MUSCULOSKELETAL DISORDERS

Musculoskeletal disorders are among the most common of human afflictions. They affect all age groups and frequently cause disability, impairments, and handicaps. They consist of a variety of different diseases that cause pain or discomfort in the bones, joints, muscles, or surrounding structures, and they can be acute or chronic, focal, or diffuse. Approximately 33 percent of U.S. adults are affected by musculoskeletal signs or symptoms, including limitation of motion or pain in a joint or extremity. In one study of Detroit residents who kept track of daily health symptoms in a diary, musculoskeletal symptoms constituted the most frequent category of health symptoms. The prevalence of musculoskeletal disorders generally increases with age, with the majority of persons aged seventy-five and over having some form of musculoskeletal disorder, especially arthritis.

Not only are musculoskeletal disorders highly prevalent, but, because of their association with aging, they are likely to become more prevalent as the population ages throughout the world. All racial groups are affected. While many of these disorders are not devastatingly disabling to affected individuals, their prevalence is so great that more mobility and other limitations are accountable to these disorders than to any other type. While much of the substantial cost of these disorders is due to the medical care and medications and other treatments required by patients, the preponderance of costs is due to work loss, which is a frequent consequence of these disorders.

Contained within the broad category of musculoskeletal disorders are a number of specific diseases and causes of pain, several of which affect a large percentage of the population. Musculoskeletal disorders range from back pain to rheumatoid arthritis and gout, and include different types of arthritis, tendinitis, and musculoskeletal pain. The most common musculoskeletal disorders are listed in Table 1, along with their point prevalence among adults in Western populations. The most prevalent disorders are low back pain, osteoarthritis, and so-called soft tissue rheumatism. Even though they afflict millions of persons around the world, several of the common musculoskeletal disorders fall into the category of moderately prevalent, including gout, a form of episodic arthritis; fibromyalgia, a disorder of diffuse muscular pain and a subtype of soft tissue rheumatism; and rheumatoid arthritis, an inflammatory systemic disorder that causes widespread joint pain.

LOW BACK PAIN

Low back pain, one of the most frequent of musculoskeletal disorders, affects up to 80 percent of people sometime in their lives, and in any given month 20 to 30 percent of adults have an episode. Generally, the pain is in the lower back on one or both sides, occasionally extending into the buttocks or thighs. In most persons the cause of back pain is unknown. It may arise from any number of pain-sensitive structures in the lumbar spinal column, including joints, ligaments, muscles, and soft tissues.

Generally, back pain is episodic, with half of the episodes remitting within a week and 90 percent going away within a month. Back pain of long duration, which occurs in only a small minority of patients, accounts for most of the societal cost of low back pain and much of the work loss and disability. Persons at high risk of low back pain include those between age twenty and forty, and those whose jobs involve physical labor—especially lifting, pushing, or pulling heavy objects, or twisting during lifting. Truck drivers are the occupational group who experience the most back pain. Another risk factor for low back pain is cigarette smoking, and poor physical fitness may also contribute to its occurrence. The high rate of back pain in particular occupations has suggested

Table 1

that altering work tasks may be a successful way to prevent episodes of back pain. Indeed, industry training programs have achieved success in lessening the rate of low back pain in some occupations.

OSTEOARTHRITIS

Osteoarthritis is the most common form of arthritis and, depending on how it is defined, affects 10 to 20 percent of all adults and a much larger percentage of the elderly.

SOFT TISSUE RHEUMATISM

Among the most common of musculoskeletal disorders are those which cause pain in muscular or tendinous areas of the extremities but not in joints. These are collectively termed "soft tissue disorders" and include a variety of localized forms of tendinitis and bursitis, as well as other more generalized pain disorders. These disorders are common causes of pain in the shoulder, elbow, hip, neck, and foot.

Muscles are attached to the bones they move by string-like structures called tendons. While soft tissue pain can often be localized to particular muscles and their attached tendons, the cause of this pain is poorly understood. For tendinitis, the cause may be related to muscle and tendon over-use. For shoulder and neck pain, overuse may be coupled with an acute or chronic injury. These disorders are often self-limited and respond to anti-inflammatory medications, but they often recur. Seven percent of the U.S. population has had an episode of shoulder pain lasting at least a month. Ten percent of the population reports neck pain of this duration. The prevalence of most of these disorders increases with age, and they are more prevalent in women than men.

Fibromyalgia is a generalized chronic disorder of diffuse muscular pain that constitutes a subtype of soft tissue rheumatism. Fibromyalgia affects up to 2 percent of women of all ages (it is much less prevalent in men) and is associated with a sleep disorder; with diffuse aching in the neck, back and extremities; and with fatigue and depressive symptoms (either as a trigger of the disorder or as a consequence of it). Treatment includes analgesic and sleep medications.

David T. Felson

(see also: Osteoarthritis; Rheumatoid Arthritis )

Bibliography

Felson, D. T. (2000). "Epidemiology of the Rheumatic Diseases." In Arthritis & Allied Conditions, ed. W. Koopman. Philadephia, PA: Lippincott, Williams & Collens.