What is transient synovitis?
Transient synovitis is a reaction of the joint’s inner lining (the synovium) to irritation, in which the lining thickens and/or excess joint fluid is produced. The synovium usually reacts to a viral antigen that has entered the bloodstream following a previous viral infection of the respiratory or digestive system. A joint irritated in this way, often with an effusion, becomes painful and its movement is restricted. Because of this reaction of the joint to external factors, transient synovitis is also called reactive arthritis. The onset of symptoms is usually sudden, "overnight". For example, if transient synovitis affects the hip, the child wakes up in the morning unable to walk, or limping, which understandably worries parents. However, transient synovitis is more a symptom of a recently resolved viral infection – children remain in good general condition, and the symptoms resolve within a week.
What is transient synovitis of the hip?
Transient synovitis most often occurs in the hip, and it is in fact the most common hip disorder in children. The age most affected is around 6 years old. In a quarter of cases, it occurs in both hips at the same time. Hip symptoms are linked to a previous viral infection, a reaction of the synovium, and the development of a joint effusion and pain. Parents usually describe the child limping, or even being unable to walk, after getting up in the morning. Everyone tries to recall a traumatic event or more intense play the day before, but these circumstances are not the cause of transient synovitis.
How is transient synovitis of the hip diagnosed?
A great deal can be learned from talking with the child, parents or accompanying adult. It is necessary to:
- ask about the presence of a raised body temperature or a possible hip injury
- examine hip range of motion and check for pain on movement
- assess the child's general condition and gait
- perform a hip ultrasound and look for a joint effusion
If the child is limping and has a hip effusion, basic laboratory tests should be carried out to rule out a bacterial hip infection – septic arthritis – as an urgent and dangerous condition. In septic arthritis, children appear unwell, have a raised body temperature, are unable to walk, and have elevated CRP and ESR values. In contrast, children with transient synovitis are in good general condition without a raised temperature, although they sometimes have mildly elevated CRP values. Other conditions that can cause similar symptoms include mesenteric lymphadenitis, juvenile idiopathic arthritis, leukaemia, inflammatory bowel disease, and Legg-Calvé-Perthes disease. However, these diagnoses should be suspected if there is no improvement within a week, in which case further investigations may be needed (X-ray, MRI, bone scintigraphy, or broader laboratory work-up).
How is transient synovitis of the hip treated?
Transient synovitis of the hip is treated with rest from activity and analgesics. Young children naturally avoid weight-bearing if it hurts. Restricting play and jumping for a few days, together with adequate pain relief using a syrup, usually resolves the symptoms within a week. During this time, it is a good idea to monitor body temperature. If the child still has a raised body temperature and/or difficulty walking or pain after a week, a follow-up appointment with a paediatric orthopaedic specialist is needed.
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