How Common Are Shoulder Problems?
According to the American Academy of Orthopaedic Surgeons, about 4 million people in the U.S. seek medical care each year for shoulder sprain, strain, dislocation, or other problems. Each year, shoulder problems account for about 1.5 million visits to orthopaedic surgeonsdoctors who treat disorders of the bones, muscles, and related structures.
What Are the Structures of the Shoulder and How Does the Shoulder Function?
The shoulder joint is composed of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone) (see diagram). Two joints facilitate shoulder movement. The acromioclavicular (AC) joint is located between the acromion (part of the scapula that forms the highest point of the shoulder) and the clavicle. The glenohumeral joint, commonly called the shoulder joint, is a ball-and-socket type joint that helps move the shoulder forward and backward and allows the arm to rotate in a circular fashion or hinge out and up away from the body. (The ball is the top, rounded portion of the upper arm bone or humerus; the socket, or glenoid, is a dish-shaped part of the outer edge of the scapula into which the ball fits.) The capsule is a soft tissue envelope that encircles the glenohumeral joint. It is lined by a thin, smooth synovial membrane.
The bones of the shoulder are held in place by muscles, tendons, and ligaments. Tendons are tough cords of tissue that attach the shoulder muscles to bone and assist the muscles in moving the shoulder. Ligaments attach shoulder bones to each other, providing stability. For example, the front of the joint capsule is anchored by three glenohumeral ligaments. Structures of the Shoulder
The rotator cuff is a structure composed of tendons that, with associated muscles, holds the ball at the top of the humerus in the glenoid socket and provides mobility and strength to the shoulder joint. Two filmy sac-like structures called bursae permit smooth gliding between bone, muscle, and tendon. They cushion and protect the rotator cuff from the bony arch of the acromion.
What Are the Origin and Causes of Shoulder Problems?
The shoulder is the most movable joint in the body. However, it is an unstable joint because of the range of motion allowed. It is easily subject to injury because the ball of the upper arm is larger than the shoulder socket that holds it. To remain stable, the shoulder must be anchored by its muscles, tendons, and ligaments. Some shoulder problems arise from the disruption of these soft tissues as a result of injury or from overuse or underuse of the shoulder. Other problems arise from a degenerative process in which tissues break down and no longer function well.
Shoulder pain may be localized or may be referred to areas around the shoulder or down the arm. Disease within the body (such as gallbladder, liver, or heart disease, or disease of the cervical spine of the neck) also may generate pain that travels along nerves to the shoulder.