Shoulder Injuries

The shoulder joint is exposed to as broad a range of forces as is any other joint in the body. Every sport requires the full function of the shoulder, whether to throw an object, strike an opponent or a target, the propulsion of the athlete, or to provide balance in movement. No matter how extensively an athlete works to protect and to strengthen the shoulder and its supporting structure, the joint is constantly exposed to a variety of sports injury.

The shoulder joint is both powerful, flexible, and fragile, as there is less bone-on-bone contact within the shoulder joint than other joints of the body, such as the hinges created at the knee or the ankle. Less bone means a correspondingly greater reliance on the muscle and the connective tissue to support the stresses of joint movement, and a greater risk of soft tissue injury. The skeletal components of the shoulder are the humerus, the long bone of the upper arm, the scapula (shoulder blade), and the clavicle (collarbone). In a technical sense, the sternum (breastbone) is also a shoulder bone as it supports the end of the clavicle that is opposite to the shoulder. Each of these bones is covered at the end with articular cartilage, with reduces the friction that otherwise results from movements where bones make contact against one another within the joint.

The shoulder is commonly referenced as if it were a single entity; the shoulder structure is in fact four distinct joints, each an integrated unit that functions within the shoulder. The four joints include the glenohumoral joint, which is the largest of the shoulder joints and is the most exposed to injury; it is the "ball and socket" created between the head of the humerus and the portion of the scapula known as the glenoid; the acromioclavicular (AC) joint, formed between the meeting of the clavicle and the portion of the scapula called the acromion; the sternoclavicular joint, created where the opposite end of the clavicle is secured to the sternum, providing the shoulder with stability; and the scapulothoracic articulation, a structure that is often classified as a joint, when it is more accurately described as a muscle and tendon configuration that permits the scapula to slide along the back as the shoulder is raised and lowered.

Each of the individual shoulder joints has its own supporting network of ligaments. The entire shoulder is encased in various muscles and tendon groups to power the variety of movements of which the shoulder is capable. One of the most important of the connective tissues is the rotator cuff, an assembly of four muscles and tendons positioned on top of the shoulder, under a portion of the scapula, that serves to both permit the arm to be raised and used in a powerful fashion, as well as hold the shoulder joint in place. The joint capsule that surrounds the glenohumoral (ball and socket) joint is also commonly examined in cases of shoulder injury. A further soft tissue component of the shoulder structure is the bursa, located between the glenohumoral joint and the rotator cuff. The bursa is a gel-filled fibrous cushioning device that absorbs some of the forces directed into the shoulder.

Shoulder injuries are most often caused by one of three general mechanisms. The first is overhead motion, during which the hand and forearm are extended through shoulder movement to a point furthest away from the body, the point where the shoulder is at its most vulnerable to overload. The second cause is that of repetitive movement, which places a strain on the shoulder structure. The repetitive strain injuries may be in the form of tendonitis, bursitis, rotator cuff injury, or over the longer term, osteoarthritis. The third class of injury is that caused by a blow absorbed by the joint, caused through a fall or by trauma. These injuries may take the form of a fracture to one or more of the bones of the shoulder, or soft tissue damage such as a joint dislocation.

Rotator cuff injuries are very common in sports. Baseball pitchers may have the highest incidence of occurrence, but all sports where the shoulder and arm are moved forcefully and repetitively create an environment for an entire range of shoulder cuff problems. American football quarterbacks, swimmers, golfers, and volleyball players commonly experience these injuries.

A rotator cuff injury will most often be the result of a wearing against the surface of the rotator cuff structure, creating a tear to the rotator cuff tendon. The same repetitive movement can create a pinching between the cuff and the overlying scapula bone of the shoulder joint. The injury may reveal itself as either a sudden onset of significant pain and reduced shoulder movement, or a more gradual decline in apparent joint function. The inability of a pitcher to throw as hard as previously, or a loss of power in a volleyball player's spike are the type of diminution caused by a damaged rotator cuff.

A rotator cuff injury may also present as an impingement of the shoulder motion. In such cases, often in repetitive movements such as throwing, swimming, or the motion to deliver a tennis serve, the acromion region of the scapula repeatedly rubs against the surface of the rotator cuff. Impingements, while a less serious form of rotator cuff injury than a tear of one of the four soft tissue components, represent a significant problem for an athlete because impingements are a present limitation in the athlete's range of motion in the joint, and also tend to become progressively worse.

Rotator cuff injuries are revealed through the use of x rays (often by way of an arthrogram, the injection of a dye into the joint for a better x-ray image), or through magnetic resonance imaging (MRI). Physio therapy, with a particular emphasis on the preventa-tive strengthening of the surrounding shoulder muscle structures, is the preferred remedy in over 90% of rotator cuff injuries. Stretching and flexibility exercises are essential to maintain an optimal range of motion in the recovering joint. Nonsteroidal anti-inflammatory drugs (NSAIDs) have also been proven as effective in the management of shoulder pain arising from both the rotator cuff injury as well as the discomfort experienced in rehabilitation. In more extreme cases, especially where there has been a degree of tearing to the rotator cuff, corticosteroid injections are used to manage the inflammation. Rotator cuff surgery is decidedly a last resort, as it is invasive and depending on the extent of the rotator cuff tear, surgery is successful in only 80% of all cases.

A separated shoulder is a common injury that results from physical contact to the shoulder region. The injury is actually sustained to the AC joint on the top of the shoulder, where the force of a blow, often a fall on the shoulder, causes a tearing of the ligaments that joint the clavicle and the scapula. The injury is immediately noticeable to an athlete, as there is significant pain and a bump forms at the site of the injury. The degree by which the bones are separated at the AC junction dictates the severity of the injury. Most separated shoulders heal with rest, the frequent application of ice in the first 48-78 hours after the event, and the use of a sling to permit the arm to be rested.

A dislocated shoulder is the coming apart of any of the joints of the shoulder, but is most common in the ball and socket joint. In contact sports such as American football, rugby, or ice hockey, the shoulder, as the body's most mobile joint, can be struck from almost any angle with great force. In competitions such as downhill skiing and gymnastics, an athlete can fall awkwardly with significant force and dislocate the joint. The force of dislocation may cause the humerus bone to become detached from the joint capsule in which it is held; the surrounding ligaments or tendons may also be torn on impact. The rehabilitation for such injuries is similar to that of the separated shoulder, with a likelihood that the progress will be slower as the injury is usually more serious.

A fractured clavicle (collarbone) is the most common type of fracture to any of the bones of the shoulder joints. Usually the result of a hard fall, a fracture will result in the immediate impairment of the athlete's ability to use the arm. There is most often a noticeable sharp lump under the skin in the immediate vicinity of the break. Subject to related damage such as a ruptured blood vessel or nerve damage, the clavicle will heal cleanly within six to eight weeks of the injury.

In cases where the shoulder has been subjected to the progressive wearing away of the articular cartilage of the shoulder bones, the resulting osteoarthritis may require joint replacement surgery. This procedure is most common as a result of osteoarthritis in the glenohumoral joint. An artificial socket is the remedy, permitting the humerus bone to move against a synthetic surface.

see also Baseball injuries; Musculoskeletal injuries; Shoulder anatomy and physiology; Tendinitis and ruptured tendons.