The glenohumeral joint is the most mobile joint in the human body. The stability of the joint is provided by a combination of both static and dynamic factors. The bones, the ligaments, and the capsule represent the static stabilizers. The ligamento-capsular complex is crucial to the end range of motion when they are stretched . The rotator cuff muscles are m. supraspinatus, m. infraspinatus, m. teres minor, and m. subscapularis and are the dynamic stabilizers. They provide “contraction-compression” model of stability . The contraction both centers the head and compresses it against the glenoid fossa. They are most effective in the mid- and end-range of motion. Their action is best described as stability by balancing the force couples. Infraspinatus, teres minor, and subscapularis provide a net inferiorly directed force; deltoid muscle provides a net superiorly directed force resulting in net force balance in coronal plane. In the analogous manner, subscapularis is balancing infraspinatus and teres minor muscles in sagittal plane . The rotator cuff actively stabilizes and opposes upward motion of the humeral head during contraction of the deltoid muscle.
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