MUSCULOSKELETAL RISKS ASSOCIATED WITH POSTURE AND REPETITIVE MOVEMENT
Upper limb disorders (ULDs) can be difficult to define since the effect is often diffuse, i.e. various parts of the limbs may be affected. Diffuse injuries typically start centrally and then spread peripherally, starting in the muscular system, then affecting the cardiovascular system and finally affecting the nerves. The soft tissues which connect the muscle to the bone (the connective tissue, especially the tendons) are also affected, including those in the hands, wrists, arms and shoulders. The term repetitive strain injury (RSI) is also used to describe such effects.
The most familiar type of ULD is possibly that associated with keyboard workers such as secretaries, who may experience diffuse pain throughout the upper limbs in the neck, shoulders and upper arms, as well as pain in the wrists and elbows.
A strain injury caused by keyboard work is addressed under the Health and Safety (Display Screen Equipment) Regulations 1992.
There is an increasing tendency for todays population to spend many hours in the sitting position, both at work and in leisure time. Approximately 70% of people’s waking days are spent sitting. It is also thought that the incidence of musculoskeletal disorders is higher in those people whose jobs involve long periods of sitting. Postural problems can start at an early age, as children sit for longer periods, with less physical activity.
When sitting down the normal shape of the spine changes. This has a major effect on the way the joints work and on the types of stresses the vertebrae are exposed to. On feeling pain, the person may alter the sitting position to try to relieve the symptoms. However as the pressure of work may demand high levels of concentration, feelings of discomfort may frequently be ignored until the level of pain is reached. It is this painful stimulus that can interrupt the persons concentration and so cause him or her to shift position. However, by this stage , the damage to the tissues has already started and it will, therefore, take longer for the tissues to heal.
The human body has great recuperative powers if given the time to repair itself. When the recovery time is insufficient, however, and when high repetition rates are combined with mental and physical stressors such as awkward postures and unreasonable deadlines, a worker may be at risk of developing a strain injury. Such injuries can occur in any part of the musculoskeletal system - the muscles, tendons, ligaments, joints and joint capsule, and in particular the nerves in the case of a diffuse syndrome.
The main distinction between work related strain injuries and normal strains is that the latter generally occurs from one single act such as an injury which may occur from a slip, trip or fall. In contrast, work related strain injuries have few of the distinctive or dramatic features which characterise other strain injuries. In the case of an overuse injury, the worker may be exposed to years of microtrauma and never realise that work may contribute to an injury. In todays work environment, such injuries are more commonly associated with the upper limbs and it is due to the complex nature of the onset of injury that they are more commonly called work related upper limb disorders (WRULDs), which as mentioned earlier is more medically precise than the term RSI.
There are commonly two different types of overuse injuries found in todays working environment those which originate from fixed postures and those which originate from variable postures. Keyboard operators are exposed to risk from a fixed posture.
When a person remains sitting with arms stretched constantly forward for typing, the mechanics of the skeletal structure are altered. The muscles which hold the arms forward shorten. This muscle shortening pulls on the bones, thus adjusting the mechanics around the shoulder and chest and, on occasion, the upper back. This can result in nerve compression or entrapment as these nerves pass under or around the bones and shorten soft tissue structures. The nerves may become damaged and less able to work correctly. This in turn affects the ability of the lower arms to function correctly and secondary injuries may occur at the site where there is repetition. The result is diffuse pain throughout the upper limbs, discomfort in the neck, shoulders and upper arms, with more specific pain around the elbows and wrists.
When using a keyboard there is also an increased static loading on the spine, as the arms and head are held outside the body’s centre of gravity. Muscles in the upper back, neck and shoulders contract to hold this posture, to enable the keyboard user to strike the keys with the hands and fingers. The lower arms, hands and fingers, which require a healthy supply of blood to perform, are severely disadvantaged due to the poor upper limb mechanics when seated.
Injuries sustained when using a keyboard are widespread and diffuse and hence cannot be compared to the sorts of repetitive strain injuries that are associated with more dynamic postures, which are more likely to result in injuries in local areas, such as the wrist
It is important that employers understand the risks to keyboard operators and the need for constant breaks. Work should be designed in such a way that the operator is able to take a break from the keyboard to carry out other clerical duties.
Staff who manage keyboard operators or use secretaries / typists, must also be made aware of the risks. Keyboard operators are entitled to a duty of care from those they work to.
Regular assessment of the workstation can help in the identification of potential problems.
Unrealistic deadlines combined with heavy work loads, can only increase the risk of musculoskeletal problems developing.
