Measures of functional ability (disability) in arthritis in relation to impairment of range of joint movement.

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Abstract
In the World Health Organisation's supplementary classification of the consequences of disease a distinction is made between impairments, such as are related to the site and nature of joint involvement, and any disabilities in everyday activities to which these may give rise. This paper considers the application of these ideas to people with arthritis by examining the extent of graded relationship between individual impairments, reflected by limitations in the range of joint movement, and the number or type of disabilities. Ninety-five people with three different types of arthritis were studied. A 41-item disability questionnaire was completed. Most of the variation was described by only 24 of the latter items. These fell into five broad functional groups--predominantly concerned with mobility, bending down, manual dexterity, bending the arm, and reaching above the head. The constituent activities could be scaled in order of difficulty of accomplishment. Aggregated scores for each of the functional groups were correlated with observed ranges of motion in relevant joints, and the ordering of difficulty was related to decreasing ranges of movement. These findings shed light on the genesis of disability and have implications for the development of more sensitive, specific, and simple methods of assessment in rheumatology. Appreciation of how disability relates to the localisation of disease manifestations provides a means for evaluating current methods of functional assessment and exposes potential biases in such appraisals.