Shoulder Cartilage
There are two types of cartilage in the shoulder joint. The first type is the white cartilage on the ends of the bones (called articular cartilage) which allows the bones to glide and move back and forth on each other. The labrum is a second type of cartilage in the shoulder joint, and it is more fibrous or rigid than the articular cartilage. The labrum cartilage is also found only around the socket where it is attached.
 

 

 

The shoulder must be mobile enough for the wide range actions of the arms and hands, but also stable enough to allow for actions such as lifting, pushing, and pulling. The compromise between mobility and stability results in a large number of shoulder problems not faced by other joints such as the hip.

The Aromioclavicular Joint (AC Joint)
The AC joint is formed by the lateral end of the clavicle and acromion process of the scapula, and has a cartilaginous intraarticular disc. The joint provides a connection between the trunk and upper extremity through the sternoclavicular joint, clavicle, and acromioclavicular joint. The AC joint is stabilized by two separate ligamentous structures: the AC ligament and the scapuloclavicular ligament. The much stronger stabilizing system consists of the conoid and trapezoid ligaments, which run obliquely from the coracoid to the clavicle in opposing directions and are analogous to the cruciate ligaments of the knee, preventing anterior-posterior and upward displacement of the clavicle and acting as a rotational guide. The acromioclavicular capsule is relatively more lax and is reinforced by a superior AC ligament.