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Study Design. A retrospective clinical and radiographic review of adult patients with progressive isthmic lumbosacral spondylolisthesis.

Objectives. To describe the clinical presentation of adult-onset progression of isthmic spondylolisthesis and to analyze its causes.

Summary of Background Data. Until recently, progression of lumbosacral spondylolisthesis in adults was rarely reported. On the contrary, although slip progression before skeletal maturity has been widely recorded, its occurrence in adults has been doubted. Only sporadic case reports of adult slip progression and only brief notes on the subject in clinical studies describing other aspects of spondylolisthesis have been published.

Methods. Patients with isthmic lumbosacral spondylolisthesis who had serial radiographs of the lumbar spine on which slip progression during adult life was noted were evaluated. The amount of vertebral slip was calculated in millimeters from decubitus lateral spinal radiographs. The calculation was expressed as the percentage of slipped vertebral body length.

Results. From 1989 to 1995, 18 patients (9 women and 9 men), ages 32 to 55 years, with documented adult isthmic slip progression were identified at the Spinal Surgery Unit of the Hadassah University Hospital. All patients reported incapacitating low back pain, accompanied in most by significant sciatica. Documented slip progression ranged from 9% to 30% (average, 14.6%), and occurred during a period of 2 to 20 years (average duration, 6.8 years). Slip progression started after the third decade of life and coincided with marked disc degeneration at the olisthetic level. Slip progression associated with disc degeneration (i.e., intervertebral space narrowing and the formation of spondylophytes and vacuum phenomenon) brought about severe clinical symptomatology related to segmental instability and spinal stenosis. Of the 18 patients in this study, 14 were treated with surgery. All these patients except 1 underwent decompression, pedicle screw fixation, and bilateral lateral fusion. One patient underwent posterolateral fusion without instrumentation. Immediate postoperative complications were observed in three patients, including two superficial wound infections and one transient foot drop. Solid fusion was obtained in 11 of the 14 patients who underwent surgery.

Conclusions. The concurrent occurrence of disc degeneration at the slip level and adult slip progression explains how an asymptomatic developmental lesion, present for at least two to three decades, may become symptomatic.

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