Topic updated: December 2012

Shoulder Injuries / Disorders

What Are the Most Common Shoulder Problems?

The most movable joint in the body, the shoulder is also one of the most potentially unstable joints. As a result, it is the site of many common problems. They include sprains, strains, dislocations, separations, tendinitis, bursitis, torn rotator cuffs, frozen shoulder, fractures, and arthritis.

How Common Are Shoulder Problems?

According to the Centers for Disease Control and Prevention, nearly 1.5 million people in the United States visited an emergency room in 2006 for shoulder problems.

What Are the Structures of the Shoulder and How Does It Function?

To better understand shoulder problems and how they occur, it helps to begin with an explanation of the shoulder’s structure and how it functions.

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 (ah-KRO-me-o-klah-VIK-u-lahr; AC) joint is located between the acromion (ah-KRO-me-on; 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,” or humerus, is the top, rounded portion of the upper arm bone; 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.

In contrast to the hip joint, which more closely approximates a true ball and socket joint, the shoulder joint can be compared to a golf ball and tee, in which the ball can easily slip off the flat tee. Because the bones provide little inherent stability to the shoulder joint, it is highly dependent on surrounding soft tissues such as capsule ligaments and the muscles surrounding the rotator cuff to hold the ball in place. Whereas the hip joint is inherently quite stable because of the encircling bony anatomy, it also is relatively immobile. The shoulder, on the other hand, is relatively unstable but highly mobile, allowing an individual to place the hand in numerous positions. It is in fact, one of the most mobilejoints in the human body.

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. The rotator cuff is a structure composed of tendons that work along with associated muscles to hold the ball at the top of the humerus in the glenoid socket and provide mobility and strength to the shoulder joint. Two filmy sac-like structures called bursae permit smooth gliding between bones, muscles, and tendons. They cushion and protect the rotator cuff from the bony arch of the acromion.

What Are the Origins and Causes of Shoulder Problems?

The shoulder is easily injured 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.

Although the shoulder is easily injured during sporting activities and manual labor, the primary source of shoulder problems appears to be the natural age-related degeneration of the surrounding soft tissues such as those found in the rotator cuff. The incidence of rotator cuff problems rises dramatically as a function of age and is generally seen among individuals who are more than 60 years old. Often, the dominant and nondominant arm will be affected to a similar degree. Overuse of the shoulder can lead to more rapid age-related deterioration.

Shoulder pain may be localized or may be felt in 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. However, these other causes of shoulder pain are beyond the scope of this book, which will focus on problems within the shoulder itself.

How Are Shoulder Problems Diagnosed?

As with any medical issue, a shoulder problem is generally diagnosed using a three-part process:

  • medical history - The patient tells the doctor about any injury or other condition that might be causing the pain.
  • physical examination - The doctor examines the patient to feel for injury and to discover the limits of movement, location of pain, and extent of joint instability.
  • tests - The doctor may order one or more of the tests listed below to make a specific diagnosis. These tests may include the following:
    • Standard x ray - a familiar procedure in which low-level radiation is passed through the body to produce a picture called a radiograph. An x ray is useful for diagnosing fractures or other problems of the bones. Soft tissues, such as muscles and tendons, do not show up on x rays.
    • Arthrogram - a diagnostic record that can be seen on an x ray after injection of a contrast fluid into the shoulder joint to outline structures such as the rotator cuff. In disease or injury, this contrast fluid may either leak into an area where it does not belong, indicating a tear or opening, or be blocked from entering an area where there normally is an opening.
    • Ultrasound - a noninvasive, patient-friendly procedure in which a small, hand-held scanner is placed on the skin of the shoulder. Just as ultrasound waves can be used to visualize the fetus during pregnancy, they can also be reflected off the rotator cuff and other structures to form a high-quality image of them. The accuracy of ultrasound for the rotator cuff is particularly high.
    • MRI (magnetic resonance imaging) - a noninvasive procedure in which a machine with a strong magnet passes a force through the body to produce a series of cross-sectional images of the shoulder. Other diagnostic tests, such as one that involves injecting an anesthetic into and around the shoulder joint, are discussed in detail in other parts of this booklet.

Read the rest of this excellent article on shoulder problems, including diagnosing and treating specific problems, produced by the National Institute of Arthritis and Musculoskeletal and Skin Diseases.

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