Introduction: This study aims to evaluate demographic and operative factors which influence and predict occurrence of adjacent segment disease (ASD) after fusion for lumbar degenerative pathologies.
Methods: A retrospective review was performed on patients who had undergone lumbar fusion for degenerative pathologies (stenosis, spondylolisthesis, or disc degeneration) within the L1 to S1 segments between 2007 and 2016. Patients without any follow-up data were excluded from the study. Effects of demographic (age, gender, smoking status, osteoporosis, diebetes) and technical factors (surgical approach, type of procedure, number of fused levels, performing decompression in any segments without fusion, type of bone graft) on ASD rates were analyzed.
Results: 779 patients met our inclusion criteria, 170 (21.8%) of whom were re-operated for ASD. Mean follow-up was 2.7 years, and mean time to ASD was 4.9 years. Univariate analysis showed that unfused decompression adjacent to the fused segments was significantly associated with higher ASD rates (P=0.003), as was laminotomy (P=0.05), discectomy (P=0.031), number of decompressed segments (P=0.007), and combination of allograft and autograft (P=0.014). There was no statistically significant association between fusion technique (pedicular screw only vs. interbody fusion only vs. both), surgical approach (anterior vs. posterior vs. combined), smoking, osteoporosis or diabetes and ASD. Multivariate analysis identified that presence of unfused decompression adjacent to the fused segments (OR=3.34, P=0.001), the number of segments decompressed (OR=1.47, P=0.004), and the type of bone graft used (OR=0.75, P=0.023), were independently associated with ASD rates.
Conclusions: No difference in ASD rates was identified between pedicular screw fixation with and without interbody fusion. Additionally, spinal decompression adjacent to the fused segments may possibly weaken the structural integrity of the remaining segments and lead to higher rates of ASD.
Patient Care: This research identified technical details regarding lumbar spinal fusion, which should be highlighted and can be improved on in the future. Notably, we found that it is not the number of segments fused, but the number of segments decompressed, that is most strongly associated with subsequent ASD.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the factors predicting adjacent segment disease after lumbar fusion for degenerative spinal disease; 2) Discuss, in small groups which operative techniques may influence ASD rates; 3) Identify an effective management plan for degenerative spinal disease to potentially decrease ASD rates.