Comparison of adjacent segment degeneration after successful posterolateral fusion with unilateral or bilateral pedicle screw instrumentation: a minimum 10-year follow-up

BACKGROUND CONTEXT: In the instrumented fusion, adjacent segment facet joint violation or impingement by pedicle screws is unavoidable especially in cephalad segment, despite taking specific intraoperative precautions in terms of surgical approach. In such circumstances, unlike its original purpose, unilateral pedicle screw instrumentation can contribute to reduce the degeneration of cephalad adjacent segment by preventing contralateral cephalad adjacent facet joint from the unavoidable injury by pedicle screw insertion. However, to our knowledge, no long-term follow-up study has compared adjacent segment degeneration (ASD) between unilateral and bilateral pedicle screw instrumented fusion. PURPOSE: To compare ASD after successful posterolateral fusion using either unilateral or bilateral pedicle screw instrumentation for patients with lumbar spinal stenosis and/or Grade 1 spondylolisthesis. STUDY DESIGN: Retrospective case-control study. PATIENT SAMPLE: One hundred forty-seven patients who had undergone one- or two-level posterolateral fusion with unilateral or bilateral pedicle screw instrumentation for lumbar spinal stenosis with or without low-grade spondylolisthesis and achieved successful fusion, with a minimum 10-year follow-up. OUTCOME MEASURE: The occurrence of radiologic ASD, Oswestry disability index (ODI) scores, and revision rates. METHODS: A total of 194 consecutive patients were contacted and encouraged to visit our hospital and to participate in our study. Radiologic ASD was evaluated at three motion segments: cephalad adjacent segment (first cephalad adjacent segment), one cephalad to cephalad adjacent segment (second cephalad adjacent segment), and caudal adjacent segment. Clinical outcomes were compared by ODI scores and revision rates. RESULTS: In total, 147 of 194 (75.8%) patients were available for at least 10 years of radiologic and clinical follow-up. Adjacent segment degeneration (in first cephalad or caudal adjacent segment) was noted in 55.9% (33 of 59 patients) of the unilateral group and 72.7% (64 of 88 patients) of the bilateral group (p=.035). The occurrence of ASD in each first cephalad and caudal adjacent segment was not significantly different between groups but that in second cephalad adjacent segment was significantly different between groups (p=.004). Clinical outcomes according to ODI showed significant difference between groups (p=.016), especially when ODI scores were compared in patients with ASD (p=.004). CONCLUSIONS: In a minimum 10-year follow-up retrospective study of posterolateral fusion for lumbar spinal stenosis and/or Grade 1 spondylolisthesis, unilateral pedicle screw instrumentation showed a lower rate of radiologic ASD, especially in second cephalad adjacent segment, and a better clinical outcome by ODI.ope