This cadaveric biomechanical study asked whether the infraspinatus, teres minor, and subscapularis actively help abduct the arm or only depress and compress the humeral head. Using five fresh shoulder girdles in a custom rig that simulated deltoid and cuff contraction while reproducing normal scapulohumeral rhythm, the authors measured how much deltoid force each muscle group saved. The goal was to define each cuff muscle's role and the arc of motion where it matters most.
The classic teaching splits the cuff into an abductor (supraspinatus) and depressors (infraspinatus, teres minor, subscapularis). This paper reframes that model.
All four cuff muscles add an abduction moment, and the inferior cuff contributes as much as the supraspinatus, mostly in the first 90 degrees. The mental model: the cuff both compresses the head into the glenoid and adds abduction torque, and these roles coexist.
When the supraspinatus is deficient from tendinitis or a tear, strengthening the infraspinatus and subscapularis can restore abduction efficiency and offload the deltoid. The authors offer this as the mechanical basis for why nonoperative therapy helps in impingement syndrome.
For the OITE, remember scapulohumeral rhythm is roughly 2:1 overall with glenohumeral motion alone in the first 30 degrees, and peak deltoid demand occurs at 90 degrees.
This cadaveric biomechanical study asked whether the infraspinatus, teres minor, and subscapularis actively help abduct the arm or only depress and compress the humeral head. Using five fresh shoulder girdles in a custom rig that simulated deltoid and cuff contraction while reproducing normal scapulohumeral rhythm, the authors measured how much deltoid force each muscle group saved. The goal was to define each cuff muscle's role and the arc of motion where it matters most.
The classic teaching splits the cuff into an abductor (supraspinatus) and depressors (infraspinatus, teres minor, subscapularis). This paper reframes that model.
All four cuff muscles add an abduction moment, and the inferior cuff contributes as much as the supraspinatus, mostly in the first 90 degrees. The mental model: the cuff both compresses the head into the glenoid and adds abduction torque, and these roles coexist.
When the supraspinatus is deficient from tendinitis or a tear, strengthening the infraspinatus and subscapularis can restore abduction efficiency and offload the deltoid. The authors offer this as the mechanical basis for why nonoperative therapy helps in impingement syndrome.
For the OITE, remember scapulohumeral rhythm is roughly 2:1 overall with glenohumeral motion alone in the first 30 degrees, and peak deltoid demand occurs at 90 degrees.