The human shoulder is the most mobile joint in the body. This mobility provides both upper extremities with tremendous range of motion such as adduction, abduction, flexion, extension, internal rotation, external rotation, and 360° circumduction in the sagittal plane. Furthermore, the shoulder allows for scapular protraction, retraction, elevation and depression. What the shoulder gains in this wide range of motion it lacks in joint stability. This instability is compensated for by rotator cuff muscles, tendons, ligaments, and the glenoid labrum. [1]
A capsule is a membrane or sac enclosing a body part, usually a joint. The shoulder joint capsule is a fibrous sheath which encloses the structures of the joint. In the case of the shoulder joint, the capsule is one continuous structure which extends from the anatomical neck of the humerus to the border of the glenoid fossa (even though the capsule is an irregularly shaped sac, it is sometimes referred to as a ligament e.g. the capsular ligament of the shoulder or as the articular capsule of the humerus).
The shoulder joint capsule is lax permitting greater mobility (particularly abduction). [2] Although it completely covers the joint, the capsule is very loose and by itself would be unable to keep the bones of the joint in close contact without the aid of the fibers around It. The shoulder joint capsule is therefore surrounded and reinforced by muscles, tendons and ligaments which are largely responsible for keeping the articulating bones together. [3] The tendons of the rotator cuff muscles in particular fuse into one structure near their insertion onto the greater and lesser tubercles of the humerus [4] which is why the scapular/rotator cuff muscles become weakened or are also damaged in the event of an anterior capsule damage (recall that all the rotator cuff muscles originate from the scapula and terminate on the humerus – on either the greater or lesser tubercle).
Anterior shoulder dislocations are much more common than posterior dislocations. Also, Anterior instability accounts for 95% of acute traumatic dislocations. Non-operative rehabilitation is utilized in patients diagnosed with shoulder instability to regain their previous functional activities through specific strengthening exercises, dynamic stabilization drills, neuromuscular training, proprioception drills, scapular muscle strengthening program and a gradual return to their desired activities. The specific rehabilitation program should be varied based on the type and degree of shoulder instability present and desired level of function. [5]
Reference 1, Reference 2, Reference 3, Reference 4, Reference 5
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