Is limited shoulder abduction associated with poor scapulothoracic mobility after reverse shoulder arthroplasty?

ABSTRACT

INTRODUCTION: The contribution of the glenohumeral joint to shoulder abduction is acknowledged as an important factor for reverse total shoulder arthroplasty (RTSA) patients. In contrast, the degree of scapulothoracic joint contribution and its relation to RTSA patients with poor to excellent shoulder abduction are unclear. MATERIALS AND METHODS: Twenty-three selectively recruited patients (74 ± 7 years, 11 males) with shoulder abduction ranging from poor to excellent at least 6 months after primary, unilateral RTSA participated in this study. Individual scapulothoracic and glenohumeral contributions at maximum shoulder abduction in the scapular plane were measured using 3D motion capture and correlations between scapulothoracic and glenohumeral contributions to shoulder abduction were assessed. Multiple regression analysis was used to determine the influence of age, body mass index, follow-up period, abduction strength and passive glenohumeral mobility on scapulothoracic and glenohumeral function. RESULTS: Maximum shoulder abduction (range 48°-140°) was not significantly correlated with the scapulothoracic contribution (range 39°-75°, r = 0.40, p = 0.06), but there was a strong and significant correlation with the glenohumeral contribution (range - 9°-83°, r = 0.91, p < 0.001). Abduction strength was strongly associated with glenohumeral (p = 0.006) but not scapulothoracic (p = 0.34) joint contributions. CONCLUSIONS: Limited shoulder abduction is not associated with insufficient scapulothoracic mobility, which rather provides a basic level of function for RTSA patients. Good to excellent shoulder abduction could only be achieved by increasing the glenohumeral contribution that was associated with postoperative abduction strength.