EXTENDED REPORT Pain and joint mobility explain individual subdimensions of the health assessment questionnaire (HAQ) disability index in patients with rheumatoid arthritis

Objective: To explore the associations between individual subdimensions of the health assessment questionnaire (HAQ) and clinical variables in patients with rheumatoid arthritis. Methods: 304 patients with rheumatoid arthritis (73% female, mean (SD) age, 58 (13) years; disease duration 6 (9) years, 69% rheumatoid factor positive) completed the HAQ for functional capacity (0–3) and a 100 mm visual analogue scale for pain. Grip strength, range of motion of the large joints, Larsen score for radiographic damage of hand and foot joints, and the number of tender and swollen joints were recorded. A logit regression model was used to study associations between subdimensions of the HAQ and other variables. Results: Mean (range) total HAQ score was 0.92 (0 to 2.88) and varied from 0.73 to 1.04 in the subdimensions. Disability was lowest in the "walking" and highest in the "reach" subdimension. Pain was an explanatory variable in all individual subdimensions. Decreased grip strength, limitation of shoulder and wrist motion, and a larger number of swollen and tender joints in the upper extremities were related to several subdimensions. A higher pain score and swollen joint count in the upper extremities, decreased grip strength, and limited motion of wrist, shoulder, and knee joints explained increased disability (higher total HAQ scores). Conclusions: In patients with rheumatoid arthritis, pain and range of movements of joints have the greatest impact on individual subdimensions of the HAQ. Extent of radiographic damage in peripheral joints and the number of swollen and tender joints are of lesser importance for function.