Perthes disease (summary)

This is a basic article for medical students and other non-radiologists

Introduction

Summary

Perthes disease is the name given to idiopathic AVN (avascular necrosis) of the femoral epiphysis in children. It most often occurs in children around the age of 5-6 and is one of the common considerations when children present with an atraumatic limp or hip pain.

Epidemiology

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

Demographics

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.

Background

Aetiology

The cause of avascular necrosis in Perthes disease is unclear - the condition is idiopathic. There are no clear predisposing factors.

Pathophysiology

Lack of blood supply to the femoral epiphysis results in avascular necrosis of the femoral head with fragmentation and bone loss.

Associations

In approximately 15% of cases, AVN occurs bilaterally.

Clinical features

Presentation

Most children present with atraumatic hip pain or limp. Some children have a coincidental history of trauma which may have precipitated the presentation or the realisation of symptoms that in fact had been longer standing.

Differential diagnosis

The clinical differential diagnosis for atraumatic hip pain and limp includes:

• transient synovitis: viral prodrome
• osteomyelitis: fever, elevated inflammatory markers and effusion
• SUFE: usually older and overweight

Imaging

The most useful test to perform to diagnose Perthes is aan 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.

Other investigations

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.

Treatment

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.

Radiographic features

X-ray

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.

MRI

On MRI, we are looking for bone oedema and evidence of an effusion. Bone oedema will be bright of fluid-weighted sequences, e.g. T2/STIR.