Test 1

The cause of AVN in this case was idiopathic. Such cases are more commonly known as Perthes (or Legg-Calvé-Perthes) disease, the eponymous name for idiopathic AVN of the proximal femoral epiphysis. In the examination, it would be more accurate to write ‘avascular necrosis left proximal femoral epiphysis’ rather than ‘Perthes disease’ because you will not know the underlying aetiology in the absence of the clinical history. Perthes disease is five times more common in boys with a peak incidence of around 6 years of age and it can affect children from as young as 2 years old to those aged 14 years. The majority of children present with a painful hip or limp in the absence of trauma and it is a diagnosis of exclusion. Both proximal femoral epiphyses may be affected in up to approximately 15% of cases, but usually asymmetrically, with one side affected before the other.