Three-dimensional evaluation of stem placement accuracy with the conventional guide in reverse shoulder arthroplasty and its relevance to clinical outcomes

Abstract

Background

Placement of retroversion of the stem (RS) is important in reverse shoulder arthroplasty. A conventional guide, based on the forearm, has been used for stem placement; however, only a few studies have reported the accuracy of stem placement using conventional guides. In this study, a three-dimensional postoperative evaluation software was used to investigate the accuracy of RS placement using a conventional guide and its effect on postoperative outcomes.

Methods

This retrospective study was performed by a single surgeon (a board-certified specialist with more than 15 years of experience in performing reverse shoulder arthroplasty) using the Exactech Equinoxe Reverse Shoulder System (Exactech Inc., Gainesville, FL, USA). Forty-nine patients who were followed up for at least 2 years were included. The target RS angle of the humeral component was set to 20°. Postoperative implant placement, including RS, was assessed with a three-dimensional planning software using computed tomography images obtained postoperatively. Postoperative range of motion and its relationship with clinical outcomes were also evaluated as clinical assessment. Furthermore, a subanalysis was performed comparing the 0-20° RS group with the other groups.

Results

The mean postoperative RS was 13.2 ± 11.9° and was placed within 0-20° in 31/49 patients (63.3%). A correlation was observed between postoperative external rotation and RS (r = 0.30, P = .03). In a further subanalysis, the Constant–Murley score was significantly higher in the 0-20° RS group (P = .03).

Conclusion

Placement of the RS using a conventional guide varied from the target position. RS correlated with postoperative external rotation, and RS within 0-20° significantly improved clinical outcomes. These results suggested that accurate placement of the RS may improve clinical outcomes. Therefore, the development of surgical assistive technologies for accurate placement is necessary to ensure accurate stem placement to avoid human error.