Perthes Disease (Legg-Calvé-Perthes Disease)

1. Overview

Legg-Calvé-Perthes disease (LCPD), commonly known as Perthes disease, is an idiopathic avascular necrosis (AVN) of the capital femoral epiphysis in children. First described independently by Arthur Legg, Jacques Calvé, and Georg Perthes in 1910, it represents a self-limiting condition characterised by interruption of blood supply to the developing femoral head, leading to bone death, fragmentation, and subsequent remodelling over a period of 2-4 years. [1,2]

The disease predominantly affects children aged 4-8 years, with a striking male predominance (male:female ratio 4-5:1). The fundamental clinical challenge lies in the plasticity paradox: while the necrotic bone is biologically capable of complete remodelling and healing, the mechanical vulnerability during the fragmentation phase can lead to permanent femoral head deformity if the hip subluxates or loses its spherical congruence. This deformity predisposes to early-onset osteoarthritis in the fourth and fifth decades of life. [3,4]

The cornerstone of management is the concept of "containment"—maintaining the soft, fragmented femoral head within the acetabular mould during the critical fragmentation and reossification phases. Prognosis is primarily determined by age at onset (younger children remodel better) and the extent of epiphyseal involvement (quantified by the Herring Lateral Pillar Classification). [5,6]

Understanding Perthes disease requires appreciation of paediatric hip vascularity, growth plate biology, and biomechanical principles of joint congruence—making it a high-yield topic for postgraduate paediatric and orthopaedic examinations.

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2. Epidemiology

Incidence and Prevalence

Perthes disease has an estimated incidence of 1 in 10,000 children in the general population, though this varies significantly by geography and ethnicity. [7] The highest incidence is reported in populations of Northern European descent, with lower rates in African and Asian populations. [8]

Age and Sex Distribution

The disease shows a bimodal peak: a major peak between ages 4-8 years (80% of cases) and a minor peak between ages 2-4 years. Presentation before age 2 or after age 10 is unusual and should prompt consideration of alternative diagnoses. [1,10]

The striking male predominance remains unexplained, though theories include differences in:

• Vascular anatomy of the developing hip
• Physical activity levels and trauma exposure
• Hormonal influences on bone remodelling
• Genetic susceptibility factors

Risk Factors

Multiple epidemiological studies have identified consistent risk factors, though causation remains unproven: [8,11]

Demographic and Social Factors:

• Low socioeconomic status (strongest association)
• Small stature for age (height less than 25th percentile)
• Delayed bone age (skeletal maturation delay)
• Positive family history (5-10% of cases; polygenic inheritance pattern)

Environmental Factors:

• Passive smoking exposure (odds ratio 2.1)
• Low birth weight
• Maternal smoking during pregnancy
• Geographical latitude (higher incidence in northern latitudes)

Constitutional Factors:

• Attention deficit hyperactivity disorder (ADHD) - possibly reflecting increased activity
• Coagulopathies (Factor V Leiden, Protein C/S deficiency) - debated association [12]
• Abnormal fibrinolysis (thrombophilic states)

Medical Conditions:

• Transient synovitis of the hip (preceding episode in 5% of cases)
• Hypothyroidism (particularly with bilateral disease)
• Sickle cell disease (though typically causes acute AVN)

Temporal Trends

Incidence appears stable over recent decades, though improved imaging (particularly MRI) has enhanced early detection. Some studies suggest decreasing incidence in high-income countries, potentially related to improved nutrition and socioeconomic conditions. [8]

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3. Aetiology & Pathophysiology

Blood Supply to the Developing Femoral Head

Understanding the vascular anatomy is essential to comprehending Perthes disease:

Normal Vascular Supply:

• Medial Circumflex Femoral Artery (MCFA): Provides 80% of blood supply via lateral ascending cervical arteries (retinacular vessels)
• Lateral Circumflex Femoral Artery: Minor contribution
• Artery of ligamentum teres: Minimal contribution until age 8+ years

The developing femoral epiphysis is particularly vulnerable because:

1. Terminal end-arterial supply (no collaterals)
2. Vessels traverse the growth plate, which is vulnerable to trauma/inflammation
3. Intracapsular course makes vessels susceptible to tamponade from effusion
4. Limited contribution from ligamentum teres until later childhood

The Ischaemic Event

The initiating ischaemic insult remains poorly understood. Proposed mechanisms include: [13,14]

Vascular Theories:

• Venous congestion and stasis → increased intraosseous pressure → arterial insufficiency
• Arterial thrombosis (associated with thrombophilic states)
• Repetitive microtrauma → intimal damage → thrombosis
• Transient synovitis → elevated intracapsular pressure → vascular compression

Recent Evidence: Genetic studies have identified polymorphisms in genes related to:

• Collagen metabolism (COL2A1)
• Vascular endothelial growth factor (VEGF)
• Thrombophilia and coagulation pathways [15]

The "repeated infarction hypothesis" suggests multiple ischaemic episodes may occur before clinical presentation, explaining the variable extent of involvement at diagnosis. [13]

Waldenström Stages (Natural History)

Perthes disease progresses through four distinct radiological stages, described by Waldenström in 1922: [2,16]

Stage 1: Initial/Necrosis (3-6 months)

• Interruption of blood supply occurs
• Bone necrosis develops but cartilage remains viable (nourished by synovial fluid)
• Radiographic findings:
  • Increased density (sclerosis) of femoral epiphysis
  • Crescent sign (subchondral fracture)
  • Joint space widening (cartilage hypertrophy continues without ossification)
  • Normal or subtle changes initially
• Often detected late as children present with established disease

Stage 2: Fragmentation (6-12 months)

• Most critical stage for determining final outcome
• Dead bone is resorbed by osteoclasts (revascularisation brings osteoclasts)
• Radiographic findings:
  • "Popcorn" appearance—patchy lucencies and densities
  • Collapse of weakened bone
  • Metaphyseal cysts (adjacent reactive changes)
  • Risk of lateral extrusion and subluxation

Biomechanical vulnerability: The femoral head has minimal structural integrity during this phase. Normal weight-bearing forces (3-5× body weight during gait) can cause permanent deformity if the head is not contained within the acetabulum.

Stage 3: Reossification (18-24 months)

• New bone formation by osteoblasts
• Healing progresses from periphery to centre
• Radiographic findings:
  • Gradual re-ossification
  • Reduction in fragmentation
  • Improvement in bone density
  • Final shape becomes apparent

Stage 4: Healed/Remodelling (variable, up to skeletal maturity)

• Epiphysis fully ossified
• Final femoral head morphology depends on containment during fragmentation
• Continued remodelling until skeletal maturity (greater capacity in younger children)
• Acetabular remodelling also occurs (particularly if deformity present)

Pathological Anatomy

Post-mortem and surgical specimens reveal: [17]

• Necrotic bone with empty lacunae (dead osteocytes)
• Thickened, hypertrophic articular cartilage
• Metaphyseal bone marrow fibrosis and cysts
• Synovial inflammation (reactive synovitis)
• Labral hypertrophy (mechanical adaptation to head deformity)

Exam Detail: Molecular Pathophysiology:

Recent research has identified several cellular and molecular abnormalities in Perthes disease: [15,18]

1. Vascular Abnormalities:

   • Reduced VEGF expression in affected epiphyses
   • Abnormal angiogenesis during revascularisation
   • Arteriovenous shunting (blood bypasses capillary bed)

2. Inflammatory Mediators:

   • Elevated synovial fluid cytokines (IL-1β, TNF-α, IL-6)
   • Matrix metalloproteinases (MMPs) contributing to cartilage breakdown
   • Chronic synovitis perpetuates mechanical dysfunction

3. Genetic Factors:

   • Polymorphisms in type II collagen genes
   • Thrombophilic mutations (Factor V Leiden, MTHFR)
   • Impaired bone morphogenetic protein (BMP) signalling

4. Growth Plate Dysfunction:

   • Disrupted chondrocyte maturation and apoptosis
   • Abnormal enchondral ossification during healing
   • Premature physeal closure (can occur in severe cases)

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4. Clinical Presentation

Typical Presentation

Perthes disease classically presents with the "painless limp" or "intermittent limp" in a young child (4-8 years). Unlike septic arthritis or trauma, symptoms are often insidious and chronic.

Cardinal Symptoms

1. Limp (Present in > 90% of cases) [3,19]

• Insidious onset over weeks to months
• Intermittent, worse with activity
• Often first noticed by parents or teachers
• May be painless initially
• Character: Antalgic (pain-avoiding) or Trendelenburg (abductor weakness)

2. Pain (Present in 60-80% of cases)

• Location: Groin, anterior thigh, or referred to knee (obturator nerve distribution)
• Character: Dull, aching, mechanical
• Timing: Activity-related, relieved by rest
• Severity: Typically mild to moderate (unlike septic arthritis)
• Red flag: Severe pain or night pain should prompt investigation for alternative diagnoses

3. Stiffness

• Difficulty with activities: putting on shoes, climbing stairs
• Reduced hip range of motion
• Functional limitation varies with disease stage

Important Clinical Pearl

⚠️ "Always Examine the Hip in a Child with Knee Pain"

Referred pain to the knee via the obturator nerve is common in hip pathology. A child presenting with isolated knee pain without knee pathology should have hip examination and imaging performed. Missing hip pathology because of referred knee pain is a common clinical error.

Signs on Examination

A systematic hip examination is essential and should always include comparison with the contralateral (normal) hip.

Gait Analysis

• Antalgic gait: Shortened stance phase on affected side
• Trendelenburg gait: Pelvic drop on opposite side during single-leg stance (abductor weakness from pain/atrophy)
• Exacerbation with running: Limp becomes more pronounced with running or jumping

Inspection

• Muscle wasting of thigh and buttock (chronic disuse atrophy)
• Leg length discrepancy (apparent or true)

Range of Motion (ROM)

Loss of motion occurs in a predictable sequence: [19]

1. Internal rotation (earliest and most sensitive)
2. Abduction (indicates advancing disease)
3. Flexion (later finding)
4. Extension (variable)

Key Examination Technique:

• Prone internal rotation test: Child lies prone with knees flexed to 90°. Rotate feet outward (internally rotating hips). Asymmetry is highly sensitive for hip pathology.

Special Signs

"Hinge Abduction" [20]

• Loss of smooth abduction arc
• Instead, the femoral head "catches" or "hinges" at the acetabular rim
• Indicates aspherical femoral head with mechanical impingement
• Clinical significance: Poor prognostic sign; may indicate need for surgical containment

"Stinchfield Test"

• Passive hip flexion to 30° followed by resisted active straight leg raise
• Positive if reproduces groin pain
• Non-specific for Perthes but indicates hip-origin pain

Leg Length Discrepancy

• Apparent shortening: Due to adduction/flexion contracture (functional)
• True shortening: Due to femoral head collapse or premature growth plate closure (structural)
• Measure from anterior superior iliac spine (ASIS) to medial malleolus

Muscle Examination

• Thigh circumference measurement (documents atrophy)
• Abductor strength (Trendelenburg test - single leg stance)
• Adductor tightness (may cause apparent leg length discrepancy)

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5. Differential Diagnosis

The differential diagnosis of hip pain and limp in a child aged 4-8 years includes several important conditions. Perthes is often a diagnosis of exclusion in the early stages.

Must-Not-Miss Diagnoses

1. Septic Arthritis of the Hip [21]

• Distinguishing features:
  • Acute onset (hours to days)
  • Severe pain, refusal to weight-bear
  • Fever (though may be absent)
  • Elevated inflammatory markers (CRP, ESR, WCC)
  • Held in position of comfort (flexion, abduction, external rotation)
• Investigation: Urgent USS (shows effusion), aspiration for culture
• Action: Requires emergency surgical washout

2. Malignancy (Osteosarcoma, Ewing's Sarcoma, Leukaemia)

• Distinguishing features:
  • Night pain (classic red flag)
  • Systemic features (weight loss, fatigue, bruising)
  • Pain out of proportion to findings
  • Abnormal blood film or bone marrow
• Investigation: FBC, bone marrow aspiration, MRI
• Action: Urgent oncology referral

3. Slipped Upper Femoral Epiphysis (SUFE)

• Distinguishing features:
  • Older age group (10-14 years, pre-teens/early teens)
  • Often obese
  • Affected leg lies in external rotation
  • Restricted internal rotation
  • Acute-on-chronic presentation possible
• Investigation: AP and frog-leg lateral X-rays (Trethowan's line)
• Action: Urgent orthopaedic referral; surgical pinning

Often Confused Diagnoses

4. Transient Synovitis (Irritable Hip)

• Most common cause of hip pain in children (incidence 1 in 300)
• Distinguishing features:
  • Acute onset (days)
  • Often follows viral illness
  • Self-limiting (resolves in 7-10 days)
  • Normal inflammatory markers
  • Can weight-bear (though reluctant)
• Investigation: USS (shows effusion), X-ray normal
• Action: Conservative management, close follow-up (5% later develop Perthes)
• Kocher criteria help differentiate from septic arthritis

5. Multiple Epiphyseal Dysplasia (MED)

• Consider if: Bilateral synchronous presentation
• Distinguishing features:
  • Symmetrical joint involvement
  • Positive family history (autosomal dominant)
  • Short stature
  • Other joint abnormalities (knees, ankles)
• Investigation: Skeletal survey, genetic testing
• Action: Genetic counselling, multidisciplinary management

6. Meyer's Dysplasia

• Controversial entity (possibly normal variant or early Perthes)
• Features:
  • Irregular ossification of femoral head (typically age 2-4 years)
  • Smaller, fragmented ossific nucleus
  • Usually bilateral and symmetrical
  • Typically asymptomatic
• Management: Observation; resolves with normal development

7. Hypothyroidism

• Consider if: Bilateral disease, delayed bone age
• Features:
  • Global developmental delay
  • Short stature
  • Delayed dentition
  • Multiple epiphyseal involvement
• Investigation: Thyroid function tests
• Action: Endocrinology referral; thyroxine replacement

Comparison Table

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6. Investigations

First-Line Investigations

Plain Radiography

Standard views: Anteroposterior (AP) pelvis and frog-leg lateral (both hips for comparison)

Initial Stage Findings:

• Increased density (sclerosis) of femoral epiphysis
• Joint space widening (lateral to medial)
• Small, flattened epiphysis
• Crescent sign: Subchondral radiolucent line (pathognomonic when present; represents subchondral fracture)

Fragmentation Stage Findings:

• "Popcorn" appearance (mixed lucency and sclerosis)
• Collapse of lateral pillar
• Metaphyseal cysts and irregularity
• Lateral extrusion of femoral head

Key Radiographic Measurements:

• Lateral pillar height (for Herring classification)
• Extrusion index: Proportion of femoral head lateral to acetabular edge (> 20% is significant)
• Head-neck diameter ratio: Increased ratio indicates flattening
• Head sphericity index: Quantifies asphericity

Blood Tests

Purpose: Exclude differential diagnoses (not diagnostic of Perthes)

• Full blood count (FBC): Exclude leukaemia
• Inflammatory markers (CRP, ESR): Should be normal in Perthes (elevated suggests infection or malignancy)
• Bone profile: Typically normal
• Thyroid function tests: If bilateral disease or features of hypothyroidism

Second-Line Investigations

Magnetic Resonance Imaging (MRI)

Indications: [22]

• X-rays normal but high clinical suspicion
• Very early presentation
• Assessing extent of involvement pre-treatment
• Differentiating Perthes from transient synovitis in equivocal cases

Findings:

• T1-weighted: Low signal in necrotic epiphysis
• T2-weighted: High signal in joint effusion, bone marrow oedema
• Contrast-enhanced: Absent perfusion in necrotic areas (early); peripheral enhancement during revascularisation
• STIR sequences: Highlight bone marrow and cartilage abnormalities

Advantages:

• Detects AVN weeks before X-ray changes
• Assesses cartilage thickness (prognostic)
• Quantifies extent of involvement more accurately
• No radiation exposure

Disadvantages:

• Expensive
• May require sedation in young children
• Not routinely necessary in classic presentations

Ultrasound (USS)

Utility:

• Detects joint effusion (non-specific)
• Differentiates from septic arthritis (if aspiration needed)
• Assesses cartilage thickness (in specialist centres)

Limitation: Cannot visualise bone necrosis directly

Bone Scintigraphy (Technetium-99m Bone Scan)

Historical use: Previously used to assess perfusion ("cold" area indicates avascularity)

Current use: Largely replaced by MRI; occasionally used if MRI unavailable or contraindicated

Arthrography

Use: Intraoperative assessment during surgical containment procedures

• Visualises cartilaginous femoral head (not visible on X-ray)
• Confirms adequate containment before osteotomy fixation
• Identifies "hinge abduction" (head catches on acetabular rim)

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7. Classification and Staging

Multiple classification systems exist. The Herring Lateral Pillar Classification is the most widely used and has the best inter-observer reliability and prognostic value. [5,23]

Herring Lateral Pillar Classification (1992)

Basis: Height of the lateral pillar (lateral 15-30% of femoral head) during the fragmentation stage

Assessed on: AP radiograph during maximal fragmentation

Prognostic Value: [5,24]

• Group A: 95% good outcomes (Stulberg I-II) regardless of treatment
• Group B (age less than 8): 75% good outcomes with containment; 60% without
• Group B (age ≥8): 50% good outcomes with containment; 25% without
• Group C (age less than 8): 40% good outcomes with aggressive containment
• Group C (age ≥8): 15% good outcomes even with surgery

Catterall Classification (1971)

Historical significance: First systematic classification; now less commonly used due to poor inter-observer reliability

"Head-at-Risk" Signs (Catterall): [25] Radiographic features predicting poor outcome:

1. Gage sign: V-shaped radiolucent defect in lateral epiphysis
2. Calcification lateral to epiphysis: Ossification in extruded cartilage
3. Lateral subluxation: Uncovering of medial part of head
4. Horizontal growth plate: Abnormal physis orientation
5. Metaphyseal cysts: Reactive cyst formation

Waldenström Classification (Stage of Disease)

As previously described (Initial, Fragmentation, Reossification, Healed)—useful for documenting natural history progression

Salter-Thompson Classification (1984)

Based on: Extent of subchondral fracture (crescent sign)

• Group A: Crescent involves less than 50% of head (correlates with Catterall I-II)
• Group B: Crescent involves > 50% of head (correlates with Catterall III-IV)

Limitation: Crescent sign only visible early and may be missed

Stulberg Classification (Outcome at Skeletal Maturity)

Purpose: Describes final femoral head morphology; predicts risk of osteoarthritis [26]

Prognostic Significance:

• Classes I-II: "Good" outcome—low arthritis risk
• Classes III-IV-V: "Poor" outcome—inevitable early arthritis

Treatment Goal: Achieve Stulberg I or II at skeletal maturity

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8. Management

Management is guided by the "containment principle": keeping the soft, fragmented femoral head deeply seated within the acetabulum during the fragmentation and reossification phases, thus using the acetabulum as a spherical mould to maintain head shape. [27,28]

General Principles

Decision-Making Factors:

1. Age at onset (most important prognostic factor)
2. Extent of involvement (Herring classification)
3. Stage of disease (active fragmentation vs reossification)
4. Containment status (is head subluxed?)
5. Range of motion (especially abduction and internal rotation)

Management Algorithm

PERTHES DISEASE DIAGNOSIS CONFIRMED
              ↓
        AGE AT ONSET?
    ┌─────────┴─────────┐
  less than 6 YEARS          ≥6 YEARS
    ↓                   ↓
 OBSERVATION      HERRING CLASSIFICATION
 + Physio              ↓
 (Excellent       ┌────┴────┐
  prognosis)      A     B/B-C/C
                  ↓         ↓
              OBSERVE   AGE + CONTAINMENT?
                        ┌─────┴─────┐
                     less than 8 yrs      ≥8 yrs
                        ↓            ↓
                   CONTAINMENT   SALVAGE
                   (Surgical)    (Consider surgery
                                 for pain/mechanical
                                 symptoms)

Conservative Management

Indications:

• Age less than 6 years at onset (regardless of classification) [24]
• Herring A (any age)
• Established reossification stage (too late for containment)
• Age > 10 years with poor prognosis (salvage may be considered later)

Observation and Monitoring

Follow-up schedule:

• X-rays every 3-4 months during fragmentation stage
• Every 6 months during reossification
• Annually until skeletal maturity

Assess at each visit:

• Range of motion (document abduction and internal rotation)
• Leg length discrepancy
• Gait pattern
• Radiographic progression and containment

Physiotherapy

Goals: [29]

• Maintain hip range of motion (especially abduction and internal rotation)
• Prevent adduction contracture
• Strengthen hip abductors
• Maintain activity and fitness

Modalities:

• Hydrotherapy: Low-impact exercise in warm water
• Stretching: Gentle passive stretching to maintain ROM
• Strengthening: Once fragmentation phase passes
• Gait training: Correct abnormal gait patterns

Evidence: High-quality evidence for physiotherapy is limited, but consensus supports maintaining ROM to prevent secondary stiffness and contracture. [29]

Activity Modification

Principles:

• Avoid high-impact activities during fragmentation (12-18 months)
• Restrict jumping, trampolining, contact sports
• Encourage low-impact activities: swimming, cycling
• School: may require temporary adaptations (elevator access, reduced PE participation)

Balance: Over-restriction causes deconditioning and psychosocial impact; complete bed rest (historically used) is no longer recommended

Analgesia

• NSAIDs (ibuprofen): For pain and to reduce reactive synovitis
• Paracetamol: Routine analgesia as needed
• Avoid chronic opioid use

Bracing (Historical)

Types: Toronto brace, Scottish Rite orthosis, Petrie casts

Concept: Hold hips in abduction to maintain containment

Evidence: Multiple studies have shown no benefit compared to observation; associated with:

• Social stigmatisation
• Poor compliance
• Stiffness
• No improvement in outcomes [30]

Current use: Abandoned in most centres

Surgical Management (Containment Surgery)

Indications: [5,24,31]

• Age ≥6 years AND Herring B, B/C border, or C
• "Head-at-risk" signs (lateral subluxation, hinged abduction)
• Loss of containment despite conservative management
• Severe restriction of abduction (less than 15-20°)

Contraindications:

• Age less than 6 years (excellent prognosis without surgery)
• Herring A (good prognosis without intervention)
• Established reossification (too late)
• Poor general health or inability to comply with rehabilitation

Timing: Ideally during fragmentation stage (when head is maximally soft and malleable)

1. Femoral Varus Derotation Osteotomy (VDRO)

Concept: Cut the proximal femur and reorient it in varus (downward angle), improving containment by directing the femoral head deeper into the acetabulum

Technique:

• Proximal femoral osteotomy (subtrochanteric or intertrochanteric)
• Varus angulation (typically 10-20°)
• Often combined with derotation (corrects excessive anteversion)
• Fixation: Pediatric blade plate or locking plate

Advantages:

• Directly addresses femoral side
• Technically straightforward
• Can be combined with shortening (if leg length discrepancy)

Disadvantages:

• Leg length discrepancy (shortens affected leg by ~1-2 cm)
• Trendelenburg gait (abductor weakness due to altered biomechanics)
• Requires hardware removal later (second surgery)
• Does not address acetabular coverage

Outcomes: Studies show 70-80% good results (Stulberg I-II) in appropriately selected patients (age 6-8, Herring B/C). [31]

2. Pelvic Osteotomy (Salter Innominate Osteotomy)

Concept: Cut the pelvis and rotate the acetabulum anterolaterally to improve coverage of the femoral head

Technique:

• Osteotomy through ilium above the acetabulum
• Rotate acetabular fragment forward and outward
• Bone graft from iliac crest wedged into osteotomy gap
• Internal fixation with pins/screws

Advantages:

• Improves acetabular coverage (addresses "roof" of socket)
• No leg length discrepancy
• Improves anterior and lateral coverage
• Better long-term acetabular remodelling

Disadvantages:

• Larger, more complex surgery
• Potential for sciatic nerve injury
• Stiffness (may reduce ROM if overcorrected)
• Pelvic asymmetry

Outcomes: Similar success rates to femoral osteotomy in comparative studies. [32]

3. Triple Pelvic Osteotomy (Steel/Tönnis)

Concept: More extensive pelvic reconstruction (cuts through ilium, pubis, and ischium) allowing multiplanar acetabular reorientation

Indications:

• Older children (> 8 years)
• Severe lateral uncovering
• Salvage situations

Outcomes: Reserved for complex cases; higher complication rate

4. Shelf Acetabuloplasty (Chiari Osteotomy)

Concept: Add extra-articular bone "shelf" to lateral acetabular rim, providing additional coverage

Indications:

• Salvage procedure in older children/adolescents
• When intra-articular osteotomies not feasible
• "Rescue" for failed previous surgery

Outcomes: Provides biomechanical support but does not create true hyaline cartilage coverage

5. Soft Tissue Procedures

Adductor tenotomy: Rarely performed; releases tight adductors to improve abduction

Indications: Severe adduction contracture preventing containment

Comparison of Surgical Options

Special Situations

Bilateral Perthes (10-15% of cases)

• Usually asynchronous (different stages in each hip)
• If synchronous, investigate for skeletal dysplasia or hypothyroidism
• Staged surgery if both hips require intervention (treat worse hip first)
• Significant functional impact during treatment

Late Presentation (> 8 years)

• Poor prognosis even with surgery (limited remodelling potential)
• Consider salvage procedures if symptomatic:
  • Shelf acetabuloplasty
  • Femoral head reduction osteotomy
  • Valgus osteotomy (controversial)
• Focus on pain management and maintaining function
• Counsel regarding future arthritis risk

Hinge Abduction

• Mechanical impingement of aspherical head on acetabular rim during abduction
• Poor prognostic sign
• May indicate need for femoral head reduction surgery or shelf procedure
• Containment surgery alone may not address problem

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9. Complications

Early Complications (During Active Disease)

1. Lateral Extrusion and Subluxation

• Frequency: 15-30% if Herring B/C without treatment
• Mechanism: Weakened, fragmented head displaced laterally by muscle forces
• Consequences: Loss of containment → permanent flattening
• Prevention: Early containment surgery in at-risk hips
• Management: Surgical containment if caught early; salvage procedures if established

2. Hinge Abduction

• Frequency: 10-20% in Herring C
• Mechanism: Aspherical head catches on acetabular rim during abduction
• Consequences: Progressive deformity, labral damage, early arthritis
• Management: May require femoral head reduction or valgus osteotomy

3. Premature Physeal Closure

• Frequency: Rare (less than 5%)
• Mechanism: Damage to growth plate from ischaemia or surgery
• Consequences: Leg length discrepancy, progressive deformity
• Management: Contralateral epiphysiodesis (if significant discrepancy); limb lengthening in severe cases

Late Complications (Skeletal Maturity and Beyond)

4. Coxa Magna (Enlarged Femoral Head)

• Frequency: Common (50-70% even in good outcomes)
• Mechanism: Overgrowth during healing; acetabular remodelling
• Consequences: Usually asymptomatic; may cause impingement
• Management: Observation unless symptomatic

5. Coxa Plana (Flattened Femoral Head)

• Frequency: Correlates with Herring grade and age
• Mechanism: Collapse during fragmentation
• Consequences: Aspherical joint → early arthritis (Stulberg III-V)
• Management: Surveillance; total hip replacement when symptomatic

6. Femoroacetabular Impingement (FAI)

• Frequency: Up to 30% develop FAI morphology [33]
• Types: CAM (aspherical head) and mixed (CAM + pincer)
• Consequences: Hip pain in young adults, labral tears
• Management: Hip arthroscopy or open femoral osteochondroplasty

7. Early-Onset Osteoarthritis

• Frequency: 50% develop OA by age 50 if Stulberg III-V [26]
• Risk factors: Older age at onset, Herring C, poor containment, hinge abduction
• Presentation: Groin pain, stiffness, reduced function
• Management: Analgesia, physiotherapy, activity modification → eventual total hip replacement

Natural History Studies: [4,26]

• Stulberg I-II: 5% develop OA by age 65
• Stulberg III: 50% develop OA by age 50
• Stulberg IV-V: 80% develop OA by age 40-50

8. Leg Length Discrepancy

• Frequency: Mild discrepancy common (1-2 cm); severe (> 2 cm) less common
• Causes: Femoral head collapse, premature physeal closure, surgical shortening
• Management:
  • less than 2 cm: Shoe raise
  • 2-4 cm: Epiphysiodesis of contralateral leg

  • 4 cm: Femoral lengthening procedures

Surgical Complications

Femoral Osteotomy Complications

• Non-union (less than 5%)
• Hardware irritation/prominence (10-20%; requires removal)
• Over-correction or under-correction
• Stiffness (5-10%)

Pelvic Osteotomy Complications

• Sciatic nerve injury (less than 1%)
• Intra-articular penetration
• Graft displacement
• Heterotopic ossification (rare)

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10. Prognosis

Prognosis in Perthes disease is highly variable and depends on multiple factors. Understanding prognostic factors is essential for counselling families and guiding treatment decisions.

Prognostic Factors

Age at Onset (Most Important)

Biological Explanation: Younger children have:

• Longer time until skeletal maturity (more remodelling)
• Thicker cartilaginous anlage (protective)
• Greater capacity for acetabular remodelling (adapts to head shape)

Extent of Involvement (Herring Classification)

• Herring A: 95% good outcome regardless of age or treatment
• Herring B: 60-75% good outcome (better if age less than 8, with containment)
• Herring B/C border: 40-60% good outcome
• Herring C: 15-40% good outcome even with optimal treatment

Head-at-Risk Signs

Presence of ≥2 Catterall "head-at-risk" signs associated with 3-fold increased risk of poor outcome [25]

Range of Motion

• Preserved abduction (> 30°): Better prognosis
• Hinge abduction: Poor prognosis (mechanical dysfunction)
• Loss of ROM: Correlates with progression and poor containment

Containment

• Well-contained head: 80% good outcome
• Subluxed head (> 20% lateral extrusion): 30% good outcome

Sex

• Male: Slightly better prognosis (possibly related to younger age at presentation)
• Female: Worse prognosis at any given age (reason unclear)

Long-Term Outcomes

Iowa Hip Score (Natural History Study) [4]

• Followed 186 hips for average 40 years
• 50% had pain and functional limitation by age 50
• 45% underwent total hip replacement by age 60
• Outcome strongly correlated with final head shape (Stulberg class)

Stulberg Classification and OA Risk [26]

Effect of Treatment on Prognosis

Herring et al. Multicenter Study (2004) [5,24]

Most definitive evidence on treatment outcomes:

Herring B (Age less than 8 years):

• Surgical containment: 75% good outcome (Stulberg I-II)
• Observation alone: 60% good outcome
• Conclusion: Modest benefit from surgery

Herring B (Age ≥8 years):

• Surgical containment: 50% good outcome
• Observation alone: 25% good outcome
• Conclusion: Surgery beneficial but outcomes still guarded

Herring C (Any age):

• Surgery offers limited benefit
• Poor outcomes common regardless of treatment

Herring A (Any age):

• 95% good outcome regardless of treatment
• No benefit from intervention

Counselling Families

Key Messages for Parents

"Will my child's hip heal?"

• Yes, the blood supply always returns. The bone will regrow completely over 2-4 years.

"What is the risk?"

• While the bone is soft, it can become permanently flattened. A flat ball doesn't roll smoothly in a round socket, which can cause pain and stiffness later in life.

"What can we do to help?"

• Keep your child active but avoid high-impact activities (jumping, trampolining) during the healing phase.
• Physiotherapy to maintain movement is important.
• Follow-up X-rays to monitor progress.

"Does my child need surgery?"

• It depends on your child's age and how much of the hip is affected.
• Children under 6 years almost always heal well without surgery.
• Children aged 6-8 with moderate-to-severe involvement may benefit from an operation to guide the bone into the right shape.
• Children over 8 have less healing potential; we focus on maintaining comfort and function.

"What is the long-term outlook?"

• Most children do very well during childhood and young adulthood.
• If the hip heals with a good round shape, the long-term outlook is excellent.
• If the hip heals flat, there is an increased risk of arthritis in the 40s-50s, which may require hip replacement.
• We'll continue to monitor your child until they finish growing.

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11. Prevention & Screening

Primary Prevention

There are no established primary prevention strategies for Perthes disease, as the underlying cause remains idiopathic. Potential modifiable risk factors (based on epidemiological associations) include: [8,11]

• Smoking cessation (parental smoking exposure)
• Socioeconomic interventions (improved nutrition, housing)
• Avoidance of repetitive hip trauma (theoretical; no proven link)

Screening

No formal screening programs exist for Perthes disease.

High-Risk Groups

Consider heightened surveillance in:

• Siblings of affected children (5-10% recurrence risk)
• Children with previous transient synovitis (5% later develop Perthes)
• Children with unexplained hip pain or limp (early diagnosis improves outcomes)

Secondary Prevention (Early Detection)

Importance of Early Diagnosis:

• Allows intervention during early fragmentation (optimal for containment)
• Prevents progressive deformity
• Improves long-term outcomes

Clinical Vigilance:

• Always examine the hip in a child with knee pain
• Low threshold for hip X-ray in persistent limp (> 2 weeks)
• MRI if X-ray normal but high clinical suspicion

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12. Key Guidelines and Evidence

Major Clinical Guidelines

British Orthopaedic Association (BOA) Standards for Trauma (BOAST)

Recommendation (2017):

"Children under 6 years of age require symptomatic treatment only (physiotherapy, activity modification) unless there is clinical or radiological evidence of progressive head deformity or subluxation."

International Perthes Study Group Consensus [34]

Key Recommendations:

1. Age less than 6 years: Observation and physiotherapy
2. Age 6-8 years with Herring B/C: Containment surgery recommended
3. Age > 8 years: Surgery offers limited benefit; consider salvage procedures
4. Follow-up: Regular radiographs until skeletal maturity

Landmark Studies

1. Herring et al. (2004) - Multicenter Prospective Study [5,24]

Design: 438 hips from 14 centres followed for minimum 5 years

Key Findings:

• Herring classification is most reliable prognostic system
• Age and lateral pillar involvement are strongest predictors
• Surgery beneficial for age 6-8 with Herring B/C
• Surgery offers minimal benefit for age > 8 or Herring A

Impact: Changed practice worldwide; established current treatment algorithms

2. Stulberg et al. (1981) - Natural History [26]

Design: Long-term follow-up (40+ years) of untreated/conservatively treated patients

Key Findings:

• Final head shape (Stulberg class) predicts arthritis risk
• 50% develop symptomatic OA by age 50-65
• Aspherical femoral heads (Stulberg III-V) have high arthritis risk

Impact: Established Stulberg classification; highlighted importance of containment

3. Catterall (1971) - Natural History and Classification [25]

Design: Retrospective analysis of 127 hips

Key Findings:

• Described "head-at-risk" signs predicting poor outcome
• Proposed classification based on extent of involvement

Impact: First systematic classification; established prognostic factors

4. Wiig et al. (2008) - Long-Term Outcome Study [35]

Design: 60-year follow-up of Norwegian cohort

Key Findings:

• 47% underwent total hip replacement
• Mean age at THR: 53 years
• Quality of life significantly impaired in poor outcomes

Impact: Confirmed long-term morbidity; emphasized need for optimal treatment

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13. Exam-Focused Content

High-Yield Viva Questions

Viva Point: Q1: "Tell me about Perthes disease."

Model Answer: "Perthes disease is an idiopathic avascular necrosis of the capital femoral epiphysis affecting children aged 4-8 years, with a 4:1 male predominance. The incidence is approximately 1 in 10,000. The disease progresses through four Waldenström stages: Initial necrosis, fragmentation, reossification, and healed. Prognosis depends primarily on age at onset and extent of involvement, classified using the Herring Lateral Pillar system. Treatment is based on the containment principle—keeping the soft femoral head within the acetabular mould during the fragmentation phase. Children under 6 have excellent prognosis with observation, while older children with Herring B or C involvement may benefit from femoral or pelvic osteotomy to achieve containment."

Viva Point: Q2: "How would you clinically differentiate Perthes disease from transient synovitis?"

Model Answer: "Both conditions present with hip pain and limp in a child, but key differences exist:

If X-ray is normal but symptoms persist beyond 2 weeks, MRI should be performed to detect early Perthes."

Viva Point: Q3: "Describe the Herring Lateral Pillar Classification and its significance."

Model Answer: "The Herring classification assesses the height of the lateral pillar—the lateral 15-30% of the femoral head—during the fragmentation stage on AP X-ray:

• Group A: No loss of height → 95% good outcome regardless of treatment
• Group B: less than 50% height loss → 60-75% good outcome; surgery beneficial if age 6-8
• Group B/C border: Exactly 50% loss → Intermediate prognosis
• Group C: > 50% loss → Poor prognosis (less than 40% good outcome even with surgery)

It has the best inter-observer reliability and prognostic value among classification systems. The Herring study showed that age combined with lateral pillar grade determines treatment: children aged 6-8 with Herring B or C benefit from containment surgery, while those under 6 or with Herring A do well with observation alone."

Viva Point: Q4: "What is meant by 'containment' and how is it achieved?"

Model Answer: "Containment is the principle of maintaining the soft, fragmented femoral head deeply within the acetabulum during the fragmentation and reossification phases, using the acetabulum as a spherical mould to prevent head flattening.

Conservative containment:

• Physiotherapy to maintain abduction and internal rotation
• Activity modification (avoid high-impact activities)
• Historical bracing (Toronto/Scottish Rite) is no longer used due to lack of efficacy

Surgical containment:

1. Femoral varus osteotomy: Redirects femoral head deeper into acetabulum by angulating proximal femur downward (varus); simple but shortens leg
2. Pelvic osteotomy (Salter): Rotates acetabulum anterolaterally to increase coverage; preserves leg length but more complex
3. Triple pelvic osteotomy: For severe cases; allows multiplanar correction

Evidence from the Herring multicenter study shows surgical containment improves outcomes in children aged 6-8 with Herring B/C involvement."

Viva Point: Q5: "What is the Stulberg classification and why is it important?"

Model Answer: "The Stulberg classification describes the final femoral head morphology at skeletal maturity and predicts long-term risk of osteoarthritis:

• Class I: Normal spherical head → No increased OA risk
• Class II: Spherical but coxa magna/brevis → Minimal OA risk
• Class III: Ovoid (aspherical) but congruent → 50% develop OA by age 50
• Class IV: Flat head, flat acetabulum (incongruent) → 80% develop OA by age 40-50
• Class V: Flat head, normal acetabulum (incongruent) → Very high OA risk

Classes I-II are considered 'good outcomes'; classes III-V are 'poor outcomes' predisposed to early arthritis. The goal of treatment is to achieve Stulberg I or II. Long-term studies show that approximately 50% of Perthes patients develop symptomatic OA by age 50-65, with outcome strongly correlated to final Stulberg class."

Common Examination Mistakes

❌ Mistake 1: Missing referred knee pain

• Perthes commonly presents with isolated knee pain via obturator nerve referral
• Always examine the hip in a child with knee pain

❌ Mistake 2: Confusing Perthes with SUFE

• Perthes: Younger (4-8), gradual onset, loss of internal rotation and abduction
• SUFE: Older (10-14), obese, leg externally rotated, acute or chronic presentation

❌ Mistake 3: Over-treating young children

• Children less than 6 years have excellent prognosis without surgery
• Unnecessary surgery exposes to risks without benefit

❌ Mistake 4: Failing to recognize bilateral disease

• 10-15% have bilateral involvement (usually asynchronous)
• Synchronous bilateral disease suggests skeletal dysplasia or hypothyroidism—investigate

❌ Mistake 5: Attributing all hip pain to "growing pains"

• Perthes is painless or minimally painful; severe pain suggests alternative diagnosis
• Persistent limp > 2 weeks warrants hip X-ray

❌ Mistake 6: Not knowing the Herring classification

• Essential for prognostication and treatment decisions
• Commonly asked in viva examinations

OSCE Scenarios

Scenario 1: History Taking

"A 6-year-old boy presents to clinic with a 4-week history of limping. Take a history from his mother."

Key points to cover:

• Onset and duration: When did the limp start? Sudden or gradual?
• Pain: Where? Groin, thigh, knee? Severity? Timing (worse with activity)?
• Trauma: Any recent injury or fall?
• Weight-bearing: Can he walk? Does he refuse to walk?
• Systemic features: Fever, night pain, weight loss, fatigue?
• Past medical history: Previous hip problems? Transient synovitis?
• Development: Normal milestones? Growth pattern?
• Family history: Hip problems in family members?
• Social history: Activity level? Sports participation?

Red flags to ask about:

• Fever/night pain (septic arthritis, malignancy)
• Inability to weight-bear (urgent assessment needed)
• Bilateral symptoms (skeletal dysplasia, hypothyroidism)

Scenario 2: Examination Station

"Examine this 7-year-old child's hips. He has been limping for 6 weeks."

Examination sequence:

1. Introduction and consent
2. Inspection: Gait (antalgic, Trendelenburg), muscle wasting, leg length
3. Palpation: Tenderness over greater trochanter, anterior hip
4. Range of motion (supine):
   • Flexion (log roll to assess pain)
   • Internal and external rotation (hip flexed 90°)
   • Abduction and adduction
   • Compare to normal side
5. Special tests:
   • Prone internal rotation test
   • Trendelenburg test (single leg stance)
   • Leg length measurement (ASIS to medial malleolus)
6. Complete examination: Examine knees (referred pain), spine

Expected findings in Perthes:

• Limp (antalgic or Trendelenburg)
• Restricted internal rotation (earliest sign)
• Restricted abduction (indicates advancing disease)
• Thigh muscle atrophy
• Possible leg length discrepancy

MCQ Practice

Q1: A 5-year-old boy presents with a 3-month history of intermittent limp and mild knee pain. Hip X-ray shows sclerosis of the right femoral epiphysis with a crescent sign. What is the most appropriate management?

A. Urgent surgical washout B. Observation with physiotherapy C. Immediate femoral osteotomy D. MRI hip to confirm diagnosis E. Bone biopsy

Answer: B - Age less than 6 years with Perthes has excellent prognosis with conservative management (observation and physiotherapy). Surgery is not indicated in this age group.

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Q2: An 8-year-old girl with Perthes disease (Herring B classification) has restricted hip abduction to 15°. What is the most appropriate management?

A. Continue observation B. Bracing with Toronto orthosis C. Physiotherapy alone D. Surgical containment (femoral or pelvic osteotomy) E. Total hip replacement

Answer: D - Age 8 with Herring B and loss of containment (restricted abduction) is an indication for surgical containment to improve prognosis.

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Q3: Which of the following is the strongest prognostic factor in Perthes disease?

A. Sex B. Herring lateral pillar classification C. Age at onset D. Presence of metaphyseal cysts E. Bilateral involvement

Answer: C - Age at onset is the single most important prognostic factor. Younger children have longer remodelling potential and better outcomes.

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14. Patient and Family Resources

Explanation for Families (Layperson Level)

What is Perthes Disease?

Perthes disease happens when the blood supply to the "ball" part of the hip joint (at the top of the thigh bone) is temporarily interrupted. Without blood, the bone cells die—this is called avascular necrosis. Think of it like a bone "infarction" similar to a heart attack, but in the hip bone.

Why Did This Happen?

We don't fully understand why Perthes disease occurs. It's not caused by anything you or your child did. It's not hereditary in most cases, and it's not preventable. Some children may have risk factors like being very active, having had a hip infection before, or having certain blood clotting tendencies, but most of the time there is no clear cause.

Will My Child's Hip Heal?

Yes! The blood supply always comes back. Once blood flow returns, new bone grows and replaces the dead bone. This process takes about 2-4 years from start to finish. The hip goes through stages:

1. Initial stage (bone dies but looks relatively normal)
2. Fragmentation stage (dead bone breaks apart and is absorbed—looks worse on X-ray)
3. Re-growth stage (new bone forms)
4. Healed stage (bone is solid again)

What's the Problem If It Heals?

The issue is the shape the bone heals into. During the fragmentation stage (when the bone is soft and crumbly), it can flatten out instead of staying round. A flat ball doesn't roll smoothly in the round hip socket. If the hip heals flat, it can lead to:

• Stiffness and pain during teenage years and adulthood
• Early arthritis (wearing out of the joint) in the 40s-50s
• Possible need for hip replacement surgery later in life

What is "Containment"?

Imagine the hip socket (acetabulum) as a mould—like a Jell-O mould or a cake tin. If we keep the soft femoral head (the "ball") inside this round mould while it heals, it will grow back into a nice round shape.

Containment means using exercises, activity changes, or sometimes surgery to keep the ball deep inside the socket during the healing phase.

What Treatment Will My Child Need?

This depends on two main things:

1. Your child's age: Younger children (under 6) heal much better because they have more growing time left
2. How much of the bone is affected: Measured on X-rays using a classification system

For children under 6 years:

• Observation (watchful waiting)
• Physiotherapy to keep the hip flexible
• Avoiding high-impact activities like jumping and trampolining
• Regular X-rays to monitor healing
• Surgery is rarely needed

For children 6-8 years with moderate-to-severe involvement:

• May need surgery to improve containment
• Types of surgery: cutting the thigh bone (femur) or pelvis to angle the ball deeper into the socket
• Surgery helps the bone heal in a better shape

For children over 8 years:

• Healing is slower and outcomes are more variable
• Surgery may be offered in some cases
• Focus is on comfort and maintaining movement

How Long Will This Take?

• The whole disease process takes 2-4 years from start to finish
• The fragmentation stage (most critical) lasts about 12-18 months
• During this time, your child will need regular X-rays (every 3-4 months)
• Follow-up continues until your child stops growing (mid-teens)

Can My Child Go to School and Play Sports?

Yes, but with modifications during the fragmentation phase:

• Encourage: Swimming, cycling, gentle walking
• Avoid: Trampolining, jumping, contact sports, high-impact activities
• School adaptations may be needed (e.g., elevator access, modified PE)
• Once the bone has healed (re-ossification stage), activities can gradually resume

What About the Other Hip?

About 10-15% of children develop Perthes in both hips, though usually not at the same time. If both hips are affected simultaneously, we investigate for other medical conditions (thyroid problems, genetic bone conditions).

What's the Long-Term Outlook?

Most children do very well during childhood and teenage years. Long-term outlook depends on the final shape of the hip:

• Round, well-shaped hip: Excellent long-term outlook, low risk of arthritis
• Flattened or irregular hip: Increased risk of arthritis in the 40s-50s

We'll continue to monitor your child with X-rays until they finish growing. Many adults who had Perthes as children lead active, normal lives. Some may need hip replacement surgery later in life if arthritis develops, but modern hip replacements are excellent and long-lasting.

Support Organizations

STEPS Charity (UK)

• Supports children with lower limb conditions including Perthes
• Website: www.steps-charity.org.uk

Perthes Association (UK)

• Information and family support
• Website: www.perthes.org.uk

International Perthes Study Group

• Research and clinical information
• Website: ipsg.info

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15. Future Directions and Research

Ongoing Research Areas

1. Genetic and Molecular Studies [15,18]

• Genome-wide association studies (GWAS) identifying susceptibility loci
• Investigation of vascular endothelial growth factor (VEGF) pathways
• Thrombophilia gene polymorphisms

2. Advanced Imaging

• MRI perfusion techniques for early diagnosis
• 3D reconstruction and biomechanical modeling
• Delayed gadolinium-enhanced MRI of cartilage (dGEMRIC)

3. Biological Therapies

• Bisphosphonates to prevent bone resorption (limited evidence)
• Bone morphogenetic proteins (BMPs) to enhance healing
• Stem cell therapies (experimental)

4. Surgical Technique Refinement

• Computer-assisted surgical planning
• Minimally invasive osteotomy techniques
• Hip arthroscopy for labral pathology in late presentation

5. Long-Term Outcome Studies

• Understanding development of femoroacetabular impingement post-Perthes
• Predictors of need for total hip replacement
• Quality of life assessments in adulthood

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References

1. Legg AT. An obscure affection of the hip joint. Boston Med Surg J. 1910;162:202-204.

2. Waldenström H. The definite form of coxa plana. Acta Radiol. 1922;1:384-394.

3. Perry DC, Machin DM, Pope D, et al. Racial and geographic factors in the incidence of Legg-Calvé-Perthes disease: a systematic review. Am J Epidemiol. 2012;175(3):159-166. doi:10.1093/aje/kwr305

4. Weinstein SL. Natural history and treatment outcomes of childhood hip disorders. Clin Orthop Relat Res. 1997;(344):227-242.

5. Herring JA, Kim HT, Browne R. Legg-Calvé-Perthes disease. Part I: Classification of radiographs with use of the modified lateral pillar and Stulberg classifications. J Bone Joint Surg Am. 2004;86(10):2103-2120. doi:10.2106/00004623-200410000-00001

6. Kim HKW. Pathophysiology and new strategies for the treatment of Legg-Calvé-Perthes disease. J Bone Joint Surg Am. 2012;94(7):659-669. doi:10.2106/JBJS.K.01715

7. Perry DC, Metaizeau JP, Elbourne D, et al. Perthes' disease: deprivation and decline. Arch Dis Child. 2011;96(12):1124-1128. doi:10.1136/archdischild-2011-300374

8. Barker DJ, Hall AJ. The epidemiology of Perthes' disease. Clin Orthop Relat Res. 1986;(209):89-94.

9. Joseph B, Varghese G, Mulpuri K, et al. Natural evolution of Perthes disease: a study of 610 children under 12 years of age at disease onset. J Pediatr Orthop. 2003;23(5):590-600.

10. Catterall A. The natural history of Perthes' disease. J Bone Joint Surg Br. 1971;53(1):37-53.

11. Glueck CJ, Crawford A, Roy D, et al. Association of antithrombotic factor deficiencies and hypofibrinolysis with Legg-Perthes disease. J Bone Joint Surg Am. 1996;78(1):3-13. doi:10.2106/00004623-199601000-00002

12. Hayek S, Kenet G, Lübetsky A, et al. Does thrombophilia play an aetiological role in Legg-Calvé-Perthes disease? J Bone Joint Surg Br. 1999;81(4):686-690. doi:10.1302/0301-620x.81b4.9522

13. Kim HKW, Wiig O, Kaste SC, et al. Pathophysiology, imaging and treatment of Legg-Calvé-Perthes disease. Curr Opin Pediatr. 2012;24(1):71-76. doi:10.1097/MOP.0b013e32834ec5f3

14. Loder RT, Skopelja EN. The epidemiology and demographics of Legg-Calvé-Perthes' disease. ISRN Orthop. 2011;2011:504393. doi:10.5402/2011/504393

15. Noguchi Y, Sakamaki T, Matsuda K, et al. A possible contribution of vascular endothelial growth factor to the development of Perthes disease. J Bone Miner Metab. 2002;20(5):305-309. doi:10.1007/s007740200044

16. Joseph B. Natural history of early onset and late onset Legg-Calvé-Perthes disease. J Pediatr Orthop. 2011;31(2 Suppl):S152-S155. doi:10.1097/BPO.0b013e318223b423

17. McKibbin B, Ralis Z. Pathological changes in a case of Perthes' disease. J Bone Joint Surg Br. 1974;56(3):438-447.

18. Lappin K, Nevelos J, Kealey D, et al. Protein C and protein S deficiency in Legg-Calvé-Perthes disease. J Pediatr Orthop. 2003;23(6):732-735.

19. Fabry G, MacEwen GD, Shands AR Jr. Torsion of the femur. A follow-up study in normal and abnormal conditions. J Bone Joint Surg Am. 1973;55(8):1726-1738.

20. Reinker KA. Early diagnosis and treatment of hinge abduction in Legg-Calvé-Perthes disease. J Pediatr Orthop. 1996;16(1):3-9.

21. Kocher MS, Zurakowski D, Kasser JR. Differentiating between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm. J Bone Joint Surg Am. 1999;81(12):1662-1670. doi:10.2106/00004623-199912000-00002

22. Futami T, Kasahara Y, Suzuki S, et al. Ultrasonography in transient synovitis and early Perthes' disease. J Bone Joint Surg Br. 1991;73(4):635-639. doi:10.1302/0301-620X.73B4.2071650

23. Herring JA, Neustadt JB, Williams JJ, et al. The lateral pillar classification of Legg-Calvé-Perthes disease. J Pediatr Orthop. 1992;12(2):143-150.

24. Wiig O, Terjesen T, Svenningsen S. Prognostic factors and outcome of treatment in Perthes' disease: a prospective study of 368 patients with five-year follow-up. J Bone Joint Surg Br. 2008;90(10):1364-1371. doi:10.1302/0301-620X.90B10.20649

25. Catterall A. Legg-Calvé-Perthes disease. Curr Opin Pediatr. 1999;11(1):76-79.

26. Stulberg SD, Cooperman DR, Wallensten R. The natural history of Legg-Calvé-Perthes disease. J Bone Joint Surg Am. 1981;63(7):1095-1108.

27. Salter RB, Thompson GH. Legg-Calvé-Perthes disease. The prognostic significance of the subchondral fracture and a two-group classification of the femoral head involvement. J Bone Joint Surg Am. 1984;66(4):479-489.

28. Sponseller PD, Desai SS, Millis MB. Comparison of femoral and innominate osteotomies for the treatment of Legg-Calvé-Perthes disease. J Bone Joint Surg Am. 1988;70(8):1131-1139.

29. Wenger DR, Ward WT, Herring JA. Legg-Calvé-Perthes disease. J Bone Joint Surg Am. 1991;73(5):778-788.

30. Meehan PL, Angel D, Nelson JM. The Scottish Rite abduction orthosis for the treatment of Legg-Perthes disease. A radiographic analysis. J Bone Joint Surg Am. 1992;74(1):2-12.

31. Vukasinovic Z, Spasovski D, Vucetic C, et al. Combined pelvic and femoral osteotomy in the treatment of severe forms of Legg-Calvé-Perthes disease. Int Orthop. 2009;33(4):1177-1182. doi:10.1007/s00264-008-0625-6

32. Larson AN, Sucato DJ, Herring JA, et al. A prospective multicenter study of Legg-Calvé-Perthes disease: functional and radiographic outcomes of nonoperative treatment at a mean follow-up of twenty years. J Bone Joint Surg Am. 2012;94(7):584-592. doi:10.2106/JBJS.K.00308

33. Sankar WN, Flynn JM. The development of acetabular retroversion in children with Legg-Calvé-Perthes disease. J Pediatr Orthop. 2008;28(4):440-443. doi:10.1097/BPO.0b013e31816d1ebb

34. Kim HKW, Herring JA. Pathophysiology, classifications, and natural history of Perthes disease. Orthop Clin North Am. 2011;42(3):285-295. doi:10.1016/j.ocl.2011.03.002

35. Wiig O, Terjesen T, Svenningsen S. Inter-observer reliability of the Stulberg classification in the assessment of Perthes disease. J Child Orthop. 2007;1(2):101-105. doi:10.1007/s11832-007-0020-y

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This topic generates 42 Anki cards across three types:

Basic Cards (24 cards)

• Definition of Perthes disease
• Epidemiology: incidence, age, male:female ratio
• Blood supply to femoral head
• Four Waldenström stages
• Herring A/B/C definitions
• Stulberg I-V classifications
• "Head-at-risk" signs (5 cards—one per sign)
• Treatment indications for age groups
• Red flags (4 cards)
• Complications (6 cards)

Cloze Deletion Cards (12 cards)

• "The lateral pillar classification assesses the lateral 15-30% of the femoral head during the fragmentation stage."
• "Children under 6 years have excellent prognosis and require observation and physiotherapy only."
• "Containment is achieved by keeping the femoral head deeply within the acetabulum during fragmentation and reossification."
• "Stulberg class III-V leads to early osteoarthritis by age 40-50."
• (Additional 8 cloze cards on pathophysiology, management, investigations)

Scenario Cards (6 cards)

• Viva scenario: Differentiate Perthes from transient synovitis
• Viva scenario: Management of 7-year-old with Herring B
• Viva scenario: Explain containment principle
• Clinical scenario: Child with knee pain—when to suspect hip pathology
• Radiological scenario: Interpret AP pelvis showing lateral pillar collapse
• Management scenario: Counsel family of 5-year-old with new diagnosis

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