OI

Question 1

Orthopaedic manifestations

Answer 1

• bone fragility and fractures
  
  • fractures heal in normal fashion initially but the bone does not remodel
  • can lead to progressive bowing
• ligamentous laxity
• short stature
• scoliosis
• codfish vertebrae (compression fx)
• basilar invagination
• olecranon apophyseal avulsion fx
• coxa vara (10%)
• congenital anterolateral radial head dislocations

Question 2

Non-Orthopaedic manifestations

Answer 2

• blue sclera
• dysmorphic, triangle shaped facies
• hearing loss
  
  • 50% of adults with OI
  • may be conductive, sensorial and mixed
• brownish opalescent teeth (dentinogenesis imperfecta)
  
  • alteration in dentin
  • brown/blue teeth, soft, translucent, prone to cavities
  • affects primary teeth > secondary teeth
• wormian skull bones (puzzle piece intrasutural skull bones)
• hypermetabolism
  
  • increased risk of malignant hyperthermia
  • hyperhidrosis, tachycardia, tachypnoea, heat intolerance
• thin skin prone to subcutaneous hemorrhage
• cardiovascular
  
  • mitral valve prolapse
  • aortic regurgitation

Question 3

Sillence Classification of Osteogenesis Imperfecta (simplified)

Question 4

Symptoms

Answer 4

• mild cases
  
  • multiple fractures during childhood
• severe cases
  
  • present with fractures at birth and can be fatal
  • number of fractures typically decreases as patient ages and usually stops after puberty
• basilar invagination
  
  • presents with apnea, altered consciousness, ataxia, or myelopathy
  • usually in third or fourth decade of life, but can be as early as teenage years

Question 5

Physical exam

Answer 5

• multiple fractures leads to
  
  • saber shin appearance of tibia
  • bowing of long bones
• trendelenburg gait
  
  • if coxa vara present

Question 6

Radiographs

Answer 6

• thin cortices
• generalized osteopenia
• saber shins
• skull radiographs reveal wormian bones
• coxa vara

Question 7

Evaluation

Answer 7

• Labroratory
  
  • mildly elevated ALP
• Histology
  
  • increased diameter of haversion canals and osteocyte lacunae
  • replicated cement lines
  • increased number of osteoblasts and osteoclasts
  • decreased number of trabeculae
  • decreased cortical thickness
• Diagnosis
  
  • diagnosis is based on family history associated with typical radiographic and clinical features
  • Labs
    
    • no commercially available diagnostic test due to variety of genetic mutations
    • laboratory values are typically within normal range
  • possible methods diagnosis include
    
    • skull radiographs to look for wormian bones
    • fibroblast culturing to analyze type I collagen (positive in 80% of type IV)
      
      • can be used for confirmation of diagnosis in equivocal cases
    • biopsy
      
      • collagen analysis of a punch biopsy
      • iliac crest biopsy which shows a decrease in cortical widths and cancellous bone volume, with increased bone remodeling.

Question 8

Treatment of Fractures

Answer 8

• Fracture prevention
  
  • early bracing
    
    • indicated to decrease deformity and lessen fractures
  • bisphosphonates
    
    • indicated in most cases of OI to reduce fracture rate, pain, improve ambulation
      
      • marked improvement in pain at 1-6wk after initiation
    • inhibits osteoclasts
      
      • increases cortical diameter 88%
      • increases cancellous bone volume 46%
    • does not affect development of scoliosis
    • chronic use causes horizontal metaphyseal bands seen on radiographs
      
      • growth arrest lines
    • maintain bisphosphonate-free period around the time of IM rodding
      
      • interferes with osteotomy healing >> fracture healing
  • growth hormone
  • bone marrow transplantation < >has been used with some successFracture treatment
    
    • nonoperative
      
      • observation
        
        • indications
          
          • indicated if child is <2 years (treat as child without OI)
    • operative
      
      • fixation with telescoping rods
        
        • indications
          
          • consider in patients > 2 years
          • allow continued growth
      • fixation with load sharing device
        
        • indications
          
          • consider in patients > 2 years
          • fracture with deformity beyond accepted tolerances after closed reduction

Question 9

Treatment of Long Bone Bowing Deformities

Answer 9

Operative

• realignment osteotomy with rod fixation (Sofield-Miller procedure)
  
  • indications
    
    • severe deformity to reduce fracture rates
  • techniques include
    
    • nontelescopic devices (Rush rods, Williams rods)
    • telescopic devices (Sheffield rod, Bailey-Dubow rod, Fassier-Duval rod)

Question 10

Treatment of Scoliosis

Answer 10

• Vital capacity drops to 40% of expected for a 60° curve
• Nonoperative
  
  • observation
    
    • indications
      
      • if curve is <45 °
  • bracing is ineffective and not recommended
    
    • because of fragility of ribs
• Operative
  
  • posterior spinal fusion
    
    • indications
      
      • for curves > 45 ° in mild forms and > 35 ° in severe forms
    • technique
      
      • challenging due to fragility of bones
      • use allograft instead of iliac crest autograft due to paucity of bone
      • ASF only indicated in very young children to prevent crankshaft
      • associated with a large blood loss

Question 11

Treatment of Basilar Invagination

Answer 11

Operative

• decompression and posterior fusion
  
  • indications
    
    • radiographic features of invagination and cord compression with physical exam findings of myelopathy
  • techniques
    
    • resection of bony compression via transoral approach

Question 12

OI

Answer 12

• A hereditary condition resulting from a decrease in the amount of normal Type I collagen
• Pathophysiology
  
  • can result from
    
    • decreased collagen secretion
    • production of abnormal collagen
  • leads to insufficient osteoid production
    
    • physeal osteoblasts cannot form sufficient osteoid
    • periosteal osteoblasts cannot form sufficient osteoid and therefore cannot remodel normally
• Genetics
  
  • 90% have an identifiable genetic mutation
    
    • COL 1A1 and COL 1A2
      
      • causes abnormal collagen cross-linking via a glycine substitution in the procollagen molecule
  • autosomal dominant and autosomal recessive forms
    
    • milder autosomal dominant forms (Types I and IV)
    • severe autosomal recessive forms (Types II and III)