The Use of Silver-Coated Orthopaedic Implants

Are All Silvers the Same?

Guy V. Morris, BSc, MBChB, FRCS (Tr & Orth); Jakub Kozdryk, MBChB, FRCS (Tr & Orth); Jonathan Gregory, FRCS BSc, MBChB, (Tr & Orth); Lee Jeys, MBChB, MSc (Orth Engin), FRCS (Tr & Orth)

Disclosures

Curr Orthop Pract. 2017;28(6):532-536. 

In This Article

Abstract and Introduction

Abstract

The use of silver in the treatment and prevention of infection is widespread in the medical community today. Advances in technology have enabled its use to be incorporated into orthopaedic practice with increasing success. This review aims to examine the different types of silver use in orthopaedics along with a review of the literature to assess the clinical efficacy of this emerging treatment.

Introduction

Periprosthetic joint infection remains one of the most significant challenges facing the orthopaedic community today. The healthcare burden of an infected joint replacement is significant and carries with it substantial morbidity.[1] Historically, research has shown that infection rates can be substantially decreased by incorporating a number of strategies such as the administration of prophylactic antibiotics, the use of ultra-clean-air operating rooms, and the use of exhaust suits.[2,3] The introduction of antibiotic containing cement also has lowered the rate of prosthetic joint infection.[4–6] Nevertheless, infection rates continue to be unacceptably high.[7] In revision or tumor surgery, these rates are even higher.[8] Infecting pathogens may be introduced during surgery by hematogenous spread or by postoperative wound contamination. Once bacteria has invaded the surface of an implant or other foreign body, they produce a glycocalyx biofilm that protects them against the hosts' immune response.[9–11] This can occur within 12–18 hr.[9,12,13] Biofilms can grow not only on orthopaedic implants but on any in-dwelling device, such as a catheter, endotracheal tube, or on natural tissue in conditions of chronic infection (e.g. cystic fibrosis).[9,14] The organisms within a biofilm are termed "sessile", while free-floating organisms are considered to be planktonic. A host's immune response and antibiotics can eliminate the planktonic bacteria; however, it has little effect on the sessile bacteria, which remain dormant but alive under their protective biofilm. In addition to the survival advantage to bacteria, a biofilm is also metabolically less active resulting in antibiotic resistance.[14,15] Biofilms can remain undetected by conventional investigation techniques and may require more specific analysis such as sonification.[14–16]

It is has been established that different material properties such as porosity, surface roughness, and hydrophilicity or hydrophobicity affect the ability of bacteria to bind to an implant.[17,18] In an effort to combat infection, research has attempted to target the mechanisms of adherence of bacteria to implants.[13,19] Some techniques include pretreatment of implants with ultraviolet light to increase wettability thereby improving hydrophilicity and reducing bacterial adherence capability.[20,21] Other methods involve surface coating of implants with substances that prevent adherence (Figure 1)[22–26] or with antibiotics for their bactericidal effect.[27,28]

Figure 1.

Titanium disc coated with silver in Escherichia coli culture showing reduction in colonization.

Various metals such as copper[29–32] and zinc[33] also display antibacterial properties and are being investigated for their future use in implant technology, although there is concern about systemic toxicity. Silver is another metal that has proven antibacterial properties and is widely used for prevention of infection in indwelling foreign bodies, such as catheters and endotracheal tubes, and wound dressings. There have been numerous studies investigating the antimicrobial properties of silver.[34–37] Silver takes two forms, colloidal and ionic. Colloidal silver contains silver particles immersed in a liquid, while ionic silver is soluble in liquid. The mode of action is thought to result from the presence of silver cations that disrupt the bacterial cellular membrane, the cellular metabolism,[34] and DNA formation.[35,36] An in-vitro study showed that, in isolation, silver-coated implants could control, but not prevent, a bacterial infection (Staphylococcus aureus or epidermidis).[37] Similarly, in the same study, when treating with daptomycin and vancomycin alone neither could prevent an infection. However, an antibiotic used in combination with a silver implant had a prevention rate of 100%. The antimicrobial properties of silver-coated implants are dependent on the release of silver ions at a concentration level of at least 0.1 parts per billion (ppb) in order to maintain a bacteria repellent surface.[38,39] The biological performance of silver ions in concentrations less than 35 ppb are mainly bactericidal, but higher doses (>4–6 g total silver content in the body) can be a toxic to human cells and can result in local toxicity or even systemic effects.[39,40]

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