Effect of disk fenestration on sagittal kinematics of the canine C5-C6 intervertebral space

Objective-To determine the effect that ventral intervertebral disk fenestra tion has on the sagittal range of motion about the C5-C6 intervertebral spa ce. Study Design-A repeated measures in vitro mechanical study of spinal range of motion under controlled loading conditions before and after fenestration . Sample Population-A total of 10 canine cervical vertebral specimens (C4-C7) collected from clinically normal animals within 12 hours of euthanasia. Methods-Specimens were loaded as cantilever beams fixed at C7. Weights (1 t o 5 kg) were progressively applied to C4 to produce flexion or extension in the sagittal plane. Radiographs were taken at each load, 3 times before an d 3 times after fenestration of the C5-C6 disk. The positions of radiodense markers embedded in the vertebrae were used to calculate flexion and exten sion angles and range of motion. Results-Range of motion (difference between flexion and extension) and flex ion and extension angles (individually) significantly increased after fenes tration (P < .0001). Conclusion-Ventral fenestration produces sagittal instability of the C5-C6 disk space. Clinical Relevance-In surgical fusion of caudal cervical intervertebral spa ces in dogs, radiographically normal disks adjacent to the affected space a re often fenestrated to facilitate distraction before surgical stabilizatio n. This study shows that ventral fenestration produces instability of a cau dal cervical intervertebral space in the model used. Such instability may c ontribute to the development of the secondary instability ("domino lesions" ) seen in some surgically treated dogs. (C) Copyright 1999 by The American College of Veterinary Surgeons.