Adjacent Segment Disease and Reoperation at L5-S1 after an L4-L5 Fusion

Study Design: Systematic review and meta-analysis Objective: This review determines the rate of adjacent segment disease (ASD) and reoperation at L5-S1 after an L4-L5 fusion. Summary of Background Data: Lumbar degenerative disc disease is one of the most common spine diseases associated with high morbidity. Lumbar spinal fusion provides added stability and can improve decompression when indicated. However, there is no consensus on what should be done with the L5-S1 segment during a L4-L5 fusion. Methods: A systematic review was conducted according to PRISMA guidelines. A search was conducted on March 20th, 2024, of PubMed, EMBASE, and Scopus databases. The systematic review software Rayyan was used for initial deduplication, leading to manual inclusion or exclusion of studies. After full text analysis for final inclusion, demographic data as well as those regarding adjacent segment disease rates, type of surgery, and reoperation rates after ASD diagnosis. Meta-analysis of proportions was conducted using R version 4.3.3. Results: A total of 10 studies were included investigating ASD at the L5-S1 segment after L4-L5 fusion in 855 patients. A random effects model meta-analysis of proportions of clinically significant ASD demonstrated an overall incidence rate of 0.10 (95% CI: 0.06, 0.17). A random effects model meta-analysis of proportions of reoperation rates across both radiologically and clinically significant ASD was 0.05 (95% CI: 0.03, 0.07). An analysis was not possible between different types of fusion due to sample size limitations of each fusion group. Conclusions: There was a cumulative clinical ASD incidence at segment L5-S1 was 10% in those who had an L4-L5 operation. The reoperation rate was 5% among both radiologic and clinical ASD. Further studies are needed to determine the effects of different forms of fusion on ASD rates along with other associated risk factors.