RISK FACTORS FOR ADJACENT SEGMENT COLLAPSE AFTER POSTERIOR LUMBAR INTERBODY FUSION

Abstract

Study design: Prospective clinical and radiologic study.

Objective: The purpose of this study was to investigate the risk factors for adjacent segment degeneration after posterior lumbar interbody fusion (PLIF).

Summary of Background data: Although several authors have reported the adjacent segment degeneration after lumbar or lumosacral fusion, there is no consensus regarding the risk factors for adjacent segment degeneration.

Methods: Sixty-five patients were studied after PLIF after a minimum follow up time of 6 years. Plain and flexion/ extension radiographs and MRI scans were obtained and compared to preoperative and postoperative. Progression of segment degeneration was defined as a condition in which the distinction between nucleus and annulus is lost, and the disc space is collapsed according to the grading system (Grade 1–5) described by Pfirrmann et al evaluated with T2 weighted MRI scans. Patients were divided into three groups: Group 1 with no radiological progression of disc degeneration, Group 2 with radiological progression of disc degeneration, and Group 3 with radiological progression of disc degeneration and clinical deterioration. Risk factors for progression of adjacent disc degeneration as lumbar lordosis, lordosis at the fused segment, facet sagittalization, and pre-existing disc degeneration were evaluated. The images were evaluated by two independent radiologists.

Results: Fifteen patients (23%) showed no radiological progression of disc degeneration on MRI scans and were classified into Group 1. Forty patients (62%) developed some cranial or caudal deterioration of the adjacent segment without clinical deterioration and were classified into Group 2. Ten patients (15%) required reoperation for neurological and clinical deterioration caused by cranial or caudal degeneration of the adjacent disc (Group 3). No statistically significant differences were found in lumbar lordosis, lordosis at the fused segment, facet sagittalization between each group. Patients in Group 3 showed on preoperative MRI already moderate to severe alteration of the adjacent disc (mean Grade 4) compared to Group 1 (mean Grade 2) and 2 (mean Grade 2,5) (p< 0.01).

Conclusion: After PLIF disc degeneration appear homogeneously at several levels cranial and caudal to fusion over the years in most of the patients (79%). Only pre-existing degeneration of the adjacent cranial and caudal segment is a potential risk factor for clinical deterioration caused by disc collapse.