Knowlwdge Center

Glenohumeral Joint Mechanics

The classic mechanical framing: the glenohumeral joint is the most mobile joint in the body but the least intrinsically stable — a shallow socket (glenoid) holding a much larger ball (humeral head), stabilized dynamically rather than by bony geometry. Around 20% of stability comes from the labrum; the rest is muscular.

Scapulothoracic rhythm refers to the coordinated movement of the scapula and the thoracic wall during shoulder motion. It is essential for achieving a full range of motion at the shoulder and involves the activity of multiple muscles to stabilize the scapula. This rhythm is coupled with the glenohumeral rhythm, which is the movement of the humerus relative to the scapula, and together they facilitate efficient shoulder movement. The proper functioning of scapulothoracic rhythm is crucial for activities that require arm elevation and overall shoulder stability

Rotator cuff loading is the mechanical stress placed on the cuff muscles and tendons as they stabilize the shoulder during movement. When that stress is repeatedly applied—especially with frequent overhead or high‑volume use—it can exceed the shoulder’s capacity and lead to cumulative overload and pain

The subacromial space is a narrow gap in the shoulder where the rotator cuff tendons pass between the humeral head and the acromion bone above. Manual landing gear cranking progressively fatigues the rotator cuff, which allows the humeral head to migrate upward and compress those tendons in that space with every rotation — turning a normal motion into a repetitive grinding event