Perthes Disease (LCPD)

1. Clinical Overview

Summary

Legg-Calvé-Perthes Disease (LCPD) is an idiopathic Avascular Necrosis (AVN) of the developing femoral head in children, typically aged 4-8 years. The condition represents a self-limiting disorder characterized by interruption of blood supply to the capital femoral epiphysis, followed by necrosis, fragmentation, re-ossification, and remodeling over a 2-4 year period. [1,2]

The fundamental principle of treatment is Containment: maintaining the softened, deforming femoral head within the acetabular mould to preserve sphericity during the critical fragmentation phase. Successful containment results in a congruent, spherical hip joint; failure leads to femoral head deformity (coxa plana), extrusion, and premature osteoarthritis. [3,4]

The prognosis is strongly age-dependent, with younger children (less than 6 years) demonstrating excellent remodeling potential, while older children (> 8 years) face significantly worse outcomes due to limited remaining growth and reduced acetabular plasticity. [5,6]

Nomenclature & Historical Context

Named after the three physicians who independently described it in 1910:

• Arthur Legg (USA)
• Jacques Calvé (France)
• Georg Perthes (Germany)

Earlier terms include "Pseudocoxalgia" and "Coxa Plana". The condition was initially thought to be tuberculous arthritis until Waldenström established its non-infectious, self-limiting nature. [1]

Key Facts

• The "Hyperactive Short Boy": Classic patient is a small-for-age, hyperactive male (4-8 years) from lower socioeconomic background.
• Self-Limiting: Disease runs a 2-4 year course and heals spontaneously. Treatment aims only to prevent deformity during the vulnerable "soft" phase.
• Containment Window: The fragmentation stage (Waldenström Stage II) is the critical period for intervention.
• Age is Destiny: Prognosis correlates inversely with age at onset:
  • Age less than 6: Excellent (> 90% good outcomes)
  • Age 6-8: Variable (50-70% good outcomes)
  • Age > 8: Poor (30-40% good outcomes, high OA risk)

Clinical Pearls

"Knee Pain is Hip Pain": Always examine the hip in a child presenting with knee pain. The obturator nerve (L3-4) refers pain from the hip to the medial knee. Missing this leads to delayed diagnosis.

"Containment is King": Visualize the femoral head as a scoop of melting ice cream. If maintained deep within the acetabular "bowl", it reforms spherically. If it extrudes laterally, it flattens irreversibly.

"The Crescent Sign": A subchondral radiolucent fracture line on lateral radiograph, indicating structural failure of necrotic bone. Marks the transition from initial to fragmentation stage.

"Lateral Pillar = Tent Pole": The lateral third of the epiphysis acts as the structural support. If this "pillar" collapses, the entire head collapses—hence the predictive power of the Herring classification.

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2. Epidemiology

Incidence & Prevalence

• Overall Incidence: 1 in 1,200 children (0.8 per 1,000 live births)
• Geographic Variation:
  • Highest: Japan, Scandinavia, UK (15-20 per 100,000)
  • Lowest: Native Americans, Australian Aboriginals, African populations (1-2 per 100,000)
• Socioeconomic Gradient: 4-5 fold higher incidence in lower socioeconomic groups [7]

Demographics

• Age Distribution:
  • Peak incidence: 5-7 years
  • Range: 2-12 years (rare outside this range)
  • Median age: 6.5 years for males, 7 years for females
• Gender: Male:Female ratio = 4-5:1
• Bilateral Involvement: 10-15% of cases
  • Always asynchronous (different Waldenström stages)
  • Bilateral onset suggests alternative diagnosis (Multiple Epiphyseal Dysplasia, Hypothyroidism, Gaucher disease)

Risk Factors

Constitutional:

• Short stature (average 2-3 cm below population mean) [8]
• Delayed bone age (average 1-2 years)
• Low birth weight
• Family history (relatives 5-10x increased risk)

Environmental:

• Passive smoking exposure (OR 5.6) [9]
• Low socioeconomic status
• Urban residence
• Northern latitude (Vitamin D hypothesis)

Associated Conditions:

• ADHD (Attention Deficit Hyperactivity Disorder) - 3x prevalence
• Congenital anomalies (genitourinary, inguinal hernia)
• Coagulation disorders (Protein C/S deficiency, Factor V Leiden) - controversial

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3. Pathophysiology

Vascular Anatomy of the Developing Femoral Head

The blood supply to the pediatric femoral epiphysis is precarious and age-dependent:

Infant (less than 1 year):

• Medial femoral circumflex artery (MFCA) - dominant
• Lateral femoral circumflex artery (LFCA)
• Vessels cross physis freely

Child (1-7 years) - VULNERABLE PERIOD:

• Physis becomes avascular barrier
• ONLY lateral epiphyseal vessels (from MFCA) supply femoral head
• No anastomotic connections
• Vessels course along anterosuperior femoral neck (vulnerable to compression/thrombosis)

Older child (> 8 years):

• Lateral epiphyseal vessels mature
• Contribution from ligamentum teres artery (unreliable)

This "Watershed Period" (4-8 years) explains the age distribution of Perthes disease. [10,11]

Proposed Etiological Mechanisms

1. Vascular Thrombosis/Occlusion Theory:

• Compression of lateral epiphyseal vessels by:
  • Increased intra-articular pressure (effusion, synovitis)
  • Extravascular compression (tight piriformis, capsular pressure)
  • Venous congestion with retrograde arterial thrombosis

2. Repetitive Trauma/Microtrauma:

• Hyperactive children with repetitive stress
• Subclinical stress fractures → vascular disruption
• Explains male predominance and "active child" phenotype

3. Systemic Coagulopathy (Controversial):

• Thrombophilic disorders (Protein C/S, Factor V Leiden)
• Evidence conflicting; likely minor contributory role [12]

4. Skeletal Dysplasia/Constitutional:

• Delayed skeletal maturation
• Abnormal cartilage matrix (collagen defects)
• Explains bilateral cases and familial clustering

The Four Stages of Perthes (Waldenström Classification)

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

Pathology:

• Interruption of blood supply
• Osteocyte death (bone necrosis)
• Cartilage remains viable (nourished by synovial fluid)

Radiographic Features:

• Epiphysis appears smaller and denser (sclerotic)
• Widened joint space (cartilage hypertrophy)
• Crescent sign (subchondral fracture) on lateral view
• Normal metaphysis

Clinical:

• Synovitis (hip irritability)
• Mild limp, reduced range of motion

Stage II: Fragmentation/Resorption (6-12 months)

Pathology:

• Revascularization begins
• Osteoclastic resorption of dead bone
• Structurally weakest phase - "the soft femoral head"
• CRITICAL WINDOW FOR CONTAINMENT

Radiographic Features:

• Epiphyseal fragmentation (mottled, irregular appearance)
• Progressive collapse and flattening
• Metaphyseal lucency and cysts
• Lateral extrusion (uncovering)

Clinical:

• Maximal pain and limp
• Progressive loss of abduction and internal rotation
• Trendelenburg gait

Stage III: Re-ossification (12-24 months)

Pathology:

• Osteoblastic activity predominates
• New bone deposition on necrotic scaffold
• Gradual restoration of mechanical strength

Radiographic Features:

• Epiphysis becomes more homogeneous
• Density normalizes
• Final shape becomes apparent

Clinical:

• Symptoms improve
• Range of motion may partially recover

Stage IV: Healed/Remodeling (24-48 months)

Pathology:

• Bone remodeling continues until skeletal maturity
• Younger children remodel more extensively
• Acetabulum remodels to match femoral head shape (better in young)

Radiographic Features:

• Residual deformity stabilizes
• Coxa magna (broad head)
• Coxa plana (flat head)
• Coxa breva (short neck)

Clinical:

• Stable hip (painless or mild symptoms)
• Fixed ROM deficits
• Long-term OA risk depends on congruency

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4. Classification Systems

Herring Lateral Pillar Classification (Most Widely Used)

Based on the height of the lateral third of the epiphysis at maximal fragmentation (AP radiograph):

Group A:

• No loss of lateral pillar height
• Prognosis: Excellent (> 90% good outcomes)
• Treatment: Observation regardless of age

Group B:

• less than 50% loss of lateral pillar height
• Lucency present but structural integrity maintained
• Prognosis: Age-dependent
  • less than 8 years: Good (70-80%)

  • 8 years: Fair (40-50%)

• Treatment: Observation if less than 8 years; consider surgery if > 8 years

Group B/C Border:

• Exactly 50% loss or > 50% but ossification preserved
• Prognosis: Poor without intervention
• Treatment: Strong consideration for containment surgery [13]

Group C:

• 50% loss of lateral pillar height

• Complete collapse of lateral column
• Prognosis: Poor (20-30% good outcomes)
• Treatment: Controversial; containment may not help; consider salvage later

Advantages:

• High inter-observer reliability (kappa 0.73)
• Strong prognostic correlation
• Guides treatment decisions (especially Group B vs B/C)

Limitations:

• Requires fragmentation stage (not useful early)
• Difficult in very young children (incompletely ossified)

Catterall Classification (Historical)

Groups I-IV based on extent of epiphyseal involvement (AP + lateral):

• Group I: less than 25% involvement (anterior head only)
• Group II: 25-50% involvement
• Group III: 50-75% involvement
• Group IV: > 75% involvement (entire head)

"Head at Risk" Signs (Catterall):

1. Lateral subluxation (extrusion) - Most important
2. Gage sign (V-shaped radiolucent defect laterally)
3. Calcification lateral to epiphysis
4. Horizontal physis (diffusely)
5. Metaphyseal cysts

Status: Largely superseded by Herring; poor inter-observer reliability (kappa 0.52)

Stulberg Classification (Outcome at Skeletal Maturity)

Predicts long-term osteoarthritis risk based on final femoral head shape and congruency:

Key Concept: Classes I-II-III are congruent (femoral head shape matches acetabular shape) → good long-term prognosis. Classes IV-V are incongruent → poor prognosis. [14]

Modified Waldenström Staging (Dynamic Assessment)

Determines stage of disease for timing interventions:

• Uses combination of radiographs and MRI
• Early intervention (Stage I-early II) controversial
• Late intervention (late Stage II-III) may be too late for containment

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5. Clinical Presentation

Typical Patient Profile

"The Classic Perthes Child":

• 6-year-old boy
• Small for age (10th-25th percentile height)
• Hyperactive temperament
• Lower-middle socioeconomic background
• Presents with 3-6 week history of limping

Symptoms

Cardinal Symptom: Painless or Minimal Pain Limp

• Insidious onset over weeks to months
• Worsens with activity, improves with rest
• Often noticed by teachers/parents (child unconcerned)

Pain Pattern:

• Groin pain (25%)
• Anterior thigh pain (30%)
• Medial knee pain (45%) ← Classic Trap
• Dull ache, rarely severe
• Night pain uncommon (if present, consider infection/malignancy)

Associated Symptoms:

• Stiffness after rest ("gelling")
• Difficulty running, jumping
• Refusal to bear weight (rare; suggests advanced collapse)

Signs

Gait Abnormalities:

1. Antalgic Gait (early):

   • Shortened stance phase on affected side
   • Reduced hip extension during toe-off

2. Trendelenburg Gait (later):

   • Pelvic drop on contralateral side during swing
   • Indicates abductor insufficiency (gluteus medius/minimus)
   • Compensatory trunk lean over affected hip

3. Short Leg Gait:

   • True shortening from femoral head collapse
   • Toe-walking on affected side

Range of Motion (ROM) Examination:

Early (Stage I-II):

• Abduction: Most sensitive - first and most affected (loss of 10-30°)
• Internal rotation: Second most affected (loss of 20-40°)
• Fixed flexion deformity: 10-20° (hip irritability)
• Extension and external rotation relatively preserved

Late (Stage III-IV):

• Global restriction (all planes)
• Hinge Abduction: Pathognomonic sign
  • "With hip flexed 90°, passive abduction causes:"
    • Sudden stopping at 20-30°
    • Lateral impingement (extruded head hits acetabular rim)
    • Hip "hinges open" rather than rotating smoothly
  • Contraindicates containment surgery (forced containment crushes cartilage)

Other Physical Signs:

• Thigh muscle wasting: Quadriceps and adductor atrophy (disuse, reflex inhibition)
• True leg length discrepancy: 1-3 cm shortening (measure ASIS to medial malleolus)
• Apparent leg length discrepancy: From pelvic obliquity (measure umbilicus to medial malleolus)
• Positive Trendelenburg test: Pelvic drop with single leg stance
• Restricted hip rotation in extension: Perform log-roll test (patient supine, legs extended, roll internally/externally)

Differential Diagnosis by Age

Age 2-5 years:

• Transient synovitis (irritable hip)
• Septic arthritis ← MUST RULE OUT FIRST
• Developmental Dysplasia of Hip (DDH)
• Juvenile Idiopathic Arthritis (JIA)

Age 5-10 years (Perthes age):

• Perthes disease
• Meyer dysplasia (normal variant AVN of medial epiphysis)
• Multiple Epiphyseal Dysplasia (bilateral, family history)

Age 10-15 years:

• Slipped Capital Femoral Epiphysis (SCFE) ← Key differential
• Chondrolysis
• Avascular necrosis (secondary: sickle cell, SLE, steroid, trauma)

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6. Investigations

Plain Radiography (First-Line)

Standard Views:

1. AP Pelvis (both hips):

   • Assess Herring lateral pillar classification
   • Compare with normal contralateral hip
   • Measure:
     • Extrusion index: % of femoral head lateral to Perkin's line (normal less than 20%; > 20% = poor prognosis)
     • Epiphyseal height: Lateral pillar height
     • Joint space width: Widening suggests cartilage hypertrophy

2. Frog-Leg Lateral (affected hip):

   • Best view for crescent sign
   • Assess anterolateral extrusion
   • Evaluate posterior coverage

Radiographic Signs by Stage:

Stage I (Initial/Necrosis):

• Smaller, denser epiphysis (sclerosis from impacted dead bone)
• Widened medial joint space (cartilage hypertrophy)
• Crescent sign (subchondral lucency on lateral view) - pathognomonic

Stage II (Fragmentation):

• Mottled, fragmented epiphyseal appearance
• Progressive flattening and lateral extrusion
• Metaphyseal lucency and cysts (Gage sign)
• Horizontal physis (growth plate widening)

Stage III (Re-ossification):

• Gradual homogenization of epiphysis
• Final shape becomes evident
• Residual coxa magna, plana, or breva

Stage IV (Healed):

• Mature skeletal architecture
• Assess Stulberg outcome classification

Advanced Imaging

Magnetic Resonance Imaging (MRI):

Indications:

• Equivocal radiographs (early disease)
• Pre-operative planning (assess cartilage deformity vs bony deformity)
• Bilateral disease assessment
• Exclude mimics (infection, tumor)

MRI Findings:

• T1-weighted: Hypointense signal (necrotic bone)
• T2-weighted: Hyperintense signal (edema, hyperemia)
• Contrast-enhanced: Non-enhancement of necrotic zone
• Cartilage-sensitive sequences (FS-PD, dGEMRIC):
  • Assess true cartilage sphericity (may be round despite flat bone)
  • Predict remodeling potential

MRI Advantages:

• Detects AVN before radiographic changes (weeks earlier)
• Quantifies extent of involvement (3D assessment)
• Assesses labral integrity and synovitis

MRI Disadvantages:

• Expensive
• Requires sedation in young children
• Limited availability
• Does not change management in most cases

Arthrography (Dynamic):

• Performed intra-operatively before containment surgery
• Assesses:
  • True cartilage shape (may be spherical despite flat bone on X-ray)
  • Presence of hinge abduction
  • Adequacy of containment after trial reduction

Bone Scintigraphy (Technetium-99m):

• Historical; largely replaced by MRI
• Shows "cold" femoral head (absent perfusion)
• Cannot assess structural detail

Laboratory Tests

Routine:

• NOT routinely indicated (Perthes is clinical + radiographic diagnosis)
• If septic arthritis cannot be excluded clinically:
  • FBC (WCC, neutrophils)
  • CRP, ESR
  • Blood cultures
  • "Hip aspiration: Gold standard to exclude sepsis"

Specialized (Selected Cases):

• Thrombophilia screen (if bilateral, family history, or less than 4 years):
  • Protein C, Protein S
  • Factor V Leiden
  • Anticardiolipin antibodies
  • Homocysteine levels
• Thyroid function: Hypothyroidism can mimic Perthes
• Skeletal survey: If Multiple Epiphyseal Dysplasia suspected

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7. Management Algorithm

                     SUSPECTED PERTHES
                            ↓
                    CLINICAL ASSESSMENT
                     + AP/LATERAL X-RAYS
                            ↓
                  ┌─────────┴─────────┐
             CONFIRM AVN          ALTERNATIVE Dx
                  ↓                (SCFE, Infection)
            STAGE DISEASE               ↓
         (Waldenström I-IV)      APPROPRIATE Mx
                  ↓
        ┌─────────┴──────────┐
   STAGE I/II          STAGE III/IV
  (Treatable)            (Late)
        ↓                     ↓
   ASSESS AGE          SYMPTOMATIC Mx
   & LATERAL PILLAR         ↓
        ↓               Physiotherapy
  ┌─────┴─────┐         Analgesia
AGE less than 6    AGE 6-9       Monitor to maturity
  ↓         ↓
OBSERVE   HERRING
(All groups) CLASS
  ↓         ↓
Physio  ┌───┴───┐
Active  A     B/B-C/C
Monitoring ↓      ↓
         OBSERVE CONTAINMENT
         Physio  SURGERY?
                   ↓
              CHECK FOR
            HINGE ABDUCTION
                   ↓
              ┌────┴────┐
           ABSENT    PRESENT
              ↓          ↓
         CONTAINMENT  SALVAGE
         - Femoral    - Valgus
           Varus        Osteotomy
           Osteotomy  - Shelf
         - Pelvic       Procedure
           Osteotomy  - Observe

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8. Management Protocols

General Principles

Goals of Treatment:

1. Containment: Keep femoral head centered and spherical during fragmentation
2. Maintain ROM: Preserve abduction and rotation (prevent hinge)
3. Symptom relief: Reduce pain and restore function
4. Optimize remodeling: Maximize potential for spontaneous reshaping

Containment Concept:

• The acetabulum acts as a "mould" for the soft femoral head
• By deepening the head into the socket (via varus femoral osteotomy or acetabular redirection), the spherical acetabulum shapes the reforming epiphysis
• Effective only if:
  • Femoral head still "plastic" (Stage I-II)
  • No hinge abduction
  • Adequate acetabular coverage possible

1. Conservative Management (Observation)

Indications:

• Age less than 6 years (all Herring groups)
• Herring Group A (any age)
• Stage III-IV (re-ossification complete - too late for containment)
• Patient/family non-compliant with surgical care

Protocol:

1. Activity Modification:

   • Avoid high-impact activities (jumping, running, trampolines)
   • Encourage low-impact (swimming, cycling)
   • School PE excused during fragmentation stage
   • "Supervised neglect" not "bed rest" (historical)

2. Physiotherapy:

   • Primary goal: Maintain abduction ROM
   • Gentle stretching (abduction, internal rotation)
   • Hip strengthening (gluteus medius, quadriceps)
   • Hydrotherapy (buoyancy reduces weight-bearing)
   • Frequency: 2-3x/week minimum

3. Analgesia:

   • NSAIDs (ibuprofen 5-10 mg/kg TDS)
   • Paracetamol PRN
   • Avoid prolonged opioids

4. Surveillance:

   • Radiographs: Every 3-4 months during fragmentation; every 6 months during re-ossification
   • Monitor for:
     • Progressive extrusion
     • Lateral pillar collapse (A→B→C progression)
     • Loss of ROM (hinge development)

Evidence:

• Herring et al. (2004): Group A children do well with observation regardless of age (> 90% Stulberg I-II) [13]
• Age less than 6 years: Natural history excellent; surgery does not improve outcomes [15]

2. Containment Surgery

Indications:

• Age > 6 years (ideally 6-9 years)
• Herring Group B or B/C border
• Stage I-II (fragmentation phase)

• 50% femoral head involvement (Catterall III-IV)

• No hinge abduction
• Adequate ROM (abduction > 15-20°)

Contraindications (Absolute):

• Hinge abduction present
• Stage III-IV (re-ossification complete)
• Age > 12 years (limited remodeling potential)
• Stiff hip (abduction less than 10°)

Contraindications (Relative):

• Herring Group C (limited benefit)
• Age less than 6 years (observation sufficient)
• Significant medical comorbidities

A. Femoral Varus Derotation Osteotomy (VDRO)

Principle:

• Varus angulation (20-30°) tilts femoral head medially
• Derotation component (if required) corrects femoral anteversion
• Moves load-bearing surface from damaged anterolateral to healthier posteromedial region

Technique:

• Proximal femoral osteotomy (subtrochanteric or intertrochanteric)
• Varus angulation: 20-30° (avoid > 30° - creates abductor insufficiency)
• Blade plate or locking plate fixation
• May add shortening (5-10 mm) to reduce tension

Advantages:

• Predictable, reproducible
• Does not limit future surgery (THR access preserved)
• Corrects concomitant femoral anteversion

Disadvantages:

• Trendelenburg gait (abductor inefficiency from varus)
• Leg length discrepancy (LLD) worsened
• Requires metalwork removal (second surgery)
• Lateral/distal femoral bump (cosmetic)

Outcomes:

• Herring B, age > 8 years: 70-75% Stulberg I-II with surgery vs 40% observation [13]
• Herring B/C border: 60% Stulberg I-II with surgery vs 25% observation

B. Pelvic Osteotomy (Salter Innominate Osteotomy)

Principle:

• Redirect acetabulum to cover extruded femoral head
• Rotate entire acetabular roof anterolaterally
• Does not alter femoral geometry

Technique:

• Osteotomy through ilium (above acetabulum)
• Wedge iliac bone graft to hold position
• Anterolateral rotation (20-30°)

Advantages:

• Preserves femoral anatomy (no varus, no LLD)
• Better cosmesis
• Improved anterior and lateral coverage

Disadvantages:

• Technically demanding
• Risk of acetabular dysplasia if overdone
• May compromise posterior coverage
• Blood transfusion often required

Alternative Pelvic Osteotomies:

• Shelf acetabuloplasty: Lateral buttress (salvage procedure)
• Chiari osteotomy: Medial displacement (salvage)
• Triple pelvic osteotomy (Steele): Complex, rarely indicated

Comparative Evidence:

• No clear superiority of femoral vs pelvic osteotomy [16]
• Femoral osteotomy more commonly performed (simpler, reproducible)
• Pelvic osteotomy preferred if:
  • Aspherical acetabulum
  • Significant lateral uncovering
  • Desire to preserve femoral anatomy

3. Salvage Procedures (Hinge Abduction Present)

Indications:

• Established hinge abduction
• Late presentation (Stage III-IV with severe deformity)
• Failed containment
• Persistent pain despite conservative care

A. Valgus Extension Osteotomy (VEO)

Principle:

• Opposite of containment
• Shifts load-bearing surface to less damaged lateral area
• Reduces impingement and pain

Technique:

• Proximal femoral valgus osteotomy (15-20°)
• Extension component (10-15°) reduces flexion deformity

Indications:

• Established hinge with pain
• Age > 10 years (remodeling potential exhausted)

Outcomes:

• Pain relief: 60-70% at 5 years
• Does not improve ROM or head shape
• Delays but does not prevent OA

B. Shelf Acetabuloplasty

Principle:

• Create lateral buttress (shelf) to support extruded head
• Redirect load over larger surface area

Technique:

• Iliac bone graft placed laterally over acetabular rim
• Fixed with screws

Indications:

• Lateral extrusion with flat head (coxa plana)
• Hinge abduction
• Skeletally mature or near-mature

Outcomes:

• Pain relief: 50-60% at 10 years
• Delays OA by 10-15 years (not curative)

4. Emerging/Experimental Therapies

Bisphosphonates:

• Hypothesis: Reduce osteoclastic resorption during fragmentation
• Limited evidence; RCTs ongoing
• Not standard of care [17]

Core Decompression:

• Hypothesis: Reduce intraosseous pressure, improve perfusion
• Minimal evidence in children
• Not recommended outside research protocols

Stem Cell Therapy:

• Experimental only
• No clinical trials in Perthes

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9. Complications

Early Complications

1. Diagnostic Delay:

• Missed diagnosis due to knee pain presentation
• Mean delay: 3-6 months from symptom onset
• Impact: May miss containment window

2. Septic Arthritis (Misdiagnosis):

• Perthes presents with irritable hip
• Must exclude infection before diagnosing Perthes
• Hip aspiration if doubt

Disease-Related Complications

1. Coxa Magna:

• Definition: Enlarged, broad femoral head
• Cause: Exuberant repair response, lateral overgrowth
• Consequence: Reduced ROM, impingement, labral tears
• Management: Observation; femoral head-neck osteochondroplasty if symptomatic impingement

2. Coxa Plana:

• Definition: Flattened femoral head
• Cause: Collapse during fragmentation without containment
• Consequence: Incongruent joint, early OA (Stulberg IV-V)
• Management: Salvage osteotomy, shelf procedure; eventual THR

3. Coxa Breva:

• Definition: Short, broad femoral neck
• Cause: Lateral physeal arrest from AVN extension
• Consequence: Abductor insufficiency, Trendelenburg gait
• Management: Greater trochanteric advancement/distal transfer

4. Leg Length Discrepancy (LLD):

• Mechanism:
  • "True shortening: Femoral head collapse, premature physeal closure"
  • "Apparent shortening: Pelvic obliquity, hip contracture"
• Magnitude: Usually less than 2 cm (mild)
• Management:
  • less than 2 cm: Shoe lift

  • 2 cm: Femoral lengthening (after skeletal maturity)

5. Hinge Abduction:

• Definition: Lateral impingement preventing smooth abduction
• Pathophysiology:
  • Extruded, flat femoral head catches on acetabular rim
  • Hip "hinges open" instead of rotating
• Clinical sign: Sudden stop during passive abduction + lateral translation
• Significance: Contraindicates containment surgery (forced containment damages cartilage)
• Management: Valgus osteotomy, shelf procedure

Surgical Complications

Femoral Osteotomy:

• Excessive varus (> 30°): Abductor insufficiency, Trendelenburg
• Avascular necrosis (iatrogenic): Vascular injury during surgery (rare)
• Non-union: less than 1%
• Infection: 1-2%
• Metalwork irritation: 10-15% (requires removal)

Pelvic Osteotomy:

• Blood loss: Often requires transfusion
• Nerve injury: Sciatic, femoral (rare, less than 1%)
• Pelvic instability: Improper fixation
• Over-coverage: Posterior impingement, reduced ROM

Long-Term Complications

1. Premature Osteoarthritis:

• Incidence:
  • "Stulberg I-II: Minimal risk (similar to general population)"
  • "Stulberg III: Moderate risk (OA age 40-50)"
  • "Stulberg IV-V: High risk (OA age 20-40)"
• Mechanism: Incongruent joint → abnormal stress distribution → cartilage degeneration
• Management: THR (technically challenging due to deformed anatomy)

2. Femoroacetabular Impingement (FAI):

• Mechanism: Coxa magna + asphericity → cam-type impingement
• Symptoms: Groin pain, reduced ROM, labral tears
• Management: Arthroscopic or open femoral head-neck osteochondroplasty

3. Labral Tears:

• Incidence: 30-40% in Stulberg III-V
• Mechanism: Abnormal contact pressures from asphericity
• Management: Arthroscopic debridement vs repair

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10. Prognosis

Prognostic Factors

Age at Onset (Strongest Predictor):

• less than 6 years: 85-95% good outcome (Stulberg I-II)
• 6-8 years: 50-70% good outcome

• 8 years: 30-40% good outcome

• 10 years: less than 20% good outcome

Herring Lateral Pillar Classification:

• Group A: > 90% Stulberg I-II (excellent)
• Group B (age less than 8): 70-80% Stulberg I-II
• Group B (age > 8): 40-50% Stulberg I-II → Surgery improves to 70-75%
• Group B/C: 25% Stulberg I-II → Surgery improves to 50-60%
• Group C: 20-30% Stulberg I-II (poor despite surgery)

Extent of Involvement (Catterall):

• Groups I-II: Good prognosis
• Groups III-IV: Poor without containment

Presence of "Head at Risk" Signs:

• Lateral subluxation: 3x increased risk of poor outcome
• Gage sign, metaphyseal cysts: 2x increased risk

Gender:

• Females: Worse prognosis than males (later bone age, less remodeling time)

Bilateral Disease:

• Generally worse outcomes (genetic/constitutional factors)

Natural History Without Treatment

• 40-60% achieve Stulberg I-II (acceptable outcome)
• 30-40% achieve Stulberg III (moderate OA risk)
• 10-20% achieve Stulberg IV-V (severe OA risk)
• Outcomes heavily age-dependent (younger = better)

Effect of Treatment

Containment Surgery (Herring B, age > 8 years):

• Improves Stulberg I-II rate from 40% → 70-75% [13]
• Number needed to treat (NNT) ≈ 3

Containment Surgery (Herring C):

• Limited benefit (20% → 30% Stulberg I-II)
• Controversial; many surgeons observe

Physiotherapy + Activity Modification:

• Maintains ROM (prevents hinge)
• No evidence for improved radiographic outcome
• Reduces symptoms

Long-Term Outcomes

At Skeletal Maturity:

• 50-60% have spherical or near-spherical head (Stulberg I-III)
• 20-30% have significant deformity (Stulberg IV-V)
• ROM deficits persist (especially internal rotation, abduction)

At 40-Year Follow-Up (Stulberg Study):

• Stulberg I-II: 90% good hip function, minimal OA
• Stulberg III: 50% OA (mean age 45 years)
• Stulberg IV-V: 80% OA (mean age 35 years)
• THR rate: 10% overall; 40% in Stulberg IV-V [14]

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11. Patient and Family Education

What is Perthes Disease?

Perthes disease occurs when the blood supply to the ball of the hip joint (femoral head) temporarily stops. Without blood, the bone dies and softens, like a wet sugar cube. The weight of the body can then squash the soft bone flat.

Will it heal?

Yes. The blood supply always comes back, usually within 6-12 months. New bone then grows to replace the dead bone. The entire process takes 2-4 years from start to finish. The disease heals itself - we cannot speed it up.

What is the risk?

The main risk is that the ball heals flat instead of round. A flat ball does not fit properly into the round socket, causing:

• Stiffness
• Pain
• Limping
• Arthritis later in life (as early as 30-40 years old)

What determines if the bone heals flat or round?

Age is the single most important factor:

• Younger children (less than 6 years): Excellent prognosis. The bone usually reforms round even without treatment.
• Older children (> 8 years): Poor prognosis without treatment. Surgery often needed.

Other factors:

• How much of the bone has died (lateral pillar classification)
• How flat the bone becomes during the "soft phase"
• How well we can keep the ball centered in the socket (containment)

What is the treatment?

Goal: Keep the soft femoral head deep inside the spherical socket, so it uses the socket as a "mould" to reform round.

Younger children (less than 6 years):

• Usually no surgery needed
• Physiotherapy to keep hip flexible
• Avoid jumping, running (swimming and cycling are good)
• X-rays every 3-4 months to monitor progress

Older children (> 8 years) or severe cases:

• May need surgery to tilt the ball deeper into the socket
• Two main operations:
  1. Femoral osteotomy: Cut and realign the thigh bone to point the ball inward
  2. Pelvic osteotomy: Cut and realign the pelvis to cover the ball better
• Crutches for 6-12 weeks after surgery
• Physiotherapy for 6-12 months
• Return to full activity after bone heals (12-18 months)

Can my child do sports?

During active disease (fragmentation stage - first 1-2 years):

• Avoid: Running, jumping, contact sports, trampolines
• Encourage: Swimming, cycling, upper body activities

After re-ossification stage (2-4 years):

• Gradual return to impact activities
• Guided by X-rays and symptoms

What is the long-term outlook?

Good outcome (round ball, Stulberg I-II):

• Normal or near-normal hip function
• Minimal arthritis risk
• 60-80% of young children (less than 6 years)
• 70-75% of older children with surgery

Moderate outcome (oval ball, Stulberg III):

• Good function in childhood/young adulthood
• Arthritis risk in 40s-50s
• May need hip replacement eventually

Poor outcome (flat ball, Stulberg IV-V):

• Stiff, painful hip
• Arthritis risk in 20s-30s
• Hip replacement likely needed
• 10-20% of cases overall; higher in untreated older children

Key Messages for Families

• Perthes always heals - but the shape it heals into determines the future
• Age is critical - younger children do much better
• Treatment does not heal faster - it only prevents deformity
• Compliance is essential - missing physiotherapy or activity restrictions risks poor outcome
• Regular X-rays are mandatory to monitor progress and guide treatment decisions

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12. Evidence & Guidelines

Landmark Studies

1. Herring et al. (2004) - Lateral Pillar Classification & Treatment Outcomes

• Multi-center prospective study (438 children)
• Key findings:
  • "Group A: Excellent outcomes regardless of treatment"
  • "Group C: Poor outcomes regardless of treatment"
  • "Group B (age > 8 years): Surgery superior to observation (75% vs 44% good outcome)"
  • "Group B/C border: Worst group; surgery beneficial"
• Impact: Established Herring classification as treatment guide
• Reference: J Bone Joint Surg Am. 2004;86(10):2121-2134. PMID: 15466720 [13]

2. Stulberg et al. (1981) - Long-Term Natural History

• 40-year follow-up of Perthes patients
• Developed 5-class outcome classification (Stulberg I-V)
• Key findings:
  • "Classes I-II: Minimal OA risk"
  • "Class III: 50% OA at age 45"
  • "Classes IV-V: 80% OA at age 35; 40% THR rate"
• Impact: Defined long-term outcomes and OA risk stratification
• Reference: J Bone Joint Surg Am. 1981;63(7):1095-1108. PMID: 7276045 [14]

3. Catterall (1971) - Classification & Head at Risk Signs

• Defined 4-group classification (I-IV) based on extent of involvement
• Identified 5 "Head at Risk" radiographic signs
• Impact: First systematic prognostic classification (now superseded by Herring)
• Reference: J Bone Joint Surg Br. 1971;53(1):37-53. PMID: 5578764 [2]

4. Kim et al. (2011) - Containment Surgery Outcomes

• Systematic review of femoral vs pelvic osteotomy
• No significant difference in outcomes (both ~70% Stulberg I-II)
• Femoral osteotomy more predictable; pelvic osteotomy better coverage
• Reference: J Bone Joint Surg Am. 2011;93(7):610-622. PMID: 21471415 [16]

Current Guidelines

British Society for Children's Orthopaedic Surgery (BSCOS):

• Age less than 6 years: Observation (all groups)
• Age 6-9 years, Herring B/B-C: Consider containment surgery
• Age > 9 years, Herring B/B-C: Strong recommendation for surgery
• Physiotherapy mandatory (all groups)

Pediatric Orthopaedic Society of North America (POSNA):

• Similar age-based algorithm
• Emphasizes shared decision-making with families
• Notes limited evidence for Herring C surgery (Grade C recommendation)

Cochrane Review (2023):

• Insufficient high-quality RCTs to definitively guide treatment
• Observational data supports surgery in Herring B, age > 8 years
• Call for multicenter RCTs

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13. Examination Focus (Viva Vault)

Core Knowledge Questions

Q1: Describe the blood supply to the pediatric femoral head and why Perthes occurs at age 4-8.

Model Answer: The blood supply to the femoral epiphysis changes with age. In infants, vessels from the medial and lateral femoral circumflex arteries cross the physis freely. Between ages 1-7 years, the physis becomes an avascular barrier, and the epiphysis relies exclusively on lateral epiphyseal vessels from the MFCA, which course along the anterosuperior femoral neck. There are no anastomotic connections - this creates a vulnerable "watershed" period. Any insult (thrombosis, compression, venous congestion) during this time can cause AVN. By age 8-10, vessels mature and the ligamentum teres artery contributes, reducing vulnerability.

Key Point: The precarious single-source blood supply between ages 4-8 explains the disease's age distribution.

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Q2: What are the "Head at Risk" signs and which is most important?

Model Answer: Catterall described 5 radiographic signs predicting poor outcome:

1. Lateral subluxation (extrusion) ← Most important
2. Gage sign (V-shaped lateral metaphyseal defect)
3. Calcification lateral to epiphysis
4. Diffusely horizontal physis
5. Metaphyseal cysts

Lateral subluxation is most critical because it indicates:

• Loss of containment
• Femoral head deforming outside the acetabular mould
• Highest correlation with Stulberg IV-V outcome
• Measurement: Extrusion index > 20% (% of head lateral to Perkin's line)

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Q3: Explain the concept of "Hinge Abduction" and its clinical significance.

Model Answer: Hinge abduction occurs when the femoral head is so flat and broad that it cannot slide smoothly within the acetabulum during abduction. Instead, the lateral edge of the extruded head impinges against the acetabular rim, and the hip "hinges open" rather than rotating concentrically.

Clinical Test:

• Hip flexed 90°
• Passive abduction performed
• Positive test: Sudden stop at 20-30° + palpable/visible lateral impingement

Significance:

• Contraindication to containment surgery: Forcing the head into the socket would crush articular cartilage
• Indicates salvage procedures needed (valgus osteotomy, shelf)
• Poor prognosis (Stulberg IV-V)

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Q4: Why is age such a critical prognostic factor?

Model Answer: Age determines remodeling potential, which depends on:

1. Remaining growth time:

   • Age 4: 10+ years of growth remaining
   • Age 10: 2-4 years remaining
   • Longer growth → more time for bone and acetabulum to remodel

2. Acetabular plasticity:

   • Young acetabular cartilage is malleable and reshapes to match femoral head deformity (maintaining congruency)
   • Older acetabulum is more rigid (incongruency persists → OA)

3. Reossification quality:

   • Younger bone has higher osteoblastic activity
   • Better neovascularization

Evidence: Age less than 6 years: 90% good outcome; Age > 8 years: 40% good outcome (doubles to 75% with surgery)

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Q5: Describe the Herring Lateral Pillar Classification and how it guides treatment.

Model Answer: The Herring classification assesses the height of the lateral third of the femoral epiphysis at maximal fragmentation on AP radiograph:

• Group A: No loss of lateral pillar height → Excellent prognosis (observe, any age)
• Group B: less than 50% loss → Age-dependent prognosis (observe if less than 8 years; surgery if > 8 years)
• Group B/C: Exactly 50% or > 50% with ossification preserved → Poor without surgery (strong surgery indication)
• Group C: > 50% loss with complete collapse → Poor prognosis (surgery controversial)

Rationale: The lateral pillar acts as a "tent pole" supporting the epiphysis. If intact, the head maintains structure. If collapsed, global flattening occurs.

Treatment Algorithm:

• Group A (any age) or Group B (less than 8 years) → Observation
• Group B or B/C (> 8 years) → Containment surgery
• Group C → Controversial (many observe; surgery limited benefit)

Evidence: Herring et al. 2004 showed surgery improved Group B (age > 8) outcomes from 44% → 75% Stulberg I-II.

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Clinical Scenario Questions

Scenario 1: A 7-year-old boy presents with 6-week history of limping. He has knee pain. Examination: Hip ROM - abduction 20° (normal 40°), IR 15° (normal 40°). X-ray: Small, dense femoral epiphysis; widened joint space; crescent sign. What is the diagnosis, stage, and management?

Model Answer:

• Diagnosis: Perthes disease (Legg-Calvé-Perthes)
• Stage: Waldenström Stage I (Initial/Necrosis)
  • Dense epiphysis (sclerosis from compacted dead bone)
  • Crescent sign (subchondral fracture)
  • Widened joint space (cartilage hypertrophy)
• Management:
  • "Immediate: Exclude septic arthritis (clinical assessment ± aspiration if doubt)"
  • "Classification: Await fragmentation stage to assess Herring lateral pillar (requires repeat X-ray in 3-4 months)"
  • "Current treatment:"
    • Physiotherapy (maintain abduction ROM - critical to prevent hinge)
    • Activity modification (avoid impact sports; swimming/cycling encouraged)
    • NSAIDs for pain
    • Serial X-rays every 3-4 months
  • "Definitive treatment decision: Based on age (7 = borderline) + Herring classification when apparent"
    • If Herring A → Observe
    • If Herring B/B-C → Consider containment surgery (age 7 = surgical gray zone; individualize based on ROM, family compliance, extrusion)

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Scenario 2: A 9-year-old boy with established Perthes (fragmentation stage, Herring B). You are considering femoral varus osteotomy. On examination, when you flex the hip to 90° and abduct, the hip stops at 25° and you feel a lateral bump. What is the significance and how does it change management?

Model Answer:

• Finding: Hinge abduction (lateral impingement)

• Significance:

  • Flat, extruded femoral head impinges on acetabular rim
  • Hip cannot abduct smoothly (hinges open instead of rotating)
  • Absolute contraindication to containment surgery
    • Forcing the head into the socket (via varus osteotomy) would crush articular cartilage
    • Worsens damage rather than improves containment

• Management Change:

  • Abandon containment surgery
  • "Options:"
    1. Observation: Accept deformity; allow reossification to complete; monitor symptoms
    2. Salvage procedures (if symptomatic):
       • Valgus osteotomy: Shift weight-bearing to less damaged medial surface; reduce impingement
       • Shelf acetabuloplasty: Lateral buttress to support extruded head
    3. Long-term: Plan for THR (likely needed age 30-40; Stulberg IV-V outcome expected)

• Key Principle: Hinge abduction indicates the "containment window" has closed; treatment shifts from preventive to salvage.

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14. References

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2. Catterall A. The natural history of Perthes' disease. J Bone Joint Surg Br. 1971;53(1):37-53. PMID: 5578764

3. 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. PMID: 6707028

4. Weinstein SL. Natural history and treatment outcomes of childhood hip disorders. Clin Orthop Relat Res. 1997;(344):227-242. PMID: 9372775

5. Ippolito E, Tudisco C, Farsetti P. Long-term prognosis of Legg-Calvé-Perthes disease developing during adolescence. J Pediatr Orthop. 1985;5(6):652-656. PMID: 4066928

6. McAndrew MP, Weinstein SL. A long-term follow-up of Legg-Calvé-Perthes disease. J Bone Joint Surg Am. 1984;66(6):860-869. PMID: 6725318

7. 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. PMID: 22223709

8. Hall AJ, Barker DJ, Dangerfield PH, Taylor JF. Small feet and Perthes' disease: a survey in Liverpool. J Bone Joint Surg Br. 1988;70(4):611-613. PMID: 3403611

9. Garcia Mata S, Ardanaz Aicua E, Hidalgo Ovejero A, et al. Legg-Calvé-Perthes disease and passive smoking. J Pediatr Orthop. 2000;20(3):326-330. PMID: 10823598

10. Trueta J. The normal vascular anatomy of the human femoral head during growth. J Bone Joint Surg Br. 1957;39(2):358-394. PMID: 13429036

11. Chung SMK. The arterial supply of the developing proximal end of the human femur. J Bone Joint Surg Am. 1976;58(7):961-970. PMID: 977628

12. Glueck CJ, Freiberg RA, Crawford A, et al. Secondhand smoke, hypofibrinolysis, and Legg-Perthes disease. Clin Orthop Relat Res. 1998;(352):159-167. PMID: 9678044

13. Herring JA, Kim HT, Browne R. Legg-Calvé-Perthes disease. Part II: Prospective multicenter study of the effect of treatment on outcome. J Bone Joint Surg Am. 2004;86(10):2121-2134. DOI: 10.2106/00004623-200410000-00002. PMID: 15466720

14. Stulberg SD, Cooperman DR, Wallensten R. The natural history of Legg-Calvé-Perthes disease. J Bone Joint Surg Am. 1981;63(7):1095-1108. PMID: 7276045

15. 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. PMID: 18827248

16. 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. PMID: 21742142

17. Young ML, Little DG, Kim HKW. Evidence for using bisphosphonate to treat Legg-Calvé-Perthes disease. Clin Orthop Relat Res. 2012;470(9):2462-2475. DOI: 10.1007/s11999-011-2240-0. PMID: 22125246

18. Nguyen NA, Klein G, Dogbey G, et al. Operative versus nonoperative treatments for Legg-Calvé-Perthes disease: a meta-analysis. J Pediatr Orthop. 2012;32(7):697-705. DOI: 10.1097/BPO.0b013e318263a00e. PMID: 22955535

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