Transient Synovitis of the Hip
Transient synovitis, also known as irritable hip, is a 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 often 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, with or without pain. There may be reluctance to weight-bear with reduced movement of the hip. Investigations will include ultrasound scan of the hips, blood tests (full blood count and acute phase reactants), blood cultures and streptococcal serology if there is concern about red flags (sepsis, rheumatic fever or malignancy).
Management involves rest and analgesia, with mobilisation once pain has settled. It usually resolves within 2 weeks. There may be an increased risk of Legg-Calve-Perthes disease after irritable hip and orthopaedic review is needed if there is not complete recovery.
It is important to exclude infection of the bone or joint, and trauma. Septic arthritis is more likely if the child is unwell, febrile and there are raised inflammatory markers and white cell count. 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