Inside the Shoulder Joint

Shoulder Bones Overview
The humerus (upper arm) and the scapula (shoulder blade) are the two largest bones of the shoulder joint.  The head portion of the humerus bone is covered by smooth cartilage, which glides over the shoulder joint cavity.  The scapula is a large triangular bone located on the  back side of the upper body.  The shallow cavity in the scapula is the glenoid where the humerus head is inserted.

The acromion projects forward from the top of the shoulder blade to form the “roof” of the shoulder.  The clavicle (collarbone) attaches the shoulder to the rib cage and holds the shoulder out from the body.  The acromioclavicular joint connect the acromion to the collarbones.  The ends of the bones are protected by cartilage which allows for smooth movement.

Shoulder Soft Tissue Overview
Several ligaments make up the shoulder’s stabilizing joint capsule.  Other soft tissue helps the joint to flex and move with ease.  The rotator cuff muscles and tendons raise and lower the arm from the side.  The rotator cuff also helps stabilize the shoulder joint by holding the humeral head in the socket.  The biceps tendon connects the biceps muscle to the humerus.  Muscles move bones by pulling on these tendons.

The coracoacromial ligament is a bridge attaching the acromion bone end to the coracoid process.  The bursa lies between the rotator cuff muscles and the larger surrounding muscles.  The bursa contains a lubricating fluid allowing free movement of the muscles over each other.  The labrum is a ring of fibrous cartilage, surrounding the glenoid and the scapula.  It helps attach the head of the humerus to the scapula.