Superior Capsular Reconstruction: Proposed Biomechanical Advantages

The intact rotator cuff provides dynamic stability for the glenohumeral joint through range of motion by compressing the humeral head to the center of the glenoid. Maintenance of articular congruity provides a stable fulcrum for the more forceful muscles of the shoulder girdle. Massive rotator cuff tears disrupt the concavity-compression mechanism and lead to unopposed superior pull of the deltoid. As a result, superior migration of the humerus, abutment of the acromion, and, in some cases, progression to cuff tear arthropathy occur. Arthroscopic superior capsular reconstruction has emerged as an effective treatment in select indications. Several potential biomechanical advantages to SCR have been described on the basis of cadaver studies. By tethering the greater tuberosity to the glenoid, superior migration is resisted, and the center of rotation is stabilized. The interpositional spacer effect describes reduced subacromial contact pressure, and the reduction is greater with thicker grafts. Side-to-side suturing of the graft to residual tendon and capsule achieves capsular continuity and may further improve the stabilizing function of the residual capsule and prevent medial-lateral elongation of the graft. Although these biomechanical principles overlap to some degree, their summation offers an explanation for the improved pain and function seen in patients who undergo superior capsular reconstruction.