The canine intervertebral disk. Part Two: Degenerative changes--nonchondrodystrophoid versus chondrodystrophoid disks.

In the second of a two-part article on the canine intervertebral disk, the morphological changes which occur within the disk during aging and degeneration are described. Degeneration of the intervertebral disk appears to be a self-perpetuating process as a consequence of disruption to the annulus fibrosus, cellular remodeling, altered biomechanical loading, and nutritional deficiencies. In the nonchondrodystrophoid disk, premature acceleration of the aging process can occur following traumatic disruption to the annulus fibrosus. This degeneration usually occurs in isolated disks along the length of the vertebral column. By contrast, disk degeneration in the chondrodystrophoid breeds occurs simultaneously in all disks along the vertebral column and usually is well advanced by two years of age. Ultrastructural differences between the intervertebral disk of the nonchondrodystrophoid dog and that of the chondrodystrophoid dog may explain the rapidity and severity of degenerative changes in the latter breeds.