perthes disease 20 mark exam written answer

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Legg-Calvé-Perthes Disease (Perthes Disease)

Definition and Aetiology

Perthes disease (Legg-Calvé-Perthes disease, LCPD) is an idiopathic avascular necrosis (osteonecrosis) of the capital femoral epiphysis in children, resulting from interruption of blood supply to the femoral head. The aetiology is unknown, but a vascular insult leads to ischaemic necrosis of the proximal femoral epiphysis, followed by revascularisation, resorption, and eventual remodelling through a process of creeping substitution. There is a predominance of femoral head resorption over reformation, which risks permanent femoral head deformity.

— Miller's Review of Orthopaedics 9th Edition; ROSEN's Emergency Medicine

Epidemiology and Risk Factors

Most common in boys aged 4–8 years (male:female ≈ 4–5:1)
Peak incidence 5–8 years of age
Bilateral in 10–15% of cases; when bilateral, involvement is typically asymmetrical and non-simultaneous
Associated with: delayed skeletal maturation, positive family history, low birth weight, abnormal birth presentation, attention deficit hyperactivity disorder
Female sex, older age at onset, and bilateral presentation carry a worse prognosis

— ROSEN's Emergency Medicine; Miller's Review of Orthopaedics 9th Edition

Clinical Features

Symptoms:

Limp — the most common presenting complaint; often insidious onset
Pain — typically in the hip, groin, or referred to the thigh or knee (referred knee pain is a classic trap for delayed diagnosis)
Pain is worse with activity and relieved by rest
Effusion from reactive synovitis

Signs:

Restricted hip range of motion — particularly abduction and internal rotation
Trendelenburg gait (abductor weakness)
In advanced disease: muscular atrophy of the buttocks, thigh and calf; limb length discrepancy up to 2.5 cm

Differential diagnosis: Septic arthritis, transient synovitis, blood dyscrasias (sickle cell), hypothyroidism, multiple epiphyseal dysplasia, Gaucher disease

— ROSEN's Emergency Medicine; Miller's Review of Orthopaedics 9th Edition

Pathological Stages (Waldénström Classification)

There are four sequential stages that all cases pass through:

Stage	Findings
1. Initial (Ischaemic)	Sclerotic epiphysis, medial joint space widening; radiographs may be normal for 4–6 months
2. Fragmentation	Bone resorption and collapse of the femoral head; crescent sign develops
3. Reossification	New bone appears; femoral head gradually reshapes; may last up to 18 months
4. Healed/Remodelled	Continued remodelling until skeletal maturity; residual deformity may persist

— ROSEN's Emergency Medicine; Miller's Review of Orthopaedics 9th Edition

Investigations

Plain radiography (first line):

AP pelvis and frog-leg lateral views
Earliest sign: crescent sign — a radiolucent subchondral fissure indicating subchondral fracture
Progression: loss of height, fragmentation, sclerosis, and widening of the medial joint space
May be normal early in disease

Perthes disease radiographs: (A) Early disease showing subtle right femoral head changes; (B) Advanced disease with marked fragmentation, sclerosis, and deformity of both femoral heads

Fig. — Perthes Disease. (A) Frog lateral at presentation showing the crescent sign (subchondral lucency) of early AVN of the right capital femoral epiphysis. (B) Rapid progression with irregularity, loss of height and sclerosis of the femoral head 8 months later. — Grainger & Allison's Diagnostic Radiology

MRI:

Now the imaging modality of choice when plain radiographs are normal but symptoms persist >6 weeks
Highly sensitive for early avascular necrosis
Intravenous contrast helps identify viable versus dead bone in equivocal cases
Dead bone loses signal on both T1 and T2; MRI also defines extent of involvement

Bone scintigraphy: Highly sensitive and specific, but largely replaced by MRI

— Grainger & Allison's Diagnostic Radiology; ROSEN's Emergency Medicine

Classification Systems

1. Herring Lateral Pillar Classification (most prognostically important)

Assessed during the fragmentation stage on the AP radiograph; based on height of the lateral pillar of the capital femoral epiphysis:

Group	Lateral Pillar Height	Prognosis
A	Little/no involvement	Uniformly good outcome
B	>50% of height maintained	Good if bone age <6 years; poorer if older
B/C	Borderline (50% height, narrow or poorly ossified)	Intermediate
C	<50% of height maintained	Poor in all age groups

2. Catterall Head-at-Risk Signs (radiographic poor prognostic indicators)

Lateral calcification
Gage sign (V-shaped defect at lateral physis)
Lateral subluxation of the femoral head
Metaphyseal cyst formation
Horizontal growth plate

3. Modified Catterall Classification (I–IV)

Based on the extent of femoral head involvement (used alongside Herring in some centres).

— Miller's Review of Orthopaedics 9th Edition; Grainger & Allison's Diagnostic Radiology

Prognosis

The single most important determinant of outcome is maintenance of femoral head sphericity. An aspherical femoral head at skeletal maturity leads to early degenerative hip disease.

Poor prognostic factors:

Older age at onset (chronological age >8 years; bone age >6 years)
Female sex
Lateral pillar C classification (poor at any age)
Lateral pillar B in older children (bone age >6 years)
Restricted hip range of motion (especially decreased abduction)
Presence of Catterall head-at-risk signs

— Miller's Review of Orthopaedics 9th Edition

Management

Principles

The overarching goal is containment — keeping the femoral head centred within the acetabulum during the vulnerable period of fragmentation and reossification, to allow the malleable femoral head to remodel into a spherical shape.

Conservative (Non-operative)

Activity restriction and partial weight-bearing with crutches (days to weeks depending on symptoms)
NSAIDs/anti-inflammatory medications for pain and synovitis
Physiotherapy to maintain hip range of motion
Traction (inpatient or outpatient) to relieve pain and restore abduction
Petrie casting (bilateral hip abduction cast) — maintains containment
Bracing (Scottish Rite orthosis and other dynamic abduction orthoses) — used for containment though evidence for bracing over observation alone is debated

Surgical (Operative)

Indicated for older children (chronological age >8 years, bone age >6 years) with lateral pillar B and B/C disease, where surgery improves radiographic outcome at skeletal maturity.

Containment procedures:

Proximal femoral varus osteotomy — redirects femoral head into acetabulum
Pelvic osteotomy (Salter, triple, Dega, or Pemberton) — redirects acetabulum over the femoral head
Shelf osteotomy — prevents lateral subluxation and epiphyseal overgrowth

Salvage procedures (for hips that can no longer be contained or have hinge abduction):

Valgus femoral osteotomy — for hinge abduction deformity
Chiari pelvic osteotomy and/or shelf procedure — for irreducible hips
Later in life: total hip arthroplasty for established secondary osteoarthritis

— Miller's Review of Orthopaedics 9th Edition; ROSEN's Emergency Medicine; Grainger & Allison's Diagnostic Radiology

Complications and Long-Term Outcome

Early degenerative hip arthritis — the principal long-term complication, arising from aspherical femoral head deformity (coxa magna)
Coxa magna — enlarged, flat femoral head with lateral uncovering
Limb length discrepancy — up to 2.5 cm
Hinge abduction — flattened head catches on the acetabular rim on abduction, a mechanically unfavourable pattern
Children presenting at bone age <6 years with lateral pillar A or B disease generally have good outcomes even without surgical intervention

Summary Table

Feature	Detail
Age	4–8 years (peak 5–8)
Sex	Boys >> girls (4:1)
Aetiology	Idiopathic AVN of capital femoral epiphysis
Presentation	Limp, hip/knee pain, restricted abduction & IR
Key radiograph sign	Crescent sign (subchondral fracture)
Best prognostic tool	Herring lateral pillar classification
Treatment goal	Containment — preserve femoral head sphericity
Worst outcome	Lateral pillar C, age >8, female sex

Sources: Miller's Review of Orthopaedics 9th Edition | ROSEN's Emergency Medicine | Grainger & Allison's Diagnostic Radiology | Tintinalli's Emergency Medicine

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