Perthes disease

Perthes disease (also referred to as Legg-Calvé-Perthes disease) refers to idiopathic avascular necrosis (AVN) of the femoral epiphysis seen in children. It should not be confused with Perthes lesion of the shoulder.

It is a diagnosis of exclusion and other causes of avascular necrosis (including sickle cell disease, leukaemia, corticosteroid administration, Gaucher disease) must be ruled out 8.

Epidemiology

Perthes disease is relatively uncommon and in Western populations has an incidence approaching 5-15 per hundred thousand.

Boys are five times more likely to be affected than girls. Presentation is typically at a younger age than SUFE with peak presentation at 5-6 years, but confidence intervals are as wide as 2-14 years 8.

Clinical presentation

Most children present with atraumatic hip pain or limp 3,5-6. Some children have a coincidental history of trauma. This may precipitate the presentation or  precipitated the presentation or the realisation of symptoms that in fact had been longer standing.

Diagnosis

The most useful test to perform to diagnose Perthes is an x-ray pelvis. In a small number of patients with Perthes, the x-ray will be normal and persistent symptoms will trigger further imaging, usually an MRI.

The investigation of atraumatic limp will often include a hip ultrasound to look for effusion. It is unlikely (unless the avascular necrosis is established) that ultrasound will pick up AVN.

Bloods will typically be normal. It is important to be certain that there is no other cause of AVN (e.g. Sickle cell disease) during the workup.

Pathology

Lack of blood supply to the femoral epiphysis results in avascular necrosis of the femoral head with fragmentation and bone loss. In approximately 15% of cases, AVN occurs bilaterally.

Aetiology

The cause of avascular necrosis in Perthes disease is unclear. The condition is idiopathic and there are no clear predisposing factors.

Radiographic features

The radiographic findings are those of avascular necrosis. There is a separate system for staging of Perthes disease (see Catterall Classification).

Plain radiograph

The radiographic changes to the femoral epiphyses depend on the severity of AVN and the amount of time that there has been alteration of blood supply:

  • early: there may be no appreciable change
  • established: reduction in epiphysis size, lucency
  • late: fragmentation, destruction

As changes progress, the width of the femoral neck increases (coxa magna) in order to increase weight-bearing support.

Early signs
  • joint effusion: widening of the medial joint space
  • asymmetrical femoral epiphyseal size (smaller on affected side)
  • apparent increased density of the femoral head epiphysis
  • blurring of the physeal plate (stage 1: see staging of Legg-Calve-Perthes syndrome or Catterall classification)
  • radiolucency of the proximal metaphysis 
Late signs

Eventually, the femoral head begins to fragment (stage 2), with subchondral lucency (crescent sign) and redistribution of weight-bearing stresses leading to thickening of some trabeculae which become more prominent.

The typical findings of advanced burnt out (stage 4) Perthes disease are:

  • femoral head deformity with widening and flattening (coxa plana)
  • proximal femoral neck deformity: coxa magna
  • "sagging rope sign" (thin sclerotic line running across the femoral neck)

Additionally, tongues of cartilage sometimes extend inferolaterally into the the femoral neck, creating lucencies, which must be distinguished from infection or neoplastic lesions 4. The presence of metaphyseal involvement not only increases the likelihood of femoral neck deformity, but also make early physeal closure with result leg length disparity more likely.

Arthrography

Traditionally arthrography performed under general anaesthesia with conventional fluoroscopy is performed to assess congruency between the femoral head and the acetabulum in a variety of positions 3. MRI is increasingly replacing this, in an effort to eliminate pelvic irradiation.

MRI

MRI is gaining an increasing role in a number of scenarios:

  • early diagnosis, before the onset of x-ray findings
  • assessing extent of cartilaginous involvement, important in prognosis
  • assessing joint congruence in a variety of joint positions (requires open magnet and dynamic imaging) 2

Both arthrography and dynamic MRI asses three main features 3:

  • deformity for the femoral head (also assessed on static x-rays and MRI)
  • congruence: how well the femoral head contour matches that of the acetabulum
  • containment: the amount of lateral subluxation of the flattened femoral head out of the acetabulum
    • when severe this may lead to hinge abduction, whereby rather than rotation and medial movement of the femoral head during hip abduction, the flattened head 'hinges' on the lateral lip of the acetabulum, widening the medial joint space 2-3

Treatment and prognosis

Treatment in Perthes disease is largely related to symptom control, particularly in the early phase of the disease. As the disease progresses, fragmentation and destruction of the femoral head occur. In this situation, operative management is sometimes required to either ensure appropriate coverage of the femoral head by the acetabulum, or to replace the femoral head in adult life.

The younger the age at the time of presentation, the more benign disease course is expected and also for same age prognosis is better in boys than girls due to less maturity 5,8. Prognosis is also influenced by the percentage of femoral head involvement and degree of primary deformity of the femoral head and the secondary osteoarthritic changes that ensue. The aim of therapy is to try and maintain good femoroacetabular contact and a round femoral head.

Bracing may be used in milder cases, although femoral neck and acetabular osteotomies may be required to correct more severe abnormal femoroacetabular malalignment.

In later life, hip replacements may be necessary.

History and etymology

The condition was first described in 1897 by Maydl, with Legg, Calvé and Perthes popularising it in 1910 in separate publications 7.

  • Karel Maydl (1853-1903): Austrian surgeon
  • Aurthur Thornton Legg (1874-1939): American orthopaedic surgeon
  • Jacques Calvé (1875-1954): French orthopaedic surgeon
  • Georg Clemens Perthes (1869-1927): German surgeon

Differential diagnosis

General imaging differential considerations include:

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Article Information

rID: 1574
Section: Pathology
Tag: hip
Synonyms or Alternate Spellings:
  • Legg-Calvé-Perthes disease (LCPD)
  • Legg-Calve-Perthes disease
  • LCPD

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