Bioactive Surface Coatings for Orthopaedic Implants
The percentage of cases in which minimally invasive surgical (MIS) techniques are used has increased and is expected to continue to climb. However, it is generally recognized that many MIS techniques can present a challenging environment for arthrodesis.1 Additionally, most biologics are more effectively used as graft extenders with local autologous bone. However, in MIS, often no bone needs to be “extended,” and no source of cells is known other than the limited amount of decorticated surface. All of these factors might play a role in the increased use of rhBMP-2 in these settings. In contrast, awareness of related complications is growing, and researchers are seeking safer options that will improve bone healing over inert implants such as traditional polyetheretherketone spacers. Total joint surgeons have known for decades what spine surgeons are rediscovering: that implant material and surface and structural characteristics can influence osseointegration and bone formation. Recent in vitro and in vivo basic science research is beginning to elucidate the cellular mechanisms involved in macro, micro, and even nanoscale architectural changes that can promote adhesion, osteoprogenitor differentiation, and osteoblast activity.2 Implants that allow physiologic degrees of tensile strain to be transferred to osteoblasts, those that have macroscale roughened surfaces that promote a stable bone/implant interface acutely, and those that have optimized surfaces with micro and upper nanoscale pits with specific architecture all have been shown to improve the production of biomarkers for bone formation. Early clinical data are promising. However, questions remain regarding how much autologous bone is needed for these devices, and whether the preclinical data will translate to better bone healing in human patients, particularly in challenging environments such as MIS.