BONE GRAFT SUBSTITUTES dnb ms question answers

BONE GRAFT SUBSTITUTES

• autogenous material remains the gold standard for filling bony defects – drawbacks are :
• donor site morbidity
• prolonged anaesthesia time and bleeding
• limited availability

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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

Collagraft

• 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

Orthograft

• 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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