Management of bone defects

OSTEOBIOLOGICS

DBM (Demineralized Bone Matrix)

  • Acid extraction of mineralized extracellular matrix allograft leaving proteins, including bone morphogenic proteins
  • Problems:
    • Variable composition & quality depending on manufacturing and donor
    • Highly osteoconductive but not very inductive
  • Good reports when used with autologous cancellous graft & titanium cages for very large defects, but all anecdotal with low quality evidence

Bone Marrow Aspirations

  • Theory: eliminates graft site morbidity and has a high level of osteoprogenitor cells, providing osteoinductive properties
  • Used in combination with cancellous allograft, has had good results but very poor quality evidence

Bone Morphogenic Proteins (BMPs)

  • Extensive research into these - multiple potential applications
  • Benefit: Highly osteogenetic and inductive
  • When used with a structural allograft, shown to be at least equal to cancellous autograft for tibial non-union (Level 1 RCT)
  • Potential issues: Cost implications & availability

LARGE DIAPHYSEAL DEFECTS

  • Options include some of the above or:
    • Free fibula transfer
    • Bone transport
    • Amputation

Free Fibula Transfer (FFT)

  • Extensive resources and time required
  • Relatively high failure rate (of vascular anastomoses)
  • Graft site morbidity
  • Recent comparative study favored bone transport over FFT

Bone Transport (BT)

  • Probably the gold standard for limb salvage of large post-traumatic defects
  • Dock and distract together or shorten then transport separately
  • Requires patient compliance due to long treatment time
  • Complications include pin site infection, re-fracture, and non-union

Amputation

  • Must be considered a viable option, but no comparative evidence supports it over salvage
  • Include the patient in the decision-making process
  • Cheap, least complications, and lower monetary cost

Principles of Ilizarov and Distraction Osteogenesis

  • Powerful means of correcting deformity, lengthening a limb, or stabilizing a fracture

Principles of Distraction

  • Corticotomy (low energy) with a drill and osteotome
  • Solid stabilization in a frame
  • Latent period of 7-10 days
  • Distraction at 1mm per day maximum in 3 divided increments
  • Monitoring by serial X-rays to look at regenerate
  • Static phase to allow regenerate to consolidate:
    • Should be at least as long as distraction phase
  • Regenerate comprises a central radiolucent fibrous zone of type 1 collagen:
    • Consolidation of the initially radiolucent zone occurs by trabecular formation spanning the bone ends
    • Trabecular columns are oriented parallel to the direction of distraction
    • Columns are surrounded by blood vessels
  • 10% lengthening at a time is tolerated by muscle; histologic changes after 30%
  • Nerve and vascular changes occur but tend to be temporary

Mechanical Properties of Ilizarov Fixators

  • Stability determined by the ring and connecting bars
  • Complete rings are more rigid
  • Reducing ring size by 2cm increases rigidity by 70%
  • Use the smallest possible ring
  • Leave 2cm between skin and frame
  • Partial rings are useful around joints
  • 2 rings (near-far) per bone segment
    • Intervening free rings if distances are very long
  • Wires:
    • Minimum of 2 wires per ring – more if possible
    • 90 degrees crossing angle (minimum 60 degrees – allows bone to slide)
    • Thicker wires are stiffer
    • Olive tip wires are better
    • Tensioning the wires increases stiffness (aim for 130Nm)
  • HA Coated Half Pins:
    • Better resistance against loosening
    • Good in deformity correction where frames are on for long durations
  • Taylor Spatial Frame:
    • Easier for deformity correction but can also be done with Ilizarov
    • Utilizes frames with strategically placed hinges
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