Legg-Calve-Perthes (or just Perthes) disease is a condition that affects the hip in children between the ages of four and eight.Perthes was named in honor of three physicians who each described the disease.

In this condition, bone in the growth center of the hip (the capital femoral epiphysis) dies because of a lack of blood supply. No one knows exactly why this happens. Nutrition may be part of it since children who are malnourished are more likely to develop this condition.

Abnormal blood clotting is part of the problem. Children with Perthes have blood that clots easier and faster than normal. This may lead to blood clotting that blocks the small arteries going to the femoral head. Why just the hip?

Again, scientists aren't exactly sure. One suggestion is the anatomy of the hip. The veins around the top part of the hip spiral around the arteries in young children. The veins are thin-walled in the upper part of the femoral head.

These two factors put together may result in sluggish blood flow in this area. Blood pooling can lead to blood clotting. Blood clots that clump together can block blood flow to an area.