The Shoulder Joint
The glenohumeral joint, or as it is more commonly referred to the shoulder joint , is one of the most flexible and unstable joints in the body. As a ball and socket joint the shoulder allows circular motion and hinge movement. The rounded head or ‘ball’ of the humerus rests in the shallow dish shaped cavity or ‘socket’ created by the glenoid fossa of the scapula. This allows for a wide range of motion around several axes. There are two main bones that make up the shoulder joint, the humerus and the scapula. The ball of the humerus is stabilized and cushioned by cartilage around the glenoid fossa socket. Ligaments connect the bones together and tendons then connect those bones to surrounding muscles. For example, the bicep tendon attaches to the biceps muscle to the shoulder to stabilize the joint and the muscles and tendons in the rotator cuff also play an important role in supporting the shoulder joint. The shoulder joint is held in place by the rotator cuff muscles. These four muscles are: supraspinatus, infraspinatus, teres major, and subscapularis. All four are share the same insertion point on the greater tubercle of the humerus. Injury to any of these four muscles results in severe damage, restricted movement, and pain to all the others. Pitchers in baseball, swimmers, tennis players, and boxers commonly tear their rotator cuff muscles from overuse. Even with proper treatment athletes may still find it hard to abduct and laterally/medially rotate about the shoulder. Movement at the shoulder also moves the scapula and the rotator cuff musles that surround it, namely the supraspinatus, infraspinatus, teres minor and subscapularis muscles. Larger surrounding muscles like the trapezius, deltoid, serratus anterior, pectoralis major, rhomboid, and terses major also play a large role when performing any movement witht eh shoulder. The scapula is suspended in muslce and moves against the body wall when movement occurs.
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