Synthetic Bone Materials
Research and development in orthopedic biomaterials is emerging in order to challenge the use of autografts and allografts and establish the preferred options for the nearly half-million spinal fusion procedures and other bone grafts annually performed in the United States.
Autogenous (autologous) bone has been the preferred implant for most bone graft procedures and still is the graft source in approximately 60 percent of bone grafts in the US, to be compared with 34 percent allograft and 7 percent other materials. However, this technique poses some disadvantages. Eventually, the initial harvesting procedure from the iliac crest can increase chronic pain, significant blood loss, infection and other complications, prolonged hospital stay and recovery time.
Allograft, the second most frequent technique, precludes the need for a second surgery. Allograft also may present some risk of viral infection. In addition, the effectiveness of allograft material is inconsistent. The processed tissue in view of lowering contamination risk can also substantially degrade the biologic and mechanical properties initially present in the donated tissue. Also, a constant supply is not assured; for instance donor bone could not be always available at the time of surgery.
A variety of synthetic bone graft substitutes has become available during the last years. Despite the fact that synthetic materials are currently used in only 10 percent of orthopedic procedures worldwide, the progress and evaluation of these products demonstrate the prospect of rapid evolution. Through preclinical and clinical trials, all materials available, synthetic or not, are being monitored. through clinical tests
Synthetic bone graft substitutes should possess similar mechanical characteristics to that of the cortical bone being replaced. These characteristics include tensile strength and modulus of elasticity similar to that of bone in an attempt to prevent stress shielding as well as maintaining adequate toughness to. prevent, under cyclic loading, fatigue fracture
Specific Materials
Tricalcium Phosphate
A tricalcium phosphate scaffold intended as bone void filler in trauma and spinal procedures was developed in the US and gained certification in the European Union. A porous, fine-particle structure encourages the flow of blood and nutrients through the matrix which is gradually replaced by structured bone similar to adjacent trabecular bone. The matrix guides regeneration of host bone in three dimensions. The polyporosity of resorbable calcium phosphate allows interaction with host bone. The fine nano-particle composition enhances resorption, facilitating an effective and rapid bone remodeling. Products based on tricalciumphosphate gained US, Australia and European Union Certification.
Silicate-Substituted Calcium Phosphate
The use of silicate-substituted calcium phosphate (Si-CaP) is focused especially for orthopedic applications (i.e. filler for gaps and voids that are not directly correlated to the stability of the bony structure).
These products provide a bone void filler that will be resorbed and replaced by bone during the healing process. Studies have shown that an optimal amount of silicate enhances local bone bioactivity; and this is supported by the finding that a crystalline silicate-substituted porous calcium phosphate containing 0.4-1.6% substituted as silicate showed higher in vivo bioactivity than silicate-free materials.
More on the materials used for bone implants.
