Legg-Calvé-Perthes Disease

Legg-Calvé-Perthes disease (also called Perthes disease or coxa plana) is idiopathic avascular necrosis of the femoral head in children. It is a self-limiting condition characterized by interruption of blood supply to the femoral epiphysis, followed by necrosis, fragmentation, revascularization, and remodeling.

Key features:

• Idiopathic AVN - cause unknown (unlike traumatic or sickle cell AVN)
• Self-limiting - natural history is 2-4 years from onset to healing
• Outcome depends on containment - maintaining head within acetabulum during healing
• Remodeling potential - younger children have excellent potential for recovery

Epidemiology:

Blood supply to the femoral head:

The pediatric femoral head receives blood from:

• Lateral epiphyseal vessels (branches of medial femoral circumflex) - primary supply
• Foveal vessels (from ligamentum teres) - minimal in young children
• Metaphyseal vessels - blocked by growth plate

Pathophysiology theories:

• Vascular occlusion - thrombosis of lateral epiphyseal vessels (? coagulopathy)
• Repetitive microtrauma - mechanical stress on vulnerable vessels
• Anatomical watershed - terminal vessels predisposed to ischemia
• Venous outflow obstruction - increased intraosseous pressure

Natural history - four stages:

The Containment Principle:

The biological rationale for containment:

• The femoral head is soft and moldable during reossification
• The acetabulum acts as a mold to shape the reossifying head
• If the head extrudes laterally (loses containment), it reossifies in a non-spherical, mushroom shape
• Maintained containment → spherical head → good long-term outcome
• Lost containment → aspherical head → early osteoarthritis

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Multiple classification systems exist, but Herring lateral pillar is most reliable for prognosis and treatment decisions.

The natural-history section divides the disease into the four classic Waldenström stages, and the containment-prerequisites note warns that surgery must be at the "correct stage - not too early in necrosis, not too late in remodeling". That timing limb deserves to be developed, because it is what makes containment work or fail.

The modified Waldenström staging subdivides the classic four stages to time intervention, and is the staging used in current outcome studies (it showed good intra- and interobserver reliability in Nakamura 2022, PMID 36374570).

Typical presentation:

Physical examination findings:

Key findings in order of sensitivity:

1. Limited abduction - most sensitive early sign
2. Limited internal rotation - especially in flexion
3. Muscle spasm - protective spasm in hip flexors, adductors
4. Leg length discrepancy - apparent shortening from muscle spasm
5. Trendelenburg gait - abductor dysfunction

Differential diagnosis:

The epidemiology and imaging sections note that 10-15% of cases are bilateral and that both hips must be radiographed. A crucial examiner point sits behind that figure: the PATTERN of bilateral involvement determines whether it is Perthes at all.

True bilateral Perthes is almost always asynchronous - the two hips are at different stages at the same time, because the two ischaemic events occur at different times. By contrast, bilateral SYMMETRIC femoral-head changes (both hips at the same stage, mirror-image) are NOT Perthes and should trigger a search for a generalised cause.

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Radiographic signs by stage:

Key radiographic measurements:

• Lateral pillar height: compare affected to normal side (Herring classification)
• Extrusion index: percentage of femoral head lateral to Perkin's line (normal less than 20%)
• Epiphyseal quotient: width of affected epiphysis / normal side (measures coxa magna)

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Algorithm

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Treatment depends on age at onset and extent of involvement (Herring classification).

General principles:

• Goal: spherical, congruent femoral head at skeletal maturity
• Containment: maintain head within acetabulum during reossification
• ROM: maintain hip ROM to prevent stiffness
• Natural history: disease lasts 2-4 years regardless of treatment

Long-term outcomes:

• Stulberg I-II: excellent long-term function, low risk of OA
• Stulberg III: moderate risk of OA, typically after age 50-60
• Stulberg IV-V: high risk of early OA, often requiring THA by age 40-50

Key Rehabilitation Principles:

Follow-up Schedule:

• Surgical cases: 2 weeks (wound), 6 weeks (healing), 3 months, 6 months, then every 6 months until reossification complete
• Non-operative cases: Every 3-4 months until reossification complete
• Long-term: Annually until skeletal maturity (assess final Stulberg classification)
• Transition: To adult services for ongoing OA risk monitoring

Perthes disease has no single international clinical-practice guideline; management is guided by the prospective cohort evidence above and by paediatric-orthopaedic registries. The picture below is deliberately global rather than tied to any one health system.

Global epidemiology (population-based):

Reported incidence therefore varies several-fold worldwide (single figures to mid-teens per 100,000), with a consistent male predominance (roughly 3-5:1) and a robust association with socioeconomic deprivation. A Swedish national-register study also found increased rates of obesity, hypertension and other osteochondroses in affected children, supporting a possible systemic component (Hailer 2018, DOI).

Where management genuinely differs (and where it agrees):