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Malformations of the Musculoskeletal System in Children

Class Discussion Guide — Definitions, Etiology, Pathogenesis, Diagnosis & Treatment

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I. Overview & Definition

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II. Etiology & Pathogenesis — General Mechanisms

A. Genetic / Chromosomal

• Single gene mutations (e.g., FGFR3 in achondroplasia; COL1A1/COL1A2 in osteogenesis imperfecta)
• Chromosomal trisomies (Trisomy 21 → ligamentous laxity; Trisomy 18 → multiple deformities)
• Multifactorial inheritance (most common — e.g., clubfoot, DDH, scoliosis)

B. Teratogenic / Environmental

• Antiseizure drugs: Valproic acid carries a 7–20% risk of fetal malformations, including musculoskeletal and cardiovascular defects; the risk increases with polytherapy (up to 10–20% with 3 drugs). (Harrison's, p. 12086)
• Thalidomide → limb reduction defects (phocomelia)
• Alcohol (FAS) → joint and limb anomalies
• Mechanical (oligohydramnios, uterine constraint) → deformations

C. Intrauterine Mechanical Factors

• Reduced amniotic fluid → compression deformities
• Abnormal fetal position → congenital hip dislocation, foot deformities
• Amniotic band syndrome → limb constrictions

D. Vascular / Ischemic

• Transverse limb defects from vascular disruption in first trimester

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III. Major Conditions — Detailed

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1. Developmental Dysplasia of the Hip (DDH)

Etiology & Risk Factors

Pathogenesis

1. Shallow acetabulum fails to provide adequate containment of femoral head
2. Femoral head migrates superolaterally out of acetabulum
3. Chronically dislocated head causes: acetabular fibrofatty changes (pulvinar), labral eversion (limbus), capsular elongation, and shortened hip adductors/iliopsoas
4. If untreated: secondary osteoarthritis by 3rd–4th decade

Classification (Graf Ultrasound)

• Type I: Normal
• Type IIa: Immature (< 3 months)
• Type IIb: Delayed ossification (> 3 months — pathological)
• Type III: Subluxation
• Type IV: Dislocation

Clinical Presentation

• Neonate: Asymmetric skin folds, leg length discrepancy, limited hip abduction
• Ortolani test (+): Dislocated hip reduces with abduction — "clunk" of reduction
• Barlow test (+): Stable hip dislocates with adduction + posterior pressure
• Walking child: Trendelenburg gait, waddling (bilateral DDH), leg shortening

Diagnosis

Treatment

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2. Congenital Talipes Equinovarus (CTEV / Clubfoot)

Etiology

• Idiopathic (most common — 50%): multifactorial; 2–3% recurrence in siblings
• Neurogenic: spina bifida, cerebral palsy, arthrogryposis
• Syndromic: associated with other anomalies
• Male predominance (2:1); bilateral in ~50%

Pathogenesis

• Primary defect likely in the talar anlage (cartilaginous talar neck is deviated medially and plantarward)
• Leads to sequential deformity:
  • Calcaneus: inverted under talus (varus)
  • Navicular: displaced medially
  • Forefoot: adducted and supinated
  • Ankle: plantarflexed (equinus)
• Shortened medial structures: tibialis posterior tendon, plantar fascia, spring ligament, deltoid ligament
• Muscles: anterior compartment relatively weak; posterior/medial compartment contracted

Diagnosis

• Clinical diagnosis at birth: assess CAVE components
• Pirani Score: 6-point scoring system (3 midfoot + 3 hindfoot signs) — guides Ponseti treatment
• Dimeglio Classification: I–IV based on reducibility
• Postnatal X-ray: Talo-calcaneal angle (Kite's angle) < 20° (normal 20–40°); talus-first metatarsal angle abnormal
• Rule out: neural tube defects, hip dysplasia (associated in ~2%)

Treatment

1. Serial casting (weekly) — corrects C, A, V components sequentially over ~6–8 weeks
2. Percutaneous Achilles tenotomy (in ~90%) — corrects equinus
3. Foot abduction brace (Denis Browne splint) — worn 23 hrs/day × 3 months, then nights until age 4

• Posteromedial soft tissue release (Carroll/McKay procedure)
• Tibialis anterior tendon transfer (to lateral cuneiform) for dynamic supination

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3. Congenital Scoliosis

Classification (Winter)

Etiology & Pathogenesis

• Failure of normal somite differentiation between weeks 5–8 of embryogenesis
• Unilateral unsegmented bar: tethers one side → asymmetric growth → progressive curve
• Frequently associated with VACTERL syndrome (Vertebral, Anal, Cardiac, Tracheo-Esophageal, Renal, Limb anomalies)
• Spinal cord anomalies in ~18–38% (diastematomyelia, syrinx, tethered cord) — MRI mandatory

Diagnosis

• Screening: Adams forward bend test (rib hump)
• X-ray (AP + lateral standing): Cobb angle measurement; vertebral anomaly typing
• MRI spine: mandatory — assess intraspinal anomalies
• CT 3D reconstruction: surgical planning
• Echocardiogram + renal ultrasound: rule out associated anomalies

Treatment

• Observation: curves < 20° with low progression risk
• Growing rods / VEPTR (Vertical Expandable Prosthetic Titanium Rib): for thoracic insufficiency syndrome in young children
• Spinal fusion: for progressive curves, once growth nears completion; type II (unsegmented bar) requires early surgery

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4. Achondroplasia

Etiology & Pathogenesis

• Autosomal dominant; > 80% are new mutations
• Gain-of-function mutation in FGFR3 gene (chromosome 4p16.3) — most commonly Gly380Arg
• FGFR3 normally inhibits chondrocyte proliferation; mutant receptor is constitutively active → severely inhibited endochondral ossification
• Intramembranous ossification is normal → skull vault, clavicle normal; long bones abnormally short

Clinical Features

• Rhizomelic shortening of limbs (proximal > distal)
• Large head (macrocephaly), frontal bossing, midface hypoplasia
• Trident hands, thoracolumbar kyphosis (infantile), lumbar hyperlordosis (adult)
• Normal intelligence; normal lifespan (with monitoring)

Complications

• Foramen magnum stenosis → cervical cord compression (sudden death in infancy)
• Spinal canal stenosis in adulthood
• Obstructive sleep apnea
• Recurrent otitis media

Diagnosis

• Clinical + X-ray: shortened tubular bones, rhizomelia, "champagne glass" pelvis, "tombstone" shaped pelvis, small foramen magnum
• Molecular genetic testing (FGFR3)
• Prenatal: ultrasound (femur length < 5th percentile after 22 weeks), amniocentesis

Treatment

• Primarily supportive and symptomatic
• Vosoritide (CNP analogue — FGFR3 inhibitor): FDA-approved (2021) for pediatric achondroplasia — improves annualized height velocity
• Foramen magnum decompression if symptomatic stenosis
• Limb lengthening (controversial)
• Avoid contact sports

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5. Osteogenesis Imperfecta (OI)

Etiology & Pathogenesis

• Most commonly autosomal dominant mutations in COL1A1 or COL1A2 (encoding Type I collagen)
• Leads to: quantitative deficiency (Type I OI) or qualitative defect in collagen fibril assembly (Types II–IV)
• Bone matrix is disorganized and poorly mineralized → pathological fractures from minimal trauma

Sillence Classification

Diagnosis

• Clinical: fractures disproportionate to trauma, blue sclerae, dentinogenesis imperfecta, hearing loss
• X-ray: osteopenia, wormian bones (skull), bowing deformities
• DXA scan: reduced BMD
• Molecular testing: COL1A1/COL1A2 sequencing
• Key differential: non-accidental injury (NAI/child abuse) — history, pattern of fractures, multidisciplinary assessment

Treatment

• Bisphosphonates (pamidronate/zoledronate): IV cyclic therapy — increases bone density, reduces fracture rate; given in children with recurrent fractures
• Physiotherapy: muscle strengthening, mobility
• Intramedullary rodding (Fassier-Duval rods): for long bone stabilization and correction of bowing
• Hearing aids, dental management

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6. Polydactyly & Syndactyly

• Polydactyly: Supernumerary digits (extra fingers/toes)
• Syndactyly: Fusion of adjacent digits (most common congenital hand anomaly)

Etiology & Pathogenesis

• Limb development regulated by: Zone of Polarizing Activity (ZPA), Apical Ectodermal Ridge (AER), and Wnt/BMP signaling
• Polydactyly: defective ZPA signaling (sonic hedgehog pathway excess)
• Syndactyly: failure of interdigital apoptosis (programmed cell death) between weeks 6–8
• Both may be isolated or syndromic (Apert syndrome — complex syndactyly; Ellis-van Creveld — polydactyly + short stature)

Classification

• Polydactyly: Preaxial (radial/tibial side), Central, Postaxial (ulnar/fibular — most common)
• Syndactyly: Simple (skin only) vs. Complex (bone fusion); Complete vs. Incomplete

Diagnosis

• Clinical examination + X-ray of hand/foot
• Genetic workup if syndromic features present

Treatment

• Polydactyly: Surgical excision — timing depends on type; postaxial soft-tissue type can be tied off in neonates; bony types need reconstruction at 1–2 years
• Syndactyly: Surgical separation + skin grafting at 6–18 months (earlier if bordering digits of unequal length — index-middle, ring-small — to prevent deformity)

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7. Limb Reduction Defects

Classification (ISO/ISPO)

• Transverse: Complete absence distal to a level (amputation-like)
• Longitudinal: Absence along the axis of the limb (radial/ulnar/fibular hemimelia)

Etiology

• Vascular disruption in first trimester
• Amniotic band syndrome
• Teratogenic exposure (thalidomide, misoprostol)
• Chromosomal anomalies

Treatment

• Prosthetic fitting (age-appropriate)
• Radial club hand (radial hemimelia): centralization surgery; associated with Fanconi anemia — must screen
• Fibular hemimelia: Syme amputation vs. limb lengthening

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IV. Diagnostic Approach — Summary Table

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V. Pathogenesis — Unifying Concepts for Class Discussion

Embryological insult (genetic/teratogenic/mechanical)
           │
    ┌──────┴──────┐
    ▼             ▼
Failure of    Failure of
formation     segmentation
(hemivertebra) (fusion anomaly)
           │
    Asymmetric growth forces
           │
    Progressive deformity over time
           │
    Secondary joint/soft tissue adaptation
           │
    Functional disability if untreated

1. The earlier the insult in embryogenesis, the more severe and complex the malformation
2. Many conditions are progressive during growth spurts — regular surveillance mandatory
3. Multisystem association is common (VACTERL, skeletal dysplasias) — always screen
4. Timing of intervention is critical — early treatment exploits growth remodeling potential

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VI. Treatment Principles Summary

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VII. Key Discussion Points

1. Why is early diagnosis critical? — Growth remodeling is possible only while skeletal immaturity persists; delayed diagnosis leads to secondary adaptive changes requiring more complex surgery
2. How do you differentiate positional from true malformations? — Positional deformities are flexible/passively correctable; true malformations are rigid
3. Role of genetics clinic: Any child with multiple malformations needs chromosomal microarray + dysmorphology assessment
4. Teratogen counseling: Valproic acid in epileptic mothers — risk of musculoskeletal + cardiovascular malformations (1.4–1.8%); always discuss risk/benefit with neurologist (Harrison's, p. 12086)
5. Clubfoot management has been revolutionized — Ponseti method (non-surgical) achieves >95% success and has replaced extensive surgical release as first-line globally
6. Scoliosis vs. congenital scoliosis: Congenital has structural vertebral anomaly, always get MRI to rule out spinal cord anomaly before any treatment

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Malformations of the Musculoskeletal System in Children

Complete Class Discussion Notes

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1. DEFINITION

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2. EMBRYOLOGICAL BASIS

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3. GENERAL ETIOLOGY

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4. MAJOR CONDITIONS

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A. Developmental Dysplasia of the Hip (DDH)

Definition

Etiology & Risk Factors

Pathogenesis

Shallow/underdeveloped acetabulum
        ↓
Femoral head inadequately contained
        ↓
Head migrates superolaterally
        ↓
Secondary changes:
  • Pulvinar (fibrofatty tissue) fills acetabulum
  • Labrum everts/inverts (limbus)
  • Capsule elongates and hourglass constricts
  • Iliopsoas & adductors shorten
        ↓
If untreated → secondary OA by 3rd–4th decade

Clinical Features

• Neonate: Asymmetric skin folds, apparent leg shortening (Galeazzi sign), limited hip abduction
• Ortolani test: Hip reduced → gentle abduction → dislocated head clunks back in ("in sign")
• Barlow test: Hip reduced → adduction + posterior pressure → head clunks out ("out sign")
• Walking child: Trendelenburg gait, waddling (bilateral), apparent leg shortening
• Note: Ortolani/Barlow become negative after 6–8 weeks as soft tissues tighten — do not exclude DDH

Diagnosis

• Type I: Normal (α angle > 60°)
• Type IIa: Immature (α 50–59°, age < 3 months — physiological)
• Type IIb: Delayed ossification (α 50–59°, age > 3 months — pathological)
• Type III: Subluxed cartilaginous roof
• Type IV: Dislocated

• Hilgenreiner line: Horizontal through both triradiate cartilages
• Perkin line: Vertical from lateral acetabular edge
• Normal: ossific nucleus in inner lower quadrant
• Shenton's line: Disrupted in subluxation/dislocation

Treatment

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B. Congenital Talipes Equinovarus (CTEV / Clubfoot)

Definition

• C — Cavus (high arch of midfoot)
• A — Adductus (forefoot adducted)
• V — Varus (hindfoot inverted)
• E — Equinus (ankle plantarflexed)

Epidemiology

• 1–2 per 1,000 live births; male 2:1; bilateral in ~50%
• Most common congenital foot deformity

Etiology

Pathogenesis

• Primary defect: deviated talar neck (medially and plantarward rotated)
• All other bones displace around the abnormal talus:
  • Calcaneus: inverted, equinus position
  • Navicular: displaced medially onto medial talar neck
  • Cuboid: follows calcaneus medially
• Contracted structures: tibialis posterior, FHL, FDL, plantar fascia, spring ligament, deltoid ligament, posterior capsule
• Relatively weak/lengthened: peronei, anterior tibialis, extensor tendons

Assessment

• Midfoot score (3 points): Curved lateral border, medial crease, talar head coverage
• Hindfoot score (3 points): Posterior crease, rigid equinus, empty heel

• Grade I: Soft/postural (benign)
• Grade II: Soft/resistant (moderate)
• Grade III: Resistant/soft (severe)
• Grade IV: Rigid (very severe)

Treatment

1. Serial casting (weekly, 5–7 casts): Corrects C → A → V in sequence; hindfoot corrects last
2. Percutaneous Achilles tenotomy (in ~85–90%): Corrects equinus; local anesthesia; cast for 3 weeks post-procedure
3. Foot Abduction Brace (Denis Browne orthosis): 70° abduction, 10° dorsiflexion; 23 hrs/day × 3 months, then nights/naps until age 4–5 years
   • Non-compliance = #1 cause of relapse

• Tibialis anterior tendon transfer to lateral cuneiform — corrects dynamic supination
• Posteromedial soft-tissue release (McKay/Carroll) — historically used; now reserved for failures

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C. Congenital Scoliosis

Definition

Etiology

• Failure of normal somite differentiation at weeks 5–8 of gestation
• Environmental triggers: maternal hyperthermia, diabetes, antiepileptic drugs
• Associated with VACTERL syndrome (Vertebral, Anorectal, Cardiac, Tracheo-Esophageal, Renal, Limb)
• Spinal cord anomalies in 18–38% (diastematomyelia, tethered cord, syringomyelia) — always get MRI

Classification (Winter)

• Fully segmented (free growth plates both ends) — most progressive
• Semi-segmented — moderate progression
• Incarcerated (wedged between normal vertebrae) — minimal progression
• Non-segmented (fused) — least progressive

Pathogenesis

Vertebral anomaly (e.g. unsegmented bar)
        ↓
Asymmetric longitudinal growth
        ↓
Progressive lateral curve + rotation
        ↓
Rib cage deformity → Thoracic Insufficiency Syndrome
        ↓
Restrictive lung disease + cor pulmonale (severe cases)

Diagnosis

• Adams Forward Bend Test: rib hump/trunk asymmetry
• Standing AP + lateral X-ray: Cobb angle; vertebral anomaly characterization
• MRI whole spine: Mandatory before any surgery — intraspinal anomalies
• CT 3D reconstruction: Surgical planning
• Echocardiogram + renal ultrasound: VACTERL screening
• Pulmonary function tests (older children)

Treatment

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D. Osteogenesis Imperfecta (OI) — "Brittle Bone Disease"

Definition

Pathogenesis

• Mutations in COL1A1 or COL1A2 genes (most common — autosomal dominant)
• Newer forms: CRTAP, LEPRE1, PPIB mutations (autosomal recessive — severe)
• Result: disordered collagen fibril assembly → abnormal bone matrix → osteoporosis + fracture susceptibility
• Bone heals promptly but in disorganized fashion → progressive bowing deformities
• ALL collagen-containing structures affected: bone, ligaments, sclerae, dentin, middle ear ossicles

Sillence Classification

Diagnosis

• Clinical triad: Fractures disproportionate to trauma + blue sclerae + dentinogenesis imperfecta
• X-ray: Generalized osteopenia, wormian bones (skull), bowed long bones, vertebral compression fractures
• DXA scan: Reduced bone mineral density (BMD) Z-score
• Molecular genetic testing: COL1A1/COL1A2 sequencing
• Skin biopsy: Collagen biochemical analysis (historical)
• Critical differential: Non-accidental injury (NAI/child abuse) — history inconsistency, dating of fractures, multidisciplinary team assessment essential

Treatment

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E. Achondroplasia

Definition

Etiology & Pathogenesis

• Autosomal dominant; > 80% are de novo mutations (associated with advanced paternal age)
• Gain-of-function mutation in FGFR3 (fibroblast growth factor receptor 3) gene — most commonly Gly380Arg (c.1138G>A, chromosome 4p16.3)
• FGFR3 normally inhibits chondrocyte proliferation in growth plate; mutant receptor is constitutively active
• Result: severely suppressed endochondral ossification → short long bones
• Intramembranous ossification is normal → normal skull vault and clavicles; skull base (endochondral) → small foramen magnum

Clinical Features

• Rhizomelic limb shortening (humerus/femur disproportionately short)
• Macrocephaly, frontal bossing, midface hypoplasia
• Trident hand configuration
• Thoracolumbar kyphosis in infancy → lumbar hyperlordosis with age
• Normal intelligence; near-normal lifespan
• Homozygous achondroplasia = lethal (respiratory failure)

Complications

Diagnosis

• Clinical + skeletal survey X-ray: Shortened tubular bones, "champagne glass" pelvis (narrow sacrosciatic notch), tombstone-shaped iliac wings, small foramen magnum, interpediculate distance narrows caudally (opposite of normal)
• Molecular genetics: FGFR3 point mutation
• Prenatal: Ultrasound (femur length < 5th percentile after 22 weeks); amniocentesis for FGFR3

Treatment

• Vosoritide (CNP analogue; FGFR3 inhibitor) — FDA-approved 2021; daily SC injection; improves annualized height velocity in children ≥ 2 years
• Foramen magnum decompression if symptomatic stenosis
• Guided growth / osteotomy for symptomatic genu varum
• Limb lengthening (Ilizarov/LON technique) — controversial; performed in specialist centres

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F. Polydactyly & Syndactyly

Polydactyly — Extra Digits

• Preaxial: Radial/tibial side (thumb/great toe duplication) — often associated with genetic syndromes
• Central: Middle digits — rare, usually syndromic
• Postaxial: Ulnar/fibular side (little finger/5th toe) — most common; Type A (fully formed), Type B (rudimentary)

• Type B postaxial: suture ligation at birth or excision
• Bony types: surgical reconstruction at 1–2 years (before school age)

Syndactyly — Fused Digits

• Most common congenital hand anomaly (1 in 2,000–3,000)
• Simple: skin/soft tissue only
• Complex: bony fusion
• Complete: to fingertip; Incomplete: partial

• Surgical separation + skin grafting at 6–18 months
• Priority: digit pairs of unequal length (ring-little, index-middle) — separate earlier to prevent tethering and angular deformity

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G. Congenital Limb Reduction Defects

Definition

Classification

• Transverse: Complete absence distal to a level (amputation-like)
• Longitudinal: Absence along the limb axis
  • Radial hemimelia (radial club hand) — associated with Fanconi anemia, TAR syndrome, Holt-Oram syndrome; screen with CBC and bone marrow biopsy
  • Fibular hemimelia — most common longitudinal deficiency; associated with femoral and tarsal anomalies
  • Tibial hemimelia — rare; associated with polydactyly and split hand/foot

Etiology

• Vascular disruption in first trimester
• Amniotic band syndrome (Streeter dysplasia)
• Teratogenic: thalidomide (phocomelia — absent proximal + present distal limb), misoprostol
• Chromosomal

Treatment

• Radial hemimelia: Centralization of hand over ulna + pollicization (creating thumb from index finger)
• Fibular hemimelia: Syme amputation (well-accepted in infancy) vs. limb lengthening (Ilizarov); decision based on foot function, leg length discrepancy
• Prosthetic fitting: Age-appropriate; upper limb from 6 months (sitting), lower limb from 9–12 months (standing)

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H. Larsen Syndrome (Multi-joint Dislocation)

• Mutation in FLNB (filamin B) — regulates cytoskeletal organization
• Multiple large joint dislocations (hips, knees, elbows) + clubfoot + cervical spine instability
• Treatment: serial casting, surgical stabilization, cervical spine fusion if needed

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5. UNIFIED DIAGNOSTIC APPROACH

Suspected MSK Malformation
        │
        ├── History: Family history, maternal drugs/illness,
        │   birth presentation, fetal movements, amniocentesis results
        │
        ├── Physical Examination:
        │   • Dysmorphic features (syndromic?)
        │   • Range of motion, flexibility vs rigidity
        │   • Neurological exam (spine anomaly?)
        │   • Skin: cafe-au-lait, haemangiomas
        │
        ├── Imaging:
        │   • X-ray (skeletal survey if dysplasia suspected)
        │   • Ultrasound (hips < 4 months; soft tissue/cord)
        │   • MRI (spinal cord anomalies, soft tissue detail)
        │   • CT 3D (complex bony anomalies, surgical planning)
        │
        └── Investigations:
            • Karyotype / chromosomal microarray
            • Gene panel / WES (if syndromic/dysmorphic)
            • Echocardiogram + renal USS (VACTERL)
            • CBC (radial hemimelia → Fanconi)

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6. TREATMENT PRINCIPLES SUMMARY

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7. KEY CLASS DISCUSSION POINTS

1. Why does timing matter? — The growing skeleton has remodeling potential unavailable after skeletal maturity. DDH treated at birth with harness avoids surgery; treated at 5 years requires complex osteotomy.
2. Flexible vs. rigid deformity — Always assess passively. Flexible = deformation (positional); corrects with stretching. Rigid = true malformation; requires casting/surgery.
3. Don't miss associations — Congenital scoliosis → VACTERL screen + MRI spine before any surgery. Radial hemimelia → rule out Fanconi anemia (fatal if missed).
4. Neonatal hip examination is a clinical skill — Ortolani and Barlow tests must be performed by every clinician. They become unreliable after 6–8 weeks as soft tissues tighten.
5. Ponseti has changed everything — Before 1990s, extensive posteromedial surgical release was standard for clubfoot, with high rates of stiffness and arthritic feet. Ponseti (non-surgical casting) now achieves > 95% correction with excellent long-term outcomes globally.
6. OI vs. NAI — Every child presenting with multiple unexplained fractures requires multidisciplinary assessment. Blue sclerae, wormian bones, and family history support OI; however, both can coexist.
7. Genetic counseling — Essential for families. Achondroplasia (> 80% de novo), OI (AD with variable expressivity), multifactorial conditions (recurrence risk counseling for DDH, clubfoot).

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