The mechanical joint score: a new clinical index of joint damage in rheumatoid arthritis.

OBJECTIVES To evaluate the mechanical joint score (MJS) in terms of its reliability between observers and over time, its ease of use and its relationship with conventional measures of rheumatoid arthritis (RA) disease activity, severity and functional outcome. METHODS The MJS was evaluated in 103 patients with reference to the following joints: total proximal interphalangeal (PIP) joints, total metacarpophalangeal (MCP) joints, wrists, elbows, shoulders, hips, knees, ankles and total metatarsophalangeal (MTP) joints. The score was based on the appearance of the joints on a scale of 0-3, 0 representing no abnormality and 3 severe abnormality or previous surgery. The MJS was evaluated in terms of its intra- and inter-observer variability and its content, construct and criterion validities. A subset of 29 patients were re-evaluated after 5 yr to examine change in MJS over time. RESULTS The MJS performed well in terms of inter-observer and intra-observer reliability. The MJS showed strong correlation with the Larsen X-ray score of hands and feet (Spearman correlation coefficient 0.74) and with the modified Health Assessment Questionnaire (Spearman correlation coefficient 0.56) and only weak correlation with indices of disease activity, such as the Ritchie index and erythrocyte sedimentation rate. The MJS showed highly significant positive change over time. CONCLUSION The MJS is a reliable clinical index of joint damage and may be a useful new outcome measure in RA.