In medical parlance, this is often referred to as Legg Calve Perthes disease. Here, the name 'Avascular necrosis of the capital femoral epiphysis' is preferred to emphasize that the term refers to a phenotypic feature rather than a disease entity. Avascular necrosis of the femoral head may result in pain in the hip, limp, stiffness and reduced range of motion, and some degree of atrophy of the affected leg. The phrase Legg Perthes syndrome or Legg Calve Perthes disease is also used to refer to a number of diseases, including the idiopathic form and a form that is related to mutation in the COL2A1 gene (MIM 150600). Legg-Calve-Perthes disease usually occurs in boys 4 to 10 years old, and is clinically characterized by limping, hip stiffness, limited range of motion, and can result in restriction of growth of the affected leg and wasting of the muscles of the upper thigh.