Methods for evaluating work-related musculoskeletal neck and upper-extremity disorders in epidemiological studies

Abstract

The aim of this thesis was to develop, evaluate and characterise assessment methods used within epidemiological studies of work-related musculoskeletal disorders in the neck and upper extremities. Special attention was paid to self-administered methods, relations to psychosocial risk factors and signs of nerve compression.

Work-related musculoskeletal disorders in the neck and upper extremities are common and costly in many respects. Knowledge about the progression of these disorders and their causality, especially in relation to psychosocial conditions, is insufficient. Methods, mainly self-administered, for their assessment in epidemiological studies are limited.

Main affected structures, common disorders and their symptoms and signs, different assessment methods and their qualifications were discussed in this thesis. The existence of a high and low rating behaviour was proposed. If both exposure and outcome are rated by the subjects in an epidemiological study, such a rating behaviour could introduce uncontrollable bias to the risk estimates, most commonly an over-estimation. No such rating behaviour was found, however, and no effects on risk estimates could be demonstrated.

A self-administered physical examination protocol was developed and evaluated against traditional medical examination. The validity was poor, however. A self-administered pain drawing method was developed and studied among working population with symptoms in the neck and shoulder regions. The average outline showed two palm-sized areas in the neck-shoulder angles, with a symmetrical distribution between the right and left sides. Long-lasting or severe disorders and signs of tenderness were associated with large areas and multiple loci. Gender differences were noted.

The brachial plexus can be compressed in several locations in the neck and shoulder region. The diagnosis of this compression is mainly based on symptoms and medical examination, where the Abduction External Rotation test has been used. Prospective aspects and the outcome of the test were studied among male industrial and office workers. The results gave support to multi-causality and to the "double or multiple crush" theory of nerve compression. Evaluation of neck and upper extremity nerve compression diseases should therefore attend to all probable locations of such compression, even when a specific location is in focus.

Psychosocial working conditions have been recognised as important risk factors for musculoskeletal disorders. This thesis gave support to the hypothesis that high psychosocial load has specific associations with symptoms and signs of muscular (soft tissue) tenderness from central body regions - the neck and back. Studies of these relations should therefore distinguish between different clinical signs and different body regions in order to avoid attenuation of risk estimates. Suggestions were discussed for further development of reliable and valid methods for assessment of these disorders feasible for epidemiological studies and in health surveillance.