Perthes' disease

Synonyms: Calvé-Legg-Perthes disease, Perthes-Calvé-Legg disease

What is Perthes' disease?

This is a self-limiting hip disorder caused by varying degrees of ischaemia and subsequent necrosis of the femoral head.¹ The essential lesion is loss of blood supply (avascular necrosis) of the nucleus of the proximal femoral epiphysis.

Characteristic features include:

• Abnormal growth of the epiphysis results.

• Eventual remodelling of regenerated bone.

• The incidence varies widely ranging from 0.4/100,000 to 29.0/100,000 children.

• Perthes' disease usually appears from the age of 3 to 12 years old, with the highest rate of occurrence at the age of 5 to 7 years old.

• Boys are affected three to five times as often as girls.

• The disorder is bilateral in 10–24% of patients, with a correlation to inheritance in approximately 8–12% of patients.

• Most commonly seen in white people.

The primary event is avascular necrosis of the femoral epiphysis, which results in delayed ossific nucleus:

• The articular cartilage is nourished by synovial fluid and continues to grow.

• The cartilage columns become distorted with some loss of their cellular components.

• They do not undergo normal ossification, which results in excess of calcified cartilage in the primary trabecular bone.

• Revascularisation proceeds from peripheral to central.

• Symptoms occur with subchondral collapse and fracture.

• Onset is usually over weeks, with no history of trauma; the child typically presents with limitation of hip rotation and a subacute limp sometimes with referred pain to the groin, thigh, or knee.

• It is typically unilateral, though bilateral involvement is present in 10% of cases.

• The child is systemically well with no other joint involvement and no evidence of joint inflammation.

• On examination all movements at the hip are limited. In the early phase there is limited abduction of the hip and limited internal rotation in both flexion and extension.

• There is an antalgic gait (due to pain) and a Trendelenburg gait is seen in the late phase.

• Roll test: with the patient lying in the supine position, the examiner rolls the hip of the affected extremity into external and internal rotation. This test should invoke guarding or spasm, especially with internal rotation.

Investigations will include:

• FBC and ESR.

• Early X-rays may show widening of the joint space (the best view is frog lateral), or may be normal.

• Technetium bone scan or MRI scanning can be used to identify pathology (seen as an area of reduced perfusion).⁵

• Later, there is a decrease in the size of the nuclear femoral head with patchy density on X-ray.

• Later still, there may be collapse and deformity of the femoral head with new bone formation. Severe deformity of the femoral head risks early arthritis.

• An arthrogram and/or MRI scan are often needed to assess congruency throughout full range of movement. A flat-topped incongruent head has the worst prognosis. It can rule out hinge abduction where the enlarged femoral head impinges on the acetabular rim.

• Hip aspiration if a septic joint is suspected.

The most likely other diagnoses for an acute limp in a child aged 3-10 years are:⁴

• Transient synovitis.

• Fracture or soft tissue injury (including stress fracture or non-accidental injury).

Bilateral Perthes' disease⁵

This requires a skeletal survey as part of the work-up.

• Hypothyroidism.

• Multiple epiphyseal dysplasia (MED).

• Spondyloepiphyseal dysplasia tarda.

• Sickle cell disease.

Unilateral Perthes' disease⁵

• Septic arthritis.

• Sickle cell disease.

• Spondyloepiphyseal dysplasia tarda.

• Gaucher's disease.

• Eosinophilic granuloma.

• Transient synovitis (this was thought to lead to Perthes' disease; however, it is now believed there is no causal relationship).

The goals of treatment include pain and symptom management, restoration of hip range of motion, and containment of the femoral head in the acetabulum.

Non-operative treatment is often indicated for children with a bone age less than 6 years, and includes:

• Restriction of activities and weight-bearing until ossification is complete.

• Physiotherapy (but there is no strong evidence for the use of orthotics, braces or casts).

• NSAIDs can be prescribed for pain relief.

• Good outcomes reported in up to 60% of patients receiving non-operative treatment.

Operative treatments include:⁶

• Femoral or pelvic osteotomy.

• Valgus or shelf osteotomies.

• Hip arthroscopy.

• Hip arthrodiastasis (controversial).

Most children with Perthes' disease have good outcomes; 50% recover with no long-term sequelae. Hip osteoarthritis (a common complication) rarely develops before 50 years of age and these may require hip replacement.⁷

For patients who are less than 6.0 years of age, outcome is good, regardless of treatment.⁸Age under 6 years at the onset of the disease is prognostically favourable because of the higher remodelling potential.

In one study moderate or severe osteoarthritis change was found on x-ray in 44% approximately 20 years after diagnosis in patients who were treated non-operatively.⁹

Prognostic factors include age, limitation of movement, radiologically visible involvement of the femoral head, lateralisation of the femoral head in the acetabulum (subluxation), lateral epiphyseal calcification and metaphyseal cyst formation.

Residual deformities may include coxa magna (broadening of the head and neck of the femur), coxa plana (osteochondritis of the femoral head), coxa breva (structural shortening of the neck of the femur) and hinged abduction (this occurs when an enlarged femoral head is pushed laterally and it impinges on the acetabular rim when the hip is abducted).

Femoral head deformity is well tolerated in short and intermediate terms, but 50% of patients develop disabling arthritis in the sixth decade of life.