Use of isokinetic muscle strength as a measure of severity of rheumatoid arthritis: a comparison of this assessment method for RA with other assessment methods for the disease.

The aim of this study was to study the association between isokinetic muscle strength (IMS) and other clinical indicators of disability and disease activity in patients with rheumatoid arthritis (RA). A cohort of 36 RA patients was followed over a 1-year period with five measurements of disease activity at regular intervals during this time. IMS was measured at seven angular velocities in both knees, on five separate occasions. The measurement was expressed by the level of the fitted line of the seven peak torque values--IMS30. The association between IMS30 and clinical indicators was stated. As an indicator of disability the score from the Stanford Health Assessment Questionnaire (HAQ) was used. As indicators of disease activity morning stiffness, an index of swelling and pain in the joint, erythrocyte sedimentation rate (ESR) and haemoglobin (Hb) were chosen. Larsen's X-ray score was used as an indicator of bone destruction due to longer-lasting disease activity. IMS was significantly associated with the HAQ score, but not with indicators of disease activity or radiological findings. IMS was significantly associated with changes in indicators of disease activity, but not with the changes in the HAQ score, or in the X-ray-score. IMS showed the strongest association with changes in the degree of arthritis of the knee. In conclusion, IMS was associated with the HAQ score and can therefore be used when measuring outcome in a specific group of RA patients. Changes in IMS were associated with indicators of changes in disease activity, and are therefore usable as a measure of patient outcome. Of particular importance is that IMS decreased if a patient developed active arthritis in the knee, and normalised again when the inflammation decreased.