Perthes Disease

Perthes Disease is a rare childhood disorder that affects the hip joint and leads to reduced mobility, pain, and limping. These symptoms may be linked to Mucopolysaccharidosis type IVA (MPS IVA, or Morquio A syndrome), another rare genetic condition.

In these patients, changes in bone and cartilage caused by MPS IVA can closely mimic Perthes disease on X-rays, which may delay the correct diagnosis. Understanding this connection is essential for ensuring that children receive the right tests, care, and access to appropriate treatment as early as possible.

What is Perthes Disease?

Perthes Disease, also known as Legg-Calvé-Perthes Disease, is a rare childhood hip disorder, in which the blood supply to the femoral head (the “ball” of the hip joint) is temporarily reduced. As a result, the bone tissue in this area becomes weakened and necrotic (osteonecrosis) and may gradually collapse and then remodel.

Over time, the bone re-vascularises and rebuilds, but the shape of the femoral head does not always return to normal. This can increase the risk of early hip osteoarthritis in adulthood.

Main symptoms

Symptoms usually develop slowly and can be subtle at first, including:

• Limping, sometimes with little or no pain at the beginning
• Hip, groin, thigh, or knee pain may occur, and the pain can radiate, so the child may complain only of knee pain even though the problem is in the hip
• Stiffness and reduced range of mobility, especially reduced abduction and internal rotation in the hip
• Pain that worsens with activity and improves with rest

Later on, as the disease progresses:

• Muscle wasting of the affected thigh
• A slight leg length discrepancy
• Clear deformity of the femoral head on imaging
  

How common is it?

Perthes disease is considered a rare condition. It affects roughly 1 in 1,200–10,000 children, more often boys than girls, and in about 10–20% of cases both hips are involved (usually to a different degree).

What causes it?

The exact cause is unknown. The key mechanism is a temporary interruption of blood flow to the femoral head, but why this happens is not fully understood.

Reported risk factors include:

• Male sex
• Age 4–10 years
• Low birth weight and short stature
• Possible clotting abnormalities and other vascular factors
• Passive smoking and lower socioeconomic status

In most children, no single clear trigger is identified, so the disease is considered idiopathic.

Diagnosis

A doctor may suspect Perthes disease when a child of the typical age presents with:

• Limping
• Hip/groin/thigh/knee pain
• Limited hip motion

Key investigations include:

• Physical examination (gait assessment, hip range of motion)
• X-ray of the hips
• MRI in early or unclear cases, when X-ray changes are minimal.

Treatment and prognosis

The main goals of treatment are to reduce pain, maintain good hip mobility, and preserve the spherical shape of the femoral head, so it fits properly in the socket and reduces the risk of early osteoarthritis later in life.

Management depends on the child’s age at diagnosis, the severity of deformity and symptom intensity.

Possible approaches might include:

• Limiting weight-bearing on the affected leg (crutches, wheelchair in acute phases)
• Physiotherapy to maintain range of motion and muscle strength
• Temporary braces or casts
• In selected cases, surgery (e.g. osteotomy) – especially in older children or when there is marked deformity.

In general, younger children tend to have a better prognosis, especially if hip function and the shape of the femoral head can be preserved during the healing process.

Perthes Disease and MPS IVA

In some children, Perthes-like hip problems can be linked to a rare genetic condition called Mucopolysaccharidosis (MPS), especially a type known as MPS IVA (Morquio Disease Type A). 

MPS affects how the body breaks down certain natural substances. When these substances build up in the body, they can damage bones, joints, and cartilage. Because of this, children with MPS can develop hip changes that look very similar to Perthes disease on X-rays.

This similarity can sometimes lead to confusion or delayed diagnosis. A child may first be told they have Perthes disease because of hip pain, limping, or reduced movement. 

However, if the hip problem is caused by MPS, the child may also have other signs, such as short stature, spine problems, breathing difficulties, frequent ear infections, or joint stiffness. These extra signs help doctors understand that the hip problem may be part of a bigger condition.

Understanding the link between MPS and Perthes-like symptoms is important because it helps children get the right diagnosis and care earlier. While Perthes disease is treated mainly with orthopedic care, MPS also requires follow-up with genetic and metabolic specialists. 

Early diagnosis allows families to access the right treatments, therapies, and long-term support as soon as possible, improving quality of life for both the child and the family.

If your child has been diagnosed with Perthes disease and you would like to check the risk of MPS IVA, please fill out the form below.

Sources:

• Armando O. Rodríguez-Olivas, Edgar Hernández-Zamora & Elba Reyes-Maldonado; Legg–Calvé–Perthes disease overview; Springer Nature.
• Tammy Ng, Ruikang Liu, Vedant A Kulkarni; Legg-Calvé-Perthes disease: Diagnosis, Decision Making, and Outcome; PubMed. 
• Hugo Flores-Navarro, Douglas Colmenares-Bonilla; Bilateral Perthes Masking Morquio Disease; PubMed Central.