord in relation to the ventral and lateral compressive component(s) and to image the protruding intervertebral disc. CLINICAL RELEVANCE: Intraoperative ultrasonography can be used to provide valuable information on the spinal cord and surrounding soft tissues for the neurosurgeon.     

Management of spinal trauma in 69 cats

This study sought to evaluate a series of clinical and radiological findings on spinal trauma in cats and the outcome that emerged from conservative or surgical treatment using 2 types of spinal stapling: stabilization using a Steinmann pin and coated polypropylene. Case records were reviewed for their diagnostic approaches on the basis of physical and neurological conditions, and concurrent disorders in addition to spinal trauma. Radiological examinations of the vertebral column were carried out using survey radiography, myelography and epidurography. All cases were classified according to etiopathogenesis of the disease. Surgical treatment consisted of decompression (laminectomy, hemilaminectomy and durotomy), or decompression with stabilization which was performed by one of two methods. The first one was the employment of translaminar stapling at the base of a spinous process and the other involved spinal stapling at the spinous process. The spinal lesions were identified as cervical (n = 2), thoracic (n = 35), lumbar (n = 22), sacral and caudal (n = 10). While 19 out of 30 conservatively managed cases recovered, the rest had persistent residual paresis and ataxia. Complete recovery was seen in 4 cats that underwent hemilaminectomy and 3 subjected to laminectomy. Partial recovery was observed in 5 cases involving laminectomy; however, there was no improvement observed in another 2 cases. Each animal was followed for at least a 3-month period to evaluate the clinical assessment of the results following treatment. The results of conservative and operative management of spinal trauma indicated that the type and degree of spinal cord degradation strongly influenced any prognosis. The results emerging from decompressive procedures seemed satisfactory for those cases where instability was not an issue. Both stabilization techniques were not ideal in terms of their methodological versatility or regarding weaknesses of bone structure observed in intra- and postoperative periods. However, translaminar stapling at the base of a spinous process was deemed to be the superior technique.     

Combined Kirschner-Ehmer apparatus and dorsal spinal plate fixation of caudal lumbar fractures in dogs: biomechanical properties

The strength and rigidity of a new surgical technique for the stabilization of caudal lumbar fractures in dogs, using a Kirschner-Ehmer apparatus and a dorsal spinal plate (KE/DSP), were compared with 2 other methods of internal spinal fixation and with intact (control) spines, using a spinal test system that subjected the spines to 4-point bending. The fixation devices were applied to isolated canine lumbosacral spines (L1 to S3) from cadavers. A complete spinal separation was made in the spine implant specimens at L5-L6 by sharp dissection of all ligamentous structures connecting the two vertebrae. Bending moment vs L5-L6 angular deformation curves, and rigidity and load sustained at 10 degrees angular deformation (failure) were recorded for each fixation method and for the control spines. Values were compared by statistical analysis. The combined KE/DSP fixation and a combined vertebral body plate/dorsal spinal plate (VBP/DSP) fixation were stronger and more rigid than were the control spines and those fixed with a modified segmental-fixation method (P less than 0.05). There were no statistical differences in strength and rigidity between the 2 combined-fixation techniques. Although the VBP/DSP technique is not applicable to clinical caudal lumbar (L5-L6) fractures, it was compared in this study to the KE/DSP technique because a similar VBP/DSP technique was reported strongest in a similar study of L3-L4 simulated fractures, compared with 3 other spinal-fixation techniques that have been used in repair of caudal lumbar fractures. The technique has been used successfully in 6 dogs with caudal lumbar fractures.     

Thoracic vertebral osteochondroma in a cat

A thoracic vertebral (T5) osteochondroma was discovered in a 1 1/2-year-old male blue Persian cat with a history of acute hind limb paresis. Myelography revealed a mass on the dorsal surface of the vertebral body, which resulted in dorsal compression of the spinal cord. A dorsal laminectomy was performed, and the mass was rongeured entirely from the vertebral body. Although the cat's progress was initially slow after surgery, its neurologic status was assessed to be near normal, 15 months later.     

Comparison of the access window created by hemilaminectomy and mini-hemilaminectomy in the thoracolumbar vertebral canal using computed tomography

Hemilaminectomy and mini-hemilaminectomy were performed on opposite sides of the spine at T11–T12, T13-L1, and L2–L3 in 11 canine cadavers in order to report differences in the access provided to the thoracolumbar vertebral canal. Measurements of the vertebral canal height, defect height, and dorsal and ventral remnants of the vertebral arch were obtained after computed tomography. A median of 7% to 20% of the vertebral canal height was not removed dorsally after mini-hemilaminectomy compared to 1% to 2% in hemilaminectomy. Thirteen to 25% of the vertebral canal height was left ventrally in mini-hemilaminectomy and 11% to 27% in hemilaminectomy. Potential for a restricted exposure of thoracolumbar lesions should be considered if lesions are located in the ventral 11% to 27% vertebral canal height when performing either procedure or in the dorsal 7% to 20% of the canal height when performing a mini-hemilaminectomy.