A functional evaluation of the rotator cuff length after reverse total shoulder arthroplasty.

BACKGROUND

A biomechanical result of the reverse total shoulder arthroplasty (rTSA) design is the medialization and inferiorization of the greater tuberosity, which influences the length of the cuff muscles. A well-known complication after rTSA is a lack of external rotation force. The purpose of this study was to investigate the difference in the length of the cuff muscles in a native shoulder and in shoulders treated with six commercial rTSA designs.

METHODS

Six implant systems were implanted on identical sawbones. A robotic setup was used to perform and control the shoulder's position and measurements. The muscle lengths were measured by draw wire encoders.

RESULTS

In the three functional positions, the length of the cuff muscles was significantly lower in the Delta Xtend. In all measured positions, there was a strong negative correlation between the medialization of the humerus and the length of the cuff muscles. A lower position of the humerus after rTSA had a positive impact on the length of the infraspinatus and subscapularis.

DISCUSSION

This study found a distinct difference in the slackening of the cuff muscles. Still, in the commercial reverse shoulder arthroplasty designs studied, this slackening never exceeded 15% in the above-mentioned maneuvers, which is functional and safe for the remnants of the muscles.