The incidence of cervical lesions in the dog ranges from 13.9-25.4%. Clinical signs associated with cervical intervertebral disc disease include severe neck pain, low head carriage, thoracic limb lameness/paresis, proprioceptive ataxia, and varying degrees of tetraparesis. Although the diagnosis and treatment of many disorders of the cervical spine have been described in the literature, few studies have aimed at understanding the pathogenesis of these diseases. The aims of this study were (1) to describe the micromorphometry of the cervical intervertebral discs in the dog and identify differences between chondrodystrophic and nonchondrodystrophic dogs, and (2) to determine the kinematic motion patterns of the cranial and caudal cervical spine in large breed dogs.
All 5 cervical discs from 6 chondrodystrophic and 6 nonchondrodystrophic dogs were harvested for the micromorphometry study. The specimens were decalcified and two hematoxylin and eosin slides prepared from each disc. Slides were scanned using an Aperio Scanner and the scans analyzed. The nucleus of chondrodystrophic dogs was small, rounded and more dorsally-located compared to those of nonchondrodystrophic dogs. The mean width of the dorsal annular fibers was smaller in chondrodystrophic dogs. Cells were elongated in the outer regions of the disc and rounded in the inner regions. Cell grouping occurred more frequently in the inner regions than the outer regions.
Eight spines were harvested from Foxhound dogs for the kinematic study. The spines were determined to be free of any spinal pathology using radiography, CT and MRI. Spines were stripped of all musculature, leaving ligaments and joint capsules intact, and sectioned into cranial (C2-C4) and caudal (C5-C7) segments. Specimens were loaded into a custom jig and LED markers attached to the vertebral bodies. Spines were tested using pure moment loading in flexion/extension, left/right lateral bending and left/right axial rotation and motion tracked using an optical tracking system. Flexion/extension was relatively decreased at C5-C6. Lateral bending and axial rotation were coupled to the same side. The extent of axial rotation possible in the caudal segments was approximately three times that of the cranial segments.
These results may have significant implications into the pathogenesis of cervical disc disease in the dog by proposing mechanisms to explain the pathogenesis of IVDD in chondrodystrophic dogs and CSM in large breed dogs.