Pediatric Musculoskeletal Imaging

Normal Growth & Variants - Bones in Bloom

• Ossification Centers: Primary (diaphysis), Secondary (epiphysis). Appearance/fusion age varies (e.g., elbow: CRITOE 📌).
  • Order of elbow ossification: Capitellum (1yr), Radial head (3yr), Internal (medial) epicondyle (5yr), Trochlea (7yr), Olecranon (9yr), External (lateral) epicondyle (11yr).
• Physes (Growth Plates): Cartilaginous; weakest part of growing bone. Salter-Harris fractures involve physis.
  • Zones: Resting, Proliferative, Hypertrophic (weakest), Calcification.
• Apophyses: Secondary ossification centers at tendon/ligament attachments (e.g., tibial tuberosity - Osgood-Schlatter, calcaneal - Sever's).
  • Prone to avulsion fractures.
• Normal Variants Mimicking Fractures:
  • Bipartite patella (superolateral fragment)
  • Os trigonum (posterior to talus)
  • Accessory navicular

⭐ The physis is radiolucent and represents the weakest point in a child's bone, making it susceptible to Salter-Harris fractures, which can affect growth if not managed properly (especially types III, IV, V).

Pediatric MSK Trauma - Twigs & Snaps

• Incomplete Fractures (Elastic bones):
  • Torus/Buckle: Compression causes cortex to bulge.
  • Greenstick: Tension side breaks, compression side bends.
  • Plastic Bowing: Bone bends, no distinct fracture line.
• Salter-Harris (Growth Plate Injuries) 📌 SALTER:
  • I: Slipped (through physis)
  • II: Above (physis + metaphysis) - Most common.
  • III: Lower (physis + epiphysis)
  • IV: Through (metaphysis, physis, epiphysis)
  • V: Rammed (crush of physis)
• Common Sites: Supracondylar (elbow), distal radius.
• NAI Clues:
  • Metaphyseal corner/bucket-handle fractures.
  • Posterior rib fractures (squeezing).
  • Multiple fractures, varied healing stages.

⭐ Salter-Harris Type II fractures are the most common type of physeal injury.

MSK Infections/Inflammation - Fiery Joints & Bones

• Osteomyelitis:
  • Spread: Hematogenous (metaphysis in children), direct, contiguous.
  • X-ray: Early: soft tissue swelling. Late (10-14 days): periosteal reaction, lytic lesions, sequestrum.
  • US: Subperiosteal fluid/abscess, soft tissue edema.
  • MRI: Most sensitive for early changes (marrow edema, abscess).
• Septic Arthritis: (Esp. Hip)
  • US: Joint effusion (key!), synovial thickening. 📌 US guides aspiration.
  • MRI: Cartilage/bone involvement, synovitis.
• Juvenile Idiopathic Arthritis (JIA):
  • Key features: Periostitis, erosions (marginal), joint space narrowing (late), osteopenia. Affects large joints (knee, ankle, wrist).

⭐ MRI is the most sensitive imaging modality for early diagnosis of osteomyelitis, detecting marrow changes within 24-48 hours of onset.

Developmental Dysplasia of Hip (DDH) - Hip Hip Hooray?

• Risk Factors: 📌 Female, Firstborn, Family Hx, Frank breech, Oligohydramnios.
• Clinical: Barlow (provocative, dislocates), Ortolani (reductive, relocates), Galeazzi sign.
• Imaging:
  • Ultrasound (<4-6m): Graf classification.
    • Alpha angle (bony roof): Normal > 60°.
    • Beta angle (cartilage roof).
  • X-ray (>4-6m):
    • Lines: Hilgenreiner (H), Perkin (P), Shenton (S-arch).
    • Acetabular Index (AI): Normal < 25-30° (↑ in DDH).
    • Center-Edge Angle (CE): Normal > 20-25° (↓ in DDH).

⭐ Shenton's line disruption is a key X-ray sign indicating hip subluxation or dislocation.

Common Pediatric MSK Conditions - Growing Pains Plus

• Legg-Calvé-Perthes (LCPD): Avascular necrosis, femoral head.

  • Stages: Incipient, Fragmentation, Re-ossification, Healed.
  • X-ray: Crescent sign, ↑medial joint space.

• SCFE (Slipped Capital Femoral Epiphysis): Femoral epiphysis slips posteroinferiorly.

  • Klein's line (AP view): Fails to intersect lateral epiphysis.
  • Grading: Mild (<30% slip), Moderate (30-50%), Severe (>50%).

• Rickets: Defective physeal mineralization. X-ray: Physeal cupping, fraying.

• Benign Bone Lesions:

  • Non-ossifying fibroma (NOF): Eccentric, cortically based, sclerotic rim.
  • Osteochondroma: Cartilage-capped bony projection from metaphysis.
  • Simple Bone Cyst (SBC): Central, lytic, well-defined.

⭐ SCFE is a common hip disorder in adolescents; bilateral involvement occurs in 20-40% of cases, often within 18 months of initial presentation on one side.

High‑Yield Points - ⚡ Biggest Takeaways

• DDH: Ultrasound < 6 months (Graf), X-ray > 6 months (Hilgenreiner, Perkin, Shenton lines).
• SCFE: Klein's line fails to intersect epiphysis; "ice cream off cone" sign.
• Legg-Calvé-Perthes: Avascular necrosis of femoral head; stages include fragmentation, re-ossification.
• Rickets: Widened, cupped, frayed physes; bowing deformities.
• NAI: Suspect with metaphyseal corner fractures, posterior rib fractures, multiple healing-stage fractures.
• Salter-Harris fractures: Involve growth plate; Type II most common.