Background: Juvenile idiopathic arthritis (JIA) is a chronic illness with a high risk of developing long-term disability.\nDisease activity is currently being monitored and quantified by ACR core set. Here, joint inflammation is determined;\nhowever joint function is the crucial component for developing disability. The aim of this study was to quantify and\ncompare dynamic joint function in healthy and arthritic knee joints and to evaluate response to improvement.\nMethods: A single center cohort study of consecutive children presenting to the rheumatology outpatient clinic\nwas performed to measure dynamic knee joint function. Serial measures were performed if possible. Splint\nfixed electrogoniometers were used to measure dynamic knee joint function including ROM and flexion and\nextension torque.\nResults: A total of 54 children were tested including 44 with JIA, of whom eight had to be excluded for non-JIA-related\nknee problems. The study included 36 JIA patients of whom eight had strictly unilateral knee arthritis, and nine controls.\nDynamic joint function ROM and torque depended on age and bodyweight, as demonstrated in healthy joints. ROM\nand torques were significant lower in arthritic compared to unaffected knee joints in children with unilateral arthritis\nand across the cohort. Importantly, extension torque was the most sensitive marker of impaired joint function. Follow\nup measurements detected responsiveness to change in disease activity.\nConclusions: Measuring dynamic joint function with electrogoniometers is feasible and objective. Active ROM and\ntorque during flexion and extension of arthritic knee joints were significant lower compared to unaffected. In dynamic\njoint measurement extension torque is a sensitive marker for disease activity
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