Perthes disease (also known as Legg-Calve-Perthes disease) affects children between the ages of 3 years and 11 years. It affects boys more commonly than girls. The condition is not fully understood but for some reason the blood supply to the head of the femur (ball part of the joint) is transiently reduced. This causes the head of the femur to become soft and potentially misshapen. The disease process can last up to 4 years and the long term result depends upon the shape of the femoral head when the blood supply has fully recovered. If the femoral head is spherical then the prognosis will be good but if it is flattened the hip will be stiff and may well become arthritic in adult life.
Most children develop symptoms slowly over a period of weeks or months. Parents may notice a limp and the child may complain of pain which can be in the groin or the thigh. Symptoms are usually worse after exercise. The child will be otherwise fit and healthy.
Once established the condition is easily diagnosed using a standard X ray. However in the first month or two the X ray may be normal. If there is a strong suspicion MRI scans are very sensitive at picking up Perthes disease.
Younger patients with Perthes disease generally have a better prognosis than older children since there is more time for the femoral head to remodel with remaining growth. Non operative treatment is the rule for children less than seven years old at presentation. Assessment of the true shape of the femoral head can be made by injecting dye into the joint (arthrogram). In older children surgery may sometimes be indicated.