Normal x rays in Perthes disease

摘要

A 6-year-old boy was referred to the regional paediatric rheumatology service with a 1-year history of limp.The patient was initially thought to have an irritable hip and x rays including the frogs legs view requested by the GP were reported as normal. In view of this no action was taken. However, his symptoms persisted and he was referred to a paediatric rheumatologist. On examination he had severe restriction of internal rotation and a clinical diagnosis of Perthes disease was suspected despite the normal x ray. An MRI showed partial collapse of the left femoral head with areas of necrosis, confirming the diagnosis of Perthes disease.