Perthes disease is a disease of the hip in which the bone in the hip joint loses its blood supply. This may cause the bone (femur) to change shape so that it no longer fits into the hip joint (femoral head) properly. The disease runs a 2-year course, and if left untreated, can cause permanent damage to the bone. (See glossary at end for definition of technical terms.)
The first stages of Perthes disease are silent. This means that the patient dose not limp or complain of pain. The bone in the hip joint (top of the thigh bone or femoral head) loses its blood supply and that part of bone subsequently dies. The bone weakens and a small fracture develops, with the result that the femur head begins to flatten. Circulation returns to the head of the femur within months, rejuvenating the bone but causing pain and a limp (and a visit to the doctor). If left untreated, the femoral head may flatten over the course of months, leading to arthritis in later years.