Knee magnetic resonance imaging in childhood chronic monarthritis

Objective. To describe the usefulness of magnetic resonance imaging (MRI) o f the knee in the evaluation of chronic monarthritis of uncertain cause in childhood. Methods. We retrospectively reviewed 21 children referred to our clinic wit h a putative diagnosis of chronic inflammatory monarthritis of the knee who had MRI performed between May 1993 and June 1997. The median age was 13 ye ars (range 2-17) and 11 were girls. Results. The clinical diagnosis prior to MRI assessment was inflammatory ar thritis in 16 patients, and a primary noninflammatory cause in 5, MRI was d one in the patients with presumptive inflammatory arthritis when there were atypical symptoms, signs, or radiographs (n = 14), or when they failed to respond to therapy (n = 2). In the patients with a presumptive noninflammat ory diagnosis, MRI was performed to clarify the diagnosis. Twelve children (57%) had MRI evidence of a noninflammatory diagnosis. In 4 children (19%) the MRI study indicated the presence of arthritis, and in 5 children (24%) the MRI studies were normal. The noninflammatory diagnoses included: lipoma arborescens (n = 1), vascular malformation [intraarticular (n = 1), extraa rticular (n = 1)], synovial chondromatosis (n = 2), partial anterior crucia te ligament tear (n = 2), traumatic bone contusion (n = 2,), possible menis cal tear (n = 1), osteochondritis dissecans (n = 1), and a soft tissue mass of uncertain significance in the suprapatellar pouch (n = 1). Conclusion. Inflammatory arthritis is usually diagnosed by clinical assessm ent alone. Uncommonly, when a single joint is involved, and atypical featur es are identified by a pediatric rheumatologist, other causes of chronic pa in and swelling need to be excluded. In this selected patient population, M RI is a useful tool either to confirm the presence of inflammatory arthriti s or to investigate a wide range of pathology that can mimic knee joint art hritis.