Perthes Disease: What Is It and Why Does Your Child Need Repeat Imaging?

Key takeaways

• Perthes disease most often affects children between the ages of 4 and 10.
• The femoral head (ball of the hip) loses its blood supply for a while and then regrows.
• Recovery takes two to four years, with regular scans needed at every stage.
• Radiation from repeat X-rays adds up and is a real concern. Low dose EOS imaging uses about 90% less radiation than a standard X-ray.
• Diagnosis and treatment decisions are made by a paediatric orthopaedic team, not an imaging clinic.

What are the symptoms of Perthes disease?

The first sign is usually a limp that comes and goes. Sometimes there is a mild ache in the hip, groin or knee. The pain can show up in the knee rather than the hip, so Perthes disease is sometimes missed at first.

If your child has a limp that does not clear up within a week or two, or complains of hip or knee pain with no clear injury, see your child's doctor. They can arrange the first check-up.

What causes Perthes disease?

The cause is a short-term break in the blood supply to the femoral head, the rounded top of the thigh bone that sits inside the hip socket. Without enough blood, the bone weakens (a process sometimes called avascular necrosis). Nobody knows exactly why this happens. It is not caused by injury, diet or anything a parent did or did not do.

What are the stages of Perthes disease?

Perthes disease passes through four known stages over roughly two to four years. Each stage looks different on scans. This is why regular scans are needed to follow progress and guide the orthopaedic team's decisions.

How is Perthes disease monitored with imaging?

Serial imaging, meaning repeat scans taken at set times over months and years, is the backbone of Perthes care. Scans show the orthopaedic team how the femoral head is reshaping, whether it is staying well seated in the socket, and whether the treatment plan needs to change.

A child with Perthes disease may need many sets of hip images over the full course of the condition. That is a lot of radiation if each session uses a standard X-ray dose. This is where the total, built-up dose matters most.

Your child's paediatric orthopaedic consultant decides when each scan is needed and which views are required. Paediatric imaging at ScanAlign simply provides the images at a much lower radiation dose, then sends the results to your child's medical team.

Why does low dose imaging matter for children with Perthes disease?

Children are more sensitive to radiation than adults, because their cells are still dividing quickly as they grow. The more scans a child has, the more the doses add up. Perthes disease needs years of follow-up, so keeping each single dose as low as possible is a sensible precaution.

EOS captures the hip and pelvis in a single standing sweep using about 90% less radiation than a standard X-ray, around ten times less. Over many appointments, that reduction becomes meaningful. Standing imaging also shows how the hip behaves under the child's own body weight. This can be useful for judging how the joint works in daily life.

ScanAlign, low dose standing imaging, is available at 19 Harley Street, London. You can book a paediatric monitoring scan once your child's consultant has asked for follow-up imaging.

What is the long-term outlook for Perthes disease?

The outlook depends mainly on two things: the age at which the condition starts, and how round the femoral head is when it finishes regrowing. Younger children (under six at onset) tend to do better. They have more growing time for the bone to reshape into a good form.

Many children recover with a hip that works well and causes little or no trouble into adult life. Some are left with a femoral head that is flatter or less even. This can affect the range of movement and may raise the chance of hip problems later in life.

What helps during recovery?

The paediatric orthopaedic team may advise physiotherapy to keep the hip moving, periods of rest or less activity, or in some cases a brace or surgery to keep the femoral head well held in the socket. These are called containment treatments. ScanAlign does not provide treatment, but the images we produce support the team making those decisions.

Before your child starts a treatment, or changes the one they are on, it is worth getting a detailed diagnosis. Knowing whether the cause sits in the pelvis, the legs or the spine changes what will actually help.

Frequently asked questions about Perthes disease