Rheumatology: 16. Diagnosing musculoskeletal pain in children.

The case A 7-year-old girl has a 2-month history of a mildly swollen and slightly painful knee, which her parents believe was caused by a fall at school. There is no other relevant history. Examination reveals a small swelling of the knee, with a small flexion contracture, loss of full flexion and some discomfort at the end of the range of motion. The results of the rest of the examination are normal. A complete blood count and the erythrocyte sedimentation rate are normal. A test for rheumatoid factor is negative, and an antinuclear antibody test is positive at a low titre (1:40). The child is referred to a pediatric rheumatologist with a provisional diagnosis of juvenile rheumatoid arthritis, although the referring physician is concerned about a possible injury to the knee caused by the fall.