What causes Perthes' disease?
Perthes' disease occurs in a part of the hip joint called the femoral head. This is the rounded top of the thigh bone (femur) which sits inside the hip socket (acetabulum). Something happens to the small blood vessels which supply the femoral head with blood. So, parts of the femoral head lose their blood supply. As a result, the bone cells in the affected area die, the bone softens and the bone can fracture or become distorted. The amount of bone damage can vary from mild to severe.
The exact cause of the blood vessel problem that occurs in the first place is not known. A child with Perthes' disease is usually otherwise well.
Over several months the blood vessels regrow, and the blood supply returns to the bone tissue. New bone tissue is then made so the femoral head reforms and regrows. This is similar to how bone reforms and regrows after any normal fracture or break to a bone. But, with Perthes' disease, it takes longer (often between two and three years).
The main concern with regrowth of the femoral head is to ensure that it forms a good rounded (spherical) shape. This helps it to fit well into the hip joint socket. If the femoral head is less rounded, hip movements may continue to be affected after the blood vessels have regrown and there may be more wear and tear on the hip joint.
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- Larson AN, Sucato DJ, Herring JA, et al; A prospective multicenter study of Legg-Calve-Perthes disease: functional and radiographic outcomes of nonoperative treatment at a mean follow-up of twenty years. J Bone Joint Surg Am. 2012 Apr 4 94(7):584-92. doi: 10.2106/JBJS.J.01073.
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