BONE GRAFT SUBSTITUTES dnb ms question answers - DNB Orthopaedics MS Orthopedics MRCS Exam GUIDE -

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Saturday 21 October 2017

BONE GRAFT SUBSTITUTES dnb ms question answers


  • autogenous material remains the gold standard for filling bony defects – drawbacks are :
    • donor site morbidity
    • prolonged anaesthesia time and bleeding
    • limited availability
bone graft substitues dnb ms ortho
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  • cancellous allograft has been used successfully – drawbacks are :
    • risk of transmitting infections
    • limited bone banking facility
  • alternative synthetic substitutes for bone grafts – ideal bone graft substitute means
    • provide scaffolding for osteoconduction
    • provide progenitor cells for osteogenesis
    • growth factors for osteoinduction
most available materials do not fulfill all three criteria.

Porous calcium phosphate ceramics
  • osteoconductive material
  • two types
    • hydroxy apatite
    • tricalcium phosphate
  • prepared from coral using hydrothermal conversion reaction and washing away organic material
  • porous material mimics cancellous bone in appearance and architecture
  • used to fill traumatic defects in cancellous metaphysis of long bone along with fixation
  • advantages
    • biocompatible
    • no inflammatory reaction
  • disadvantages
    • inability to bear cyclic loading
    • fixation required along with bone graft
    • unresorbed ceramics have got adverse effect on bone healing and remodelling
  • granular composite of calcium phosphate with collagen
  • used along with autogenous bone marrow aspirate to have both osteoconductive and osteoinductive agents
  • used to fill both metaphyseal or diaphyseal defect along with stable fixation
  • made of pure tricalcium phosphate
  • when implanted in body undergoes partial conversion to hydroxy apatite
  • resorbed by dissolution
  • can be also used as carrier for biological and pharmacological agents such as BMP and antibiotics
Hydroxy apatite cement
  • mixture of inorganic calcium phosphate and water
  • can be made into paste form and contoured to fill any bony defects before setting
  • bear minimum load
  • replaced by host bone (at 3-4mm in 6-8 month) by cell mediated response
  • no adverse effect in bone remodelling
  • percutaneous insertion techniques are being developed
Platelet gel
  • blood product
  • contain growth factors
Calcium sulphate
  • used as bone filler from earlier periods
  • varying result
  • osteoconductive material
  • completely resorbed
Bone morphogenic proteins
  • growth and differentiation factors
  • Dr. Marshal Urist
  • BMP 2 and 7 most important
  • powerful stimulators of bone growth
  • better spinal fusion capability than autogenous
  • used in non union, large bone defect, spinal fusion, congenital malformations
Bio active glass (SiO2 and minerals)
Sintered bovine cancellous bone block
Demineralised bone matrix in osteoset medium

  • Current status
    • calcium based bone grafts are best used as
      • void fillers
      • areas perfectly surrounded by host bone ( metaphyseal fractures)
    • graft substitutes are used in areas where the tensile strain is minimum ie. No structural support
    • calcium sulfate based material used where compressive strength is required for a short period
    • graft substitutes not used to bridge gaps
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