In this condition, there is loss of blood supply to part of the femoral head called the epiphysis and it dies due to Avascular Necrosis (AVN). Part, or all of the epiphysis can subsequently collapse. Although the epiphysis blood supply usually returns, if significant collapse has occurred it will leave the femoral head abnormally shaped and with possible deformity of the femoral neck. The more deformed the head becomes, the higher the risk of osteoarthritis developing. Again, early hip replacement is seen in patients with Perthes disease.