Perthes Disease

Legg-Calvé-Perthes disease (LCPD) is an idiopathic avascular necrosis (AVN) of the proximal femoral epiphysis in skeletally immature children, classically aged 4–8 years. It is a self-limiting but potentially deforming condition where the central question for the examiner — and the surgeon — is always containment of the femoral head within the acetabulum to allow biological remodelling.

Definition & key demographics

Perthes disease is a non-inflammatory, idiopathic osteonecrosis of the femoral head epiphysis caused by a temporary interruption of its blood supply, followed by revascularisation and reossification. It is one of the osteochondroses.

Feature	Typical value (high-yield)
Age	4–8 years (range 2–12)
Sex	Boys >> Girls (4–5 : 1)
Laterality	Unilateral in ~85–90%; bilateral in 10–15% (asymmetric, sequential)
Body habitus	Short stature, delayed bone age, "thin, active, fidgety" child
Race	Common in Caucasian/Asian; rare in Africans

High-yield: If a child presents with bilateral, symmetrical epiphyseal changes at the same stage, the diagnosis is NOT Perthes — think of epiphyseal dysplasia (Meyer dysplasia, multiple epiphyseal dysplasia) or hypothyroidism. True Perthes is bilateral in only 10–15% and always asymmetric/sequential.

Etiology & pathophysiology

The cause is idiopathic, but the final common pathway is interruption of blood supply to the femoral head. The proximal femoral epiphysis in children aged 4–8 is especially vulnerable because the lateral epiphyseal vessels (branches of medial circumflex femoral artery) are the sole supply after the involution of the metaphyseal supply and before the ligamentum teres vessels mature.

Proposed mechanisms / associations:

• Repeated micro-trauma / vascular insult (most accepted)
• Thrombophilia — deficiency of protein C, protein S, antithrombin III; raised factor V Leiden (controversial but tested)
• Passive smoking, low socioeconomic status, delayed bone age
• ADHD-like hyperactivity associations

Stages of disease (Waldenström radiological staging)

The disease evolves through predictable phases. The classic Waldenström staging is the radiological backbone:

1. Initial / avascular (necrosis) stage → smaller, sclerotic, dense epiphysis; widened joint space (medial). Crescent sign appears.
2. Fragmentation stage → the head fragments as revascularisation/resorption occurs; appears "moth-eaten."
3. Reossification / healing stage → new bone fills in.
4. Remodelling / residual stage → the head remodels into its final (possibly deformed) shape.

High-yield: The crescent sign (Caffey sign) = a subchondral radiolucent fracture line in the superolateral epiphysis, best seen on a frog-leg lateral view. It marks the subchondral fracture during the avascular stage and predicts the extent of the segment that will eventually fragment.

Pathophysiology flow: Vascular interruption → infarction of epiphyseal bone → marrow necrosis & cessation of ossification → subchondral fracture (crescent sign) under load → revascularisation with osteoclastic resorption (fragmentation) → new woven bone deposition (reossification) → remodelling. Because cartilage is nourished by synovial fluid, the articular cartilage survives and even overgrows (which is why the head often appears enlarged — coxa magna).

Clinical features

• Insidious limp, often painless or with mild groin/thigh/knee pain — classically referred pain to the knee (obturator nerve). Always examine the hip in a child with knee pain.
• Pain worse with activity, relieved by rest.
• Antalgic / Trendelenburg gait.
• Restricted abduction and internal rotation (the first movements lost).
• Roll test positive — guarding/spasm on gentle log-rolling of the limb.
• Thigh/gluteal muscle wasting in chronic cases; mild limb-length shortening later.
• No systemic signs — afebrile, no toxaemia (distinguishes from septic arthritis).

High-yield: The earliest movements restricted in any hip pathology, including Perthes, are abduction and internal rotation. Loss of internal rotation in a 5–8 year old boy with a limp = Perthes until proven otherwise.

Investigations & diagnosis

Plain radiograph (AP pelvis + frog-leg lateral) is the investigation of first choice and the basis of all classifications.

Radiological signs (frequently tested)

Sign	What it represents
Crescent / Caffey sign	Subchondral fracture, superolateral epiphysis (frog-leg lateral)
Sagging rope sign	Sclerotic line across femoral neck = a healed metaphyseal defect; sign of previous severe disease / metaphyseal involvement
Gage sign	V-shaped radiolucency in lateral epiphysis & adjacent metaphysis → head-at-risk sign
Coxa magna / plana	Enlarged, flattened head (residual)
Coxa breva	Short femoral neck from physeal damage
Medial joint space widening	Early sign (synovitis + cartilage overgrowth)
Hinge abduction	Deformed lateral head impinges on acetabular rim during abduction

Catterall "Head-at-risk" signs (predict poor outcome)

1. Gage sign (V-shaped lucency lateral epiphysis)
2. Lateral calcification outside the epiphysis
3. Lateral subluxation of the head
4. Horizontal physis (instead of oblique)
5. Metaphyseal cysts/rarefaction

High-yield: Presence of "head-at-risk" signs shifts management toward active containment (surgical), regardless of Catterall group.

Other investigations

• MRI — most sensitive for early disease (detects marrow necrosis before radiograph changes) and best maps the extent of necrosis & cartilage. Now increasingly the modality for early/equivocal cases.
• Bone scan (Tc-99m) — shows a cold spot (reduced uptake) early in the avascular phase, before X-ray changes.
• Arthrography (dynamic) — assesses containment and detects hinge abduction intra-operatively.
• Labs (ESR, CRP, WBC) — normal; ordered mainly to exclude septic arthritis/transient synovitis.

Classification systems

1. Catterall classification (extent of epiphyseal involvement)

Group	Head involvement	Prognosis
I	Anterior epiphysis only (<25%)	Best — no sequestrum, no collapse
II	Up to ~50%, sequestrum present, intact lateral pillar	Good
III	~75% involved, only small medial/lateral fragment spared	Poor
IV	Whole head (100%)	Worst

2. Herring / Lateral Pillar classification (MOST useful prognostically; based on the lateral 15–30% of the epiphysis on AP film during early fragmentation)

Group	Lateral pillar height	Prognosis
A	Normal (no loss)	Excellent — uniformly good
B	>50% height maintained	Good if onset < 8 yrs
B/C border	~50%, very thin/poorly ossified	Intermediate
C	<50% height maintained	Worst — poor outcome regardless of treatment

High-yield: The lateral pillar (Herring) classification is the single best predictor of outcome and is age-dependent: in children < 6 years, outcome is good regardless of group; age at onset > 8 years is itself a poor prognostic factor.

3. Salter-Thompson classification (early, based on the subchondral fracture/crescent)

• Group A — crescent involves < 50% of the head → corresponds to Catterall I–II → better prognosis.
• Group B — crescent involves > 50% of the head → corresponds to Catterall III–IV → worse prognosis. The advantage of Salter-Thompson is that it can be applied early (the crescent appears before fragmentation reveals full extent).

4. Stulberg classification (final outcome / congruency — predicts late osteoarthritis)

Class	Head shape	Outcome
I–II	Spherical, congruent	Good — low OA risk
III	Ovoid/aspherical but congruent	Aspherical congruency
IV	Flat head, flat acetabulum, congruent	Aspherical congruency
V	Flat head, normal acetabulum — incongruent	Aspherical incongruency → early OA

High-yield: "Aspherical incongruency (Stulberg V)" carries the highest risk of early osteoarthritis. The single best predictor of a good radiological outcome is a spherical, congruent, well-covered head at maturity.

Principles of management — "Containment"

The treatment philosophy is containment: keeping the soft, plastic femoral head deeply seated within the acetabulum so the acetabulum acts as a mould, allowing the head to remodel into a spherical, congruent shape during healing. Containment must be achieved before the head deforms (i.e., during the active fragmentation/healing phase).

Decision flow: Confirm Perthes (X-ray/MRI) → assess AGE + Herring group + range of motion + head-at-risk signs → decide containment strategy.

Factors favouring conservative (non-operative) management

• Age < 6 years (excellent remodelling potential)
• Catterall I–II / Herring A or early B
• Full/near-full range of motion, no head-at-risk signs

Conservative measures:

• Activity restriction, rest, NSAIDs for synovitis
• Physiotherapy to maintain abduction & internal rotation (the key "containment" movements)
• Abduction bracing/casts (Petrie casts, Scottish Rite brace) — historically used; current evidence shows limited benefit; largely abandoned in many centres but still examinable.
• Maintain motion + observe through stages.

Factors favouring surgical (operative) containment

• Age > 8 years
• Herring B/C border or C, Catterall III–IV
• Head-at-risk signs present
• Progressive subluxation / loss of containment

Surgical options:

• Femoral varus derotation osteotomy (FVO) — redirects the head into the acetabulum (most common).
• Pelvic (Salter innominate) osteotomy — redirects/augments acetabular cover.
• Combined femoral + pelvic in severe cases.
• Shelf / Chiari procedures — salvage for older children or established deformity.
• Valgus / abduction-extension osteotomy — for hinge abduction in the deformed (late) head.

High-yield: The two pillars of treatment are "contain the head" and "maintain range of motion." Containment is futile once the head has already deformed and hinge abduction is present — there the goal shifts to salvage (valgus osteotomy / shelf).

High-yield: Age at onset is the most important patient prognostic factor; lateral pillar (Herring) group is the most important radiological factor. Younger child + lower Herring group = better outcome.

Complications & sequelae

• Coxa magna (enlarged head from cartilage overgrowth) and coxa plana (flat head).
• Coxa breva — short neck from premature physeal arrest → Trendelenburg gait, abductor weakness.
• Greater trochanteric overgrowth (relative, from neck physeal arrest).
• Hinge abduction — deformed lateral head levers against acetabular rim.
• Osteochondritis dissecans of the femoral head.
• Limb-length discrepancy (usually mild).
• Premature secondary osteoarthritis in adulthood — the major long-term concern (correlates with Stulberg class).

Key differentials (heavily exam-tested)

The classic NEET PG triad to separate is Perthes vs Transient synovitis vs SUFE (slipped upper femoral epiphysis), plus septic arthritis.

Feature	Transient (toxic) synovitis	Perthes disease	SUFE	Septic arthritis
Typical age	3–8 yrs	4–8 yrs	10–16 yrs (adolescent)	Any (often infant/toddler)
Sex	M > F	M >> F	M > F (often obese)	—
Onset	Acute, often post-viral URTI	Insidious limp	Sub-acute / acute (after minor trauma)	Acute, severe
Systemic	Mild/none, often afebrile	None	None	Toxic, high fever
Body habitus	Normal	Thin, short	Obese / hypogonadal	—
Hip position	Mild flexion	Variable	External rotation, shortening; limited internal rotation	Flexion-abduction-ext rotation; pseudoparalysis
Pain on movement	Mild, resolves in days	Mild, chronic	Worse on internal rotation	Severe, all movements
Labs (ESR/CRP/WBC)	Normal/mildly raised	Normal	Normal	Markedly raised
X-ray	Normal	Epiphyseal changes (see above)	Slipped epiphysis — "ice-cream slipping off cone"; Klein line abnormal; Trethowan sign	Widened space ± destruction
Management	Rest, NSAIDs, self-limiting (resolves 1–2 wks)	Containment	Urgent in-situ pinning (CC screw)	Emergency drainage + IV antibiotics

High-yield: Drehmann sign — obligatory external rotation of the hip on passive flexion — is classic for SUFE, not Perthes. Klein's line (drawn along superior femoral neck) failing to intersect the epiphysis (Trethowan sign) confirms SUFE.

High-yield: Kocher criteria (for septic arthritis vs transient synovitis): (1) non-weight-bearing, (2) ESR > 40 mm/hr, (3) fever > 38.5 °C, (4) WBC > 12,000. 4/4 → ~99% probability of septic arthritis. Use this to exclude infection before calling a limp "Perthes."

Other differentials

• Multiple/Meyer epiphyseal dysplasia (bilateral, symmetric, same stage).
• Hypothyroidism, sickle-cell disease, Gaucher disease, steroid-induced AVN (secondary AVN; consider if atypical age or bilateral).
• Septic arthritis / tubercular hip (chronic limp + constitutional signs).

Mnemonics & eponyms

• "CATS HERd" for the named classifications: Catterall, Salter-Thompson, Herring (lateral pillar), Stulberg (outcome).
• Catterall head-at-risk signs — "G-L-S-H-M": Gage sign, Lateral calcification, Lateral Subluxation, Horizontal physis, Metaphyseal cysts.
• Eponyms: Legg (USA) – Calvé (France) – Perthes (Germany) described it independently c. 1910; Waldenström (staging), Caffey (crescent), Gage (V-sign), Drehmann/Klein/Trethowan (for the SUFE mimic).
• "Contain to remodel" — the one-line treatment philosophy.

Recently asked / exam angle

• Most-tested single fact: The lateral pillar (Herring) classification is the best prognostic indicator; identify which group has the worst prognosis (Group C).
• Image-based: Recognise the crescent (Caffey) sign, sagging rope sign, and coxa magna/plana on X-ray; identify frog-leg lateral as the best view for the crescent.
• Differentiation MCQs: Age-based separation of Perthes (4–8 yrs) vs SUFE (10–16 yrs, obese, external rotation, Drehmann/Klein/Trethowan) vs transient synovitis (post-viral, self-limiting). SUFE pairing with obesity / hypothyroidism / hypogonadism is a frequent stem.
• "Head-at-risk" signs — name them; recognise that their presence pushes toward operative containment.
• Best investigation: X-ray (first), MRI most sensitive for early disease, bone scan = cold spot early.
• Treatment principle: "Containment" + age dependence (< 6 yrs do well regardless).
• Stulberg V (aspherical incongruency) → highest risk of early osteoarthritis (long-term outcome question).
• Distinguishing bilateral symmetric epiphyseal disease = dysplasia/hypothyroidism, NOT Perthes is a classic trap.

Rapid revision

1. Perthes = idiopathic AVN of femoral head, boys 4–8 yrs, unilateral in ~85–90%.
2. Blood supply lost = lateral epiphyseal branches of medial circumflex femoral artery.
3. Staging = Waldenström (avascular → fragmentation → reossification → remodelling).
4. Crescent (Caffey) sign = subchondral fracture, superolateral, best on frog-leg lateral.
5. Sagging rope sign = healed metaphyseal defect = severe past disease.
6. Herring lateral pillar = best prognostic classification; Group C = worst.
7. Catterall head-at-risk signs: Gage, lateral calcification, lateral subluxation, horizontal physis, metaphyseal cysts → favour surgery.
8. Investigation of choice: X-ray first; MRI most sensitive early; bone scan shows cold spot; labs normal.
9. Treatment = containment + maintain motion; age < 6 → good outcome regardless; surgery (FVO ± Salter osteotomy) for older/at-risk.
10. Refers pain to knee (obturator nerve) — always examine the hip in a child with knee pain.
11. SUFE is the adolescent (10–16 yr, obese) mimic — Drehmann, Klein, Trethowan signs; treat by in-situ pinning.
12. Stulberg V = aspherical incongruent head = highest risk of early osteoarthritis; bilateral symmetric changes = think dysplasia/hypothyroidism, not Perthes.