Influence of surgical approach on the efficacy of the intervertebral disk fenestration: a cadaveric study

OBJECTIVES: To investigate the influence of different approach angles on the amount of nucleus pulposus removed during intervertebral disc fenestration in dogs. METHODS: Twenty cadavers of beagle dogs were randomly divided into four groups: a control group and three treatment groups in which intervertebral fenestration was performed using either a dorsal, dorsolateral or lateral approach between the 12th thoracic and second lumbar spaces. The volume of nucleus pulposus, the weight of the residual nucleus pulposus and the angle of the working sector were measured. The ratio of the residual nucleus pulposus weight to the nucleus pulposus volume was used to evaluate the efficacy of the performed fenestration. Data were analysed with Kruskal-Wallis analysis of variance between groups on ranks with correction for ties and Bonferroni correction for multiple comparisons. Correlation between ratio and working angle was calculated using a Spearman's rank test (P<0.05). RESULTS: The calculated ratio of nuclear weight to volume was significantly less in the lateral approach group than that in the other groups. The working sector was widest in the dorsolateral approach group, but this did not correlate with efficient fenestration. CLINICAL SIGNIFICANCE: Using the lateral approach for intervertebral disc fenestration may increase the efficiency of the fenestration procedure.

Classification of intervertebral disk degeneration with axial T2 mapping

OBJECTIVE: The aim of this study was to establish an MRI classification system for intervertebral disks using axial T2 mapping, with a special focus on evaluating early degenerative intervertebral disks. MATERIALS AND METHODS: Twenty-nine healthy volunteers (19 men, 10 women; age range, 20-44 years; mean age, 31.8 years) were studied, and axial T2 mapping was performed for the L3-L4, L4-L5, and L5-S1 intervertebral disks. Grading was performed using three classification systems for degenerative disks: our system using axial T2 mapping and two other conventional classification systems that focused on the signal intensity of the nucleus pulposus or the structural morphology in sagittal T2-weighted MR images. We analyzed the relationship between T2, which is known to correlate with change in composition of intervertebral disks, and degenerative grade determined using the three classification systems. RESULTS: With axial T2 mapping, differences in T2 between grades I and II were smaller and those between grades II and III, and between grades III and IV, were larger than those with the other grading systems. The ratio of intervertebral disks classified as grade I was higher with the conventional classification systems than that with axial T2 mapping. In contrast, the ratio of intervertebral disks classified as grade II or III was higher with axial T2 mapping than that with the conventional classification systems. CONCLUSION: Axial T2 mapping provides a more T2-based classification. The new system may be able to detect early degenerative changes before the conventional classification systems can.

Effects of adjunct electroacupuncture on severity of postoperative pain in dogs undergoing hemilaminectomy because of acute thoracolumbar intervertebral disk disease

OBJECTIVE: To compare severity of postoperative pain in dogs undergoing hemilaminectomy because of acute thoracolumbar intervertebral disk disease treated with a combination of conventional analgesics and electroacupuncture (EAP) or with conventional analgesics alone. DESIGN: Controlled clinical trial. ANIMALS: 15 dogs undergoing surgery because of acute thoracolumbar disk disease. PROCEDURES: Dogs were alternately assigned to treatment (conventional analgesics and adjunct EAP) and control (conventional analgesics alone) groups. Analgesic treatment was adjusted as necessary by the attending clinician, who was not aware of group assignment. Pain scores were assigned 1, 3, and 12 hours after surgery and every 12 hours thereafter for 72 hours by the same individual who performed acupuncture treatments. RESULTS: Total dose of fentanyl administered during the first 12 hours after surgery was significantly lower in the treatment group than in the control group, but dosages of analgesics administered from 12 through 72 hours after surgery did not differ between groups. Pain score was significantly lower in the treatment group than in the control group 36 hours after surgery, but did not differ significantly between groups at any other time. CONCLUSIONS AND CLINICAL RELEVANCE: Results provided equivocal evidence that adjunct EAP might provide some mild benefit in regard to severity of postoperative pain in dogs undergoing hemilaminectomy because of acute thoracolumbar intervertebral disk disease.

Laser-Doppler measurements of spinal cord blood flow changes during hemilaminectomy in chondrodystrophic dogs with disk extrusion

OBJECTIVES: (1) To assess spinal cord blood flow (SCBF) during surgical treatment of disk extrusion in dogs and (2) to investigate associations between SCBF, clinical signs, presurgical MRI images, and 24-hour surgical outcome. STUDY DESIGN: Cohort study. ANIMALS: Chondrodystrophic dogs with thoracolumbar disk extrusion (n=12). METHODS: Diagnosis was based on clinical signs and MRI findings, and confirmed at surgery. Regional SCBF was measured intraoperatively by laser-Doppler flowmetry before, immediately after surgical spinal cord decompression, and after 15 minutes of lavaging the lesion. Care was taken to ensure a standardized surgical procedure to minimize factors that could influence measurement readings. RESULTS: A significant increase in intraoperative SCBF was found in all dogs (Wilcoxon's signed-rank test; P=.05) immediately after spinal cord decompression and after 15 minutes. Changes in SCBF were not associated with duration of clinical signs; initial or 24-hour neurologic status; or degree of spinal cord compression assessed by MRI. CONCLUSION: SCBF increases immediately after spinal cord decompression in dogs with disk herniation; however, increased SCBF was not associated with a diminished 24-hour neurologic status. CLINICAL RELEVANCE: An increase in SCBF does not appear to be either associated with the degree of spinal cord compression or of a magnitude sufficient to outweigh the benefit of surgical decompression by resulting in clinically relevant changes in 24-hour outcome.

Chronic intervertebral disk herniation associated with fused vertebrae treated by vertebral lateral corpectomy in a cat

A 10-year-old Domestic Shorthair cat was admitted for chronic ambulatory paraparesis and a spinal malformation. The clinical examination revealed paraparesis accentuated on the left side. Thoracolumbar radiographs revealed a spinal malformation with a narrowed intervertebral space between L1 and L2, and a dorsal fusion at the level of L2-L3 with a common dorsal process. Magnetic resonance imaging (MRI) revealed an intervertebral disk herniation with a ventral compression of the spinal cord at the level of L1/2. A standard vertebral lateral corpectomy with a foraminotomy was performed with a good outcome.

Magnetic resonance imaging findings in dogs with traumatic intervertebral disk extrusion with or without spinal cord compression: 31 cases (2006-2010)

OBJECTIVE To determine the prevalence of spinal cord compression subsequent to traumatic intervertebral disk (IVD) extrusion in dogs, characterize factors associated with spinal cord compression in dogs with traumatic IVD extrusion, and evaluate the outcomes of dogs with traumatic IVD extrusion with or without spinal cord compression. DESIGN Retrospective case series. ANIMALS 31 dogs with traumatic IVD extrusion. PROCEDURES Medical records and MRI findings were reviewed for dogs with a history of trauma to the spinal region. Dogs were included in the study if a neurologic examination and MRI were performed and there was a description of clinical signs and MRI findings including identification of the spinal cord segment affected by IVD extrusion, presence or absence of spinal cord compression, treatment, and outcome available for review. RESULTS 31 of 50 (62%) dogs had traumatic IVD extrusions without any other detectable vertebral lesions; 9 (29%) and 22 (71%) of those 31 dogs did and did not have spinal cord compression, respectively. Dogs with spinal cord compression were significantly older and more likely to be chondrodystrophic and have evidence of generalized IVD degeneration, compared with dogs without spinal cord compression. The outcome for dogs with spinal cord compression was similar to that for dogs without spinal cord compression. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated traumatic IVD extrusion was common and should be considered as a differential diagnosis for dogs with trauma to the spinal region, and spinal cord compression should be evaluated, especially in older or chondrodystrophic dogs.

Clinical and pathological analysis of epidural inflammation in intervertebral disk extrusion in dogs

BACKGROUND Little is known about the pathologic changes in the epidural space after intervertebral disk (IVD) extrusion in the dog. OBJECTIVES To analyze the pathology of the epidural inflammatory response, and to search for correlations between this process and clinical findings. METHODS Clinical data from 105 chondrodystrophic (CD) and nonchondrodystrophic (NCD) dogs with IVD extrusion were recorded. Epidural material from these dogs was examined histopathologically and immunohistochemically. Using statistical analysis, we searched for correlations between severity of epidural inflammation and various clinical and pathologic variables. RESULTS Most dogs exhibited an epidural inflammatory response, ranging from acute invasion of neutrophils to formation of chronic granulation tissue. The mononuclear inflammatory infiltrates consisted mostly of monocytes and macrophages and only few T and B cells. Surprisingly, chronic inflammatory patterns also were found in animals with an acute clinical history. Severity of the epidural inflammation correlated with degree of the epidural hemorrhage and nucleus pulposus calcification (P = .003 and .040), but not with age, chondrodystrophic phenotype, neurologic grade, back pain, pretreatment, or duration. The degree of inflammation was statistically (P = .021) inversely correlated with the ability to regain ambulation. CONCLUSION AND CLINICAL IMPORTANCE Epidural inflammation occurs in the majority of dogs with IVD extrusion and may develop long before the onset of clinical signs. Presence of calcified IVD material and hemorrhage in the epidural space may be the triggers of this lesion rather than an adaptive immune response to the nucleus pulposus as suggested in previous studies. Because epidural inflammation may affect outcome, further research is warranted.

Accuracy of the withdrawal reflex for localization of the site of cervical disk herniation in dogs: 35 cases (2004-2007)

OBJECTIVE To evaluate the accuracy of neurologic examination versus magnetic resonance imaging (MRI) in localization of cervical disk herniation and evaluate the usefulness of withdrawal reflex testing in dogs. DESIGN Retrospective case series. ANIMALS 35 client-owned dogs with a single-level cervical disk herniation as determined via MRI. PROCEDURES 1 of 2 board-certified neurologists performed a complete neurologic examination in each dog. Clinical signs of a cervical lesion included evidence of neck pain and tetraparesis. The withdrawal reflex was used for neuroanatomic localization (C1-C5 or C6-T2). Agreement between results of neurologic and MRI examinations was determined. RESULTS Agreement between neurologic and MRI diagnoses was 65.8%. In 11 dogs in which the lesion was clinically localized to the C6-T2 segment on the basis of a decreased withdrawal reflex in the forelimbs, MRI revealed an isolated C1-C5 disk lesion. In 1 dog, in which the lesion was suspected to be at the C1-C5 level, MRI revealed a C6-T2 lesion. Cranial cervical lesions were significantly associated with an incorrect neurologic diagnosis regarding site of the lesion. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that the withdrawal reflex in dogs with cervical disk herniation is not reliable for determining the affected site and that a decreased withdrawal reflex does not always indicate a lesion from C6 to T2.

Assessment of Intramedullary Spinal Pressure in Small Breed Dogs With Thoracolumbar Disk Extrusion Undergoing Hemilaminectomy

OBJECTIVE To assess intramedullary spinal pressure (IMP) in small breed dogs with thoracolumbar disk extrusion. STUDY DESIGN Prospective cohort study. ANIMALS Small breed dogs (n = 14) with thoracolumbar disk extrusion undergoing hemilaminectomy and healthy chondrodystrophic laboratory dogs (control; n = 3) without spinal disease. METHODS Diagnosis was based on clinical and neurological examinations and magnetic resonance imaging (MRI) and was confirmed intraoperatively. A standardized anesthesia protocol and surgical procedure were used to minimize factors that could influence IMP. Intramedullary pressure was measured through a minidurotomy at the site of spinal cord compression using a fiber optic catheter inserted perpendicular to the longitudinal axis of the spinal cord. Measurements were taken after hemilaminectomy and again after removal of extruded disk material. RESULTS Affected dogs had significantly higher IMP compared to control dogs (P = .008) and IMP decreased significantly post-decompression compared with initial values (P < .001). No correlation was found between IMP and neurologic grade, degree of spinal cord compression on MRI, or signal intensity changes on MRI. CONCLUSION Acute thoracolumbar disk extrusion is associated with increased IMP in small breed dogs and surgical decompression results in an immediate decrease of IMP.