Scapular Disconnection

This disconnection permits scapular mobility in many directions, such as retraction, protraction, elevation, depression, anterior/posterior tilt, external/internal and upward/downward rotation. During humeral motion, the scapula provides a stable base and helps with the transfer of energy. The scapula is not the only device that supports upper extremity movement, but movement is also assisted by the acromioclavicular, sternoclavicular, and scapulothoracic joints that are within the shoulder. The acromioclavicular joint is a synovial joint located superior to the GH joint and consists of the junction between the acromion and the clavicle. The sternoclavicular joint is a synovial saddle joint between the manubrium of the sternum and the clavicle
With a large range of motion there is a dependence on active control to stabilize the scapula. The main stabilizers of the scapula are the serratus anterior, rhomboid major and minor, levator scapulae, and upper and lower trapezii. Stability of the scapulothoracic joint depends on the coordination of the surrounding musculature. Dysfunction or weakness in the scapular musculature alters mechanics and positioning of the scapula and may lead to alterations in the biomechanics of the GH joint. An unstable scapular base may affect the center of rotation of the GH joint and alter the length-tension relationship of the muscles involved in humeral movement. There is a possibility that any inefficiency in scapular stabilization could cause a decrease in neuromuscular performance and possibly predispose the individual to injury of the GH
The rotator cuff has the ability to rotate, depress, and stabilize humeral head within the GH joint. The persistent force pulls the humeral head into the glenoid fossa during arm movement in order to stabilize it into position . The infraspinatus and the subscapularis are the external rotators and humeral stabilizers. The infraspinatus is a key external rotator of the humerus and, because it is the only muscle of the rotator cuff accessible with surface EMG, offers a convenient entry point for studying the role of fatigue in rotator cuff function The infraspinatus also has a role in keeping the humeral head stabilized and separated from the glenoid within the GH joint. Consequently, a weak or damaged infraspinatus could lead to instability of the humeral head and further lead to shoulder impingement syndrome