Perthes' disease

Clinical History

The patient presented with right knee pain and a limp. He was otherwise well, with no pyrexia and there was no significant past medical history. Radiographs of the right knee and the pelvis were taken.

Imaging Findings

The patient presented with right knee pain and a limp. He was otherwise well, with no pyrexia and there was no significant past medical history. Radiographs of the right knee and the pelvis were taken. Knee x-rays were normal, but the pelvis x-ray showed an abnormal right hip. There was widening of the joint space and reduced height of the right proximal femoral epiphysis, which also showed some increased density (sclerosis). No further imaging was performed and he was treated conservatively. A repeat x-ray 10 months later showed further reduction in height of the epiphysis, epiphyseal broadening and fragmentation. Secondary changes in the metaphysis had also occurred.

Discussion

Perthes' disease (or Legg-Calvé-Perthes disease) is an idiopathic osteonecrosis of the proximal femoral epiphysis. The pathophysiology is an avascular necrosis, but the underlying cause is not known. The condition is most frequent in the age range 4-10 years, with a peak incidence of 6 years. There is a 4:1 male to female ratio and it is bilateral (but asymmetrical) in 10% of cases.

Perthes' disease commonly presents with pain in the groin or knee and a limp. The earliest radiographic changes are widening of the joint space and sub-cortical lucency or fissuring in the epiphysis, which may develop a slightly irregular outline. These early changes are often best demonstrated on a frog-lateral view (abduction with external rotation) which demonstrates the antero-lateral aspect of the proximal femoral epiphysis, where the changes of Perthes' disease are usually first evident.

Early changes in the femoral head may be detected using high-resolution ultrasound. Isotope bone scan and MRI can detect avascular necrosis before there are any plain film changes.

As the disease progresses and the avascular necrosis heals, there is increased flattening, fragmentation and sclerosis of the femoral head. The metaphysis may develop lucencies and become broadened resulting in exclusion of the lateral part of the femoral head from the acetabulum. In very severe cases, secondary changes can develop in the acetabulum.

The prognosis is generally favourable, but depends on the extent that the femoral head is affected. Children with less than half of the femoral head affected have a better prognosis. The goal of treatment in Perthes' disease is to maintain the full range of movement at the joint and contain the femoral head within the acetabulum to minimise deformity. This may involve osteotomy in some cases. There are at least 4 different classifications of Perthes’ disease accepted in the international literature, all of which aim to determine treatment and predict prognosis. In 1973 Catterall devised a four-group classification for Perthes’ based on the extent of epiphyseal involvement. This study was based on a group of untreated patients and compared their early radiographs with those taken later in order to determine the natural history of the disease. Stulberg et al (1981) classified the disease into 5 groups. This classification was based on the involvement of the femoral head (using Catterall’s criteria), but also included any degree of femoral head subluxation, and any metaphyseal or acetabular changes present. Salter et al (1984) proposed a two-group classification based on early appearances of the disease, at the stage where a subchondral lucency (fracture) was present. They proposed that the extent of this subchondral fracture – whether it extended over less than half of the femoral head or more than half of it, and particularly whether it reached the lateral margin of the epiphysis, would predict the final state of the femoral head and degree to which it eventually became resorbed. More recently in 1992, Herring et al described the Lateral Pillar classification of Perthes’ disease. This divides the femoral head into 3 pillars, lateral, central and medial, each representing a proportion of the epiphysis. Four groups were defined with progressive involvement of the lateral pillar. The classification was made on radiographs taken early in the course of the disease. References for these classification systems are given below.

Differential Diagnosis List

Final Diagnosis

Perthes' disease

URL:	https://www.eurorad.org/case/1546
DOI:	10.1594/EURORAD/CASE.1546
ISSN:	1563-4086