36. Understanding the role of pelvic obliquity and leg length discrepancy in adult spinal deformity patients with coronal malalignment: unlocking the black box

BACKGROUND CONTEXT Achieving optimal coronal alignment can be a formidable challenge in adult spinal deformity surgery, and how pelvic obliquity and leg length discrepancy relate to coronal malalignment remains poorly studied. PURPOSE Pelvic obliquity (PO) and leg length discrepancy (LLD) are associated with preoperative and postoperative coronal malalignment (CM) in surgical adult spinal deformity (ASD) patients. STUDY DESIGN/SETTING Retrospective cohort. PATIENT SAMPLE A total of 237 patients undergoing ASD surgery at a single institution. OUTCOME MEASURES Pelvic obliquity, leg-length discrepancy, coronal malalignment. METHODS Patients undergoing ASD surgery (≥6 level fusions) were reviewed from a single-institution. Variables were:1) Pelvic obliquity (PO): angle between horizontal plane and a line touching bilateral iliac crests; 2) Leg-length discrepancy (LLD): distance from femoral head to the tibial plafond. Coronal vertical axis (CVA) and sagittal vertical axis (SVA) were collected, both measured from C7. Coronal malalignment (CM)= CVA >3cm. Oswestry Disability Index (ODI) was collected at preoperative and 2-years postoperative. RESULTS Of 237 patients undergoing ASD surgery, 90 (37.0%) had preoperative CM. Patients with preoperative CM had a higher PO (2.8±3.2 vs 2.0±1.7, p=0.013), higher percent of patients with PO>3° (35.6% vs 23.5%, p=0.044), and higher percent of patients with LLD>1 cm (21.1% vs 9.8%, p=0.014). While preoperative PO was significantly correlated with CVA (r=0.26, p CONCLUSIONS Clinically significant pelvic obliquity ≥3° or leg-length discrepancy ≥1 cm was seen in 44.1% of patients with preoperative coronal malalignment, but also 23.5% of patients with normal coronal alignment. Preoperative pelvic obliquity was significantly associated with preoperative coronal vertical axis and max Cobb angle, while preoperative leg-length discrepancy was only associated with preoperative coronal vertical axis. The direction of pelvic obliquity and leg-length discrepancy showed no consistent pattern with coronal vertical axis. Preoperative pelvic obliquity was independently associated with complications but not 2-year ODI scores. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.