Incidence and Characteristics of Clinical L5-S1 Adjacent Segment Degeneration after L5 Floating Lumbar Fusion: A Multicenter Study.

Study Design: Retrospective study.

Purpose: This study aimed to evaluate the incidence, characteristics, and risk factors for clinical L5-S1 adjacent segment degeneration (ASD) after L5 floating lumbar fusion.

Overview Of Literature: ASD is known to occur after lumbar spine fusion at a certain frequency. Several studies on radiological L5- S1 ASD have been reported. However, there are only a few studies on L5-S1 ASD with clinical symptoms, including back pain and/or radiculopathy.

Methods: In total, 306 patients who received L5 floating lumbar fusion were included in this study. Clinical L5-S1 ASD was defined as newly developed radiculopathy in relation to the L5-S1 segment. Patients' medical records and imaging data were retrospectively analyzed. The risk factors for clinical ASD were assessed by an inverse probability of treatment weighting-adjusted logistic regression analysis.

Results: Clinical L5-S1 ASD occurred in 17 patients (5.6%). The mean onset time of L5-S1 ASD was 12.9±7.5 months after the primary surgery. Among these patients, 10 (58.8%) presented with clinical L5-S1 ASD within 12 months. Reoperation was performed in three patients (1.0%). The severity of L5-S1 disk degeneration did not affect the occurrence of L5-S1 ASD. Logistic regression analysis showed that the number of fusion levels was a significant risk factor for clinical L5-S1 ASD.

Conclusions: The incidence and characteristics of clinical L5-S1 ASD after L5 floating lumbar fusion were retrospectively investigated. This study established that the number of fusion levels was a significant candidate factor for clinical L5-S1 ASD. Careful clinical follow-up is deemed necessary after L5 floating lumbar fusion surgery, especially for patients who received multiple-level fusions.