P96. The lordosis distribution index does not impact failure rates after surgical treatment of adult spinal deformity

Abstract

BACKGROUND CONTEXT The risk factors for developing proximal junctional failure (PJF) after surgery for adult spinal deformity (ASD) continue to evolve. The lordosis distribution index (LDI) describes the amount of lower arc lordosis (L4-S1) as a fraction of total lumbar lordosis (L1-S1) and has been postulated to influence the outcomes of ASD. PURPOSE The purpose of this study is to determine if the LDI is a risk factor for mechanical failure after ASD. STUDY DESIGN/SETTING Retrospective review. PATIENT SAMPLE Adult patients with ASD treated with thoracolumbar fusion (>4 levels, caudal to T9). METHODS Demographic variables and surgical data were recorded and radiographic data including proximal junctional angle (PJA), pelvic tilt (PT), sacral slope (SS), lumbar lordosis (LL), pelvic incidence (PI), T1 and T9 spinopelvic inclination (T1-SPI and T9-SPI), and LDI were calculated preoperatively, immediately postoperatively and at 6 months, 1 year and 2 years. Patients were categorized by LDI (severe hypolordosis, moderate hypolordosis, aligned and hyperlordosis) pre- and post-operatively along with the change in LDI between the two time points. Acute PJF ( RESULTS There were 187 patients that met the inclusion criteria. Acute PJF occurred in 48 (25.6%) patients. At final follow up, 58 (31.0%) patients underwent surgery for acute PJF or late failure. There was no difference in the prevalence of acute PJF or late failure for patients that were severely hypolordotic (LDI 0.8) at the preoperative and immediate postoperative time points. Similarly, there was no difference in acute PJF or late failure when the amount of change in LDI was considered. Univariate cox proportional hazard models demonstrated the number of levels fused, exclusion of the sacrum and/or pelvis during instrumentation, postoperative change in PI-LL and T9-SPI were predictors of early or late failure. CONCLUSIONS The lordosis distribution index is increasingly recognized as a relevant surgical variable in ASD treatment. This study sought to ascertain the association of LDI with mechanical failure. In this cohort of patients, the LDI did not impact the failure rate. However, this study corroborates previously known risk factors for failure including the number of levels fused, excluding the sacrum/pelvis, and amount of PI-LL mismatch correction. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.