Friday, September 28, 2018 10:30 AM–12:00 PM abstracts: deformity: technical factors: 171. The amount of curve correction is more important than upper instrumented vertebra selection for ensuring postoperative shoulder balance in Lenke type 1 adolescent idiopathic scoliosis

Abstract

BACKGROUND CONTEXT Postoperative shoulder height imbalance is a common complication following adolescent idiopathic scoliosis (AIS) surgery. It is thought that a more cephalad upper instrumented vertebra (UIV) decreases the risk of shoulder imbalance in Lenke type 1 curves, however this has not been proven. PURPOSE To test the hypothesis that “over-correction” of the main thoracic curve without control of the proximal curve increases the risk for shoulder imbalance in Lenke type 1 AIS. STUDY DESIGN/SETTING Clinical photo and x-ray review of patients with Lenke 1 Main Thoracic AIS curves. PATIENT SAMPLE Surgically-treated patients with Lenke type 1 AIS were reviewed from a large multicenter database. OUTCOME MEASURES Postoperative shoulder height balance on clinical photos and PA radiographs. METHODS A total of 13 surgeons reviewed preop and 5-year postop clinical photos and PA radiographs of patients from a large multicenter database with Lenke type 1 AIS curves who were corrected with pedicle screw or rod constructs. Predictors of postop shoulder imbalance were identified by univariate analysis; multivariate analysis was done using the classification and regression tree (CART) method to identify independent drivers of shoulder imbalance. RESULTS A total of 145 patients were reviewed. The UIV was T3-T5 in 87% of patients, with 8.9% instrumented up to T1 or T2. 52 (36%) had shoulder imbalance at 5 years. On CART analysis: when the proximal thoracic (PT) Cobb angle was corrected more than 52%, 80% of the patients had balanced shoulders. Similarly, when the PT curve was corrected less than 52% and the main thoracic (MT) curve was corrected less than 54%, 87% were balanced. However, when the PT curve was corrected less than 52%, and the MT curve was corrected more than 54%, only 41% of patients had balanced shoulders (p=0.05). This relationship was maintained regardless of the UIV level. CONCLUSIONS In Lenke type 1 AIS curves, “over-correction” of the main thoracic curve (>54%) with simultaneous “under-correction” (