171. Overcorrection of the upper instrumented vertebra relative to the center of the femoral heads is associated with proximal junctional kyphosis

BACKGROUND CONTEXT Although matching lumbar lordosis (LL) with pelvic incidence (PI) is an important surgical goal for adult spinal deformity (ASD), there is concern that overcorrection may lead to proximal junctional kyphosis (PJK). We introduce the upper instrumented vertebra – femoral angle (UIVFA) as a measure of appropriate postoperative position in the setting of lower thoracic to pelvis surgical correction for patients with sagittal imbalance. We hypothesize that a more posterior UIV position in relation to the center of the femoral head is associated with an increased risk of PJK given compensatory hyperkyphosis above the UIV. PURPOSE The purpose of this study is to evaluate if increased UIVFA is associated with PJK in operative management of ASD. STUDY DESIGN/SETTING Retrospective cohort study. PATIENT SAMPLE Adult patients undergoing lower thoracic (T9-T12) to pelvis correction of ASD with a minimum of two-year follow-up were included. OUTCOME MEASURES The primary outcome is PJK and proximal junctional failure (PJF). Methods In this retrospective cohort study, adult patients undergoing lower thoracic (T9-T12) to pelvis correction of ASD with a minimum of two-year follow-up were included. UIVFA was measured as the angle subtended by a line from the UIV centroid to the femoral head center to the vertical axis. UIV posterior to the femoral head center was positive (+) and UIV anterior the femoral head center was negative (-). A >10° kyphotic angle between the UIV and UIV+2 or a >10° increase from preop to postop were used to determine PJK. Patients with PJK that required revision surgery were defined as proximal junctional failure (PJF). Patients who developed PJK and those who did not were compared with preoperative and postoperative UIVFA, change between postoperative and preoperative UIVFA (deltaUIVFA), sagittal vertical axis (SVA), pelvic tilt (PT), sacral slope (SS), pelvic incidence (PI), lumbar lordosis (LL), pelvic incidence minus lumbar lordosis (PI-LL), thoracic kyphosis at T5-12 (TK) and the central sacral vertical line (CSVL). Results Of the 119 patients included in the study with an average 3.6-year follow-up, 51 (42.9%) had PJK and 24 (20.2%) had PJF. The average preoperative UIVFA was 7.0±0.7°, the average postoperative UIVFA 10.8±0.6°, and the average deltaUIVFA was 3.8±0.6°. Patients with PJK had significantly higher postoperative UIVFA (12.6±4.8° vs 9.4±6.6°, p=0.04), deltaUIVFA (6.1±7.6° vs 2.1±5.6°, p Conclusions The more posterior the UIV is from the femoral head center after lower thoracic to pelvis surgical correction for ASD, the more patients are at risk for PJK. The greater the magnitude of posterior translation of the UIV from the femoral head center from preop to postop, the greater the likelihood for PJF. Further investigation into the consequences of sagittal overcorrection in the setting of ASD is warranted. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.