5 year old boy presents with acute left ankle pain and associated joint swelling with no history of trauma. ESR and WBC were within normal limits. The patient was placed in a posterior short leg splint and advised to be non-weight bearing. Improved over the course of 2 weeks.

Transient synovitis (TS) is a benign and self-limiting condition that involves inflammation that typically occurs in the hip joint. Although the exact cause of TS remains under investigation, it is commonly associated with a viral infection in children between 3 and 8 years old.

TS of the hip in children presents with pain, refusal to bear weight, fever, and limp. A fraction of children presenting with a limp also has ankle and knee joint involvement. TS usually resolves within 3-10 days with RICE treatment, and resolution of joint effusion occurs after 1 week.

It is crucial to differentiate TS from septic arthritis. Fever (temperature >38.0 C) and elevated CRP (>20 mg/L) are the most significant predictors for septic arthritis. Imaging can be very helpful, and plain radiographs typically range from normal to joint space widening.  MRI can be used to distinguish the two conditions in complicated cases. The characteristics findings of TS on MRI include joint effusions and absence of signal intensity abnormalities in the bone marrow.

Though the other differential considerations for ankle joint effusions include early-onset Juvenile Rheumatoid Arthritis (JRA), Juvenile Idiopathic Arthritis (JIA), traumatic hemarthrosis, and much less likely leukemia or metastatic disease. An easy mnemonic for causes of the pediatric joint effusion is "TIM" (Trauma, Infection/Inflammation, Malignancy/Miscellaneous).

This case was submitted with supervision and input from:

Soni C. Chawla, M.D.
Associate Professor
Department of Radiological Sciences
David Geffen School of Medicine at UCLA
Olive View - UCLA Medical Center