Analysis of sagittal lumbar alignment before and after posterior instrumentation: Risk factor for adjacent unfused segment

Abstract

The sagittal plane alignment of the degenerative lumbar spine before and after posterior spinal instrumentation surgery was retrospectively studied by radiographic analysis to evaluate the risk factor for adjacent unfused segments. One hundred and thirty-six patients were studied radiographically. The minimum follow-up period was three years. Lordotic angles were obtained from L1 to L5 and from L1 to S1. Lordotic values before and after posterior instrumentation surgery were compared, and degenerative changes in the adjacent unfused segments were analyzed. Significant degenerative changes in the adjacent unfused segments occurred in 21 cases (15.4%). The mean lordotic angles were decreased by approximately 10° after surgery in patients with postoperative changes in the adjacent unfused segment. Conversely, these angles were slightly increased in patients without adjacent segmental changes. These differences in postoperative changes in the angle of lordosis between patients with and without degenerative changes of the adjacent unfused segment were significant (p < 0.01). Loss of lordosis after posterior spinal instrumentation surgery is a significant risk factor for degenerative changes in the adjacent unfused segments.