HOW BONE GRAFTS HELP WITH BONE HEALING
Bone grafts assist in the formation of new bone by providing scaffolding, stimulating bone healing, or both to create permanent stabilisation.
MECHANISMS OF ACTION
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 source of osteogenic cells, with osteoconduction serving as a scaffold and osteoinduction as the stimulator for growth.
Osteogenesis
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 Mechanical 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
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
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.
*
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
1
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.
2
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.