Transient Synovitis of the Hip
Transient synovitis, also known as irritable hip, is a common cause of acute hip pain in young children. It is a self-limiting condition, but is a diagnosis of exclusion and especially to exclude septic arthritis. It is more common in boys, and tends to present in ages 4-8. It is sometimes preceded by a virus, such as gastroenteritis or a viral upper respiratory tract infection.
Patients tend to be systemically well, with normal or mildly elevated inflammatory markers. Limp is invariably present, often with pain. There may be reluctance to weight-bear with reduced movement of the hip. Investigations should include blood tests (full blood count and acute phase reactants) and assessment of body temperature. In typical cases, the body temperature is normal or slightly elevated (below 38°C). Ultrasound of the hips will demonstrate increased fluid (effusion) in the affected hip. Often a pelvic radiograph including frog-leg view is advised in order to exclude other causes of hip pain, such as Perthes disease and malignancy.
Management involves rest and analgesia, with mobilisation once pain has settled. The condition usually resolves within 2 weeks. An orthopaedic review is needed if there is not a complete recovery.
It is imperative to exclude infection of the bone or joint. Septic arthritis is more likely if the child is unwell, febrile (above 38°) and there are raised inflammatory markers and white cell count. In such cases, the child must be fasted and immediately prepared for hip puncture and possibly joint lavage under general anaesthesia.
In some countries Mycobacterial infection can be an indolent presentation.
Kocher's rules can be helpful to differentiate septic arthritis at the hip joint from transient synovitis. It is noteworthy however that Kocher's rules are not universally used (e.g., are not used in New Zealand) and are not useful to differentiate sepsis from acute rheumatic fever (ARF). In endemic areas for ARF, a monoarthritis is a common presentation and should be suspected with a raised ESR even if the white cell count is not elevated (see Further Reading below).
Kocher MS, Zurakowski D, Kasser JR. Differentiating between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm Journal of Bone and Joint Surgery J Bone Joint Surg Am. 1999 Dec;81(12):1662-70.
Mistry RM, Lennon D, Boyle MJ, Chivers K, Frampton C, Nicholson R, Crawford H. Septic arthritis and acute rheumatic fever in children: the diagnostic value of serological inflammatory markers. J Pediatr Orthop 2015;35:318-322