Is limited scapular mobility associated with poor functional outcomes after reverse shoulder arthroplasty?

Reverse shoulder arthroplasty (RSA) usually leads to favourable clinical and functional results, yet some patients experience persisting limitations in shoulder range of motion (ROM). Shoulder abduction ROM is comprised of individual contributions of scapular rotation (between scapula and thorax) and glenohumeral rotation (between scapula and humerus). Based on visual observations during routine clinical postoperative exams, it was speculated that patients with insufficient shoulder abduction ROM are predominantly limited by poor scapular rotation. Shoulder abduction ROM was quantified in 21 patients after RSA using a 3D motion capture system and was correlated to scapular and glenohumeral rotation contributions. Glenohumeral rotation showed a strong correlation to shoulder abduction ROM while scapular rotation correlated poorly. In contrast to visual clinical observations, glenohumeral rather than scapular rotation appears to be the limiting factor for patients with poor shoulder abduction ROM after RSA.