spondylolisthesis

n.
Forward displacement of one of the lower lumbar vertebrae over the vertebra below it or on the sacrum.

[New Latin spondylolisthēsis : Greek spondulos, vertebra + Greek olisthēsis, dislocation, slipping (from olisthanein, to slip).]

A fracture of the pars interarticularis (the weakest part of the neural arch of a vertebra) resulting in complete separation of the anterior region of the vertebra from the region below it. The most common site for this injury is the lumbosacral joint. Spondylolisthesis reduces flexibility and results in tightening of the hamstrings.

Forward displacement of a vertebra over a posterior segment due to a congenital defect or fracture in the pars interarticularis. Occurs in the giant breeds of dogs as wobbler syndrome and as a developmental defect called kinky back in broiler chickens. Affected birds are unable to stand normally and may be completely paralyzed. The causative lesion is a deformity of the sixth thoracic vertebra but the cause of the defect is unknown.