- Loss of bone can occur in several situations including
- Trauma
- Tumours
- Man-made prostheses
- Bone grafts can be used to fill the defect
Classification of bone grafts
- Autograft = bone from the same individual
- Allograft = bone from another individual of the same species
- Xenograft = bone from another species
Autografts
- Autogenous bone is the best graft material
- May only be available in a limited amount
- Also not suitable for significant load bearing
- Cancellous bone can be used to fill cavity defects
- Cortical bone can be used to provide structural support
- Forms scaffold into which osteoblasts and osteoclasts can grow
- Osteoblast differentiation leads graft resorption
- Stimulates local bone growth by the process of osteoinduction
- Remodelling occurs as load is applied to the graft
Harvesting of bone grafts
- Bone can be harvested from the following sites
- Iliac crest
- Proximal tibia
- Distal radius
- Iliac crest is the most common but its use is associated with significant morbidity
- Cortico-cancellous grafts are harvested as strips
- Cancellous bone can be taken from the inner or outer table
Vascularised grafts
- Segments of bone can be transplanted as free vascularised grafts
- Local rotational bone grafts may also be used
- Blood supply to the graft is maintained
- Technically difficult to perform
- Results are unpredictable
Allografts
- Allograft bone is more plentiful
- Can be harvested from living donors or cadavers
- Donor site morbidity is eliminated
- Cadaveric bone and femoral heads are stored in tissue banks
- Bone is frozen at -20 to -86 degrees
- Freeze drying and storage at room temperature is occasionally used
- Used in reconstruction after:
- Tumour resection
- Revision hip surgery
- Infection is the major concern with the used of allografts
- Bacterial contamination may occur, especially with cadaveric grafts
- Can be eliminated with irradiation of the graft
- Viral contamination with hepatitis of HIV is a concern
- Bone should be kept in quarantine and living donors tested 90 days post surgery
- Allograft bone is available as:
- Morsellised bone for impaction grafting
- Strut grafts to cover cortical bone
- Massive allografts to replace significant proportions of native bone
Bone substitutes
- Interest exists in artificial bone substitutes
- Would eliminate supply and infection problems associated with auto and allografts
- Possible bone substitutes include:
- Calcium triphosphate
- Hydroxyapatite
- Calcium carbonate
- Glass-based cements
- Most bone substitutes are brittle
- Unable to withstand significant load bearing
Bibliography
Finkemeir C G. Bone-grafting and bone graft substitutes. J Bone Joint Surg Am 2002;
84A: 454-464
Pairkh S N. Bone graft substitutes in modern orthopaedics. Orthopedics 2002; 25;
1301-1309
Rees D C, Haddad F S. Bone transplantation. Hosp Med 2003; 64: 205-209 |