Enhancement of Fracture Healing

• fracture healing = specialized type of wound healing with bone regeneration
• incidence of delayed healing in USA = 5 to 10%

Causes

• inadequate immobilization
• distraction
• repeated manipulations
• excessive early motion
• excessive periosteal stripping
• other soft tissue damage
• contamination/infection
• anatomical structure e.g. NOF, scaphoid, talus

2 aspects

1. biological interventions
2. mechanical interventions

Biological enhancement

Local approaches

• stimulate bone healing = osteogenic, osteoconductive, osteoinductive methods

Osteogenic methods

• autogenous bone graft (Macewen 1881)
• allograft
• autogenous bone marrow graft
• haematoma forms around graft
• release of bio-active materials
• necrosis of graft & an inflammatory response, development of a fibro-vascular stroma with host derived blood vessels & osteogenic precursor cells
• graft is penetrated by osteoclasts - graft resorption
• a few cells from the graft may survive but main function is osteoconductive properties + osteoinduction d/t factors which stimulate the local inflammatory response with # healing
• cancellous graft allows more rapid revascularization & leads to better incorporation than cortical bone
• inlay grafts are better than onlay grafts
• rigid fixation enhances graft survival & revascularization
• bone of endochondral origin eg. tibia have > rate of revascularization compared to bone of membranous origin eg. iliac blade but must be securely fixed
• once the graft is adherent to the host bed, fixation plays no further role
• concern with allograft - infection, blood borne disease, histocompatibility.
• bone marrow - contains osteogenic precursors
• marrow derived mesenchymal cells in the future

Osteoconductive methods

• supports the ingrowth of vascular tissue & osteogenic cells
• Ca based ceramics - HA (marine coral), tricalcium phosphate
• Ca-collagen grafts
• bio-active glass
• synthetic polymers - inorganic Ca & phosphate paste which is injected into the # site & hardens

Osteoinductive methods

• process that supports formation of osteoprogenitor cells with the capacity for new bone formation
• can get bone formation at extra-skeletal sites
• BMP (bone morphogenic proteins)
• fibroblast growth factors
• platelet derived growth factor
• transforming growth factor-beta
• the above are growth factors
• these are cytokines which modulate & regulate fracture healing

Systemic approaches

• humoral factors
• #’s heal faster & with more callus in head injuries
• prostaglandins
• anabolic effect, esp PGE2
• effect blocked by indocid ie. anti-prostaglandin
• circulating osteogenic substances

Mechanical enhancement

• Rx of a fresh # may differ from the Rx of a non-union
• # healing is retarded by over-distraction or instability
• controlled micromotion or controlled rythmic distraction may enhance # healing
• in general, motion at a # site will cause formation of callus: hypermotion = hypertrophic non union

Effects of weight bearing

• Sarmiento - improved # healing
• Some report no difference in healing with weight bearing

• early stability improves blood flow, intra-medullary reaming + a tight fitting nail decreases blood flow
• electrical stimulation - most research has been with non-unions, may be beneficial
• electromagnetic stimulation - useful in delayed union
• ultra-sound - has a role in # healing