Dynamic contributions to superior shoulder stability.
Level 5 - mechanism / opinion, no new human data
Cadaveric biomechanical bench study without living human participants.
PubMed 11347692 · doi:10.1016/S0736-0266(00)00028-0
What was done
Ten fresh-frozen human cadaver shoulders were tested in a shoulder-loading device at 0°, 30°, 60°, and 90° of glenohumeral abduction under a constant 20 N superior force applied to the humerus. Tendons of the rotator cuff (supraspinatus, infraspinatus, subscapularis), teres major, latissimus, pectoralis major, deltoid, and biceps were loaded sequentially in proportion to cross-sectional area, and humeral head translations relative to the glenoid were tracked using a 3Space Fastrak system.
What was found
Humeral head depression was greatest for the latissimus (5.6 ± 2.2 mm) and teres major (5.1 ± 2.0 mm). Subscapularis (4.7 ± 1.9 mm) and infraspinatus (4.6 ± 2.0 mm) provided similar degrees of depression, while the supraspinatus was less effective (2.0 ± 1.4 mm).
Why it matters
The findings suggest that infraspinatus, subscapularis, and large adductors provide the primary muscular depression to counterbalance superior deltoid pull, whereas supraspinatus plays a smaller role in direct superior stability.
Limits
The study is limited by a small sample size (n = 10 cadavers) and an in vitro setup with sequential static tendon loading, which does not reproduce dynamic, coordinated in vivo muscle activation patterns.