1. Lumbar Spine)

Spondylolysis is a bony defect in the pars interarticularis (a segment near the junction of the pedicle with the lamina) of the vertebra; the etiology of the defect may be a stress fracture in a congenitally abnormal segment. The defect (usually bilateral) is best visualized on oblique projections in plain x-rays or by CT scan and occurs in the setting of a single injury, repeated minor injuries, or growth.

Spondylolisthesis is the anterior slippage of the vertebral body, pedicles, and superior articular facets, leaving the posterior elements behind. Spondylolisthesis is associated with spondylolysis and degenerative spine disease and occurs more frequently in women. The slippage may be asymptomatic but may also cause low back pain, nerve root injury (the L5 root most frequently), or symptomatic spinal stenosis. Tenderness may be elicited near the segment that has "slipped" forward (most often L4 on L5 or occasionally L5 on S1).

A "step" may be present on deep palpation of the posterior elements of the segment above the spondylolisthetic joint. The trunk may be shortened and the abdomen protuberant as a result of extreme forward displacement of L4 on L5 in severe degrees of spondylolisthesis. In these cases, cauda equina syndrome may occur (Chap. 368).

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