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Bone grafts assist in the formation of de novo (new) bone by providing either scaffolding or stimulation to the local area where the bone is desired. Bone graft facilitates a biologic response that stimulates bone healing and creates permanent stabilization.
Successful bone healing involves three general mechanisms of action* (MOA): osteogenesis, osteoconduction, and osteoinduction. All three MOAs are necessary for a successful bone grafting procedure, but the bone graft itself does not need to contain all three MOAs. Generally the patient is the best sources of osteogenic cells, with osteoconduction serving as a scaffold and osteoinduction as the stimulator for growth.
Osteogenesis refers to living cells, such as osteoblasts, that form new bone. The success of any bone grafting procedure is dependent on having enough bone forming or "osteogenic" cells in the area. Iliac crest bone graft (ICBG), a type of autograft contains more mesenchymal stem cells than local bone. Local bone, autograft from the surgical site, consists of cortical bone and contains fewer MSCs. However, the presence of mesenchymal stem cells does not make a bone graft osteogenic. These stem cells require a signal, such as BMP, to differentiate into osteoblasts.1
Osteoconduction is the ability of materials to serve as a scaffold onto which bone cells can attach, migrate, grow, and divide. In this way, the bone healing response is conducted through the graft site, just as a vine uses a trellis for support. Osteogenic cells generally work much better when they have a matrix or scaffold for attachment. DBMs containing bone fibers produce a greater osteoconductive structure than particles.2 Ceramics are strictly osteoconductive scaffolds and fall in the category of autograft extender or bone void filler.
Passive scaffolds maintain space and allow bone formation (200% magnification).
Osteoinduction is the capacity of growth factors in the body to attract, proliferate, and differentiate MSCs or immature bone cells into osteoblast to form healthy bone tissue. Most of these signals are part of a group of protein molecules called bone morphogenetic proteins, or BMPs, and are found in normal bone. Highly osteoinductive bone grafts have been evaluated as an autograft alternative in certain indications.†
Active recruitment and stimulation of stem cells differentiate into osteoblasts and form bone.
Bone fibers are created by a proprietary milling technique, and they produce a greater osteoconductive structure.2
Medtronic was first to market with a fiber-based demineralized bone matrix (DBM). Our aseptically processed fibers have some of the highest osteoinductive scores‡ on the market and this interconnected mesh of fibers enhances the osteoconductive potential of the product by providing a path for cellular infiltration. Grafton™ Plugs are a fiber-based DBM.
Particle-based DBM, 200% magnification
With particle-based DBM, bone cells have to lay down new bone between each particle to move from particle to particle.
Fiber-based DBM, 200% magnification
With fiber-based DBM, bone cells are able to move through the network of collagen fibers. Fiber-based DBM is a more effective osteoconductive structure than particle-based DBM.2
Generally accepted mechanism of action
BMPs have been tested as an autograft alternative in multiple clinical studies for certain indications in spine, orthopedic trauma, and dental.3,4,5,6
Data on file
Cuomo AV, et al. Mesenchymal Stem Cell Concentration and Bone Repair: Potential Pitfalls from Bench to Bedside. J Bone Joint Surg Am. 2009; 91:1073–1083.
Martin GJ, Boden SD, Titus L, Scarborough NL New Formulations of Demineralized Bone Matrix as a More Effective Graft Alternative in Experimental Posterolateral Lumbar Spine Arthrodesis. Spine. 1999;24(7):637-645.
Burkus, et al. Anterior Lumbar Interbody Fusion Using rhBMP-2 With Tapered Interbody Cages. J Spinal Disorders. 2002; 15(5):337-349.
Boyne PJ, Lilly LC, et al. De Novo Bone Induction by Recombinant Human Morphogenetic Protein-2 (rhBMP-2) in Maxillary Sinus Floor Augmentation. J Oral Maxillofac Surg. 2005; 63:1693-1707.
Fiorellini JP, Howell TH, et al. Randomized Study Evaluating Recombinant Human Bone Morphogenetic Protein-2 for Extraction Socket Augmentation. J Periodontol. 2005; 76(4): 605-613.
Friedlaender, et al. Osteogenic Protein-1 (Bone Morphogenetic Protein-7) in the Treatment of Tibial Nonunions: A Prospective, Randomized Clinical Trial Comparing rhOP-1 with Fresh Bone Autograft.