Perthes Disease
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Direct answer
Perthes disease, also called Legg-Calvé-Perthes disease, is idiopathic avascular necrosis of the capital femoral epiphysis in childhood. It typically affects boys aged about four to ten years, who present with a painless or mild limp and restricted hip movement. Management aims at containment, keeping the femoral head covered by the acetabulum while it regenerates, so that it heals with a round shape.
What you must remember
- Pathology: idiopathic avascular necrosis of the femoral head, followed by fragmentation, reossification and healing over several years.
- Typical patient: boys aged about 4 to 10 years, who are affected far more often than girls.
- Presentation: a painless or mild limp, with groin, thigh or knee pain and reduced internal rotation and abduction.
- Early imaging: the first radiograph may be normal, and MRI is the most sensitive investigation in the early stage.
- Gage sign: a V-shaped lucency in the lateral part of the epiphysis, associated with a less favourable outcome.
- Catterall classification: four groups grade the extent of femoral head involvement, with group IV carrying the worst prognosis.
- Lateral pillar classification: Herring groups A, B, B/C and C, where preserved lateral pillar height predicts a better outcome.
- Age at onset: onset before about six years of age generally carries a better prognosis than later onset.
How the disease unfolds on imaging
Perthes disease is a self-limiting process, but the femoral head can deform during the active phase. The table summarises the stages and what each shows.
| Stage | Key feature | Clinical implication |
|---|---|---|
| Avascular | Radiograph may be normal; MRI shows marrow change | Diagnosis is often made late without MRI |
| Fragmentation | Femoral head flattens and breaks up | Greatest risk of deformity; containment is most useful |
| Reossification | New bone forms and the head regains shape | Pain usually settles, but shape is still at risk |
| Healed | Residual deformity or a normal head | Residual deformity may lead to early arthritis |
Containment is most valuable during fragmentation, when the head is soft and most likely to deform. Activity restriction and bracing or surgery are chosen according to age and the lateral pillar grade. Osteotomy is considered in older children or when the head remains poorly covered, since a congruent hip is the goal and an uncovered head predicts early osteoarthritis.
Where the exam tries to catch you
Questions on this topic usually turn on early diagnosis and prognostic grading.
- Trap: excluding Perthes disease because the first radiograph is normal Correct: early changes can be invisible on plain film, so MRI or repeat radiographs are used to confirm the diagnosis.
- Trap: assuming hip pain in a 13-year-old is Perthes disease Correct: slipped capital femoral epiphysis is the main differential in an adolescent, and Perthes is usually younger.
- Trap: choosing surgery on the Catterall group alone Correct: lateral pillar classification and age at onset refine prognosis and containment decisions.
- Trap: allowing unrestricted weight bearing in the fragmentation stage Correct: activity restriction protects the femoral head while it is soft.
Frequently asked questions
What is the Gage sign in Perthes disease?
The Gage sign in Perthes disease is a V-shaped radiolucency in the lateral part of the femoral epiphysis on a radiograph. It reflects necrotic bone in the lateral segment of the femoral head and is associated with a less favourable outcome.
What is the Catterall classification in Perthes disease?
The Catterall classification in Perthes disease grades the extent of femoral head involvement into four groups. Catterall group IV, with involvement of nearly the whole head, carries the worst prognosis, and the grading helps guide containment treatment.
How does age at onset affect prognosis in Perthes disease?
Age at onset strongly influences prognosis in Perthes disease, with children presenting before about six years of age generally doing better. Older children, particularly those beyond about eight years, face a higher risk of residual deformity and early arthritis.
Why is containment used in Perthes disease?
Containment is used in Perthes disease to keep the femoral head covered by the acetabulum during the fragmentation phase, so the head regenerates in a rounder shape. Methods include abduction bracing or orthosis, and osteotomy is considered in older or more severe cases.