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Legg-Calvé-Perthes disease (Perthes)
Perthes is idiopathic avascular necrosis of the femoral head in a child aged 4–8, passing through stages of necrosis, fragmentation, healing and remodelling; the aim is to keep a round, covered head inside the acetabulum.
Why it matters in the exam
The typical stem describes a boy aged 4–8, often short for his age, with a painless limp or mild knee pain and restricted abduction and internal rotation, without fever or raised inflammatory markers. It must be told apart from transient synovitis, septic arthritis and SCFE, which appears at an older age. The decision rests on age at onset and the extent of head involvement: onset younger than 6 carries a good prognosis, while age above 8 with extensive involvement usually justifies surgery. Early radiographs can be normal, so MRI shows the disease sooner. The disease passes through four stages that together last two to four years: initial necrosis with a denser head on radiographs, fragmentation of the epiphysis, healing with new bone formation and finally remodelling until skeletal maturity. During fragmentation the head is soft and can deform, so this is the window in which treatment has the greatest effect. For the exam, remember that the disease is bilateral in about one in ten cases, but almost always at different stages on the two sides. The difference between Perthes and transient synovitis is duration: transient synovitis settles within days, whereas a limp lasting weeks calls for radiographs and assessment of the femoral head. At every stage, explain to parents that the disease is long, that radiographs will look worse before they improve, and that the goal is good function in adult life rather than a perfect radiograph.
Key points
- Idiopathic necrosis of the femoral head in boys aged 4–8.
- Limp with mild pain, sometimes felt in the knee, and loss of abduction and internal rotation.
- No fever and no rise in inflammatory markers — unlike septic arthritis.
- Young age and a preserved lateral pillar mean a good prognosis.
- Treatment principle: keep motion and contain the head within the acetabulum.
Summary table
| Factor | Better prognosis | Worse prognosis |
|---|---|---|
| Age at onset | Younger than 6 | Older than 8 |
| Lateral pillar involvement (Herring) | Group A, pillar height preserved | Group C, loss of more than 50% of pillar height |
| Range of motion | Abduction and motion preserved | Fixed loss of abduction |
| Head-at-risk signs | No lateral subluxation or lateral calcification | Lateral extrusion of the head and Gage sign |
| Final head shape | Round head congruent with the acetabulum | Flat, incongruent head with early osteoarthritis |
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Sources
- Lovell and Winter's Pediatric Orthopaedics, 8th ed. (2020) — Legg-Calvé-Perthes Disease
- Apley and Solomon's System of Orthopaedics and Trauma, 10th ed. (2017) — The Hip
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.