A SOLUTION FOR FAILURE OF CORTICAL BONE GRAFT: HOW DO WE HANDLE AN EXPOSURE OF THE GRAFT?

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Bone graft exposure could be possible although meticulous handling for soft tissue that will be covered. This problem always annoy clinicians. This report describes my experience for recovering of exposure on the graft surface. I don't hope that readers could copy my experiences, my ideas and figures that is showed below as themselves' originals (31th October 2016).

Healing of bone graft
Incorporating of the grafts happens in concert with a process of initial remodeling and resorption, which is associated with a loss of bone volume. The amount and rate of resorption depends on many factors, such as dimensions of the bone graft, the quality of bone, the quality of the recipient site, biomechanics properties and fixation to surrounding bone.

Reviewing the stages of revascularisation and healing bone graft is essential to understand their behaviour and outcome.

When the bone graft is first placed the area, the cortical portion of the bone is avascular and has very few viable cells on its surface. This bone graft eventually becomes replaced by host bone.

During this substitution, a vascular sequence follows. The area surrounding the bone graft become hypervascular. The bone graft itself elicits proliferation of angioblasts and small  capillaries in early stages. This angioblastic proliferation occurs within the first week of grafting. These blood vessels carry the elements for osteogenic bone formation and replacement. Osteoclasts are present at early stage, resorbing the bone at the periphery of the graft. the bone graft is gradually replaced while new bone is laid down at the periphery and inside. The graft is replaced in a period that lasts between three and six months. when this occurs the hypervascularity gradually disappears.

There is a histological response running parallel to the vascular one. Granulation tissue with fibroblastic and angioblastic proliferation is followed by proliferation of immature osteoid tissue at the periphery of the graft. After the osteoid is replaced by mature bone, there is no evidence of the grafted avascular bone graft.

Graft healing occurs in one of three ways: osteogenesis, osteoinduction or osteoconduction. The proportions of these processes in each case depend largely on the type of graft and conditions of the host site.

Osteogenesis occurs when the graft itself supplies viable osteoblasts (osteogenic cells) as the source of new bone. It is well known that bone sources(for instance, iliac crest) with high proportions of marrow have better osteogenic properties due to an increased number of undifferentiated cells. Osteoinduction occurs when the graft activates the surrounding host tissue, through signaling factors, to stimulate osteoclastic activity and new bone formation. Osteoinduction has classically been related to autologous fresh bone transplants. More recently, recombinant bone morphogenic proteins (rh-BMP) have been developed to induce bone formation. Finally, osteoconduction occurs when undifferentiated mesenchymal cells invade the graft, which acts as a scaffold or physical matrix. this matrix allows deposition of new bone. The graft material should allow bone to form without impeding this process. (From FH Alfaro, Bone grafting in oral implantology, techniques and clinical applications, quintessence 2006)

Failing to cover the recipient site with cortical bone graft. We can see  irreparable  exposure of the bone graft. I feel be in trouble to see the situations.

Donar bone from the ramus. 75-year-old male patient with heavy smoker.

                                     

Six months later the fixation screw was removed. But bone graft was stuck firmly.

To be considered red zone might be alive.

As the bone graft was stuck on the recipient site, and so an idea had come up to me for these situations.

Like the picture, graft bone surface was shaved until bleeding on the bone surface.

The zone of shaving was covered with soft tissue after two weeks.

Next time remaining upper graft bone was shaved like the picture  until  bleeding. While shaving the upper bone graft was  come off.

Upper zone of graft bone was covered with soft tissue after two weeks

Lower zone of the graft bone was scraped with hand instrument.

After further two weeks exposure of the graft bone was smaller. 

A succesful clinical outcome for a bone grafting procedure requires an understanding of the biological and mechanical environment into which the graft will be placed. Although the biological aspects of bone graft incorporation are critical in determining this outcome, the technical aspects of the surgery are as important. A clean, well-vascularized host bed is critical in providing satisfactory host environment. Wide excision of scar tissue, treatment of infection, protection of the blood supply and satisfactory soft tissue coverage is mandatory.  The selection appropriate graft material for the desired clinical function will also help determine the clinical outcome of bone grafting. Central, however, in the  successful incorporation of the bone graft is a stable fixation and contact between the host bone and the graft. Experimental studies have demonstrated that when the host-graft interfaces are tightly apposed and fixed with internal fixation, the interfaces healed whether the grafts were autogeneic , fresh, or frozen. Even under stable conditions, but without closely apposed host bone, graft tissue retrieval studies have demonstrated that interfaces did not heal and had a profound effect on the biological characteristics of the graft. When no apposition or stability was provided at this interface, bone graft have uniformly failed. It is therefore important to provide intrinsic and stable graft-host fixation and satisfactory soft tissue coverage.  The bone graft must also be protected from full weight bearing until remodeling enables it to function fully in a loaded environment. When the appropriate bone graft is selected and surgical technique is synergistic, bone grafts do incorporate both biologically and provide clinically functional load bearing. (From Goldberg & Akhavan, Biology of bone grafts in Bone regeneration and repair 2005)