Orientation of the Glenoid Fossa changes so that instead of facing upward, forward and outward it orients downward. This compromises the structural stability of the gleno-humeral joint. Tipping and winging of the scapula results. C. Glenohumeral joint 1. The rotator cuff usually has low tone and lacks the functional movement needed to stabilize the humeral head in the glenoid fossa.
Gravity exerts a downward pull on the head of the humerus.
The biomechanics of dynamical glenohumeral joint movement are lost. Because the arm is positioned frequently in internal rotation, adduction and a few degrees of extension, the latissimus dorsi and the pectoralis major become shortened. Superior part of the GH joint capsule is initially normally taut. Because the muscles that cause the head of the humerus to glide inferiorly in the glenoid are weak, mobility of the gleno-humeral joint into flexion and abduction is impaired. The superior portion of the joint eventually becomes stretched secondary to gravitational forces.