In a prospective survey over a 2-year period we studied strength and bulk of the quadriceps muscle in the thighs of children with juvenile chronic arthritis (JCA).
Every third month for 2 years we measured isometric muscle strength in knee extensors with a hand-held dynamometer in 20 children with JCA. Ultrasound equipment was used to measure thigh muscle bulk. A joint evaluation was made using a standard severity score. The children had their ordinary medical treatment and physiotherapy during the observation period.
Children with high severity scores in the knee or hip had least strength and muscle bulk. In the 4 children with the highest severity scores muscle strength was reduced to half of that expected. In 10 of the children there were clear variations in severity scores during the study period, for either better or worse. In these children an increase in the severity score correlated significantly with reduction in muscle strength and bulk (p < 0.05). The muscle strength and bulk changed in parallel in these children. Other factors, although not independent, such as polyarticular JCA, long duration of disease, and steroid treatment, also reduced muscle strength.
The presence and intensity of local arthritis is one important factor affecting muscle function in JCA. Normal muscle strength and bulk is rapidly lost near an inflamed joint. It is difficult to maintain or achieve normal muscle function in the presence of active arthritis despite medical and physical treatment. We assume that the muscle weakness is in part caused by atrophy of the muscle, which is influenced by local arthritis.