Risk Factors of Adjacent Segment Disease Requiring Surgery After Lumbar Spinal Fusion

Study Design. A retrospective study. Objective. To determine the incidence and risk factors of adjacent segment disease (ASD) requiring surgery among patients previously treated with spinal fusion for degenerative lumbar disease and to compare the survivorship of adjacent segment according to various risk factors including comparison of fusion methods: posterior lumbar interbody fusion (PLIF) versus posterolateral fusion (PLF). Summary of Background Data. One of the major issues after lumbar spinal fusion is the development of adjacent segment disease. Biomechanically, PLIF has been reported to be more rigid than PLF, and therefore, patients who undergo PLIF are suspected to experience a higher incidence of ASD than those who underwent PLF. There have been many studies analyzing the risk factors of ASD, but we are not aware of any study comparing PLIF with PLF in incidence of ASD requiring surgery. Methods. A consecutive series of 490 patients who had undergone lumbar spinal fusion of 3 or fewer segments to treat degenerative lumbar disease was identified. The mean age at index operation was 53 years, and the mean follow-up period was 51 months (12-236 mo). The number of patients treated by PLF and PLIF were 103 and 387, respectively. The incidence and prevalence of revision surgery for ASD were calculated by Kaplan-Meier method. For risk factor analysis, we used log-rank test and Cox regression analysis with fusion methods, sex, age, number of fused segments, and presence of laminectomy adjacent to index fusion. Results. After index spinal fusion, 23 patients (4.7%) had undergone additional surgery for ASD. Kaplan-Meier analysis predicted a disease-free survival rate of adjacent segments in 94.2% of patients at 5 years and 89.6% at 10 years after the index operation. In the analysis of risk factors, PLIF was associated with 3.4 times higher incidence of ASD requiring surgery than PLF (P = 0.037). Patients older than 60 years at the time of index operation were 2.5 times more likely to undergo revision operation than those younger than 60 years (P = 0.038). There were no significant differences in survival rates of the adjacent segment according to sex, preoperative diagnosis, number of fused segments, and concomitant laminectomy to adjacent segment. Conclusion. It was predicted that 10% of patients would undergo additional surgery for treating ASD within 10 years after index lumbar fusion. In this study, PLIF showed higher incidence of ASD than did PLF. Patient age greater than 60 years was another independent risk factor. Surgeons should carefully consider these factors at the time of surgical planning of lumbar fusion.