The aim of this study was to measure lower extremity isometric strength in patients with juvenile idiopathic arthritis (JIA) and to evaluate the usefulness of an adjustable dynamometer chair in the clinical work.
Twenty-five children with JIA and 25 healthy, age-matched controls, aged 7-12 (mean age 10.1) were studied. The isometric maximal strength of knee and ankle muscles was measured on both sides using the dynamometer chair. Before and after the measurements the Children's Effort Rating Table (CERT) was used to assess physical effort and feelings of exertion during the measurements.
In all the tested muscle groups, there was a trend towards lower muscle strength values in the patients with JIA but significant differences were found only in knee extension (at 80 degrees knee angle) on both sides and in ankle plantarflexion if both ankles had had arthritis. No difference was observed in perceived exertion between patients and controls, but both groups significantly sensed the exertion after the muscle strength measurement (mean exertion before, JIA/control 2.2/2.0, and after 5.9/5.8).
Isometric muscle strength in children with JIA can be close to normal when the disease is not active. However, especially in knee extensors and ankle plantarflexors, muscle weakness may occur. From technical standpoint, an adjustable dynamometer chair can be used for assessment of isometric maximal strength in children with JIA.