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