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. 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) and blood cultures if there is concern about red flags (sepsis 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 so all patients do require orthopaedic follow up.
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.