The shoulder joint permits a fuller range of motion than any other joint, allowing the arm to raise, lower, extend and rotate a full 360 degrees. To ensure proper range of motion, the shoulder joint is supported by the shoulder ligaments, shoulder tendons and shoulder muscles. The ligaments connect the three bones — the humerus, or upper arm bone; the scapula, or shoulder blade; and the clavicle, or collar bone — to the shoulder joint. The shoulder tendons attach to the bones at one end and to one of the related muscles at the other end. In all, there are 10 muscles and 11 shoulder tendons related to shoulder mobility, with the tendons being those that attach to the supraspinatus, the infraspinatus, the teres minor, the subscapularis, the latissimus dorsi, the pectoralis major, the pectoralis minor, the deltoid and the tricep brachii and two that attach to the bicep.
The shoulder muscles and shoulder tendons involved with shoulder mobility include the four rotator cuff muscle and tendon pairs: the supraspinatus, the infraspinatus, the teres minor and the subscapularis. These are located in the shoulder blade area, and each related tendon also attaches to the humerus. The supraspinatus muscle and tendon allow the arm to raise and lower. The infraspinatus muscle and tendon allow the arm to extend forward and sideways. The teres minor and subscapularis muscles and tendons allow the arm to rotate.
The bicep is located in the front of the upper arm, and it has two heads: the long head and the short head. The bicep has a total of two shoulder tendons. The bicep long head shoulder tendon attaches to the shoulder socket. The bicep short head shoulder tendon attaches to the coracoids process, a bump on the shoulder blade. The bicep muscle and tendons assist in bending and rotating the arm at the elbow.
The triangle-shaped latissimus dorsi is the largest back muscle and is located in the lower back. The latissimus dorsi shoulder tendon attaches to the humerus. It is responsible for drawing the arm down and back and for rotating the shoulder joint inward toward the torso.
The pectoralis major is the largest chest muscle. It lies beneath the breast tissue in women. The pectoralis major shoulder tendon attaches to the humerus at the bicipital groove, an indentation in the humerus that is also called the intertubular groove. Together, the pectoralis major muscle and shoulder tendon help lift the arm away from and back toward the torso and help rotate the arm inward toward the torso.
The pectoralis minor muscle is a collection of fibers that lie beneath the pectoralis major. The pectoralis minor shoulder tendon attaches to the shoulder blade at the coracoid process. The muscle and shoulder tendon pair serves to control upward shoulder motion to prevent overextension of the shoulders upward. It also helps the ribs expand and contract during breathing.
The deltoid muscle is the largest and strongest shoulder muscle. It lends the shoulder its rounded appearance. The deltoid shoulder tendon inserts into the deltoid prominence, or groove on the humerus. The deltoid muscle and shoulder tendon pair primarily is responsible for moving the arm from a parallel position to the torso to a perpendicular position to the torso.
The tricep brachii is located on the back of the upper arm. It has three heads, one that attaches to the shoulder blade and two that attach to the humerus. These three heads converge into one tendon that attaches to the ulna, the larger of the two forearm bones. Together, the tricep brachii and its tendon work to straighten the arm and lock the elbow when it is under pressure.