CORR Insights®: Partially Melted Ti6Al4V Particles Increase Bacterial Adhesion and Inhibit Osteogenic Activity on 3D-printed Implants: An In Vitro Study

Where Are We Now?

Although our orthopaedic implants have advanced in terms of design, fixation methods, bearing materials, and reliability since the origin of modern hip replacement surgery in the 1960s and modern knee replacement surgery in the 1970s, more recently, joint replacement advancements have stalled due in part to periprosthetic joint infections (PJI). We are no strangers to adjusting our techniques as the need dictates; to try to minimize the risk of PJI, surgeons have sought efficiencies to decrease operative time, and we work hard to limit surrounding tissue injury; some surgeons add adjuvants to the cement and the wound, and we decrease transfusion usage to every degree possible. And while we have identified and tried to address host/patient factors such as diabetes and obesity (with some success), infection remains both a devastating complication for the patient and a heavy financial burden on our health system. With hospitals and surgeons accepting, through bundled services, more risk for complications in our increasingly value-based market, infection has become, in the eyes of payers, a “never event”.

The article in this month’s Clinical Orthopaedics and Related Research® by Xie and colleagues [8] advances our thinking on this important topic by illustrating that the structure and coating of our implants can be modified or treated in such a way that can influence the behavior of potentially infecting organisms. While this study shows that extra steps after treatment can impact the bacterial environment in their favor, it opens the door to the exploration of possible approaches to use implant modifications to create a more unfavorable organism habitat.

Where Do We Need To Go?

Given the human and financial burdens created by implant-related infections, we must continue to innovate our implants, approaches, and adjuvants to further reduce or eliminate PJI. Based on our history of fighting infection, this will not be an easy task. We have used betadine as a possible infection reducing adjuvant [1], only to see its utility and even its safety recently questioned [4]. Although we have made strides on eliminating wear-related complications, considered the most common cause of revision joint replacement [3], we have also seen the dismal results of metal-on-metal (MoM) implants, which had such promise in the realm of durability, but fell short on biologic compatibility [7] due to psuedotumors, pain, and early loosening. But we have seen the somewhat surprising durability of highly crosslinked polyethylene, which continues to go strong at 13 years [3]. Indeed, our implants have largely, with their modern designs and materials, achieved long-term and reliable fixation and durability.

But important questions remain. Where can we look to achieve further reductions in PJI?

In particular, we still need to determine whether the roughness and porosity of the surface of our implants effect either osteointegration or bacterial adhesion. We’d also like to know what is the potential role of surface area in contributing to PJI? Other questions include whether there is an ideal implant surface design that maximizes osteointegration while minimizing bacterial adhesion, and whether any particular implant features create less-friendly environments for stray pathogens.

How Do We Get There?

We can and should control as much of the surgical environment as possible. We must continue to treat and manage the patients who may not be ideal candidates, but who desperately need the life-changing effects that our implants can provide. We must improve their BMI and A1C as long as the data suggests that these and other data points can affect the outcomes not only for infection, but for outcomes in general [2]. We need to continue to look for other adjuvants and approaches to further supplement our antibiotics and irrigation fluids to bring infection rates down even lower. This could potentially include different chemicals in the irrigation that will destroy bacteria without harming tissue or special antibiotic impregnated suture for closures, for example.

Recent research has examined implantable devices that provide therapeutic and diagnostic capabilities [5] as well as implants coated with antimicrobial materials [6]. Both types of implants show that, without additional treatment steps, there is a potential for a better environment for bacteria. Future research should consider an optimized surface for bacterial (non) adherence along with antibiotic or other novel coating to improve long-term durable function without complication or revision.