Biomechanical effects of a titanium intervertebral cage as a stand-alone device, and in combination with locking plates in the canine caudal cervical spine.

OBJECTIVE: To evaluate the change in ex vivo biomechanical properties of the canine cervical spine, due to an intervertebral cage, both as a stand-alone device and in combination with plates. STUDY DESIGN: Experimental ex vivo study. ANIMALS: Cervical spinal segments (C5-C7) from eight canine cadavers. METHODS: The range of motion (ROM) and elastic zone stiffness (EZS) of the spines were determined with a four-point bending device in flexion/extension, lateral bending, and axial rotation for four conditions: native, discectomy, cage (at C6-C7), and cage with plates (at C6-C7). The disc height index (DHI) for each condition was determined using radiography. RESULTS: Discectomy resulted in overall increased ROM (p < .01) and EZS (p < .05) and decreased DHI (p < .005) when compared to the native condition. Placement of the cage increased DHI (p < .001) and restored total ROM during flexion/extension, lateral bending and axial rotation, and EZS during flexion/extension to the level of the native spine. Application of the plates further reduced the total ROM during flexion/extension (p < .001) and lateral bending (p < .001), but restored ROM in extension and EZS during lateral bending. No implant failure, subsidence, or significant cage migration occurred during loading. CONCLUSION: An anchorless intervertebral cage used as a stand-alone device was able to restore the disc height and spinal stability to the level of the native cervical spine, whereas the addition of plates further reduced the spinal unit mobility. CLINICAL SIGNIFICANCE: This study implies that the intervertebral cage may be used as a stand-alone device in the spinal unit fixation in the canine cervical spine.

Instrumented cervical fusion in nine dogs with caudal cervical spondylomyelopathy.

OBJECTIVE: To report the long-term outcome of nine dogs treated for caudal cervical spondylomyelopathy (CCSM) with surgical spinal fusion. STUDY DESIGN: Short case series. ANIMALS: Nine large-breed dogs. METHODS: Medical records of dogs treated for disc-associated CCSM (2013-2016) were reviewed. The surgery objective was spinal distraction by implantation of a SynCage and fixation with two Unilock plates. Follow-up included the Helsinki pain score questionnaire, neurological grading, radiography, computed tomography (CT), and micro-CT (µCT) with subsequent histopathology (two dogs). RESULTS: Clinical follow-up was obtained between 9 and 51 months (27.4 ± 13.4 months). The Helsinki pain score and neurological Griffith score improved (P < .01) in all dogs and in eight of nine dogs, respectively. According to CT, the volume of bone (mean ± SD) through the cage was 79.5% ± 14.3%, including compact bone (53.0% ± 23.4%). Subsidence was seen in one of nine dogs. Implant failure was evident in four dogs, and plates were removed in two dogs. In seven of nine dogs, infraclinical pathology was observed in adjacent segment, associated with implants engaging adjacent intervertebral discs. Radiographic evidence of bony fusion between vertebral bodies was noted in all dogs. Spinal fusion was confirmed by µCT and histopathology in two cervical spine segments that became available at 22 and 40 months postoperatively. CONCLUSION: Instrumented spinal fusion in dogs with disc-associated CCSM resulted in owner satisfaction and radiographic evidence of interbody spinal fusion in all dogs. CLINICAL SIGNIFICANCE: The fusion distraction technique reported here can be used to achieve spinal fusion with a good long-term outcome.