43. Comparison of radiographic adjacent segment pathology at five years following minimally invasive compared to open lumbar 1- to 2-level fusion surgery

Abstract

<h3>BACKGROUND CONTEXT</h3> Adjacent segment pathology remains a major cause of morbidity among patients receiving posterior lumbar instrumented fusion. Its occurrence is proposed to be secondary to the increased motion and biomechanical stresses from fused to unfused segment. Additionally, progressive degenerative processes in the spine can also be influenced by surgery-related factors that alter the spine biomechanics as a result of muscle destruction and facet joint violation. Controversy in the rates of radiographic adjacent segment pathology (RASP) after lumbar fusion surgery has stemmed by and large from variable reporting in the literature with short long-term follow-up periods and no comparison between muscle splitting minimally invasive (MIS) approach and posterior midline open fusions. We report a single-center cohort analysis of patients undergoing lumbar fusion surgery and describe the rate of RASP between patients undergoing minimally invasive tubular approach (MIS) vs open posterior fusion technique. <h3>PURPOSE</h3> The objective of this study is to evaluate the rate of RASP between MIS and open lumbar fusion surgery within 5-year follow-up period. <h3>STUDY DESIGN/SETTING</h3> Observational study. <h3>PATIENT SAMPLE</h3> Adults with degenerative lumbar disease who underwent 1- to 2-level open and MIS fusion at our institution from January 2006 to December 2016. <h3>OUTCOME MEASURES</h3> Rate of radiographic adjacent segment pathology. <h3>METHODS</h3> The authors conducted a retrospective chart review of patients diagnosed with degenerative lumbar disease who had undergone 1- to 2-level fusion between January 2006 to December 2016. Cases with upright lumbar radiographs were included in this sub-analysis. The patients were divided into an MIS fusion group and an open surgery group based on the surgical technique performed. The two groups were compared for baseline demographic features, surgical variables and diagnosis at index surgery. Adjacent segment pathology was evaluated using radiographs taken at the 5-year follow-up period. RASP is defined by the presence of any one or combination of (1) disc degeneration (height loss), (2) development of spondylolisthesis and (3) coronal deformity/lateral listhesis. Analysis was confined to rates of development of RASP with no attempt of correlating with symptomatic adjacent segment pathology. Logistic regression analysis was performed to assess relationship of demographic factors with development of RASP <h3>RESULTS</h3> A total of 165 patients were included: MIS (n = 73) and (n = 92) open. There was no significant difference between two groups in age, sex, diagnosis at index surgery, level of fusion and baseline RASP. Fusion involved one level in 72.7 % of cases and 2 levels in 27.3%. The overall incidence of RASP was 41.2%, with incidence of 36.9% in MIS group and 44.6% in the open surgery group, showing no significant difference between the two groups (p = 0.5246). In those with RASP, the most common radiographic finding was disc degeneration (height loss) for both cohorts (100% vs 87.8%, p = 0.264) with the majority occurring cephalad to previous instrumentation. Logistic regression analysis did not show significant correlation between sex, age, index diagnosis, presence of baseline RASP and the prevalence of RASP at 5 years. <h3>CONCLUSIONS</h3> The prevalence of radiographic adjacent segment pathology did not statistically differ between MIS and open lumbar fusion surgery at minimum of 5-year follow-up. Baseline demographics or primary pathoanatomical diagnosis did not correlate to the presence of RASP 5 years following surgery in either group. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.