Shoulder pain is a common complaint among baseball players, especially pitchers, regardless of age or level of play. Pain experienced during the throwing motion results in an inability to throw with velocity, causing what is commonly referred to as "dead arm" syndrome. The cause of pain is most often injury to either the bones or the soft-tissue structures of the shoulder joint.

The 4 phases of throwing
To understand pain in the throwing shoulder, it is important to understand both the throwing mechanism and the anatomy of the shoulder joint. The act of throwing can be divided into 4 phases: (1) wind up, (2) cocking, (3) acceleration, and (4) deceleration (Fig. 1). Some add a fifth phase, follow-through.The unique anatomy of the shoulder joint allows a person to generate velocity while throwing.

The shoulder, like the hip, is a ball-and-socket joint (Fig. 2). However, unlike the hip where the ball fits tightly into the socket and is restricted, the shoulder ball (humeral head) fits loosely in the socket (glenoid) and is unrestricted, much like a golf ball on a tee. The farther one is able to bring the arm back into abduction (raised away from the side of the body) and external rotation, the faster the ball will go when released. This lack of restriction is a double-edged sword: it allows tremendous range of motion in the shoulder, making it possible to cock the arm back farther and throw with tremendous velocity. However, it also forces a reliance on relatively weak soft-tissue structures to maintain shoulder stability. These soft-tissue stabilizers feel the greatest stress during the throwing motion and are, therefore, the most frequently injured structures when this stress is applied repetitively. The shoulder's soft-tissue stabilizers can be divided into two categories: static and dynamic (Fig. 3). The static stabilizers are the ligaments of the shoulder capsule and the labrum (the cartilage ring that surrounds the socket). The labrum is an important part of the thrower's shoulder anatomy because it serves as the attachment site for the capsular ligaments at the glenoid and it also deepens the socket to provide extra stability. The dynamic stabilizers, which include the rotator cuff muscles, are the muscle groups that surround the shoulder. These muscles contract at different times during the various stages of throwing. The static and dynamic stabilizers work together in a delicate balance to stabilize the humeral head in the glenoid during the act of throwing. When the soft tissue stabilizers become too loose or too tight, the delicate balance of humeral head stability is thrown off, resulting in abnormal movement of the humeral head during throwing. This abnormal movement of the humeral head puts increased stress on the labrum and can lead to a tearing away of the labrum from the glenoid, the so-called SLAP (Superior Labrum Anterior to Posterior) lesion, which is thought to be one of the major causes of pain in the thrower's shoulder (Fig. 4).

Shoulder pain
Shoulder pain can also come from the bones that make up the shoulder joint: the humerus (upper arm) and the scapula (shoulder blade), which includes the glenoid (socket) and attaches to the clavicle (collar bone). In young players whose growth plates are still open, shoulder pain is often the result of a fracture at the growth plate at the upper end of the humerus. This fracture, which results in a slight separation of the growth plate, is referred to as Little Leaguer's shoulder (Fig. 4). The excessive forces placed on the humeral head during the throwing motion cause a separation at the growth plate, a weak point in the bone. Bone pain in the shoulders of adult throwers is much less common and is usually the result of a pathologic process within the bone, such as a tumor.

Diagnosis
Diagnosing the cause of pain in the throwing shoulder is challenging and begins with the patient's history. Was the onset of pain acute or chronic? How long has the pain been present? Which stage of the throwing motion causes pain? Where is the pain located? How long has the individual been playing baseball and at what position? Once these questions have been answered, a focused physical examination by a doctor will provide additional information. What the doctor finds during the examination suggests the type of injury that has occurred and helps to determine whether diagnostic imaging studies, such as x-rays or magnetic resonance imaging (MRI) are necessary. X-rays are obtained to look at the bony structures of the shoulder. Little Leaguer's shoulder appears on x-rays as a widening of the growth plate. If the injury involves soft tissue structures, as is most common, x-rays are often normal. In these patients, an MRI may be obtained to look more closely at the soft-tissue structures of the shoulder. Unfortunately, MRI findings are also often normal in a painful shoulder.

Treatment
Treatment of shoulder pain in throwers is multi-faceted, but the best treatment is early recognition and prevention of injury. As mentioned, pain is the earliest sign of injury, so coaches should regularly question throwers regarding the presence of shoulder pain. Other signs that should be recognized by coaches are loss of velocity, stamina, and poor throwing mechanics. Avoiding high pitch counts, especially in younger players, and avoiding excessive numbers of breaking pitches (curve balls and sliders) have also been proven to decrease the chance of injury to the young throwing shoulder.¹

The ultimate goal of treatment for shoulder pain is to return the player to the field in a safe and timely manner, with a restored ability to throw with speed and accuracy. Initial treatment consists of resting the arm, thereby avoiding the activity that causes or increases the pain. In the case of Little Leaguer's shoulder, an average of 3 months of rest with a gradual return to throwing is recommended, provided the athlete has no shoulder symptoms.² If the problem is thought to be with the soft tissue stabilizers, a physical therapy program that focuses on stretching and strengthening the ligaments and muscles of the shoulder is undertaken as the mainstay of treatment. Most shoulder problems in throwers can be treated effectively with physical therapy. Achieving and maintaining range of motion in the shoulder, especially internal and external rotation, while strengthening the muscles around the shoulder at the same time is the mark of a good physical therapy program.

Surgery
When rest and physical therapy are unsuccessful in treating shoulder pain or if an injury is discovered on MRI, surgical treatment may be needed. As many as 90% of all throwers with symptoms of tightness of the shoulder capsule respond to a physical therapy program of stretching.³ The 10% who do not respond tend to be older players who are pitching at a highly competitive level. It is unusual for compliant high school and college pitchers to be unresponsive to a stretching and strengthening program. In the small group of throwers who do not improve with nonoperative treatment, arthroscopic or open surgery may be needed, depending on the location of the shoulder problem. These procedures include labral repair (stitching the cartilage ring back to the bone of the socket), posterior capsular release (cutting into the shoulder capsule to decrease tightness of the posterior, or back, portion of the capsule), and anterior capsular plication (tightening the anterior, or front, portion of the shoulder capsule to reduce looseness).

The diagnosis and treatment of shoulder pain in baseball players can be a challenging undertaking. Early recognition of a problem is an important responsibility of coaches and parents. Once a problem is recognized, diagnosis and treatment should be sought from a physician. Beginning with the history, physical examination, and findings from imaging studies, a working diagnosis can often be made and a treatment plan determined. Rest and physical therapy are the mainstays of treatment, with surgery reserved for those who do not improve with nonoperative treatment. Surgery is directed at repairing the injury and restoring the normal shoulder anatomy.

Champ L. Baker, Jr., MD, and
Andrew W. Ayers, MD
Columbus, Georgia

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