Can We Influence the Risk of Infection by Implant Design?

The use of implanted orthopaedic devices has greatly improved the quality of life for an increasing number of patients, by facilitating the rapid and effective healing of bone after traumatic fractures, and restoring mobility after joint replacement. However, the presence of an implanted device results in an increased susceptibility to infection for the patient, owing to the creation of an immunologically compromised zone adjacent to the implant. Within this zone, the ability of the host to clear contaminating bacteria may be compromised, and this can lead to biofilm formation on the surface of the biomaterial. Currently, there are only limited data on the mechanisms behind this increased risk of infection and the role of material or implant choice.

The development of an infection after implantation of a fracture fixation device is known to be influenced by design aspects of the implant such as the surface area available for colonisation, whether or not it creates dead space, bone contact area, compression, periosteal necrosis and the stability provided by the implant. In vivo studies using implants of identical dimensions and only differing in material have shown that the implant material is also a factor that can affect infection rate for intramedullary nails and dynamic compression plates. Of the commonly used orthopaedic implant materials stainless steel and titanium; stainless steel is associated with an increased infection rate in comparison with titanium for intramedullary nails and dynamic compression plates in experimental studies. Aside from bulk material differences, these implants also differ in surface topography, from the smooth electropolished surface of stainless steel implants to the non-polished microrough surface of titanium implants.

Polishing the surface of titanium and titanium alloy internal fixation plates can minimise unwanted soft-tissue adhesion and ease removal of screws and intramedullary nails in comparison with standard equivalents, with significant clinical benefit in certain situations. The effect surface polishing has on in vitro bacterial adhesion and in vivo infection rate has been uncertain to date, and recent data has emerged for locking compression plates and intramedullary nails in a non-fracture rabbit model, indicating that surface topography is not a significant factor in risk of infection, at least in a non-loaded model.