Shoulder Injuries in the Throwing Athlete

Overview

Overuse injuries from repetitive overhead throwing can place extreme stress on shoulder stability. Although most commonly occurring in baseball pitchers, repetitive overhead motions in other sports such as volleyball, tennis, and some track and field events are also prone to shoulder injuries. 

Your shoulder is a ball-and-socket joint comprised of three bones: humerus, scapula, and clavicle. It consists of ligaments, tendons, and strong connective tissue to keep your shoulder stable. Muscles that form your rotator cuff further stabilize your shoulder joint. Muscles in your upper back also play an important role in keeping your shoulder joint stable. For throwing athletes, the rotator cuff and labrum are most susceptible to throwing injuries. 

When athletes throw at high speed, repeatedly, significant stress is placed to keep the humeral head centered in the glenoid socket. With baseball pitchers, there are fives phases of pitching motion: wind-up, early cocking, late cocking, acceleration, and follow-through. Of the five phases, the late cocking and follow-through phases place the greatest strain on the shoulder. 

The late-cocking phase generate maximum pitch speed by bringing the arm and hand up and behind the body. This extreme external rotation of the arm helps the thrower put speed on the ball while forcing the head of the humerus forward, causing significant stress on the anterior ligaments of the shoulder. This promotes a loosening, which results in greater rotation and speed, but less shoulder stability. The follow-through phase occurs during acceleration when the arm rapidly rotates internally. When the pitcher releases the ball, follow-through begins, causing significant stress on the ligaments and rotator cuff tendons at the back of the shoulder. 

As the pitcher’s ligament system becomes weakened due to repetitive stress, body structures try to compensate to handle the overload. In the throwing athlete, this results in a wide range of shoulder injuries including: 

• SLAP Tears (Superior Labrum Anterior to Posterior) – causes injury to the top or superior part of the labrum. This top area is where the long head of the biceps tendon attaches to the labrum. A SLAP tear occurs both in front and in back of this attachment point. Symptoms include a catching or locking sensation with pain in certain shoulder movements.
• Bicep Tendinitis and Tendon Tears – can be caused with repetitive throwing. The upper biceps tendon can become inflamed and irritated causing biceps tendinitis and pain in the front of the shoulder. Occasionally, a tendon tear can occur due to the tendonitis causing a sudden, sharp pain in the upper arm. When it tears, some patients hear a popping or snapping noise.
• Rotator Cuff Tendinitis and Tears – occurs when a muscle or tendon is overworked. Throwing athletes irritate their rotator cuff resulting in tendinitis with pain that radiates from the front of the shoulder to the side of the arm. This pain may be present during throwing activities and even while at rest. Without medical attention, the problem progresses, and pain may occur at night. Rotator cuff tears often start by fraying. As the damage continues and is left untreated, the tendon tears. When one or more of the rotator cuff tendons are torn, the tendon is no longer fully attached to the head of the humerus. As problems with the rotator cuff persist, shoulder bursitis may develop causing further inflammation and pain.
• Internal Impingement – happens during the cocking phase of an overhead throw. The tendons of the rotator cuff at the back of the shoulder get pinched between the humeral head and the glenoid. It may result in a partial tearing of the rotator cuff tendon. Internal impingement may also damage the labrum.
• Instability – occurs when the head of the humerus slips out of the shoulder socket. When this occurs repeatedly, it is called chronic shoulder instability. In throwers, instability develops as the ligaments are stretched and creates increased laxity or looseness. When the rotator cuff is weakened and is unable to control the laxity, the shoulder will subluxate during the motion of throwing. The thrower may feel the arm “go dead.” That is why shoulder instability was referred to as dead arm syndrome in the past.
• Glenohumeral Internal Rotation Deficit (GIRD) – occurs when the ligaments at the front of the shoulder stretch and loosen, the soft tissues in the back of the shoulder tighten, resulting in a loss of internal rotation. This puts throwers at higher risk for labral and rotator cuff tears.

Scapular Rotation Dysfunction (SICK Scapula) – is characterized by drooping of the affected shoulder in throwing athletes. Pain is felt at the front of the shoulder near the collarbone. This drooping is caused by a change in the muscles that affect the position of the scapula, thereby increasing risk of shoulder injury.