The effects of progressive lateralization of the joint center of rotation of reverse total shoulder implants.

Background: There has been a renewed interest in lateralizing the center of rotation (CoR) in implants used in reverse shoulder arthroplasty. The aim of this study was to determine the sensitivity of lateralization of the CoR on the glenohumeral joint contact forces, muscle moment arms, torque across the bone-implant interface, and the stability of the implant.

Methods: A 3-dimensional virtual model was used to investigate how lateralization affects deltoid muscle moment arm and glenohumeral joint contact forces.

A comparison of range of motion change across four posterior shoulder tightness measurements after external rotator fatigue.

Background: Several glenohumeral joint (GHJ) positions have been recommended for assessing and correcting posterior shoulder tightness (PST) however, there is no agreement on which position is better for differentiating posterior muscle tightness from posterior capsular tightness. The purpose of this study was to compare the range of motion change before and after an external humeral rotator muscle fatigue protocol in order to identify a position that shows maximum range of motion change.

Methods: ROM changes across four PST measurements were compared before, immediately after, at 24 hours after, and 48 hours after an external rotator fatigue protocol.