Repetitive Motion Disorders Health Article

Definition

Repetitive motion disorders are a group of syndromes caused by injuries to muscles, tendons, nerves, or blood vessels from repeated or sustained exertions of different body parts. Most of these disorders involve the hands, arms, or neck and shoulder area. Other names for repetitive motion disorders include repetitive trauma disorders, repetitive strain injuries (RSIs), overuse syndrome, work-related disorders, and regional musculoskeletal disorders.

Description

Repetitive motion disorders are characterized by pain, loss of strength and coordination, numbness or tingling, and sometimes redness or swelling in the affected area. The symptoms come on gradually, and are usually relieved temporarily by resting or avoiding the use of the affected body part. Repetitive motion disorders are commonly thought of as work related, but they can occur as a result of academic, leisure-time, or household activities as well.

Demographics

The demographics of repetitive motion disorders vary according to the specific syndrome. As of 2004, about 50% of all industrial injuries in the United States and Canada are attributed to overuse disorders. Professional athletes, dancers, and musicians experience one of these disorders at a much higher percentage at some point in their careers. The Institute of Medicine's 2001 study, Musculoskeletal Disorders and the Workplace, reported that nearly a million American workers were treated in 1999 for work-related pain or impaired function in the arms, hands, or back. Other experts estimate that overuse injuries cost the United States economy between $27 million and $45 million every year.

Race is not known to be a factor in repetitive motion disorders. Gender has a significant effect on the demographics of some disorders, but it is not clear whether the higher incidence of some disorders in women reflects different occupational choices for men and women, or whether it reflects biological differences. For example, de Quervain's syndrome is a common overuse disorder in women involved with childcare, because repeated lifting and carrying of small children places severe strains on the wrist joint. On the other hand, some researchers think that the greater frequency of this disorder in women is related to the effects of female sex hormones on connective tissue, as women's ligaments are slightly looser during pregnancy and at certain points in the menstrual cycle.

Some repetitive motion disorders appear to be age related. Carpal tunnel syndrome is more common in middle-aged than in younger women, and trigger finger is most common in people aged 55–60. It is not yet known whether the widespread use of computers in the workplace will change the age distribution of repetitive motion disorders as present workers grow older.

Causes and symptoms

SOFT TISSUE DAMAGE Repetitive motion disorders are the end result of a combination of factors. One basic cause of repetitive motion disorders, however, is microtraumas, which are tiny damages to or tears in soft tissue that occur from routine stresses on the body or repeated use of specific muscles and joints. When microtraumas are not healed during sleep or daily rest periods, they accumulate over time, causing tissue damage, inflammation, and the activation of pain receptors in peripheral nerves.

NERVE COMPRESSION Some repetitive motion disorders are associated with entrapment neuropathies, which are functional disorders of the peripheral nervous system. In an entrapment neuropathy, a nerve is damaged by compression as it passes through a bony or fibrous tunnel. Carpal tunnel syndrome, de Quervain's syndrome, ulnar nerve syndrome, and thoracic outlet syndrome are examples of entrapment neuropathies.

Compression damages peripheral nerves by limiting their blood supply. Even slight pressures on a nerve can limit the flow of blood through the smaller blood vessels surrounding the nerve. As the pressure increases, transmission of nerve impulses is affected and the patient's sensation and coordination are affected, with further increases in nerve compression producing greater distortion of sensation and range of motion.

TECHNOLOGICAL AND SOCIAL FACTORS Economic and social factors that have affected people's occupations and leisure-time activities over the past two centuries have contributed to the increase in repetitive motion disorders. The Industrial Revolution led to increased job specialization, which meant that more and more workers were employed doing one task repeatedly rather than many different tasks. In addition, industrialization brought about the invention of complex tools and machinery that affect the tissues and organs of the human body in many ways. The high levels of psychological and emotional tension in modern life also contribute to repetitive stress injuries by increasing the physical stresses on muscles and joints.

INDIVIDUAL RISK FACTORS Risk factors that are associated with repetitive stress injuries include the following:

• Awkward or incorrect body postures. Each joint in the body has a position within its range of motion in which it is least likely to become injured. This position is called the neutral position. Any deviation from the neutral position puts increased strain on body tissues. Inadequate work space, using athletic or job-related equipment that is not proportioned to one's height, or improper technique are common reasons for RSIs related to body posture.
• Use of excessive force to perform a task. Pounding on piano keys or hammering harder than is necessary to drive nails are examples of this risk factor.
• Extended periods of static work. This type of work requires muscular effort, but no movement takes place. Instead, the muscles contract, preventing blood from reaching tissues to nourish the cells and carry away waste products. Over time, the muscle tissue loses its ability to repair microtraumas. Examples of static work include sitting at a desk for hours on end or holding the arms over the head while painting a ceiling.
• Activities that require repetitive movements. Assembly-line work and word processing are examples of job-related repetitive motion. In addition, such leisure-time activities as knitting, embroidery, gardening, model construction, golf or tennis, etc. can have the same long-term effects on the body as work-related activities.
• Mechanical injury. Tools with poorly designed handles that cut into the skin or concentrate pressure on a small area of the hand often contribute to overuse disorders.
• Vibration. There are two types of vibration that can cause damage to the body. One type is segmental vibration, which occurs when the source of the vibration affects only the part of the body in direct contact with it. An example of segmental vibration is a dentist's use of a high-speed drill. Overexposure of the hands to segmental vibration can eventually damage the fingers, leading to Raynaud's phenomenon. The second type is whole-body vibration, which occurs when the vibrations are transmitted throughout the body. Long-distance truckers and jackhammer operators often develop back injuries as the result of long-term whole-body vibration.
• Temperature extremes. Cold temperatures decrease blood flow in the extremities, while high temperatures lead to dehydration and rapid fatigue. In both cases, blood circulation is either decreased or redirected, thus slowing down the process of normal tissue recovery.
• Psychological stress. People who are worried, afraid, or angry often carry their tension in their neck, back, or shoulder muscles. This tension reduces blood circulation in the affected tissues, thus interfering with tissue recovery. In addition, emotional stress has been shown to influence people's perception of physical pain; workers who are unhappy in their jobs, for example, are more likely to seek treatment for work-related disorders.
• Structural abnormalities. These abnormalities include congenital deformities in bones and muscles, changes in the shape of a bone from healed breaks or fractures, bone spurs, and tumors. Overdevelopment of certain muscle groups from athletic workouts may result in entrapment neuropathies in the shoulder area.
• Other systemic conditions or diseases. People with such disorders as rheumatoid arthritis (RA), joint infections, hypothyroidism, or diabetes are at increased risk of developing repetitive motion disorders. Pregnancy is a risk factor for overuse disorders affecting the hands because of the increased amount of fluid in the joints of the wrists and fingers.