Estimating optimal shoulder immobilization postures following surgical repair of massive rotator cuff tears.

Although shoulder immobilization is commonly prescribed following surgical repair of rotator cuff tears there is no consensus about the best shoulder immobilization postures. A musculoskeletal model was used with a minimax algorithm to estimate optimal post-operative shoulder immobilization postures for massive rotator cuff tears involving the supraspinatus and infraspinatus. An optimal posture was defined as one in which the stresses in the repaired tendons and the angle of humerus elevation were minimized. The optimal post-operative shoulder immobilization postures were with the humerus elevated and externally rotated. Elevation increased with the severity of the tear from 21° to 45° while external rotation decreased slightly from 23° to 18°. The minimax algorithm effectively balanced the competing criteria, resulting in feasible postures that did not overstress the repaired tendons. This method could be used to guide prescription of shoulder immobilization postures for various injuries.