Musculoskeletal disorders are among the most important occupational health problems in both developed and developing countries. These disorders affect the quality of life of most people during their lifetime. The annual cost of musculoskeletal disorders is great. In the Nordic countries, for example, it is estimated to vary from 2.7 to 5.2 % of the gross national product (Hansen 1993; Hansen and Jensen 1993). The proportion of all musculo-skeletal diseases that are attributable to work is thought to be approximately 30%. Thus, much is to be gained by prevention of work-related musculoskeletal disorders. To accomplish this goal, a good understanding is needed of the healthy musculoskeletal system, musculoskeletal diseases and the risk factors for musculo-skeletal disorders.
Most musculoskeletal diseases cause local ache or pain and restriction of motion that may hinder normal performance at work or in other everyday tasks. Nearly all musculoskeletal diseases are work-related in the sense that physical activity can aggravate or provoke symptoms even if the diseases were not directly caused by work. In most cases, it is not possible to point to one causal factor for musculoskeletal diseases. Conditions caused solely by accidental injuries are an exception; in most cases several factors play a role. For many of the musculoskeletal diseases, mechanical load at work and leisure is an important causal factor. Sudden overload, or repetitive or sustained loading can injure various tissues of the musculoskeletal system. On the other hand, too low a level of activity can lead to deterioration of the condition of muscles, tendons, ligaments, cartilage and even bones. Keeping these tissues in good condition requires appropriate use of the musculoskeletal system.
The musculoskeletal system essentially consists of similar tissues in different parts of the body, which provide a panorama of diseases. The muscles are the most common site of pain. In the lower back the intervertebral discs are common problem tissues. In the neck and the upper limbs, tendon and nerve disorders are common, while in the lower limbs, osteoarthritis is the most important pathological condition.
In order to understand these bodily differences, it is necessary to comprehend basic anatomical and physiological features of the musculoskeletal system and to learn the molecular biology of various tissues, the source of nutrition and the factors affecting normal function. The biomechanical properties of various tissues are also fundamental. It is necessary to understand both the physiology of normal function of the tissues, and pathophysi- ology—that is, what goes wrong. These aspects are described in the first articles for intervertebral discs, bones and joints, tendons, muscles and nerves. In the articles which follow, musculoskeletal disorders are described for the different anatomical regions. Symptoms and signs of the most important diseases are outlined and the occurrence of the disorders in populations is described. Current understanding, based on epidemiological research, of both work-and person- related risk factors is presented. For many disorders there are quite convincing data on work-related risk factors, but, for the time being, only limited data are available on exposure effect relationships between the risk factors and the disorders. Such data are needed in order to set guidelines to design safer work.
Despite the lack of quantitative knowledge, directions for prevention can be proposed. The primary approach to prevention of work-related musculoskeletal disorders is redesign of work in order to optimize the workload and make it compatible with the physical and mental performance capacity of the workers. It is also important to encourage workers to keep fit through regular physical exercise.
Not all musculoskeletal diseases described in this chapter have a causal relationship to work. It is, however, important for occupational health and safety personnel to be aware of such diseases and consider workload also in relation to them. Fitting the work to the performance capacity of the worker will help him or her to work successfully and healthfully.