Three decades ago, Mechanics of Shoulder Stability emphasized that the function of the glenohumeral joints is dependent on unique stabilizing mechanisms. The illustrations below were provided by Steve Lippitt in Practical Evaluation and Management of Shoulder.
While the hip is supported by a deep socket to stabilize it, the glenohumeral joints have a shallow socket that allows for greater motion without the ball hitting the socket’s edge.
As pointed out in In vivo quantification of the laxity of normal and unstable glenohumeral joints laxity is not the same as instability; healthy subjects without symptoms may have as much laxity as patients needing surgical repair for symptomatic shoulder instability.
Therefore, we must ask how the large humeral heads can be supported in the tiny glenoid socket, while still allowing for greater motion than other joints and incredible feats of strength, as demonstrated in these classic videos from our late partner Douglas Harryman (see Shoulder Stability 1 & Shoulder Stability 2).
One of the most unique mechanisms of glenohumeral…