Updated: 10/10/2016

Intramembranous Bone Formation

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https://upload.orthobullets.com/topic/9007/images/compression_plate_i1_large.jpg
Introduction
  • One of the two essential processes during
    • fetal development bone formation
    • fracture healing
    • also commonly known as contact healing, and Haversian remodeling
  • Physiology
    • occurs without a cartilage model (unlike enchondral ossification)
  • Examples of intramembranous ossification
    • embryonic flat bone formation (skull, maxilla, mandible, pelvis, clavicle, subperiosteal surface of long bone)
    • distraction osteogenesis bone formation
    • blastem bone (occurs in children with amputations)
    • fracture healing with rigid fixation (compression plate)
    • one component of healing with intramedullary nailing
  • Associated conditions
    • conditions with defects in intramembranous ossification
      • cleidocranial dysplasia topic
        • caused by defect in intramembranous ossification 
        • caused by mutation in CBFA1 (also know as Runx2) located on chromosome 6
Mechanism
  • Steps of intramembranous bone formation 
    1. aggregation of undifferentiated mesenchymal cells
    2. osteoblast differentiation
    3. organic matrix deposition
  • Regulation and signaling
    • controlled by pathway called canonical Wnt and Hedgehog signaling
      • beta-catenin enters cells and induces cells to form osteoblasts which then proceed with intramembranous bone formation
      • important transcription factors include CBFA1 (also know as Runx2) and osterix (OSX)
      • sclerostin, created by the SOST gene, decreases bone mass by inhibiting the Wnt pathway
 

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Questions (1)

(OBQ12.131) All of the following statements regarding sclerostin are true EXCEPT? Tested Concept

QID: 4491
1

It is a product of the SOST gene

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(207/3889)

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Overexpression results in decreased bone mass

25%

(954/3889)

3

It is thought to be associated with sclerosteosis and Van Buchem disease

12%

(472/3889)

4

It activates the Wnt pathway

36%

(1402/3889)

5

It is derived from osteocytes

21%

(807/3889)

L 5 C

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