How bone graft 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
Passive scaffolds maintain space and allow bone formation (200% magnification).
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.
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.
Most demineralised bone products on the market are made with particles, created by grinding the bone into a powder and then demineralising it.
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 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™ DBM is fiber-based DBMs.‡
Fiber-based DBM is a more effective osteoconductive structure than particle-based DBM.2 With fiber-based DBM, bone cells are able to attach and proliferate through the network of demineralised bone fibers.
Particle-based DBM, 200% magnification.
Fiber-based DBM, 200% magnification.
Bone graft selection is critical to the outcome of any bone healing procedure. There are currently over 200 different bone grafts available to surgeons today, each with substantial differences in technology, materials, mechanisms of action, indications, and clinical evidence.
Bone grafts can be categorised based on:
- Composition
- Mechanism of action (MOA)
- Approved indication
- Performance data
Allograft bone graft
There are many different allograft products or forms available for use. Some allograft tissue functions through osteoconduction and mild osteoinduction when demineralised, and include mineralised tissue, demineralised tissue, and allograft tissue plus cells.
Grafton™ demineralised bone matrix (DBM) is the most utilised and scientifically studied DBM brand.3 Our aseptic processing technology preserves the function of naturally occurring growth factors — yielding Grafton DBM’s osteoinductivity scores. Proprietary fiber technology offers enhanced osteoconductive scaffold.2
- Composition: Donor bone and tissue
- Demineralised MOA: osteoconductive and osteoinductive.
Synthetic Bone Graft
An osteoconductor, synthetic autograft extender bulks up the supply of available autograft bone.
- Composition: Synthetically produced minerals and ceramics
- MOA: Provides an osteoconductive passive scaffold for bone formation
Mechanical stability and bone formation are critical to achieving a successful outcome for surgical procedures involving bone grafting. Bone grafts are used in a variety of surgical procedures, each with unique healing environments and varying degrees of complexity.
Spine and spinal fusion
Reasons for surgery:
- Mechanical back pain
- Neurologic impairment
- Trauma
- Deformity
- Tumor
- Spinal fusion
Common bone grafting procedures:
- Interbody spinal fusion
- Posterolateral spinal fusion
- Corpectomy
- Sacroiliac spinal fusion
General healing environments:
- Spinal fusion are challenging healing environments.
- Disc space, surface area, and load increase from cervical to lumbar spine.
- Posterolateral fusions require larger graft volume and have minimal bone cell access.
- Adding surgical levels increases the complexity of the procedure.
Orthopaedic
Reasons for surgery:
- Trauma
- Unstable joints
- Pain
- Loss of function
- Tumor
Common bone grafting procedures:
- Open reduction with internal fixation
- Segmental defect repair
- Joint fusions
- Repair from tumor or cyst resection
General healing environments:
- Open fractures are difficult to heal due to contamination and potential for infection.
- Limited soft tissue coverage around the tibia leads to a lack of bone-forming cells.
- Some areas, such as the foot, ankle, and tibia must withstand heavy loads.
- Joint fusions are challenging environments that require large volumes of graft material.
There are currently more than 200 different bone grafts available to surgeons today.
There are distinct differences in technology, materials, mechanisms of action, indications, and clinical evidence for these bone grafting options.
*
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
‡
Martin et al; Spine 24(7), 1999 pp:637-645
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.
3
Based on Pub-Med search on 8/26/14 with key words Grafton, DBX and Osteosponge.