Congenital Skeletal Anomalies

Intro & Dysplasia Types - Bone Blueprint Basics

• Skeletal Dysplasia: Intrinsic, generalized disorders of bone & cartilage growth. Affects "bone blueprint".
  • Examples: Achondroplasia (FGFR3), Osteogenesis Imperfecta (collagen defects).
• Skeletal Dysostosis: Localized malformation of individual bones or groups.
  • Examples: Cleidocranial dysostosis, Polydactyly.
• Radiological Approach:
  • Identify affected skeletal segment (epiphysis, metaphysis, diaphysis, spine).
  • Assess bone density, size, shape, modeling.
  • Note distribution (generalized vs. focal).
• Key Distinction: Dysplasia = abnormal tissue; Dysostosis = abnormal bone shape/number.

⭐ Achondroplasia: Most common non-lethal skeletal dysplasia. Caused by FGFR3 gene mutation, leading to impaired endochondral ossification & rhizomelic shortening.

Key Chondrodysplasias - Short Limb Tales

• Achondroplasia: Most common non-lethal dysplasia. FGFR3 gene. Rhizomelic shortening.
  • Signs: Trident hand, lumbar lordosis, champagne glass pelvis, foramen magnum stenosis.
• Thanatophoric Dysplasia: Most common lethal neonatal dysplasia. FGFR3 gene. Severe micromelia.
  • Signs: Cloverleaf skull (Kleeblattschädel), telephone receiver femurs, narrow thorax. Respiratory failure.
• Pseudoachondroplasia: Normal at birth; manifests by age 2. COMP gene. Normal face.
  • Signs: Short limbs, waddling gait, ligamentous laxity, early osteoarthritis.
• Diastrophic Dysplasia: SLC26A2 gene. Autosomal recessive.
  • Signs: Hitchhiker thumb, cauliflower ear, clubfoot, scoliosis.

⭐ Achondroplasia: Impaired endochondral ossification; intramembranous ossification (skull vault, clavicles) is unaffected.

OI & Fibrous Dysplasia - Bone Matrix Mayhem

• Osteogenesis Imperfecta (OI): Brittle Bones
  • Cause: Type I collagen defect (COL1A1/A2 genes).
  • Features: Blue sclera, fractures, hearing loss, dentinogenesis imperfecta.
  • X-ray: Osteopenia, multiple fractures (various healing stages), bowing, Wormian bones, codfish vertebrae.
  • 📌 BITE: Bones, I (eye), Teeth, Ear.
• Fibrous Dysplasia (FD): Fibrous Bone
  • Cause: GNAS1 mutation → ↑cAMP → abnormal osteoblast differentiation.
  • X-ray: "Ground-glass" matrix, expansile lesions, shepherd’s crook deformity (femur), Rind sign.
  • Types: Monostotic, Polyostotic. McCune-Albright Syndrome (FD + café-au-lait spots + endocrinopathy).

⭐ "Ground-glass" appearance on X-ray is a hallmark radiological sign of fibrous dysplasia, often described as a hazy or smoky pattern within the bone lesion without visible trabeculae.

Dysostoses & Spinal Defects - Segmental Slip-Ups

• Dysostoses: Localized defects in bone development.
  • Cleidocranial Dysostosis:
    • AD, RUNX2 gene.
    • Hypoplastic/aplastic clavicles.
    • Wormian bones, delayed suture/fontanelle closure.
    • Dental anomalies (supernumerary teeth).
• Congenital Spinal Defects:
  • Klippel-Feil Syndrome:
    • Congenital fusion of ≥2 cervical vertebrae.
    • 📌 Triad: Short neck, low posterior hairline, restricted neck motion.
    • Associated: Sprengel's, scoliosis, renal/cardiac issues.
  • Hemivertebrae:
    • Failure of formation of one side of vertebral body.
    • Common cause of congenital scoliosis/kyphosis.
    • Types: Segmented, semi-, non-segmented.
  • Spina Bifida:
    • Occulta: Arch defect, skin marker (hair tuft).
    • Cystica: Meningocele, Myelomeningocele (neural tissue).

⭐ In Klippel-Feil syndrome, C2-C3 is the most common level of fusion.

High‑Yield Points - ⚡ Biggest Takeaways

• Achondroplasia: Most common non-lethal dysplasia; FGFR3 mutation, rhizomelia, trident hand, champagne glass pelvis.
• Osteogenesis Imperfecta: Brittle bones; COL1A1/A2 mutations, blue sclera, recurrent fractures, wormian bones.
• Osteopetrosis: Marble bone disease; defective osteoclasts, dense bones, fractures, Erlenmeyer flask deformity.
• Cleidocranial Dysplasia: Absent/hypoplastic clavicles, wormian bones, delayed fontanelle closure, RUNX2 gene.
• Klippel-Feil Syndrome: Congenital fusion of cervical vertebrae, short neck, low posterior hairline.
• Marfan Syndrome: FBN1 gene; tall stature, arachnodactyly, aortic root dilatation.
• Down Syndrome: Atlantoaxial instability, flared iliac wings, eleven pairs of ribs.