Perthes' disease

What is Perthes' disease?

Perthes' disease, also known as Legg-Calvé-Perthes disease, is a rare childhood hip disorder that affects the blood supply to the femoral head.

It mainly affects young children who are aged between 3 and 10 years. Each year, about 1 in 10,000 children aged less than 15 years will get Perthes' disease. It is four times more common in boys than in girls.

Perthes' disease usually only affects one hip. But both hips are affected in about 1 in 7 children who have Perthes' disease.

The symptoms usually develop gradually over a period of time. The first indication that a child may have Perthes' disease is when they develop a limp. The affected hip is often but not always painful. The symptoms may include:

Pain

The affected hip is often painful and pain is also felt in the groin. The pain is also often felt in the thigh and the knee. This is not because the knee is affected but because hip pain is often felt in the knee. This is called referred pain.

Limb shortening

The leg of the affected hip may become shortened compared with the unaffected side.

Limp

Children with Perthes' disease often develop a limp, which becomes gradually worse over a few weeks.

Stiffness and a reduced range of movement

As the hip becomes more damaged, the affected hip becomes stiff. A limited range of motion of the hip develops.

Muscle wasting

Because the affected leg can't be used normally, the leg's muscles will become weaker. This causes the thigh muscles on the affected side to become wasted and so the leg looks thinner when you compare it with the other leg. This may not be obvious when both hips are affected.

Diagram detailing the hip joint

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. This is called 'avascular necrosis'. 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 diagnosis can usually be made by a specialist, by examination of the hip, plus an X-ray. Sometimes other tests may be needed if the diagnosis is not clear or if a more detailed picture of the hip joint is needed. Possible tests may include:

• A magnetic resonance imaging (MRI) scan.

• A bone scan.

• An X-ray where dye is injected into the space within the hip joint (this is called an arthrogram).

Blood tests and a sample of fluid from the hip joint may also be needed to rule out other problems, such as an infection of the bone or the joint.

The aim of treatment is to:

• Promote the healing process; and

• Ensure that the top of the thigh bone in the hip joint (the femoral head) remains well seated in the hip socket as it heals and regrows.

Which treatment is chosen will depend on the age of your child and how badly your child's hip is affected. Treatments may include observation, bed rest and/or using crutches, wearing a plaster cast or a special leg brace, or surgery. Your doctor will advise on the best treatment for your child.

Observation and physiotherapy

In younger children (less than 6 years old) and those with mild disease, Perthes' disease will usually heal well without any specific treatment. These children are treated by observation, often with physiotherapy or home exercises. The home exercises help to keep the hip joint mobile and in a good position in the hip socket.

Advice may also include:

• To encourage swimming (to keep the hip joint active in the full range of movements); but

• To avoid activities that can lead to any heavy impact on the hip joint, such as those involving trampolines and bouncy castles.

However, any advice will be tailored to your child's needs. Your child will also need regular follow-up with their specialist to check how their femoral head is healing. Regular X-rays of their hips are usually suggested.

Medication

Painkillers may also be useful to help relieve pain. Common painkillers suggested are ibuprofen and paracetamol.

Bed rest and/or crutches

This may be needed by some children for a short time if their symptoms are bad.

An operation may be considered in some cases, particularly in older children or those more severely affected. Surgery can help to keep the femoral head in the right position while it heals. Surgery can also be used to improve the shape and function of the femoral head if it has not healed well.

In many cases, the top of the thigh bone in the hip joint (the femoral head) regrows and remodels back to normal, or near-normal. The hip joint then returns to normal and is able to work as usual.

However, this can take two or more years after the condition first starts. Even after this time, there may be some stiffness remaining in the hip and there is an increased risk of osteoarthritis in later life.

The main problem is that the part of the thigh bone in the hip joint (the femoral head) may not re-form with a good rounded (spherical) shape, which helps it to fit well into the hip joint socket.

This can lead to permanent damage to the hip joint. This may cause stiffness of the hip joint. It can also cause arthritis of the hip joint at an earlier age than usual - for example, at around the age of 40 years.

The younger the child is when Perthes' disease develops, the better the chance of a good outcome. Children who develop Perthes' disease after about the age of 8-9 years have the highest risk of permanent hip joint problems, such as stiffness and arthritis.

The more severe the condition, the greater the risk of permanent problems with the hip joint.