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Perthes disease

Perthes disease is a condition that affects the upper end, or head of a child's thigh bone (femur), where it forms one part of the hip joint.

It happens in children when, as their femur is growing, the round head of the bone (the ball that fits inside the hip socket) softens, flattens and then gradually re-forms.

Diagnosing Perthes disease

Doctors may suspect Perthes disease if a child limps for more than 48 hours. Your child will need X-rays to confirm the diagnosis – Perthes disease cannot be diagnosed by blood tests.

The younger the child is when Perthes is diagnosed, the better the outcome.

How long Perthes disease lasts

Perthes disease runs a slow course. As you have probably seen with your own child, the symptoms – limping, pain in the hip or knee – develop slowly and subtly. Some children don't feel any pain. Every case is different.

It can also take a long time for your child to recover from Perthes disease. It usually takes at least 18 months, but can take more than two years. Right now, that probably seems like a very long time, but it is just a small part of your child's entire lifespan.

Causes of Perthes disease

FDPThe changes to the round, growing end (the ball, or epiphysis) of the thigh bone happen because its blood supply is cut off. Because of this it softens. We don't know why the blood supply is cut off.

The smooth cartilage (or gristle) that covers the bone grows normally, because it gets its nutrients from the joint fluid.

Perthes disease happens much more often in boys than in girls. It usually develops between the ages of 4 and 10 years, when the ball is particularly vulnerable to its blood supply being cut off. At first, your child may have some pain in their hip or knee, and they may also experience some muscle spasm related to their limping.

When their hip is X-rayed, the affected part of their bone will look denser. The body gradually, and irregularly, absorbs the bone over several months, so it looks broken-up when X-rayed.

Sometimes the ball of the thigh bone becomes swollen, and then becomes squashed out of its normal shape. When this happens, the new bone also grows into the deformed shape, and will stay that way for the rest of the child's life. This can cause some disability in their hip.

The other hip

In about one in eight cases the other hip is also affected, either at the same time or later. If your child complains about their good leg aching, tell your doctor.

Treating Perthes disease

Many patients with Perthes disease simply need to be watched, have regular X-rays, and avoid some physical activities. Sometimes they will need a period of bed rest, with no physical activity. Some children may also need to use crutches or a wheelchair, to avoid putting weight on the affected leg.

Occasionally a child will need surgery to protect the ball of the thigh bone from becoming deformed.

Your child can, and should, go to school as normal, but they may have to avoid some physical activities. They may need to do this for up to four years, as their body replaces the soft, fragmented bone with strong new bone.

How Perthes disease affects your child's future

Perthes is a self-limiting disease and will eventually get better. This may take a long time, but most children will have a painless hip with a good range of movement. A few children will be left with some stiffness and pain.

Because we don't know exactly what causes Perthes disease, we can't always predict the results. But because the outcome is usually worse if treatment is delayed (even if the treatment is just to avoid some activities), or if a child is diagnosed after the age of 8, it's very important to diagnose it early.

Written by Orthopaedic Outpatients and Paediatric Departments, Christchurch Hospital. Adapted by HealthInfo clinical advisers. Last reviewed June 2019.


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Review key: HIBOW-85151