Family study of spondylolysis and spondylolisthesis.

Seventy index patients and 222 first-degree relatives with spondylolysis or spondylolisthesis have been studied by means of interview and clinical and radiological examinations. The index patients had an average age of 18 years, and included 43 females and 27 males. Following Wiltse's classification, 18 patients had dysplastic lesions and 52 had isthmic defects. The first-degree relatives included 99 parents and 125 siblings and children of the index patients. Both isthmic and dysplastic defects occurred in most families, regardless of the classification of the index patient. Isthmic defects were consistently more frequent than dysplastic defects. Spina bifida occulta occurred at the lumbosacral area in 61% of the index patients; in the first-degree relatives, spina bifida occulta was most common among the siblings and children of index patients, and occurred more often in relatives of index patients with dysplastic lesions than in those with isthmic lesions.