The Effect of Glenohumeral Fixation Angle on Deltoid Function During Superior Capsule Reconstruction: A Biomechanical Investigation

摘要

Purpose: To evaluate the effect of dermal allograft fixation at different angles of glenohumeral abduction on deltoid forces during superior capsule reconstruction (SCR). Methods: Fifteen cadaveric specimens were tested using a dynamic shoulder simulator. Following testing in the native state, shoulders underwent SCR in 2 of 5 possible fixation angles; 0 degrees, 15 degrees, 30 degrees, 45 degrees, or 60 degrees of glenohumeral abduction, allowing for 6 specimens per group. Angles were measured radio-graphically with the glenoid fixed perpendicular to the floor. Maximum mean deltoid abduction force was compared among 5 separate conditions within each angle group: (1) native shoulder, (2) complete supraspinatus (SSP) and superior capsule tear, (3) SCR alone, (4) SCR with posterior margin sutured, and (5) SCR with anterior and posterior margins sutured. Results: SSP tears significantly increased the maximum deltoid forces for all 5 fixation angles compared with the native state (P < .05). Specimens repaired at 0 degrees, 30 degrees, and 45 degrees were unable to restore deltoid forces compared with the native state in any condition (P < .05). SCR at 15 degrees with anterior and posterior margin convergence showed similar abduction forces compared with the native state (P = .19). When fixed at 60 degrees abduction, SCR alone significantly reduced deltoid forces compared to SSP (Delta 143N, P < .001) and native (Delta 48N, P < .001). No significant differences were found between the 3 repair subtypes (SCR +/- anterior/posterior margin repair) in the 60 degrees group. Conclusions: SCR with anterior and posterior margin convergence tensioned at 15 degrees of glenohumeral abduction showed similar deltoid abduction force requirements compared with the native state, whereas graft fixation in 60 degrees significantly reduced deltoid force in all SCR conditions. Clinical Relevance: Increased graft tension with a greater abduction angle may provide greater functional outcome by placing less load on the deltoid. In contrast, graft fixation in lower abduction angles may require additional margin convergence to reproduce native forces.