BONE GRAFTS

Historical background:

Surgeons have gained their experience in reconstruction from the numerous wars

It started in WW I and concentrated around reconstruction of the mandible but without antibiotic support

In WW II distant bone blocks were transplanted from the ilium, rib and tibia with routine use of antibiotic No cancellous cellular marrow

Mowlem in 1944, introduced the concept of “Iliac cancellous bone chips” beginning the evolution of predictable bony reconstruction of the jaw bone

Boyne brought about the “use of particulate bone and cancellous marrow” with metallic trays splinted to large acellular cortical bone

Unlike other tissues, the bone can regenerate and repair itself: in many instances, bone injuries and fractures heal without scar formation .

Nevertheless, in pathological fractures or large and massive bone defects, bone healing and repair fail. Insufficient blood supply, infection of the bone or the surrounding tissues, and systemic diseases can negatively influence bone healing, resulting in delayed unions or non-unions .

Bone is the second most commonly transplanted tissue after blood.

Bone graftsautograftsallografts

demineralized bone matrix (DBM)syntheticsbone morphogenetic protein (BMP)stem cells

Epidemiologyincidence

almost 1 million bone grafting procedures performed in US each year, with a growth of almost 13% per year

Indicationsassist in healing of fractures, delayed unions,

or nonunionsassist in arthrodeses and spinal fusionsreplace bone defects from trauma or tumor

Properties

Bone graft has aspects of one or more of these three propertiesosteoconductive 

material acts as a structural framework for bone growth demineralized bone matrices (DBMs)

osteoinductive  material contains factors that stimulate bone growth

and induction of stem cells down a bone-forming lineage bone morphogenetic protein (BMP) is most common

from the transforming growth factor beta (TGF-B) superfamily

osteogenic material directly provides cells that will produce bone

including primitive mesenchymal stem cells, osteoblasts, and osteocytes  mesenchymal stem cells can potentially differentiate

down any cell line osteoprogenitor cells differentiate to osteoblasts and

then osteocytes cancellous bone has a greater ability than cortical bone

to form new bone due to its larger surface area autologous bone graft (fresh autograft and bone

marrow aspirate) is the only bone graft material that contains live mensenchymal precursor cells

AutograftBone graft transferred from one body site to another in the

same patientIndicationsgold standardProperties

osteogenic, osteoinductive, and osteoconductiveleast immunogenic cortical, cancellous, or corticocancellousvascular or nonvascularFresh autografts contain surviving cells and osteoinductive proteins such as BMP-2, BMP-7, FGF, IGF, and PDGF

Donor sites

iliac crest is the most common site for autograft  provides both cancellous and cortical graft 2% to 36% complication rate

blood loss and hematoma injury to lateral femoral cutaneous or cluneal nerves hernia formation infection fracture cosmetic defect chronic pain

fibula and ribs are most common sources of vascularized autografts

tibial metaphysis

Allograft

Bone graft obtained from a cadaver and inserted after processing

Most commonly used bone substituteProperties

osteoconductive only due to lack of viable cells the degree of osteoconduction available depends on

the processing method (fresh, frozen, or freeze-dried) and type of graft (cortical or cancellous)

cortical, cancellous, corticocancellous,

Processing methods debridement of soft tissue, wash with ethanol (remove live cells),

gamma irradiation (sterilization) dose-dependent higher doses of irradiation kills bacteria and viruses but may

impair biomechanical properties fresh allograft

cleansing and processing removes cells and decreases the immune response improving incorporation

indications rarely used due to disease transmission and immune response of recipient

frozen or freeze-dried reduces immunogenicity while maintaining osteoconductive properties reduces osteoinductive capabilities shelf life

one year for fresh frozen stored at -20 degrees C five years for fresh frozen stored at -70 degrees C indefinite for freeze-dried

Demineralized bone matrix (DBM)Acidic extraction of bone matrix from

allograft removes the minerals and leaves the

collagenous and noncollagenous structure and proteins

Propertiesosteoconductive without structural supportminimally osteoinductive despite preservation

of osteoinductive moleculesinterproduct and interlot variability is common

Synthetics

Alternative to autografts and allograftsVarious compositions availableMade in powder, pellet, or putty formProperties

osteoconductive only Outcomes

Level I evidence shows that calcium-phosphate bone substitutes allow for bone defect filling, early rehabilitation, and prevention of articular subsidence in distal radius and tibial plateau fractures

Bone morphogenetic proteins (BMP)Osteoinductive properties

stimulates undifferentiated perivascular mesenchymal cells to differentiate into osteoblasts through serine-threonine kinase receptors

rhBMP-2 and rhBMP-7 are FDA-approved for application in long bones and spine

Complicationsunder or overproduction of boneinflammatory responsesearly bone resorption