Deltoid Muscle Volume After Superior Capsule Reconstruction in Patients With Irreparable Rotator Cuff Tears: A 3-Dimensional Magnetic Resonance Imaging Analysis

Background: Shoulder function improvement after superior capsule reconstruction (SCR) for irreparable rotator cuff tears is thought to be due primarily to increased efficiency of the remaining shoulder muscles and to restoration of glenohumeral superior stability. However, the role of the deltoid muscle after SCR remains unclear. Purpose: To investigate deltoid muscle volume change after SCR and its association with clinical outcomes. Study Design: Case series; Level of evidence: 4 Methods: A total of 29 patients who underwent arthroscopic SCR using a fascia lata autograft were included. All received the same postoperative physical therapy. Active shoulder abduction and external rotation and American Shoulder and Elbow Surgeons (ASES) and Japanese Orthopaedic Association (JOA) scores were assessed preoperatively and 2 years postoperatively. Additionally, the acromiohumeral distance (AHD), rotator cuff tear size, and Goutallier/Fuchs and Hamada classifications were evaluated. Preoperative and postoperative deltoid muscle volumes were measured using a 3-dimensional reconstructed model from magnetic resonance imaging scans. Results: Across the whole group, active elevation, active external rotation, ASES score, and JOA score were significantly increased 2 years after SCR ( P < .001). The change in deltoid muscle volume after SCR was significantly positively correlated with the change in active elevation ( P = .004; r = 0.52), ASES score ( P = .03; r = 0.42), and JOA score ( P = .005; r = 0.51). Deltoid muscle volume was increased after SCR in 18 patients and decreased in 11. Patients in the increased volume group were significantly younger than those in the decreased volume group at the time of surgery ( P = .04). Two years after surgery, the increased volume group had a significantly greater AHD than the decreased volume group ( P = .04), although before SCR there was no significant between-group difference in AHD. Conclusion: The change in deltoid muscle volume was significantly positively correlated with the changes in active elevation, ASES score, and JOA score after SCR. This suggests that deltoid muscle strengthening should be recommended to improve shoulder function after SCR. An increase in AHD, which represents the restoration of glenohumeral superior stability, after SCR may be necessary to improve deltoid function.