Work-related Musculoskeletal Disorders (WMSDs)

What are work-related musculoskeletal disorders (WMSDs)?

• context Work-related musculoskeletal disorders (WMSDs) are a group of painful disorders of muscles, tendons, and nerves. Examples include carpal tunnel syndrome, tendinitis, thoracic outlet syndrome, and tension neck syndrome.
• context For the purpose of developing injury prevention strategies, many health and safety agencies include only disorders that develop gradually and are caused by the overuse of the above constituents of the musculoskeletal system. The traumatic injuries of the muscles, tendons, and nerves due to accidents are generally not considered to be WMSDs. However, some organizations, such as the European Agency for Safety and Health at Work and the National Institute for Occupational Safety and Health (NIOSH), include acute traumas and fractures within the WMSD group.
• context This document will discuss injuries resulting from overuse and those that develop over time. Frequent and repetitive work activities or activities with awkward postures cause these disorders, which may be painful during work or at rest.
• context Almost all work requires the use of the arms and hands. Therefore, most WMSDs affect the hands, wrists, elbows, neck, and shoulders. Work using the legs can lead to WMSD of the legs, hips, ankles, and feet. Some back problems also result from repetitive activities.

Are there other names for WMSDs?

WMSDs are very difficult to define within traditional disease classifications. These disorders have received many names, such as: Most of the names do not accurately describe the disorders. For example, the term "repetitive strain injuries" suggests that repetition causes these disorders, but awkward postures also contribute. Sometimes, these terms are used interchangeably. For simplicity, the WMSD term is used in this document.

• context Repetitive motion injuries.
• context Repetitive strain injuries.
• context Cumulative trauma disorders.
• context Occupational cervicobrachial disorders.
• context Overuse syndrome.
• context Regional musculoskeletal disorders.
• context Soft tissue disorders.

How do WMSDs occur?

This document discusses WMSDs that develop gradually as a result of repeated trauma. WMSDs typically include three types of injuries:

• context Muscle injury.
• context Tendon injury.
• context Nerve injury.

Muscle Injury

• context When muscles contract, they use chemical energy from sugars and produce by-products, such as lactic acid, which are removed by the blood. A muscle contraction that lasts a long time reduces the blood flow. Consequently, the substances produced by the muscles are not removed fast enough, and they accumulate in the muscles. The accumulation of these substances irritates muscles and causes pain. The severity of the pain depends on the duration of the muscle contractions and the amount of time between activities for the muscles to get rid of those irritating substances.

Tendon Injury

• context Tendons consist of numerous bundles of fibres that attach muscles to bones. Tendon disorders related to repetitive or frequent work activities and awkward postures occur in two major categories – tendons with sheaths (Fig. 1), found mainly in the hand and wrist; and tendons without sheaths (Fig. 2), generally found around the shoulder, elbow, and forearm.
• context The tendons of the hand are encased in sheaths through which the tendon slides.
• context The inner walls of the sheaths contain cells that produce a slippery fluid to lubricate the tendon. With repetitive or excessive movement of the hand, the lubrication system may malfunction. It may not produce enough fluid, or it may produce a fluid with poor lubricating qualities. Failure of the lubricating system creates friction between the tendon and its sheath, causing inflammation and swelling of the tendon area. Repeated episodes of inflammation cause fibrous tissue to form. The fibrous tissue thickens the tendon sheath and hinders tendon movement. Inflammation of the tendon sheath is known as tenosynovitis.
• context When inflamed, a tendon sheath may swell up with lubricating fluid and cause a bump under the skin. This bump is referred to as a ganglion cyst.
• context Tendons without sheaths are vulnerable to repetitive motions and awkward postures. In fact, when a tendon is repeatedly tensed, some of its fibres can tear apart. The tendon becomes thickened and bumpy, causing inflammation. Tendonitis is the general term indicating inflammation of the tendon. In some cases, such as in the shoulder, tendons pass through a narrow space between bones. A sac called the bursa, filled with lubricating fluid, is inserted between the tendons and the bones as an anti-friction device. As the tendons become increasingly thickened and bumpy, the bursa is subject to a lot of friction and becomes inflamed. Inflammation of the bursa is known as bursitis.

Nerve Injury

• context Nerves carry signals from the brain to control the activities of muscles. They also carry information about temperature, pain, and touch from the body to the brain and control bodily functions such as sweating and salivation. Nerves are surrounded by muscles, tendons, and ligaments. With repetitive motions, awkward postures, and other strenuous actions, nerves can be compressed if surrounding tissues become swollen. (Fig. 3A, 3B).
• context Compression of a nerve causes muscle weakness, sensations of "pins and needles," and numbness. Dryness of skin and poor circulation to the extremities may also occur.

What are the symptoms of WMSDs?

Pain is the most common symptom associated with WMSDs. In some cases, there may be joint stiffness, muscle tightness, redness, and swelling of the affected area. Some workers may also experience sensations of "pins and needles," numbness, skin colour changes, and decreased sweating of the hands. WMSDs may progress in stages from mild to severe. Early stage: Aching and tiredness of the affected limb occur during the work shift but disappear at night and during days off work. There is no reduction in work performance. Intermediate stage: Aching and tiredness occur early in the work shift and persist at night. Reduced capacity for repetitive work. Late stage: Aching, fatigue, and weakness persist at rest. Inability to sleep and to perform light duties. Not everyone experiences these stages in the same way. In fact, it may be difficult to say exactly when one stage ends and the next begins. The first pain, numbness, or tingling are signals that the muscles and tendons should rest and recover. Otherwise, an injury can become longstanding, and sometimes irreversible. The earlier people recognize symptoms, the quicker they should respond to them. The table below outlines occupational risk factors and symptoms of the most common upper body disorders associated with WMSDs. Repetitive wrist motions Awkward hand positions Strong gripping Mechanical stress on the palm Vibration Lifting heavy loads Awkward posture Whole body vibration

• context Disorders | Occupational risk factors | Symptoms
• context Tendonitis/tenosynovitis | Repetitive wrist motions Repetitive shoulder motions Sustained hyperextension of armsProlonged load on shoulders | Pain, weakness, swelling, burning sensation or dull ache over the affected area
• context Epicondylitis (elbow tendonitis) | Repeated or forceful rotation of the forearm and bending of the wrist at the same time | The same symptoms as tendonitis
• context Carpal tunnel syndrome | Pain, numbness, tingling, burning sensations, wasting of muscles at the base of the thumb, dry palm
• context De Quervain's disease | Repetitive hand twisting and forceful gripping | Pain at the base of thumb
• context Thoracic outlet syndrome | Prolonged shoulder flexion Extending arms above shoulder height Carrying loads on the shoulder | Pain, numbness, swelling of the hands
• context Tension neck syndrome | Prolonged restricted posture | Pain
• context Lower back pain | Pain

How are WMSDs recognized?

• context The evaluation of WMSDs includes identifying workplace risks. Evaluation begins with a discussion about the worker's job activities and requires a detailed description of all the processes involved in a typical workday. Consideration is given to the frequency, intensity, and duration of each task performed at work.
• context Diagnosis of WMSDs can be confirmed by performing laboratory and electronic tests that determine nerve or muscle damage. One such test, electroneuromyography (ENMG), encompasses two areas: electromyography (EMG) and nerve conduction velocity (NCV). Magnetic resonance imaging (MRI), an alternative to X-rays, provides images of tendons, ligaments, and muscles and improves the quality of the diagnostic information.

How are WMSDs treated?

The treatment of WMSDs involves several approaches, including the following:

• context Restriction of movement.
• context Application of heat or cold.
• context Exercise.
• context Medication and surgery.

Restriction of Movement

• context The first approach to the treatment of WMSDs is to avoid the activities causing the injury. This approach often requires work restrictions. In some cases, transfer to a different job should be considered. A splint can also be used to restrict movements or to immobilize the injured joint. However, the use of splints in occupational situations requires extreme caution. If used inappropriately, splints can cause more damage than good. Splints are usually used for two reasons: to mechanically support a joint where an excessive load on the joint is anticipated or to restrict the movement of the injured joint.
• context In the occupational context, splints should not be used as a mechanical support for the joint. Instead, the job should be redesigned to avoid the extreme load on the worker's joint in the first place. To be effective, the use of splints to immobilize an affected joint also requires that the work activity that caused the injury be stopped or changed. If injurious work continues, the worker is exposed to the risk of injury to other joints that have to compensate for the splinted one.

Application of Heat or Cold

• context Applying heat or cold seems to relieve pain and may accelerate the repair process.
• context Cold reduces pain and swelling and is recommended for injuries and inflammations (tissues that are swollen, red, hot, and inflamed). However, the use of ice is not recommended in case of muscle pain (spasms) because cold temperatures will contract the muscle even more. Applying ice is only recommended immediately after an injury occurs and only for a few days.
• context Heat is recommended for muscle pain relief. It increases the flow of blood, which facilitates the elimination of lactic acid buildup. However, it is not recommended for injuries with significant inflammation and swelling.

Exercise

• context Stretching is beneficial because it promotes circulation and reduces muscle tension. However, people suffering from WMSDs should consult a physical therapist before exercising. Stretching or exercise programs can aggravate the existing condition if not properly designed.

Medication and Surgery

• context Anti-inflammatory drugs can reduce pain and inflammation. If all other approaches fail, a doctor may try more elaborate treatments or even surgery.