Musculoskeletal disorders (MSDs) are injuries or pain in the human musculoskeletal system, including the joints, ligaments, muscles, nerves, tendons, and structures that support limbs, neck and back.[1] MSDs can arise from a sudden exertion (e.g., lifting a heavy object), or they can arise from making the same motions repeatedly repetitive strain, or from repeated exposure to force, vibration, or awkward posture.[2] Injuries and pain in the musculoskeletal system caused by acute traumatic events like a car accident or fall are not considered musculoskeletal disorders.[3] MSDs can affect many different parts of the body including upper and lower back, neck, shoulders and extremities (arms, legs, feet, and hands).[4] Examples of MSDs include carpal tunnel syndrome, epicondylitis, tendinitis, back pain, tension neck syndrome, and hand-arm vibration syndrome.[2]

Biomechanical

MSDs are caused by biomechanical load which is the force that must be applied to do tasks, the duration of the force applied, and the frequency with which tasks are performed.[6] Activities involving heavy loads can result in acute injury, but most occupation-related MSDs are from motions that are repetitive, or from maintaining a static position.[7] Even activities that do not require a lot of force can result in muscle damage if the activity is repeated often enough at short intervals.[7] MSD risk factors involve doing tasks with heavy force, repetition, or maintaining a nonneutral posture.[7] Of particular concern is the combination of heavy load with repetition.[7] Although awkward posture is often blamed for lower back pain, a systematic review of the literature failed to find a consistent connection.[8]

Individual differences

People vary in their tendency to get MSDs. Gender is a factor with a higher rate in women than men.[7] Obesity is also a factor, with overweight individuals having a higher risk of some MSDs, specifically lower back.[9]

Psychosocial

There is a growing consensus that psychosocial factors are another cause of some MSDs.[10] Some theories for this causal relationship found by many researchers include increased muscle tension, increased blood and fluid pressure, reduction of growth functions, pain sensitivity reduction, pupil dilation, body remaining at heightened state of sensitivity. Although research findings are inconsistent at this stage,[11] some of the workplace stressors found to be associated with MSDs in the workplace include high job demands, low social support, and overall job strain.[10][12][13] Researchers have consistently identified causal relationships between job dissatisfaction and MSDs. For example, improving job satisfaction can reduce 17-69 per cent of work-related back disorders and improving job control can reduce 37-84 per cent of work-related wrist disorders.[14]

Occupational

Because workers maintain the same posture over long work days and often several years, even natural postures like standing can lead to MSDs like low back pain, but postures which are less natural like twisting or tension in the upper body are typically contributors to the development of MSDs because of the unnatural biomechanical load of these postures.[2][15] There is evidence that posture contributes to MSDs of the neck, shoulder, and back.[2] Repeated motion is another risk factor for MSDs of occupational origin because workers can perform the same movements repeatedly over long periods of time (e.g. typing leading to carpal tunnel syndrome), which can wear on the joints and muscles involved in the motion in question.[2] Workers doing repetitive motions at a high pace of work with little recovery time and workers with little to no control over the timing of motions (e.g. workers on assembly lines) are also prone to MSDs due to the motion of their work.[15] Force needed to perform actions on the job can also be associated with higher MSD risk in workers, because movements which require more force can fatigue muscles quicker which can lead to injury and/or pain.[2] Additionally, exposure to vibration (as in truck drivers or construction workers, for example) and extreme hot or cold temperatures can affect a worker's ability to judge force and strength, which can lead to development of MSDs.[15] Vibration exposure is also associated with hand-arm vibration syndrome, which has symptoms of lack of blood circulation to the fingers, nerve compression, tingling, and/or numbness.[16]

Diagnosis

Assessment of MSDs are based on self-reports of symptoms and pain as well as physical examination by a doctor.[2] Doctors rely on medical history, recreational and occupational hazards, intensity of pain, a physical exam to locate the source of the pain, and sometimes lab tests, x-rays, or an MRI[17] Doctors look for specific criteria to diagnose each different musculoskeletal disorder, based on location, type, and intensity of pain, as well as what kind of restricted or painful movement a patient is experiencing.[2] A popular measure of MSDs is the Nordic Questionnaire that has a picture of the body with various areas labeled and asks the individual to indicate in which areas they have experienced pain, and in which areas has the pain interfered with normal activity.