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Knee Implants: Is Silver the Best Solution to Infection?

Harry Hothi and the Smart Spacer Project team discussed the use of silver coatings on knee implants to reduce the risk of infection. The demand for primary total knee replacements (TKRs) is now greater than that of total hip replacements (THRs).

In the UK, there were over 871,472 primary TKRs performed since 2003, compared with 796,636 primary THRs. As the patient population becomes larger, with greater expectations of mobility from younger, active patients, more of these patients are likely to outlive their implant, requiring at least one revision operation.

Analysis of joint registry data for England and Wales by Patel et al. predicted that the volume of primary TKRs will increase by 117 per cent between 2012 and 2030, while revision TKRs will increase by 332 per cent in the same time-period.

Which problem are we trying to solve?

The reason behind an early revision of an implant are multifactorial and often due to a combination of surgical, implant and patient factors.

The National Joint Registry for England, Wales, Northern Ireland and the Isle of Man (NJR) reports that infection is one of the main reasons for revision, accounting for 17% of the cases. This percentage may be underestimate of the true figures as it is sometimes difficult to diagnose an infection that can be a key underlying factor in loosening, instability and pain. Furthermore, there is a growing concern about the efficacy of traditional antibiotics due to an increase of antimicrobial resistance.

What is happening right now?

Nowadays, the most successful method for treating infection in patients with knee implants is a two-stage revision operation. An amount of 83% of infections are treated this way. This procedure involves the removal of the primary implant while retaining as much bone stock as possible and performing a thorough debridement. A temporary “spacer device” is implanted and is typically composed of an antibiotic cement to treat the infection together with intravenous antibiotics. After six weeks the spacer is removed and the permanent implant replaced.

Block spacers are designed for two-stage infections – an option used by some surgeons – which can be loaded with a range of different antibiotics, such as Gentamicin. These antibiotics, at various doses, can help treat the infection but are not designed to offer strength to the patient, otherwise it often leads to soft-tissue contractures and issues with alignment over the treatment period.

Why silver is a solution for knee implants?

Silver is known by its antimicrobial properties, used in several medical implants including catheters and bone screws to reduce the risk of infection after surgery. Silver offers a benefit in that bacterial strains that are less likely to become resistant to silver in the same way that they might with antibiotics.

Since the TKR is the most common orthopedic procedure performed in the UK. Infection-related complications in patients with TKRs is of growing concern, often requiring complex revision procedures.

There is some evidences that the traditional use of antibiotics to treat infection is becoming less effective due to an increased antimicrobial resistance.

A collaboration between industry, university and hospitals aims to produce a “silver solution” that is more effective than traditional methods of treating infection.

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