497 - Lumbar Spinal Fusion as a Risk Factor for Adjacent Segment Degeneratio...

General Session: Lumbar

Presented by: W. Sears - View Audio/Video Presentation (Members Only)

Author(s):

W. Sears(1), G. Maislin(2), R. Davis(3), J. Auerbach(4), T. Errico(5), H. Bae(6)

(1) Wentworth Spine Clinic, Sydney, NSW, Australia
(2) Biomedical Statistical Consulting, Wynnewood, PA, United States
(3) Greater Baltimore Neurosurgical Associates, Baltimore, MD, United States
(4) Albert Einstein College of Medicine, Bronx, NY, United States
(5) NYU Hospital for Joint Diseases, New York, NY, United States
(6) Cedars Sinai Spine Center, Los Angeles, CA, United States

Abstract

Background: Lumbar spinal fusion may be followed by degeneration at levels adjacent to the fusion. Despite in vitro evidence of increased mechanical burden on motion segments adjacent to simulated fusions, it has remained controversial as to whether fusion is a causative factor in adjacent segment degeneration (ASDegen). The current study aims to resolve this issue by a secondary and further analysis of X-ray data sourced from the previously published U.S. Food and Drug Administration (FDA) Investigational Device Exemption (IDE) randomized control trial (RCT) of decompression and Coflex® interlaminar-stabilization compared with decompression and instrumented postero-lateral fusion, for spinal stenosis and low-grade degenerative spondylolisthesis (Ref). Methodology: The pre-operative, 2- and 5-year post-operative imaging was subjected to secondary radiographic analysis in the 55 investigational and 27 fusion control subjects from the two-level arm of the Coflex® IDE RCT. Angular range-of-motion (ROM) and average disc-space heights were measured at the index, 1st and 2nd adjacent segments using Quantitative Motion Analysis® (Medical Metrics Inc, TX).

Results: At 24-months post-op, mean angular ROM had increased in the fusion control patients, at the 1st superior adjacent level, from 3.9° (±2.7°) pre-op to 6.3° (±4.7°) (P=0.007). ROM remained unchanged, in the interlaminar-stabilizer patients, at both the index and adjacent levels. At month-60, ROM in the fusion patients had returned to 3.9° (±2.6°). At month-60, mean disc-space heights at the 1st adjacent level had decreased in both the fusion control and investigational groups. However, the decrease was significantly greater in the fusion controls than in the investigational patients: 2.15±2.2mm (30.1%) versus 1.06±1.5mm (13.7%), respectively (P=0.007). The estimated difference between treatment cohorts in the mean reduction in disc height was 1.06mm (95%CI: 0.26 to 1.86). Pre-operatively, mean disc height was larger in the interlaminar-stabilizer patients than fusion controls (7.74mm and 6.85mm, respectively, P=0.044). Using analysis of covariance (ANCOVA) to statistically control for baseline disc height, the estimated difference between device groups at month-60 was 1.13 mm (95%CI: 0.32-1.95, p=0.002). Significant baseline differences were also observed between the investigational and fusion controls for age and patient height. Mean patient age was 66.8 years in the control fusion patients and 62.2 years in the interlaminar-stabilizer patients (p=0.02). Using ANCOVA to statistically control for all baseline differences, the estimated difference in loss of disc space height between treatment groups was again, little changed at 0.92mm (95%CI: 0.01-1.09, p=0.046). Substantially more of the interlaminar-stabilizer patients lost less than 10% of preoperative disc space height at the 1st adjacent levels when compared with the fusion patients (55% vs. 32%, respectively). Mean disc space heights decreased at the 2nd adjacent level, in both cohorts, by 1.0mm±1.5mm and 0.5±0.8mm, respectively (P=0.03).

Conclusion: Based on accurately measured post-operative changes in disc-space height, the current study provides high-level in vivo evidence that lumbar spinal fusion is a risk factor for ASDegen. The increased degeneration may be associated with the temporary increase in adjacent level angular ROM, observed post-fusion in the control patients. The finding of less severe ASDegen at 2nd adjacent levels and in patients randomized to motion preservation surgery suggests that factors other than fusion also play a role in ASDegen. Reference: Davis RJ et al. Spine 2013;38:1529-39.