Bone grafting is a process by which the surgeon takes bone cells from a donor bank or from the patient and uses them to fill in a hole, gap, or defect in bone. The lesion may be caused by failure of a fracture to heal, bone infection destroying bone cells, or surgery to remove bone for any reason.
Technically, the bone cells are no longer “alive” once they have been removed for use. But there is a small window (several hours to several days) when some bone cells are still biologically active. This means they can still promote bone formation.
Studies show that after implantation, the cells that do survive a bit longer release cytokines. Cytokines are part of the immune system response to injury. They help set up a new blood supply to the area and attract stem cells to the area that will eventually form into bone cells. In fact, researchers have shown that the graft may have a complete blood supply in as little as two days!
New bone takes a bit longer to develop (two weeks) but by the end of eight weeks remodeling efforts are clearly underway. Complete breakdown of the graft material and replacement with fresh, live, stable bone can take up to 12 months. That process is referred to as graft turnover. Graft turnover takes place one cell at a time as the old, dead cells are replaced by new, healthy cells. The cell-to-cell replacement is called creep substitution.
There is a newer graft process being used by some surgeons for large bone defects that are infected, where the bone is dying, or there has been a failure to heal for any reason. This technique is called induced membranes. It is a two-stage procedure, which means two separate operations four to six weeks apart.
In the first operation, the surgeon removes infected or necrotic (dead) bone. The hole or gap that remains is filled with a cement spacer to provide stability. The body starts to make its own tissue (called pseudomembrane) to fill in the hole.
The pseudomembrane doesn’t harden into bone so a graft is still needed. The graft placement is the second procedure. The defect or hole is filled in with autogenous bone graft. The pseudomembrane is left in place because it contains cells that will protect the graft and promote rapid integration of the graft material. It’s a win-win situation.
The time to recover varies from person-to-person depending on multiple factors. There’s the patient’s age and general health to consider. The size of the defect and type of procedure used are additional variables.
The surgeon may have a range of estimated times for each phase of recovery. It would be best to check with him or her but this information will help you gain a better big picture view of the potential complexity of the procedure. The simple term “bone graft” doesn’t begin to describe all that is involved!