BONE GRAFTALTERNATIVES North American Spine Society Public Education Series
WHAT ARE BONE GRAFTS?Bone grafts are bone that is transplanted fromone area of the skeleton to another to aid inhealing, strengthening or improving function.Bone or bone-like materials used in bone graftsmay come from you, from a donor or from aman-made source. In many cases they are usedto ﬁll in an empty space that may have beencreated in or between the bones of the spine bydisease, injury, deformity or during a surgicalprocedure such as spinal fusion. Bone graft ﬁlls in spacebetween 2 vertebrae after disc has been removed
WHAT TYPES OF BONEGRAFTS ARE THERE?Bone grafts that are transplanted directly fromone area of an individual’s skeleton into hisor her own spine are called autogenous bonegrafts, or bone autografts. In most cases,these are the preferred bone grafts to use. Thegraft bone is harvested, or taken, from thebones of the hip, the ribs or the leg. Autograftbone is one of the safest to use due to the lowrisk of disease transmission. It also offers abetter chance of acceptance and effectiveness inthe transplant site, since it contains the greatestamount of the patient’s own bone growingcells and proteins. Autograft bone provides astrong framework for the new bone to growinto. The downsides of autograft bone are thefacts that it adds another surgical site to a spineprocedure (and therefore another location tofeel postoperative pain and discomfort) and itcan increase the cost of the spinal procedure.Bone graft that comes from a donor is calledallograft bone. Allograft bone usually comesfrom bone banks that harvest the bone fromcadavers. The types of allograft bone usedfor spine surgery include fresh frozen andlyophilized (freeze dried). The bone is cleanedand disinfected to reduce the possibility ofdisease transmission from donor to recipient.Allograft, like autograft, provides a frameworkfor the new bone to grow on and into. Unlikeautograft bone, allograft bone does not alwayshave the same strength properties or the cellsand proteins that can inﬂuence the growth
of new bone. The advantages of allograftbone are the elimination of the harvestingsurgical site, the related postoperative painand the added expense of a second operativeprocedure. Disadvantages of allograft bone arethe slight chance of disease transmission anda lessened effectiveness since the bone growthcells and proteins are removed during thecleansing and disinfecting process.How safe is allograft bone?As bone grafting using allograft bone hasbecome more widely used, the methodsof screening donors, bone preparationand storage have been vastly improved inregards to diminishing the chances of diseasetransmission. Studies indicate that the risk ofcontacting HIV infection through the use ofallograft bone is less than 1 per 1 million uses.
WHO NEEDSBONE GRAFTING?Your surgeon may want to use bone graftingfor a number of reasons. Possible reasonsinclude situations where healing may bedifﬁcult due to the use of nicotine (which hasbeen shown in medical studies to limit healingof the spine) or the presence of diseases suchas diabetes or autoimmune deﬁciencies. Otherpossible reasons include a large amount ofbone or disc material that is removed duringsurgery, or spinal procedures that span manylevels of vertebrae.One of the most common uses of bone graftsin spine surgery is during spinal fusion. Theuse of autogenous bone grafts for spinal fusionhas been a standard in the spine communityfor many years and is considered to be thestandard by which other bone grafts aremeasured. Spinal fusions are performed torelieve pain and provide stability to spinesin people who have experienced a vertebralfracture or motion between the vertebraethat causes pain, have a spinal deformity, orwho have some types of disc herniations. Incertain types of spinal fusion, bone grafts orbone graft alternatives are used to replace thecushioning disc material that lies betweenthe vertebrae. When the bone graft is placedbetween the vertebrae it creates a frameworkand support that eventually aids in joining thetwo bones together. Once the bone “bridge”between the vertebrae is in place, the spine
is stabilized and movement and pressure onnerve roots is relieved, thus easing pain.Bone grafts can also be used in surgicalprocedures to stabilize the spine after afracture or to correct deformity.
WHAT ARE BONE GRAFTSUBSTITUTES?Since both allograft and autograft havedrawbacks, iscientists have long searchedfor materials that could be used in place ofthe transplanted bone. Although most ofthe substitutes available possess some ofthe positive properties of autograft, noneyet have all the beneﬁts of one’s own bone.Investigators hope one day to use thesesubstitutes to simultaneously be able tostimulate bone healing and provide a strong andbiologically compatible framework for the newbone to grow into.Some of these bone graft alternatives include:Demineralized Bone Matrix (DBM)—aproduct of processed allograft bone. DMBcontains collagen, proteins and growth factorsthat are extracted from the allograft bone. Itis available in the form of a powder, crushedgranules, putty, chips or as a gel that can beinjected through a syringe. DBM is extensivelyprocessed and therefore has little risk fordisease transmission; however, because of theform it takes it does not provide strength to thesurgical site.Ceramics—Ceramics are also used as asubstitute for bone grafts. Ceramics offer nopossibility for disease transmission, althoughthey may be associated with inﬂammation insome patients. They are available in manyforms such as porous and mesh. Althoughceramics may provide a framework for bonegrowth, they contain none of the naturalproteins that inﬂuence bone growth.
Coral—Bone implants made from coral haveshown to be useful in the treatment of bonedefects due to trauma, tumors and cysts. Itis also used for spinal surgery as either a graftadditive, or extender, or as an implant toprovide a framework for bone to grow into.The use of these substitutes, under certainconditions, has had promising outcomes.Graft Composites—A newer area of bone graftsubstitutes, graft composites use combinationsof other bone grafting materials and/or bonegrowth factors to gain the beneﬁts of a varietyof substances. Among the combinations in useare a collagen/ceramic composite, which closelyreproduces the composition of natural bone;DBM combined with bone marrow cells, whichaid in the growth of new bone; and a collagen/ceramic/autograft composite.Bone Morphogenetic Proteins—Bonemorphogenetic proteins (BMPs) are producedin our bodies and regulate bone formationand healing. Scientists have discovered thatthese proteins can speed up healing as well aslimit the negative reaction some people haveto donor bone and the nonbone substitutes.Scientists have also discovered how to extractthese substances from human or cow bonesand even produce them in the laboratory.Currently, the United States Food and DrugAdministration has not yet approved thesetherapies; however, extensive research is beingundertaken in both humans and animals todetermine their safety and effectiveness.
WHICH TYPE OF BONE GRAFTIS RIGHT FOR ME?The determination if bone graft is to be usedand the type to be used is best made by yoursurgeon. Different surgical situations may callfor different types of bone grafting and uniquebone graft materials. If your surgeon says thathe or she would like to use a bone graft onyour spine, you should discuss this decisionwith him or her to determine which bonegraft material they feel is best suited for yoursituation.As with any medical procedure, you shouldask your surgeon about any questions orconcerns you may have and make sure all ofyour questions are answered.