External fixation of the lumbar spine in a canine model

OBJECTIVE: To compare the mechanical properties of two types of external skeletal fixation of the lumbar spine with polymethylmethacrylate (PMMA)/Steinmann pin fixation in a canine unstable spine model. STUDY DESIGN: Cadaver study. SAMPLE POPULATION: Lumbar spines of 17 mature large-breed dogs. METHODS: Spine stiffness (N-m/deg) in flexion, extension, and rotation under physiological loading conditions and spine strength (N-m) in flexion were determined. Spines were destabilized at L3-L4, instrumented and retested. Fixation techniques included four-pin PMMA (PMMA4), eight-pin PMMA (PMMA8), eight-pin biplanar type I external skeletal fixator (ESF) (SK), and eight-pin spinal arch ESF (ARCHES). RESULTS: All fixation groups were as stiff as intact spines in extension and rotation and were significantly stiffer in flexion. In flexion, both PMMA8 and ARCHES were significantly stiffer than SK, and PMMA8 was significantly stiffer than PMMA4. In rotation, PMMA8 and ARCHES were significantly stiffer than SK, and in flexion to failure, PMMA8 and ARCHES were significantly stiffer than PMMA4. CONCLUSIONS: External skeletal spinal fixation (ESSF) has mechanical properties comparable to more commonly used PMMA/pin internal fixation techniques. CLINICAL RELEVANCE: External fixation of the canine spine has several potential advantages over internal fixation including minimal dissection for pin placement, the ability to span affected vertebrae with placement of implants distant from the site of injury, postoperative adjustability, and complete removal of implants after healing. This study supports the biomechanical stability ESSF of the canine lumbar spine. Further studies are indicated to evaluate zones of consistently safe and secure placement of pins and clinical efficacy.     

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.     

Thoracolumbar hemilaminectomy and spinal cord decompression in a lion-tailed macaque (Macaca silenus)

A 16-yr-old, castrated male lion-tailed macaque (Macaca silenus) presented with acute bilateral pelvic limb paralysis. Cisternal and lumbar myelograms demonstrated right-sided spinal cord compression at T13-L1. During an extradural hemilaminectomy, chronically ruptured disk material was removed at T13-L1, with moderate venous dilatation observed cranially. The macaque fully recovered from clinical signs within 2 mo.     

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.     

Contribution of the xenograft bone plate-screw system in lumbar transpedicular stabilization of dogs: an in-vitro study

We performed biomechanical comparison of a xenograft bone plate-screw (XBPS) system for achieving cadaveric lumbar transpedicular stabilization (TS) in dogs. Twenty dogs'' cadaveric L_2-4 lumbar specimens were harvested and their muscles were removed, but the discs and ligaments were left intact. These specimens were separated to four groups: the L_2-4 intact group as control (group I, n = 5), the L₃ laminectomy and bilateral facetectomy group (LBF) (group II, n = 5), the LBF plus TS with metal plate-screw group (group III, n = 5) and the LBF plus TS with XBPS group (group IV, n = 5). Five kinds of biomechanical tests were applied to the specimens: flexion, extension, left-right bending and rotation. The averages of the 16 stiffness values were calculated and then these were statistically analyzed. The statistical results show that the XBPS system contributes spinal stability and this system can be a good choice for achieving TS.     

Intervertebral disc extrusion and spinal decompression in a binturong (Arctictis binturong).

A 10-yr-old binturong (Arctictis binturong) developed an acute onset of hind limb paralysis. Neurological examination revealed sensorimotor paraplegia. Myelography and computed tomography demonstrated a ventrolateral extradural compression of the spinal cord centered over the L3-L4 intervertebral disc space. Spinal decompression was performed via hemilaminectomy and excision of degenerate nucleus pulposus, confirmed by histopathologic examination. The binturong regained slight motor function by day 8 postoperatively but succumbed to pancreatitis 19 days postoperatively.     

Biomechanical Study of Canine Spinal Fracture Fixation Using Pins or Bone Screws With Polymethylmethacrylate

Five configurations of pins or screws interconnected with polymethylmethacrylate (PMMA) were applied to isolated canine lumbar spines (L2 to L5) in which a complete fracture-luxation had been produced at L3 to L4. Twenty-five repaired spines and five intact control spines were subjected to four-point bending and tested once to failure in ventral flexion. The purpose of this study was to determine the effects of pin number, pin angle, and use of 3.5-mm cortical bone screws instead of smooth 3.2-mm diameter pins on rigidity and ultimate strength of spinal fractures repaired by the implant-PMMA fixation technique. Bending moment versus the angular deformation curves were recorded. Rigidity, bending moment at 10° angular deformation, moment at failure, and deformation at failure of each type of fixation were compared using analysis of variance. Spinal segments stabilized with eight pin-PMMA fixation had significantly greater rigidity and strength at failure than four pin-PMMA fixations ( P < .05). Furthermore, spinal segments stabilized with eight pins angled away from the fracture failed at significantly greater bending moment than those with eight pins angled toward the fracture ( P < .05). However, for four-pin fixation, greater strength was achieved by angling pins in the bone toward the fracture site ( P < .05). Screw-PMMA fixations failed by screw bending and were less rigid and weaker at failure than the corresponding configuration of pin-PMMA fixation ( P < .05).     

ULTRASONOGRAPHIC ANATOMY OF THE NORMAL CANINE SPINAL CORD AND CORRELATION WITH HISTOPATHOLOGY AFTER INDUCED SPINAL CORD TRAUMA

Prior to trauma, intraoperative ultrasound of the spinal canal in 31 normal dogs was performed through a hemilaminectomy in the left pedicle of L2. A ventral compressive model of spinal cord injury was performed as part of a clinical drug trial. Maximum ultrasonographic spinal cord diameter ranged from 4.9–7.2 mm (5.7 × 0.6). Significant positive correlation (p = 0.023, r = 0.49) was found between age and spinal cord diameter. The dura mater was a separate, well-defined, echogenic horizontal line in 28 (90%) dogs, dorsally, and in 29 (94%) dogs, ventrally. Cerebrospinal fluid was anechoic. Eighteen (58%) dogs had a well-defined anechoic dorsal subarachnoid space, whereas 22 (71%) had a well-defined ventral space. Pia mater was thin but strongly echogenic and covered spinal cord. Central canal was a double hyperechoic line in 17 (55%) dogs and a single-line in 14 (45%) dogs. A difference in the ultrasonographic appearance between gray and white matter was not seen. Epidural fat and connective tissue was a lobular echogenic material in the ventral epidural space. The periosteal-vertebral body interface was seen as a bright curvilinear echo with distal acoustic shadowing. Spinal cord parenchyma could be classified subjectively into four groups based upon ultrasonographic appearance. Spinal cord parenchyma had a uniform hypoechogenicity in 8 (27%) dogs (Group 1), subtle low level echoes in 7 (23%) dogs (Group 2), multiple clusters of defined echogenic foci in 12 (37%) dogs (Group 3), and multiple sharply-defined linear echoes in 4 (13%) dogs (Group 4). There was a significant relationship between pre-trauma ultrasonographic appearance of the spinal cord and histopathology 21 days after trauma. One (13%) dog in Group 1, 4 (57%) dogs in Group 2,10 (91%) dogs in Group 3, and 3 (75%) dogs in Group 4 had malacia on histological evaluation. Therefore, dogs with echogenic spinal cords or linear echoes within cord parenchyma were significantly more likely to develop malacia rather than Wallerian degeneration after induced spinal cord trauma (p = 0.002). Spinal cord echogenicity may indicate vascularity in a segment of spinal cord and might be prognostic following spinal cord trauma. No complications were found related to intraoperative ultrasound. Hematoma or fibrous tissue formation appeared to impede percutaneous ultrasound of the spinal cord in dogs re-evaluated forty-eight hours and one week after surgery.     

Extradural spinal juxtafacet (synovial) cysts in three dogs

Three dogs were presented for investigation of spinal disease and were diagnosed with extradural spinal juxtafacet cysts of synovial origin. Two dogs that were presented with clinical signs consistent with pain in the lumbosacral region associated with bilateral hindlimb paresis were diagnosed using magnetic resonance imaging. Both cysts were solitary and associated with the L6-7 dorsal articulations; both the dogs had a transitional vertebra in the lumbosacral region. A third dog that was presented with progressive paraparesis localised to T3-L3 spinal cord segments and compression of the spinal cord at T13-L1 was diagnosed using myelography. A solitary multiloculated cyst was found at surgery. Decompressive surgery resulted in resolution of the clinical signs in all three dogs. Immunohistological findings indicated that one to two layers of vimentin-positive cells consistent with synovial origin lined the cysts.     

Paresis secondary to an extradural hematoma in a Sumatran tiger (Panthera tigris sumatrae).

A 15-yr-old female Sumatran tiger (Panthera tigris sumatrae) was presented to the Boren Veterinary Medical Teaching Hospital at Oklahoma State University with a 3-wk history of progressive hind limb weakness. Neurologic evaluation was limited to review of videotape that demonstrated weakness and ataxia with conscious proprioceptive deficits of the tiger's pelvic limbs. Spinal radiography demonstrated disc space narrowing, and myelography demonstrated a large extradural compressive lesion at the level of L2-3. Computed tomography did not reveal bone involvement. Surgery was performed to decompress the spinal cord and obtain a definitive diagnosis. A right hemilaminectomy was performed after a dorsal approach to the lumbar spine. Histologic examination of the mass revealed a consolidated extradural spinal hematoma, presumed to be secondary to intervertebral disc herniation. Despite incomplete resection of the mass and plastic deformation of the spinal cord, the tiger returned to normal ambulation within 3 wk of surgical decompression.     

Comparison of feasibility and safety of epidural catheterization between cranial and caudal lumbar vertebral segments in dogs

To compare the technical difficulty and safety of epidural catheterization between cranial and caudal lumbar region, thirteen dogs were randomly assigned to a cranial lumbar group (group CraL, n=6) or a caudal lumbar group (group CauL, n=6) depending on different epidural sites, and one dog was used as a negative control without catheterization. After general anesthesia, an epidural catheter was advanced 10 cm cranially from the interspace of L1-L2 in group CraL or from lumbosacral space in group CauL. Dogs were euthanized and catheter position and tip location were confirmed by laminectomy. Spinal cord samples were examined by macro- and microscopic observations. Success rate, time taken for epidural space confirmation and catheter insertion were compared, and overall technical difficulty was evaluated subjectively. Epidural catheter was inserted successfully in all dogs. Time needed from needle skin puncture to catheter placement and saline injection was 226 ± 63 and 229 ± 26 sec in groups CraL and CauL without significant differences. Three dogs in group CraL suffered subcutaneous blood, but no spinal cord injuries were found. Subjective evaluation score of the overall technical difficulty was slightly but significantly higher in group CraL than in group CauL (P=0.009). Epidural catheterization in cranial lumbar region could be performed as feasible and safe as that at the caudal lumbar vertebral region in medium or large dogs.     

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.     

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.     

Canine Lumbar Spinal Internal Fixation Techniques A Comparative Biomechanical Study

The stability (flexural rigidity) and strength of five canine spinal internal fixation techniques were quantitated and compared to each other and to the rigidity and strength of the intact spine. The techniques were applied to isolated canine lumbar spines (L2–L5) on which a complete spinal injury was surgically simulated at L3–L4. The spine-implant preparations were subjected to four-point bending and tested once to failure in flexion. The bending moment vs. L3–L4 angular deformation curves were recorded; rigidity and load sustained at failure (10° angular deformation) were compared. The combination of dorsal spinous process plate and dorsolateral vertebral body plate was the most rigid and most strong of the techniques tested. The dorsolateral vertebral body plate was the most rigid and most strong of the individual techniques, followed by the dorsal spinous process plate and the polymethylmethacrylate-pin technique. Vertebral body crosspins provided the least strength and stability of any of the techniques tested.     

Hemilaminectomy and vertebral stabilisation for the treatment of thoracolumbar disc protrusion in 28 dogs

Objectives : To evaluate the results of hemilaminectomy and vertebral stabilisation (+/? annulectomy) for the treatment of thoracolumbar disc protrusion. Methods : The medical records of dogs with thoracolumbar annular protrusions treated by hemilaminectomy and vertebral stabilisation were reviewed. Neurological function was assessed 24 hours following surgery. Long‐term follow‐up was by clinical examination or telephone questionnaire. Results : Twenty‐eight dogs fulfilled the criteria. Age ranged from 4 to 12·5 years (median 8 years, mean 7·7 years), bodyweight from 5·1 to 51·5 kg (median 28 kg, mean 27·1 kg), and duration of neurological signs before presentation from 48 hours to 104 weeks (median 5 weeks, mean 9·3 weeks). At presentation 22 dogs were ambulatory and six were non‐ambulatory. Myelography and/or magnetic resonance imaging (MRI) identified 31 thoracolumbar protrusions causing spinal cord compression. Unilateral hemilaminectomy was performed in 27 dogs and bilateral hemilaminectomy in one dog. Partial annulectomy was performed in 24 of 31 protrusions. Stabilisation was performed using vertebral body bone plates in 26 dogs and vertebral body screws and bone cement in two dogs. Internal vertebral venous plexus haemorrhage was recorded in nine dogs. A screw was inadvertently placed into an intervertebral disc in two dogs. Neurological examination 24 hours postoperatively revealed deterioration in pelvic limb motor function in 17 dogs. One dog was euthanatised at the owner’s request 6 days after surgery. Long‐term evaluation of 24 cases was performed 3 to 52 months following surgery (median 21 months, mean 23·9 months). Six dogs had improved from their preoperative status and one had deteriorated as assessed by the authors. Fifteen dogs had improved from their preoperative status and two were unchanged as assessed by owners. Clinical Significance : Hemilaminectomy and vertebral stabilisation are an effective treatment for chronic spinal cord compression due to thoracolumbar annular protrusion in dogs. A temporary deterioration in neurological function is not uncommon following surgery. Internal vertebral plexus haemorrhage and inappropriate vertebral body screw placement are potential complications.     

Continuous lumbar hemilaminectomy for intervertebral disc disease in an Amur tiger (Panthera tigris altaica)

A 13-yr-old Amur tiger (Panthera tigris altaica) was presented for an acute onset of paraplegia. Spinal imaging that included plain radiographs, myelography, and computed tomography performed under general anesthesia revealed lateralized spinal cord compression at the intervertebral disc space L4-5 caused by intervertebral disc extrusion. This extrusion was accompanied by an extensive epidural hemorrhage from L3 to L6. Therefore, a continuous hemilaminectomy from L3 to L6 was performed, resulting in complete decompression of the spinal cord. The tiger was ambulatory again 10 days after the surgery. This case suggests that the potential benefit of complete spinal cord decompression may outweigh the risk of causing clinically significant spinal instability after extensive decompression.     

小型犬脊髓穿刺技术

对 30只小型犬 (京叭 2 8只 ,杂种小型犬 2只 )进行了不同部位的脊髓穿刺。以穿刺技术的难度、造影的效果比较、脑脊液 (CSF)压力的测定和 CSF的分析结果为判断标准 ,得出如下结论 :进行 CSF收集或者测量 CSF压力时的穿刺部位 ,应选择在小脑延髓池处 ;怀疑颈部或前胸部脊髓有病变时 ,应在小脑延髓池处进行脊髓穿刺造影 ;怀疑为胸腰椎脊髓有病变时 ,脊髓造影应选择在腰椎 L 5～ 6之间 ,L 6～ 7也可以作为一种选择部位 ;穿刺过程中试验犬可以俯卧操作。另外 ,对穿刺器械的选择和使用也进行了分析     

Facet joint geometry and intervertebral disk degeneration in the L5-S1 region of the vertebral column in German Shepherd dogs

OBJECTIVE: To evaluate the possible association between facet joint geometry and intervertebral disk degeneration in German Shepherd Dogs. ANIMALS: 25 German Shepherd Dogs and 11 control dogs of similar body weight and condition. PROCEDURE: Facet joint angles in the caudal portion of the lumbar region of the vertebral column (L5-S1) were measured by use of computed tomography, and the intervertebral discs were evaluated microscopically. The relationship between facet joint geometry and disk degeneration was evaluated by use of statistical methods. RESULTS: German Shepherd Dogs had significantly more facet joint tropism than control dogs, but an association with disk degeneration was not found. However, German Shepherd Dogs had a different facet joint conformation, with more sagittally oriented facet joints at L5-L6 and L6-L7 and a larger angle difference between the lumbar and lumbosacral facet joints, compared with control dogs. CONCLUSIONS AND CLINICAL RELEVANCE: A large difference between facet joint angles at L6-L7 and L7-S1 in German Shepherd Dogs may be associated with the frequent occurrence of lumbosacral disk degeneration in this breed.     

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.     

RADIOGRAPHIC DIAGNOSIS: CARTILAGINOUS EXOSTOSES IN A DOG

A 6 month-old dog was examined for progressive paraparesis. On physical examination bony malformations were palpated over the cranial lumbar vertebral bodies and on the left metatarsal bone. Neuroanatomic lesion localization for the paraparesis was a T3-L3 spinal cord lesion. Radiographs confirmed bony masses at L1-L2 and on the left 3rd metatarsal bone. Magnetic resonance imaging was performed from T3-L3. Severe spinal cord compression was identified at L1-L2. Surgical decompression and biopsy confirmed the mass to be cartilaginous exostoses. This paper is an example of cartilaginous exostoses imaged with MR.