Defining 2 Components of Shoulder Imbalance

Abstract

A single-center prospective case series. To examine 2 features of shoulder asymmetry (clavicle tilt and trapezial prominence) and their correlation with radiographical parameters. Shoulder imbalance is one of the more notable aspects of clinical deformity due to scoliosis. However, a discrepancy between radiographical and clinical shoulder balance in patients with adolescent idiopathic scoliosis (AIS) has been reported. A consecutive series of 113 preoperative right main thoracic Lenke 1 and 2 AIS curves were included. Clavicle angle (tilt), trapezial angle, and ratio of left to right trapezial area were measured on clinical photos. These were correlated with radiographical measurements of T1 tilt, first rib angle, curve magnitudes, and thoracic and lumbar apical translation to C7 plumb line and center sacral vertical line. The average age was 14.1 years. There were 82 Lenke 1 and 31 Lenke 2 curves with an average thoracic Cobb of 52.1º. The clinical clavicle angle was in the range of -10.6º to +5.2º ("+" defined as high on the left) and had modest correlation with T1 tilt, thoracic curve size, and thoracic apical deviation (r = 0.417, 0.437, and 0.408, respectively). Medial shoulder trapezial prominence as measured by the trapezial angle (range: -16.7 to +9.9) and trapezial area ratio (natural log of ratio range: -1.15 to +0.80) correlated well with the radiographical measurements of T1 tilt, first rib angle, and upper thoracic curve size (trapezial angle: 0.713, 0.679, and 0.686; trapezial area ratio: 0.597, 0.595, and 0.653, respectively). Our analysis suggests that there are 2 distinct regions (lateral and medial) of shoulder height asymmetry. Medial differences reflected in trapezial prominence relate to deformity created by upward tilted proximal ribs and T1 tilt. Lateral differences in shoulder symmetry as reflected in the clavicle angle correlate weakly with radiographical measures. This suggests that correction of trapezial prominence may be more predictable compared with clavicle angulation after scoliosis surgery.