277. Is adjacent segment disease following instrumented short lumbosacral fusion influenced by postoperative sagittal alignment?

Abstract

BACKGROUND CONTEXT Adjacent segment disease (ASD) is a common manifestation following lumbar fusion, potentially requiring revision of the construct. While several risk factor for the condition have been identified it is unclear what role sagittal imbalance following fusion plays in the development of ASD. Sagittal imbalance, when measured as mismatch between pelvic incidence and lumbar lordosis (PI-LL), has been associated with poorer clinical outcomes following lumbar surgery; however, it is unclear whether higher PI-LL contributes to ASD in the short lumbosacral fusion population. PURPOSE The aim of this study was to 1) determine the incidence of ASD among patients undergoing short lumbosacral fusion; 2) to evaluate if patients who went on to develop ASD have higher degree of PI-LL compared to those without (controls); 3) following subgroup analysis, determine if the relation between PI-LL and ASD was affected by length of fusion. STUDY DESIGN/SETTING Single institutional retrospective cohort study PATIENT SAMPLE A total of 126 patients undergoing instrumented short lumbosacral fusion were included OUTCOME MEASURES Radiographic evidence of postoperative ASD; Initial Postoperative PI-LL among ASD patients and controls METHODS Patients who underwent short instrumented lumbosacral fusion between the years of 2008 to 2019 at our institution were selected for the study. In addition, patients must have had a minimum of 2-year radiographic follow-up to meet inclusion criteria. Only elective cases for degenerative lumbar pathology were included; cases involving spinal infection, trauma, or malignancy were excluded. Postoperative PI-LL was measured using initial one-month postoperative standing radiographs. Subgroup analysis was also performed after separating the main cohort into 3 separate populations corresponding to the following fusion lengths: 5 segment (L2-S1), 4 segment (L3-S1), and 3 segment (L4-S1) fusions. PI-LL was compared between patients who went on to develop radiographic evidence of ASD and those who did not (controls) using student t-test. Significance was defined as p RESULTS Following application of inclusion and exclusion criteria, 126 patients with a mean age of 61.44 ± 12.22 years were selected for the study. Radiographic evidence of ASD was present in 59% of patients (n=74), with a mean time to ASD of 21.52 ± 21.74 months. No difference (p=0.781) was seen in initial postoperative PI-LL between ASD patients (11.42 ± 7.62) and controls (11.87 ± 9.94) in the main cohort. Following subgroup analysis, incidence of ASD was 57% (24/42) in L4-S1 fusions, 62% (29/47) in L3-S1 fusion, and 57% (21/37) among L2-S1 fusions. Postoperative rates of ASD were similar among the 3 cohorts (p=0.787). No difference was observed PI-LL between ASD patient and controls in the L4-S1 (10.74 ± 8.35 vs 8.89 ± 9.02, p=0.500), L3-S1 (11.69 ± 7.77 vs 11.24 ± 8.94, p=0.860), and L2-S1 fusion cohorts (11.81 ± 6.82 vs 15.98 ± 11.14, p=0.203). CONCLUSIONS No significant difference in PI-LL was observed between patients who went on to develop ASD and those who did not. Likewise, sagittal alignment was similar in each fusion length subgroup. Sagittal imbalance measured by PI-LL may not have a significant impact on the development of ASD following instrumented short lumbosacral fusion. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.