Spinal trauma. Pathophysiology and management of traumatic spinal injuries.

Spinal trauma can originate from internal or external sources. Injuries to the spinal cord can be classified as either concussive or compressive and concussive. The pathophysiologic events surrounding spinal cord injury include the primary injury (compression, concussion) and numerous secondary injury mechanisms (vascular, biochemical, electrolyte), which are mediated by excessive oxygen free radicles, neurotransmitter and electrolyte alterations in cell membrane permeability, excitotoxic amino acids, and various other biochemical factors that collectively result in reduced SCBF, ischemia, and eventual necrosis of the gray and white matter. Management of acute spinal cord injuries includes the use of a high-dose corticosteroid regimen within the initial 8 hours after trauma. Sodium prednisolone and methylprednisolone, at recommended doses, act as oxygen radical scavengers and are anti-inflammatory. Additional considerations are the stability of the vertebral column, other conditions associated with trauma (i.e., pneumothorax), and the presence or absence of spinal cord compression, which may warrant surgical therapy. Vertebral fractures or luxations can occur in any area of the spine but most commonly occur at the junction of mobile and immobile segments. Dorsal and dorsolateral surgical approaches are applicable to the lumbosacral and thoracolumbar spine and dorsal and ventral approaches to the cervical spine. Indications for surgical intervention include spinal cord compression and vertebral instability. Instability can be determined from the type of fracture, how many of the three compartments of the vertebrae are disrupted, and on occasion, by carefully positioned stress studies of fluoroscopy. Decompression (dorsal laminectomy, hemilaminectomy, or ventral cervical slot) is employed when compression of the spinal cord exists. The hemilaminectomy (unilateral or bilateral) causes less instability than dorsal laminectomy and therefore should be used when practical. The preferred approach for atlantoaxial subluxation is ventral, and the cross pinning, vertebral fusion technique is used for stabilization. Fracture luxations of C-2 are repaired with small plates on the ventral vertebral body. The thoracic and upper lumbar spine is stabilized with dorsal fixation techniques or combined dorsal spinal plate/vertebral body plate fixation. Several methods of fixation can be used with lower lumbar or lumbosacral fractures, including the modified segmental technique and the combined dorsal spinal plate/Kirschner-Ehmer technique.     

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.     

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.     

Spinal decompressive procedures and dorsal compartment injuries: comparative biomechanical study in canine cadavers

Effects of decompressive procedures or dorsal injuries on flexion-extension, 4-point bending properties of the L-3 and L-4 motion segment in dogs were quantitated and compared. Hemilaminectomy did not significantly (P less than 0.05) affect mechanical properties of the spine. Bilateral facetectomy caused a small increase in the range of motion and a 56% decrease in ultimate bending strength. Excision of the supraspinous and interspinous ligaments decreased the flexural stiffness of the spine, increased the range of motion of the interspace, and decreased ultimate flexion bending strength 62%. Dorsal laminectomy caused a marked decrease in spine stiffness in all phases of flexion and extension, increased the range of motion, and decreased ultimate flexion bending strength 75%. Seemingly, a hemilaminectomy was preferable to the dorsal laminectomy if adequate decompression and exploration were achieved with the hemilaminectomy.     

Biomechanical Analysis of Torsion and Shear Forces in Lumbar and Lumbosacral Spine Segments of Nonchondrodystrophic Dogs

Objective— To determine stiffness and load–displacement curves as a biomechanical response to applied torsion and shear forces in cadaveric canine lumbar and lumbosacral specimens.
Study Design— Biomechanical study.
Animals— Caudal lumbar and lumbosacral functional spine units (FSU) of nonchondrodystrophic large-breed dogs (n=31) with radiographically normal spines.
Methods— FSU from dogs without musculoskeletal disease were tested in torsion in a custom-built spine loading simulator with 6 degrees of freedom, which uses orthogonally mounted electric motors to apply pure axial rotation. For shear tests, specimens were mounted to a custom-made shear-testing device, driven by a servo hydraulic testing machine. Load–displacement curves were recorded for torsion and shear.
Results— Left and right torsion stiffness was not different within each FSU level; however, torsional stiffness of L7-S1 was significantly smaller compared with lumbar FSU (L4-5–L6-7).
Ventral/dorsal stiffness was significantly different from lateral stiffness within an individual FSU level for L5-6, L6-7, and L7-S1 but not for L4-5. When the data from 4 tested shear directions from the same specimen were pooled, level L5-6 was significantly stiffer than L7-S1.
Conclusions— Increased range of motion of the lumbosacral joint is reflected by an overall decreased shear and rotational stiffness at the lumbosacral FSU.
Clinical Relevance— Data from dogs with disc degeneration have to be collected, analyzed, and compared with results from our chondrodystrophic large-breed dogs with radiographically normal spines.     

Biomechanical evaluation of a novel nucleus pulposus prosthesis in canine cadaveric spines

Partial disc replacement is a new surgical technique aimed at restoring functionality to degenerated intervertebral discs (IVDs). The aim of the present study was to assess biomechanically the behaviour of a novel nucleus pulposus prosthesis (NPP) in situ and its ability to restore functionality to the canine IVD after nuclectomy alone or after combined dorsal laminectomy and nuclectomy. Nine canine T13-L5 specimens (L2L3 group) and 10 L5-Cd1 specimens (LS group) were tested biomechanically in the native state, after nuclectomy (L2L3 group) or after combined dorsal laminectomy and nuclectomy (LS group), and after insertion of the NPP. Range of motion (ROM), neutral zone (NZ), and neutral zone stiffness (NZS) were determined in flexion/extension, lateral bending, and axial rotation. Nuclectomy alone and combined dorsal laminectomy and nuclectomy caused significant instability in all motion directions. Implantation of the NPP resulted in significant restoration of the parameters (ROM, NZ, and NZS) towards the native state; however, fragmentation/herniation of the NPP occurred in 47% of the cases. In conclusion, the NPP has the ability to improve functionality of the nuclectomized canine IVD. The high rate of NPP failure requires modifications directed at the integrity of the NPP and its confinement to the nuclear cavity.     

Use of a four pin and methylmethacrylate fixation in L7 and the iliac body to stabilize lumbosacral fracture-luxations: a clinical and anatomic study

Objectives— To describe the clinical outcome of a 4 pin lumbosacral fixation technique for lumbosacral fracture–luxations, and to refine placement technique for iliac pins based on canine cadaver studies.
Study Design— Retrospective and anatomic study.
Sample Population— Dogs (n=5) with lumbosacral fracture-luxations and 8 cadaveric canine pelvi.
Methods— Lumbosacral fracture–luxations were stabilized with a 4 pin (positive-profile threaded) and bone cement fixation. Caudal pins were inserted in the iliac body and cranial pins were inserted into the L7 or L6 pedicle and body. Follow-up examinations and radiographs were performed to assess patient outcome. Intramedullary pins were inserted into the iliac bodies of 8 cadaver pelvi. Radiographs were taken to measure pin insertion angles and define ideal insertion angles that would maximize pin purchase in the ilium.
Results— Follow-up neurologic examination was normal in 4 dogs. Radiographic healing of the fracture was evident in 5 dogs. One implant failure occurred but did not require re-operation. For cadaver iliac pins, mean craniocaudal insertion angle was 29° and mean lateromedial insertion angle was 20°.
Conclusions— Four pin and bone cement fixation effectively stabilizes lumbosacral fracture luxations. The iliac body provides ample bone stock, which can be maximized using an average craniocaudal pin trajectory of 29° and an average lateromedial pin trajectory of 20°.
Clinical Relevance— Lumbosacral fracture–luxations can be stabilized with 4 pin and bone cement fixation in the lumbar vertebrae and iliac body, using 29 and 20° as guidelines for the craniocaudal and lateromedial pin insertion angles in the ilium.     

Cauda equina compression syndrome (CECS): retrospective study of surgical treatment with partial dorsal laminectomy in 86 dogs with lumbosacral stenosis

We report our results of partial lumbosacral laminectomy for treatment of canine Cauda equina Compression Syndrome due to a lumbosacral stenosis. Opposite to conventional techniques of dorsal laminectomy, only widening of the Spatium interarcuale is performed. This is achieved by exstirpation of the Lig. flavum and partial dorsal laminectomy of the first sacral segment. The Proc. spinosi and integrity of facet joints are fully maintained by this technique. In 96.5% of 86 dogs treated with this method relief of dorsal pressure and permanent rapid regression of clinical symptoms was achieved. In two cases recurrence of clinical symptoms was observed during follow up and one case showed no improvement at all. In conclusion partial dorsal laminectomy is a minimal invasive technique for treatment of Cauda equina compression syndrome expressed by pain reaction accompanied by minor neurological deficits caused by lumbosacral stenosis. Maintained spinal stability allows short reconvalescence and the unrestricted use of dogs immediately post operation.     

Minimally invasive approach to lumbosacral decompression in a cadaveric canine model

AIMS: To determine efficacy of a minimally invasive (MI) surgical approach using a human MI lumbar retractor for canine lumbosacral dorsal laminectomy and partial discectomy and to compare this technique to the standard open surgical (OS) approach.

METHODS: Lumbosacral dorsal laminectomy and partial discectomy was performed on 16 large-breed canine cadavers using either a standard OS (n=8) or MI (n=8) approach. Skin and fascial incision length, procedure time, and intraoperative complications were recorded. Postoperatively specimens were evaluated for laminectomy and discectomy dimensions, and visible damage to the cauda equina and exiting nerve roots.

RESULTS: Median length of skin and fascial incisions in the OS group were longer than in the MI group (p<0.001). Median laminectomy length was similar between both approaches (p=0.234) but width was greater for the MI than OS approach (p=0.002). Both approaches achieved similar partial discectomy width (p=0.279). Overall surgical time was longer for MI approaches compared to OS, with a median of 18.5 (min 15.5, max 21.8) minutes for MI compared to 14.6 (min 13.1, max 16.9) minutes for OS (p=0.001).

CONCLUSIONS: The MI approach reduced incision lengths while retaining comparable laminectomy and discectomy dimensions. For this in vitro model the MI approach required more time to complete, but this difference may not be relevant in clinical cases.

CLINICAL RELEVANCE: Dogs undergoing lumbosacral dorsal laminectomy are commonly large-breed dogs. The traditional open approach requires a large skin incision and soft tissue dissection, especially in overweight animals. A MI approach accomplishing the same surgical result while minimising soft tissue trauma could reduce post-operative pain and recovery time, and may lower wound-related complications. Clinical studies are needed to confirm postoperative benefit and assess operating times in vivo.     

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.     

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.     

Cervical Spine Locking Plate Fixation for Treatment of Cervical Spondylotic Myelopathy in Large Breed Dogs

Objective— To describe indirect decompression by means of cervical spine locking plate (CSLP) fixation with vertebral distraction, discectomy, and cancellous block bone grafting in large breed dogs with single caudal cervical dynamic spondylotic lesions diagnosed by myelography with linear traction to the cervical spine, and contrast-enhanced computed tomography.
Study Design— Prospective clinical study.
Animals— Dogs (n=12) with caudal cervical spondylotic myelopathy because of a single dynamic, traction-responsive lesion.
Methods— Single, traction-responsive, caudal cervical spondylotic lesions were treated by vertebral distraction, discectomy, cancellous block bone grafting, and CSLP fixation. Follow-up was obtained by sequential recheck examination by the author or referring veterinarian or by telephone inquiries.
Results— Ten dogs had neurologic improvement after surgery. Indirect decompression by maintained distraction with cancellous block grafting and CSLP fixation was readily accomplished with less risk of blood loss or iatrogenic spinal cord injury than that associated with direct (ventral) decompression. There were no complications of graft intrusion, extrusion or subsidence, implant loosening, foraminal impingement, or end-plate failure. Two dogs that had satisfactory short-term recoveries developed clinical signs associated with adjacent segment disease and were euthanatized. At long-term follow-up, 8 dogs had satisfactory function, either a normal gait or one with slight to moderate proprioceptive deficits.
Conclusions— CSLP fixation with cancellous block interbody grafting is an effective and perhaps safer method of treating single-level, traction-responsive cervical spondylosis in large breed dogs.
Clinical Relevance— CSLP fixation with interbody bone grafting is a viable alternative to other techniques for treatment of single-level, traction-responsive cervical spondylosis.     

SUBFASCIAL SEROMA CAUSING COMPRESSIVE MYELOPATHY AFTER CERVICAL DORSAL LAMINECTOMY

Dorsal surgical approach to the cervical vertebral canal is indicated for a variety of spinal cord diseases. Compressive myelopathy due to subfascial seroma following dorsal laminectomy has not previously been documented in dogs. We describe neurologic findings, magnetic resonance (MR) imaging characteristics and clinical outcome in a young Rottweiler experiencing this complication after a successful dorsal decompression for treatment of cervical stenotic myelopathy. MR imaging allowed detection of pockets of high signal intensity material on T2-weighted images and low signal intensity in T1-weighted images. Prompt surgical revision and drainage allowed complete recovery.     

Healing Characteristics of Free and Pedicle Fat Grafts after Dorsal Laminectomy and Durotomy in Dogs

Dorsal laminectomy and durotomy were performed at thoracic vertebrae 12 and 13 (T12-T13) and lumbar vertebrae 1 and 2 (L1-L2) in 12 normal dogs. A free fat graft harvested from subcutaneous tissue adjacent to the incision was placed over the T12-T13 laminectomy site. A 75 X 25 X 5 mm pedicle fat graft harvested from a similar location was placed over the L1-L2 laminectomy site. Three dogs each were euthanatized at weeks 2, 4, 8, and 16. With both types of fat grafts, an initial inflammatory stage reduced the size of the graft approximately 50%. Axonal degeneration and demyelination of the spinal cord resolved by week 16. At week 16, the durotomy sites had healed, but the dura mater was adhered to the spinal cord. No difference between the grafts could be demonstrated by antemortem myelography and cerebrospinal fluid analysis. There was no demonstrable advantage to the use of pedicle fat grafts.     

Asymmetric lumbosacral transitional vertebra and subsequent disc protrusion in a cocker spaniel

A 10-year-old cocker spaniel bitch presented with severe lumbosacral pain and acute onset left pelvic limb lameness. A diagnosis of asymmetric lumbosacral transitional vertebra with disc protrusion at L6-L7 was made by computed tomography. The cauda equina and left L6 nerve root were surgically decompressed with a dorsal laminectomy and lateral foraminotomy, which led to rapid resolution of the clinical signs.     

Segmental spinal fixation of a thoracic vertebral fracture in an adult chimpanzee

Accidental trauma associated with an epileptic convulsion in a 10-year-old, male chimpanzee (Pan troglodytes) resulted in incomplete paraplegia from fracture and subluxation of T4. Dorsal laminectomy and segmental spinal fixation were used in treatment. The segmental spinal fixation consisted of sublaminar wires attached to a contoured 316L stainless steel U-rod. The chimpanzee recovered sufficient function to allow reintroduction into the chimpanzee colony at a zoological park during the 12 months after surgery and continues to do well 24 months after surgery.     

Surgical treatment of lumbosacral foraminal stenosis using a lateral approach in twenty dogs with degenerative lumbosacral stenosis

Objectives— To describe clinical signs, magnetic resonance imaging (MRI) and surgical findings using a lateral approach to the lumbosacral intervertebral foramen and to evaluate clinical outcomes in dogs with or without concurrent dorsal decompression and annulectomy.
Study Design— Retrospective study.
Animals— Dogs (n=20) with degenerative lumbosacral stenosis (DLSS).
Methods— Medical records (2002–2006) of dogs that had lumbosacral lateral foraminotomy alone or in combination with dorsal decompression were reviewed. Degree of dysfunction was assessed separately for each pelvic limb; dogs with unilateral signs were included in group A, those with bilateral signs in group B. Retrieved data were: signalment, history, neurologic status on admission, 3 days, 6 weeks, and 6 months postoperatively, duration of clinical signs, results of MRI, surgical site(s), intraoperative findings, and outcome.
Results— Based on the clinical and MRI findings unilateral foraminotomy was performed in 8 dogs, bilateral foraminotomy in 1 dog, unilateral foraminotomy with concurrent dorsal decompression in 7 dogs, and bilateral foraminotomy with concomitant dorsal decompression in 4 dogs. Surgery confirmed the presence of foraminal stenosis in all dogs, with osteophyte formation and soft tissue proliferations being the most common lesions. Outcome was good to excellent in 19 dogs and poor in 1 dog. Mean follow-up was 15.2 months (range, 6–42 months).
Conclusion— Lateral foraminotomy addresses compressive lesions within exit and middle zones of the lumbosacral foramen.
Clinical Relevance— Successful surgical management of DLSS is dependent on recognition and correction of each of the compressive lesions within the lumbosacral junction.     

In vitro biomechanical comparison of cervical disk arthroplasty, ventral slot procedure, and smooth pins with polymethylmethacrylate fixation at treated and adjacent canine cervical motion units

Objective— To compare the biomechanical properties of cervical arthroplasty to a ventral slot procedure and pin‐polymethylmethacrylate (pin‐PMMA) fixation. Sample Population— Fresh cadaveric cervical (C2–T1) spines from 6 large dogs. Methods— Four spinal conditions were studied in each spinal specimen: intact, disk arthroplasty, ventral slot, and fixation with smooth pin‐PMMA at C5–C6 intervertebral space. Axial compression, torsion, flexion–extension, and lateral bending moments were sequentially tested on each specimen for the 4 spinal conditions. Data from the C3–C4, C4–C5, C5–C6, and C6–C7 vertebral motion units (VMUs) were compared among treatments. Results— In axial compression and torsion, the ventral slot procedure allowed significantly less motion than intact, pin‐PMMA, and arthroplasty groups at C5–C6. In lateral bending and flexion–extension, pin‐PMMA had the least motion of C5–C6, followed by the arthroplasty group, intact spine, and ventral slot, all of which were significantly different from each other. Overall, the artificial disk was better able to mimic the behavior of the intact specimens compared with the ventral slot and pin‐PMMA, producing similar displacements in axial compression and rotation in torsion, but more limited motion than intact in flexion–extension and in lateral bending. Conclusion— Cervical spine specimens with an implanted prosthesis have biomechanical behaviors more similar to an intact spine compared with spinal specimens with ventral slot and pin‐PMMA procedures. Cervical arthroplasty may then preserve some of the motion in the affected area after neural decompression while providing distraction. Clinical Relevance— Cervical arthroplasty should be further investigated in vivo to determine if it is a viable alternative to the ventral slot or pin‐PMMA procedures for surgical treatment of cervical diseases in dogs and in particular for treatment of disk‐associated caudal cervical spondylomyelopathy.     

Feline Ilial Fractures: A Prospective Study of Dorsal Plating and Comparison with Lateral Plating

Objective— To (1) report a technique for repair of feline ilial fractures using a dorsally applied bone plate and (2) compare outcome with cats treated by a lateral plate.
Study Design— Prospective study.
Animals— Cats (n=10) with iliac fractures.
Methods— Cats with ilial fractures (January 2005–December 2006) were treated by application of a dorsally applied bone plate. Immediate postoperative radiographs were compared with those taken 4–6 weeks later to assess screw loosening, screw purchase, and pelvic canal narrowing. Owners were contacted for medium-term (>3 month) follow-up. Data were compared with a report of outcome after lateral plating (LP) in 21 cats.
Results— Mean (± SD) screw purchase (89 ± 11 mm) was significantly greater ( P <.01) with a dorsal plate compared with a lateral plate (33 ± 8 mm). Significantly more screws ( P <.01) were used with a dorsal plate (median, 7) compared with a lateral plate (median, 6). Significantly less postoperative pelvic canal narrowing developed in the dorsal plating group between postoperative and 4–6-week follow-up radiography compared with the LP group (2% versus 15%, P <.01).
Conclusion— Dorsal plating of feline ilial fractures results in significantly less screw loosening and pelvic canal narrowing at 4–6 weeks after surgery compared with LP.
Clinical Relevance— Dorsal plating of feline iliac fractures may reduce complications associated with pelvic canal narrowing such as constipation and megacolon.