Bone Grafts

Indications

To provide stability (cortical bone best)
To provide linkage, ie replace missing bone
To stimulate osteogenesis

Bone grafts may be

Osteo-conduction
The graft provides a scaffold for bone deposition

Osteo-induction
Graft derived factors actually stimulate the recipient to invade the structure with osteogenic activity.


Physiology of remodelling and bone grafts

1. Activation
Local and systemic factors involved

2. Resorption
Appearance of osteoclasts from ? haematopoietic stem cell precursors or macrophage lineage. (pre osteoclasts may be endothelial cells, circulating monocytes, reticuloendothelial cells and fibroblasts)

3. New Bone Formation
Osteoblasts also from the marrow ® deposit osteoid ® mineralisation of the matrix.

Graft incorporation

Haematoma forms around implanted bone and only surface cells remain viable by diffusion.
Necrosis of graft follows ® inflammatory response and formation of a fibro vascular stroma.
Blood vessels and osteogenic precursors infiltrate the graft.
A neo vascular response results in increased porosity and decreased mass of the graft.
New bone formation follows and finally remodelling.

Cortical bone grafts are approximately 40-60% weaker than normal bone from 6 weeks to 6 months after transplantation. Returns to normal 1-2 years after transplant.

Factors adversely affecting incorporation
Vascularity
Infection
Foreign Material
Malnutrition
Drugs eg
(indocid, diphosphonates)

Types

Autografts

From the patient themselves, but most still dies
Vascularized autografts ® no resorption and either end of the transplanted segment heals in a way analogous to fracture healing.

Allografts

Transferred from one individual living or dead to another of the same species. Antigenicity altered by freezing / radiation. Radiation ® alters collagen ® depress graft incorporation. Osteochondral graft survival enhanced by immersion in glycerol.
Fresh grafts ® immunological response and less reliable incorporation
The sequence of events of incorporation is qualitatively similar to that for autografts, but it is delayed and less extensive (allografts are biologically inferior to autografts).

Xenografts

Bone taken from a different species, similar to allograft bone after freezing and irradiation.

Collection and distribution of donor bone in South Australia

Age limit for donation 16-60 years

Femoral Heads

Written consent required from the donor to use the bone and perform blood tests (HIV, HepB, VDRL)
Swabs taken of acetabulum and femoral head ® MCS
Biopsy of femoral head ® Histopathology
Head placed in 2 sterile bags, sterile container & un-sterile bag
Stored in -70oC ultra cold freezer
If sever osteoporosis identified bone is X-Rayed and decision made about keeping the bone

Exclusions
Hepatitis
Infection
Tumour
Rheumatoid
Alcohol / Drug abuse
Steroid treatment
Pre-senile dementia
Transfusion in last 6/12

All bone for re implantation receives 2.5 mrad of g irradiation and the bone marked ready for use.

Long bones

Consent form relatives
Tissue obtained under sterile conditions
Blood tests taken as for femoral heads
Dimensions of each bone recorded and computerised for later matching

Exclusions
Fresh bone must be 16 - 30 years old
Frozen bone can be up to 12 hours post death
Fresh bone need beating heart or in first few hours
Exclusion if in ICU > 72 hours (infection)

Allograft infection rate 10-12% and more than 80% of infected allografts are associated with clinical failure

Synthetic Grafts

Hydroxyapatite
Not biodegradable and is brittle but acts as an osteo-conductive medium

Tricalcium Phosphate
Biodegradable and is replaced by new bone but unpredictable rate of resorption and lengthy incorporation

These grafts can be used alone or mixed with autograft. Useful to fill defects where the intrinsic mechanical strength of the graft is unimportant.

Many drugs (chemotherapeutic agents, NSAIDs etc) negatively influence new bone formation in the intact skeleton and to some degree the repair associated with fractures.
Similar findings result from irradiation


Papineau Technique

Wound excision, open cancellous grafting which irradicates infection, encourages healing of the skin by granulation and results in solid bony union.

Swab for culture ® appropriate antibiotic pre-operatively
Tomograms or CT etc to define extent of sequestrum
Excision of infected tissue down to bleeding living tissue
Splint the bone if inadequate or deficient
Defect in bone must be saucerised
Development of granulation tissue ® base for subsequent graft
Secondary excision of areas not covered by granulation tissue
Within 2/52 operation for application of cancellous graft
Change dressings at 5/7 ® washing and daily dressing
Continue dressings 3/52 ( ® 3 colour changes)
By the end of the third month entire graft incorporated into granulation tissue
SSG applied if required
FWB allowed at 7/12 for osteomyelitis, 9/12 where some continuity has been preserved and 12/12 if part of the shaft was completely resected.