Pelvic Imbalance is Correlated with More Balanced Shoulders after Posterior Spinal Fusion for AIS

Purpose: Shoulder balance after surgery for adolescent idiopathic scoliosis has been correlated with patient satisfaction. Multiple studies have investigated various radiographic and soft tissue measurements to assess how shoulder balance changes after fusion. While some degree of pelvic obliquity can be related to bony limb length difference, there is a component of pelvic tilt unrelated to lower extremity measurements. The relationship between change in shoulder balance and changes in pelvic balance after spinal fusion for AIS is not well understood. Methods: All patients underwent posterior spinal fusion with instrumentation for adolescent scoliosis between 2010and 2016. Radiographic parameters measured included clavicle chest cage angle difference (CCAD), coracoid height difference (CHD), clavicular angle (CA), T1 tilt, pelvic obliquity and pelvic height. Radiographic measures were performed on X-rays done pre-operatively and at least two years post-operatively on 36 patients who met criteria for the study. Results: Clavicular angle becoming more balanced (ρ =-0.42, p=0.01) was significantly correlated with pelvic obliquity becoming more unbalanced. Coracoid height (ρ =-0.42, p=0.06), clavicular chest cage angle (ρ =-0.18, p=0.38), and t1 tilt (ρ =-0.1, p=0.50) becoming more balanced were each associated with pelvic obliquity becoming non-significantly more unbalanced. Conclusion: Pelvic obliquity appears to increase as shoulders become more balanced after spinal fusion for AIS. This correlation was strongest in the measurement of the more lateral shoulder balance of clavicle angle. As the shoulders become more balanced after spinal fusion, pelvic obliquity increases suggesting some compensation through the pelvis.