How does scapula motion change after reverse total shoulder arthroplasty? - a preliminary report

Background: Arm elevation is composed of glenohumeral and scapulothoracic motion. Many reports have addressed changes of scapular position across a spectrum of shoulder disease. However, no study has examined changes in scapular position after reverse total shoulder arthroplasty (RTSA). The purpose of this study was to evaluate the changes in scapular position after RTSA compared to patients' contralateral, nonoperated shoulder. Methods: Seven patients that underwent RTSA for cuff tear arthropathy from July 2007 to October 2008 were enrolled. The distance between the long axis of the thoracic spine and the inferior pole of the scapula (lateralization of the scapula) was measured on shoulder A-P radiographs at 0 degrees (the neutral position) and at 30, 60, 90, and 120 degrees of shoulder abduction. In addition, the angle between the long axis of the thoracic spine and medial border of the scapula was measured and compared with the patients' contralateral shoulder. Results: Scapulohumeral rhythm was 2.4:1 on the operated shoulder and 4.1:1 on the nonoperated, contralateral shoulder at 120 degrees of abduction. The distance between the line of the interspinous process of upper thoracic vertebra and the inferior pole of the scapula showed a negative slope at 0 to 30 degrees abduction on the operated side, but beyond 30 degrees of abduction, this distance showed a more sudden increase than in the contralateral shoulder. The angle between the vertical vertebral line and the scapular medial border also showed greater increase beyond 30 degrees abduction on the operated limb. Conclusions: The pattern of scapular position after RTSA, was found to differ from that of the contralateral shoulder, and showed a more scapular upward rotation.