Review of “Reverse shoulder arthroplasty for patients with cuff tear arthropathy: do clinical outcomes differ by inlay vs. onlay design?”

Introduction

Since the initial release of the Reverse Total Shoulder Arthroplasty (RTSA) in the United States in 2003, its use and indications have continued to expand. The rise of the RTSA over the past two decades has been driven by multiple improvements on Paul Grammont’s original design. Many of these key modifications include the concept of lateralization, a less valgus humeral neck-shaft angle, and the concept of convertibility which has led to the development of “onlay” designs. However, the effect of RTSA design modifications on clinical outcomes remains unknown.

Summary

The authors of this single institution retrospective cohort study aimed to compare Patient Reported Outcomes (PROs), shoulder Range Of Motion (ROM), and complication in patients undergoing RTSA for treatment of rotator cuff tear arthropathy (RCA) using a lateralized glenosphere prosthesis with a 135 neck-shaft angle and an inlay or onlay humeral tray design.

Materials and Methods

A total of 102 patients with RCA treated with RTSA prostheses using a lateralized glenosphere and 135 neck-shaft angle (with either an inlay or onlay humeral tray design) who had a minimum of 2 years of follow-up were included in the study. All patients underwent preoperative and postoperative evaluations that included shoulder ROM, PROs (American Shoulder Elbow Surgeons Score (ASES), Simple Shoulder Test (SST), Western Ontario Osteoarthritis of the Shoulder Index (WOOS), and radiographic imaging. Postoperative complications and reoperations were recorded.

Results

Mean follow up was 44 months (range, 24-125 months). Sixty-three patients (62%) had an inlay prosthesis and 39 (38%) had onlay prosthesis. Except for gender, there were no demographic differences between groups with more females noted to comprise the inlay group (75%) vs the onlay group (56%). There were no preoperative differences in ROM or PROs between groups. Postoperatively, patients in both groups had significant and clinically meaningful improvement in ASES, SST, WOOS scores with no differences between the inlay and onlay group. Final postoperative ROM was improved in both groups but not significantly different.

A total of 24 patients sustained complications with no significant difference between the inlay group (22%, N=14 of 63) and the onlay group (26%, N=10 of 39). There was no difference in the rate of baseplate loosening, prosthetic dislocation, or acromial stress fractures. A total of 4 patients in the inlay group (6%) underwent reoperation compared to 3 patients in the onlay group (7%). There was no significant difference in the rate of scapular notching between groups.

Discussion

Overall, this study demonstrated significant clinical improvements for treatment of RCA following RTSA with either inlay or onlay humeral prostheses with no significant differences in ROM, PROs or complications. These outcomes differ from some previously published data which shows an increase in certain complications between groups and significant differences in ROM. Limitations of this study include differences in implant lateralization, differences in mean follow up between groups and homogeneity of diagnostic indications (RCA) which does not allow for comparisons to prior studies with greater heterogenicity.

Reviewer Comments

Ultimately, this study makes a strong case that RTSA is successful in treatment of RCA regardless of implant design (i.e. inlay versus onlay) with no notable differences in the degree of patient improvement or complication. However, implant design is not simply limited to the position of the humeral tray either within or on the humeral cut surface. Further research is needed to determine the combined effects of both glenoid and humeral lateralization as well as its relationship to neck shaft angle of the humeral prosthesis on patient function, reported outcomes, and complications.