Idiopathic avascular necrosis of the upper femoral epiphysis (Perthes condition) often presents with a mild limp after a minor injury. The patient is usually between 3 to 9 years old, is systemically well and often gives a history of an intermittent limp for several weeks or months. Examination will reveal limited range of movement in the affected hip. Radiographs are normally diagnostic – figure below – but changes can be subtle and difficult to determine in the early stages of Perthes. Again, urgent out-patient paediatric orthopaedic consultation is required.