Perthes Disease
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Direct answer
Perthes disease is idiopathic avascular necrosis of the growing capital femoral epiphysis, affecting children between roughly 4 and 10 years with a peak near 6, a 4-5:1 boy predominance, and about 15 per cent bilateral, sequential involvement. Repeated infarcts are followed by fragmentation, reossification and remodelling over 2-4 years, so the child presents with a painless limp and hip or knee-referred pain, irritability on internal rotation and abduction, and a radiograph that changes with the Waldenstrom stage — initial, fragmentation, healing, residual. Prognosis depends chiefly on age at onset (under 6 does well, over 8 poorly) and on how much head is involved, graded by Catterall groups and the Herring lateral pillar classification. Treatment is containment — keeping the softened head inside the acetabulum — by observation in the young with small lesions, and abduction bracing or femoral or pelvic osteotomy in the older child with extensive disease.
What you must remember
- Waldenstrom stages: initial (widened joint space, densification), fragmentation (the head at its weakest), healing or reossification, residual.
- Extent classifications: Catterall I-IV by quadrant involvement; Salter-Thompson A (under half the head) versus B (over half); Herring lateral pillar A, B, B/C border, C by collapse of the lateral third — the best correlate of outcome.
- Head-at-risk signs (Catterall): lateral calcification, Gage's sign (V-shaped lateral radiolucency), lateral subluxation, metaphyseal cysts, horizontal growth plate — predict poorer outcome and push toward containment.
- Examination findings: painful restriction of internal rotation and abduction, antalgic and Trendelenburg limp; the child is afebrile and well, unlike septic arthritis.
- Containment options: Petrie cast or abduction orthosis for the 6-8 year old with moderate disease; femoral varus derotation or Salter innominate osteotomy for the over-8 group with pillar B or C hips.
- Prognostic core: age over 8, pillar C involvement, and loss of containment predict aspherical Stulberg outcomes and early osteoarthritis; spherical heads do well for decades.
- Rule out first: transient synovitis, septic arthritis, juvenile idiopathic arthritis, hypothyroidism, and multiple epiphyseal dysplasia — bilateral symmetric disease suggests dysplasia, not Perthes.
Working through a limp in an eight-year-old
An eight-year-old boy has had a limp for two months with occasional knee pain; he is afebrile, walks with a Trendelenburg lurch, and internal rotation is limited and painful. The knee is normal — the pain is referred via the obturator nerve, and treating the knee while missing the hip is the classic delay. A frog-leg lateral radiograph shows a flattened, dense head with fragmentation of the lateral third and a metaphyseal cyst: fragmentation stage, Herring lateral pillar B/C, two head-at-risk signs.
Two clocks now govern reasoning. The biological clock says the disease runs necrosis-to-reossification over 2-3 years regardless of intervention; the shape clock says the final head depends on whether the softened lateral pillar stays covered during the vulnerable period. Because he is over eight with pillar B/C disease, observation alone courts an aspherical head and early osteoarthritis, so containment is chosen — a Salter innominate or femoral varus derotation osteotomy. Had the same films belonged to a five-year-old with pillar A disease, the answer would be reassurance and review: younger heads remodel, and surgery would be over-treatment.
How the exam frames it
Image stems show either the dense flattened epiphysis of fragmentation or the healed aspherical head of a Stulberg outcome. Favourite one-liners: knee pain with hip disease (obturator referral), peak age 6, boy predominance, and the four Waldenstrom stages in order. Expect a match-the-sign question on head-at-risk signs — lateral calcification and Gage's sign most quoted — and the management split by age: under 6 observe, 6-8 contain by pillar, over 8 contain operatively when the head is at risk. In Indian outpatient reality, children present months into the disease with limps dismissed as "growing pain", and late fragmentation-stage films are the norm; bilateral symmetric involvement deserves a dysplasia check before committing to the Perthes label.
Frequently asked questions
What age group does Perthes disease affect, and who fares worst?
Typically 4-10 years, peak around 6, boys four to five times more often; onset after 8 carries the worst prognosis because remodelling potential is largely spent.
What are Catterall's head-at-risk signs?
Lateral epiphyseal calcification, Gage's sign, lateral subluxation, metaphyseal cysts, and a horizontal growth plate — two or more predict poor outcome and favour containment.
Which classification grades the lateral pillar?
The Herring lateral pillar classification (A, B, B/C border, C) grades collapse of the lateral third of the epiphysis and correlates best with final Stulberg outcome, guiding containment surgery.
Why does knee pain dominate a hip presentation?
The hip and medial knee share obturator nerve innervation, so hip pathology in children often presents as thigh or knee pain — every unexplained knee pain needs a hip examination and radiograph.
What is the principle of treatment?
Containment — keeping the mechanically weak epiphysis within the acetabulum during fragmentation and reossification, by abduction bracing or femoral varus or Salter pelvic osteotomy in higher-risk older children.