Does arm lengthening affect the functional outcome in onlay reverse shoulder arthroplasty?

BACKGROUND: The concept of onlay design reverse shoulder arthroplasty has been introduced to overcome complications observed with the traditional Grammont-type prosthesis. The aim of this study was to determine the influence of arm lengthening on the short-term clinical outcome in onlay reverse shoulder arthroplasty and investigate the effect of humeral tray offset positioning on arm lengthening and range of motion.

METHODS: We retrospectively evaluated 56 patients undergoing reverse shoulder arthroplasty with the Aequalis Ascend Flex prosthesis (Tornier, Bloomington, MN, USA) at a minimum 2 years' follow-up. Arm lengthening was determined using bilateral scaled radiographs of the entire humerus. The Constant score and active range of motion were documented preoperatively and postoperatively. The relationship between arm lengthening, humeral tray offset position, and functional outcome was analyzed.

RESULTS: The Constant score improved from 25.5 ± 9.5 points to 71.5 ± 13.8 points at a mean follow-up of 30.1 ± 5.2 months. Mean postoperative anterior elevation was 145.2° ± 21.1°, and external rotation was 30.7° ± 20.3°. Arm lengthening exceeding 2.5 cm was related to a decrease in anterior elevation. We found a relationship between arm lengthening averaging 2.2 ± 1.7 cm and increased Constant score values. Humeral tray positioning demonstrated no influence on the functional outcome. There was a trend toward increased arm lengthening in lateral offset positioning.

CONCLUSIONS: Onlay reverse shoulder arthroplasty yields good short-term clinical results. In our population, arm lengthening averaging 1 to 2.5 cm was found to be the best compromise on postoperative range of motion.