Bone Dysplasias

Table of Contents

  1. Definitions
  2. Classification
  3. Conditions
  4. Key Testing Facts

Definitions

  • Dysplasia: Failure to develop, resulting in shortening.
  • Dwarfism: A common term for all bone dysplasias.
    • Proportionate Dwarfism: Symmetric involvement of trunk and limb length.
    • Disproportionate Dwarfism: Involves either a short trunk or short limbs.

Classification

Proportionate Dwarfism

  • Mucopolysaccharidoses
  • Cleidocranial Dysplasia

Disproportionate Dwarfism

Short Limb

  1. Achondroplasia/Pseudoachondroplasia
  2. Diastrophic Dysplasia
  3. Trevor’s Disease
  4. Multiple Epiphyseal Dysplasia

Short Trunk

  1. Kniest’s Syndrome
  2. Spondyloepiphyseal Dysplasia

Conditions

Achondroplasia

Epidemiology

  • Most common skeletal dysplasia.

Aetiology

  • Mutation in FGFR3 gene.
  • Autosomal Dominant (80% are new mutations).
  • Affects the proliferative zone of the physis.

Clinical Features (GRUNTS)

  • G: Genu Varum, Coxa Valga.
  • R: Radial Head Subluxation.
  • U: Unusual Faces (frontal bossing, button nose).
  • N: Normal Intelligence.
  • T: Trident Hand.
  • S: Spinal issues (hyperlordosis, kyphosis, stenosis).

Imaging Features (SCIMP)

  • S: Spinal (scalloping, short pedicles, thoracolumbar collapse).
  • C: Champagne glass pelvis.
  • I: Inverted V-shaped distal femur.
  • M: Metaphyseal cupping.
  • P: Physeal appearance is delayed.

Management

  • Symptomatic treatment (e.g., decompression for spinal stenosis).

Pseudoachondroplasia

Differences from Achondroplasia

  • Mutation in COMP gene (Chromosome 19).
  • Normal facial features.
  • Increased cervical instability and early-onset OA.

Kniest’s Syndrome

  • Aetiology: Mutation in COL2A1 gene.
  • Disproportionate short trunk.
  • Characterized by short pelvis, dumbbell-shaped bones, and retinal detachment.

Trevor’s Disease

  • Isolated intra-epiphyseal osteochondroma.
  • Affects one joint (usually the knee).
  • Treatment: Excision (high recurrence).

Diastrophic Dysplasia

Aetiology

  • Mutation in SLC26A2 gene.
  • Autosomal Recessive.

Clinical Features

  • C’s: Cleft Palate, Cauliflower Ears, Club Feet.
  • S’s: Skew feet, Spinal stenosis, Kyphoscoliosis.

Metaphyseal Chondrodysplasias

Subtypes

Subtype Key Features
Jansen’s Rare, severe; PTHRP gene
Schmid’s Collagen type X defect; milder
McKusick’s Cartilage hypoplasia

Spondyloepiphyseal Dysplasia (SED)

  • Aetiology: Mutation in COL2A1 gene.
  • Types: Congenital (severe) and Tarda (milder, X-linked).
  • Spinal involvement distinguishes from MED.

Multiple Epiphyseal Dysplasia (MED)

  • Aetiology: Mutation in COL9A1 gene.
  • No spinal involvement.
  • Early-onset OA and epiphyseal abnormalities.

Mucopolysaccharidoses

  • Aetiology: Storage of complex sugars in multiple organs.
  • Differentiated by complex sugars in urine.
  • Most common type: Morquio’s Syndrome.

Cleidocranial Dysplasia

  • Aetiology: Mutation in CBFA1 gene.
  • Proportional dwarfism.
  • Key Feature: Clavicle aplasia (unilateral or bilateral).

Key Testing Facts

  • Achondroplasia: Most common skeletal dysplasia; FGFR3 mutation.
  • Diastrophic Dysplasia: Cauliflower ears, hitchhiker thumbs.
  • Cleidocranial Dysplasia: CBFA1 defect; hallmark is clavicle aplasia.
  • Mucopolysaccharidoses: Differentiated by urine sugars (Hunter’s is X-linked).
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