Role of middle glenohumeral ligament in external shoulder rotation

Abstract

The middle glenohumeral ligament (MGHL) is one of the three ligaments that stabilize the anterior capsule of the shoulder. Recent work suggests that it inserts distally into the deep layer of the subscapularis tendon. The role of the MGHL remains debated. The hypothesis of this study was that the MGHL plays a significant functional role in limiting external rotation of the shoulder while allowing a wide range of motion through its distal insertion into the subscapularis rather than directly onto the humerus. In a cadaveric study performed on 20 shoulders (10 subjects), the MGHL and the other anterior structures of the shoulder were successively cut according to a standardized protocol. At each stage, the external rotation range of the shoulder was measured with the arm at the side (ER 1) and in 90° abduction (ER 2) using a goniometer. After dissection, the structure of the MGHL and its distal insertion were analyzed. Cutting the MGHL led to significant increases in ER 1 but not in ER 2. Shoulder range of motion in ER 1 increased on average by 15±5° (P<.001) after cutting the MGHL and by 21±11° (P<.001) after subscapularis peel. The range of motion in ER 2 increased by 3±4° (P=.048) after cutting the MGHL, by 4±6° (P=.02) after subscapularis peel and by 25±8° (P<.001) after cutting the inferior glenohumeral ligament. The MGHL was present in all dissected shoulders. It was leaf-like in 12 cases, cord-like in 6 cases and had a vestigial appearance in 2 cases. The distal insertion was in all cases in the deep layer of the subscapularis in a thickening of the anterior capsule in the superior part of the muscle, except for two cases in which the tendinous part of the subscapularis was also involved. The MGHL limited shoulder external rotation by a similar amount as the subscapularis muscle. Further studies are required to understand the clinical relevance of these findings, notably for the treatment of shoulder stiffness.