Influence of arm lengthening in reverse shoulder arthroplasty.
Reverse shoulder arthroplasty (RSA) can improve anterior active elevation (AAE) by lengthening of the deltoid and hence increasing its lever arm. However, evaluations of functional outcomes of RSA have shown variable improvements in the range of motion. The aim of our study was to correlate humeral and arm lengthening to postoperative AAE. We reviewed 183 RSAs with a minimum follow-up of 1 year. Lengthening of the humerus and the arm was evaluated in relation to the contralateral side. We observed mean humeral lengthening of 0.2 ± 1.4 cm (range, -4.7 to +5.2 cm) and mean arm lengthening of 1.6 ± 1.9 cm (range, -5.1 to +5.4 cm). Postoperative AAE was 140° ± 27° (range, 30° to 180°). We found no significant correlation between lengthening or shortening of the humerus and AAE (P = .169). Shortening of the arm led to a mean AAE value of 122°; lengthening of 0 and 1 cm, mean AAE of 140°; lengthening of greater than 1 cm to 2.5 cm, mean AAE of 144°; and lengthening of greater than 2.5 cm, mean AAE of 147°. When we compared patients with lengthening of the arm and those with shortening, the postoperative AAE was significantly greater after arm lengthening, 145° versus 122°, with a mean difference of 23° (95% confidence interval, 13° to 33°) (P < .001). This study shows that shortening of the arm reduced AAE. With respect to arm lengthening, a lengthening threshold was not found. An objective assessment of deltoid lengthening is possible preoperatively, intraoperatively, and postoperatively, and this measure seems to correlate with the functional outcome.