초록/요약

Background: The variability in functional outcomes and the occurrence of scapular notching and instability after reverse total shoulder arthroplasty remain problems. The objectives of this study were to measure the effect of reverse humeral component neck-shaft angle on impingement-free range of motion, abduction moment, and anterior dislocation force and to evaluate the effect of subscapularis loading on dislocation force. Methods: Six cadaveric shoulders were tested with 155 degrees , 145 degrees, and 135 degrees reverse shoulder humeral neck-shaft angles. The adduction angle at which bone contact occurred and the internal and external rotational impingement-free range of motion angles were measured. Glenohumeral abduction moment was measured at 0 degrees and 30 degrees of abduction, and anterior dislocation forces were measured at 30 degrees of internal rotation, 0 degrees, and 30 degrees of external rotation with and without subscapularis loading. Results: Adduction deficit angles for 155 degrees, 145 degrees, and 135 degrees neck-shaft angle were 2 degrees +/- 5 degrees of abduction, 7 degrees +/- 4 degrees of adduction, and 12 degrees +/- 2 degrees of adduction (P <. 05). Impingement-free angles of humeral rotation and abduction moments were not statistically different between the neck-shaft angles. The anterior dislocation force was significantly higher for the 135 degrees neck-shaft angle at 30 degrees of external rotation and significantly higher for the 155 degrees neck-shaft angle at 30 degrees of internal rotation (P <. 01). The anterior dislocation forces were significantly higher when the subscapularis was loaded (P <. 01). Conclusions: The 155 degrees neck-shaft angle was more prone to scapular bone contact during adduction but was more stable at the internally rotated position, which was the least stable humeral rotation position. Subscapularis loading gave further anterior stability with all neck-shaft angles at all positions. (C) 2014 Journal of Shoulder and Elbow Surgery Board of Trustees.