Risk factors for adjacent-segment failure following lumbar fixation with rigid instrumentation for degenerative instability

Object. The authors performed a retrospective analysis of 125 consecutive p atients in whom instrumentation was placed to promote lumbar fusion for the treatment of degenerative instability. All procedures were performed by a single surgeon. The authors sought to determine the risk factors for next-s egment degeneration after lumbar spinal fusion with rigid instrumentation. Methods. Thirty-one of 125 fusion procedures were performed in women who we re postmenopausal. A total of 18 of 125 patients developed symptomatic next -segment degeneration at a previously asymptomatic level; 15 were postmenop ausal women. Data were obtained in patients with next-segment failure based on radiographic studies, neurological assessment, demographic factors, and sequential follow-up examinations. The mean follow-up period for this grou p was 44.8 months. All women were postmenopausal, and 53% received biphosph onate drugs and calcium supplementation preoperatively for osteopenia. Twen ty percent of all patients with next-segment failure were cigarette smokers . Next-segment diseases included spondylolisthesis (39%), spinal canal sten osis due to disc herniation and/or facet hypertrophy (33%), stress fracture of the adjacent vertebral body (28%), and scoliosis (17%). Patients freque ntly had more than one degenerative process at the next segment. Conclusions. The risk of adjacent-segment failure is clearly higher for pat ients in whom lumbar fusion with rigid instrumentation is performed to trea t degenerative instability. This risk appears to be especially high in post menopausal women.