Anatomy and function of the ligaments of the lower cervical spine in the dog

Ligaments of the lower cervical spine (C3 to C7) were studied in 27 canine cadavers. The gross anatomy and attachment sites were determined by dissection, and representative samples of the flaval ligament, facet capsules, and dorsal longitudinal ligament were examined by light microscopy and were stained for elastin content. Selected functional spinal units were placed in a specially constructed humidification chamber and were fixed in position, using methyl methacrylate bone cement. The specimens were stressed in flexion and extension, and vertebral displacement was measured before and after severance of the spinal ligaments. The flaval ligament had a marked elastin content and contained randomly oriented collagen bundles. The dorsal longitudinal ligament possessed a negligible elastic fiber content and demonstrated longitudinally oriented collagen bundles. The facet capsules possessed an inner synovial lining and outer fibrous layer typical of synovial joint capsules. In general, the severance of spinal ligaments resulted in small increments of displacement until failure occurred, which was often sudden and complete. The flaval ligament, facet capsules, dorsal longitudinal ligament, and intervertebral disk were the major ligamentous stabilizers of the lower cervical spine.