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Developmental Disorders Of Bone

A. ChondroosteoDysplasias

1. Epiphyseal Dysplasias

  1. Spondyloepiphyseal dysplasia
  2. Multiple epiphyseal dysplasia
  3. Dysplasia epiphyseal hemimelica (Trevor’s disease)- Hypoplasia
  4. Chondrodysplasia punctata (stippled epiphysis)- Hypoplasia

2. Physeal Dysplasia

  1. Achondroplasia -  Hypoplasia
  2. Hypochondroplasia - Hypoplasia
  3. Metaphyseal dysostosis - Hypoplasia
  4. Hyperchondroplasia - Hypoplasia
  5. Enchondromatosis (dyschondroplasia,Ollier’s disease) - Hyperplasia

3. Metaphyseal Dyplasia (Pyle’s disease)

  1. Hypophosphatasia - Hypoplasia
  2. Osteopetrosis - Hypoplasia
  3. Craniometaphyseal dysplasia - Hypoplasia
  4. Multiple exostosis (diaphyseal aclasis) — Hyperplasia

4. Diaphyseal Dysplasias

  1. Osteogenesis imperfecta  - Hypoplasia                  
  2. Idiopathic osteoporosis- Hypoplasia
  3. Diaphyseal dysplasia – Hyperplasia                                   
  4. Hyperphosphatasemia Hyperplasia

5. Mixed Dysplasias

  1. Spondylometaphyseal dysplasia    
  2. Pseudochondroplasia
  3. Diastrophic dysplasia                                             
  4. Cleidocranial dysplasia
  5. Nail patella syndrome                                            
  6. Cranio facial syndrome (Freeman- Sheldon / Whistling — Face syndrome)

B. Connective Tissue Disorders

  1. Osteogenesis imperfecta                            
  2. Fibrodysplasia ossificans progressiva
  3. Larsen’s syndrome                         
  4. Ehlers Danlos syndrome

C. Storage Disorders & Metabolic Defects

  1. Mucopolysaccharidoses eg. Hurler’s / Hunter’s / Morquio - Brails ford syndrome
  2. Gaucher’s disease
  3. Homocystinuria
  4. Alkaptonuria
  5. Congenital hyper uricemia

D. Chromosomal Disorders

  1. Down’s syndrome
  2. Sprengel’s deformity (elevation of scapula)

Unlike the physeal & epiphyseal disorders, dwarfism is not a feature in metaphyseal and diaphyseal dysplasias. But these may be associated with thickening of skull bones, with the risk of foraminal occlusion & cranial nerve entrapment.

 

E. Achondroplasia

  1. Inherited as autosomal dominant trait; however because few achondroplastic people have children, 80- 90% of cases are sporadic as a result of spontaneous point mutation in the gene coding for fibroblast growth factor receptor 3 (FGFR- 3), which apparently play role in endochondral cartilage growth to regulate linear growth
  2. Paternal age > 36 year is linked with new mutation.
  3. The risk of two parents without achondroplasia producing offspring with achondroplasia is almost negligible. But extreme rare recurrence of achondroplasia due to mosaicism in subsequent siblings of affected patients born to unaffected parents is reported.
  4. Glycine to arginine substitution (point mutation) in FGFR -3 gene on chromosome 4p is most mutable single nucleotide in human genome
  5. Enchondral ossification responsible for longitudinal growth is abnormal resulting in short bones.
     
    Intramembmous ossification are undisturbed causing normal clavicles and skull vault. Because the width of long bones is because of intramembranous periosteal ossification, these bones are of normal diameter

F. Clinical Features

  1. It is most common form of dwarfism.
  2. Disproportionate rhizomelic micromelia i.e. short stature which is most severe in proximal limbs. Trunk height tends to be normal, but arm span & standing height are diminished.
  3. Skull is large with prominent forehead (frontal bossing), saddle shaped nose (flat & depressed nasal bridge), small maxilla, prominent mandibles and normal dentition.
  4. Usually have normal intelligence.
  5. Hands are short & broad. The middle finger is shorter than usual resulting in all of the digits being of equal length (Starfish hand).
  6. There is separation between middle & ring fingers, described as trident hand or main en trident.
  7. Many infants have thraco lumbar kyphosis, but this almost always disappears in a year or two.
  8. Posture when standing is typical: excessively lordotic back, prominent buttocks, hips flexed, legs bowed, & elbows bent
  9. Shortening of vertebral pedicles may cause lumbar canal stenosis & disc prolapse, during adulthood (very common).

Description: images-1

G. Radiological features

  1. Tubular long bones are short with an apparent increase in bony diameter and density. Metaphyses are widened & flared, physis (growth plates) are U or V - shaped, but the epiphysis are uninvolved.
  2. Broad & flat pelvis with squared iliac wings, small sciatic notch & horizontal and notched acetabulae.
  3. Because the width of pelvis is greater than its depth it takes on an appearance of champagne glass.
  4. The spinal canal, as measured by interpedicular distance, normally widens as one proceeds distally in lumbar spine from L1 to L5. But in achondroplasia the spinal canal narrows & the interpedicular distance decreases.
  5. Posterior vertebral bodies in lumar spine may be scalloped. The pedicles are short & broad.

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