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

Clinical Results

Studies on the use of silver-coated megaprostheses used in oncological surgery have revealed a significant reduction in infection rates for patients immediately after surgery and in the mid-term. Donati et al.,[51] in a retrospective analysis on 68 primary and metastatic bone tumors of the proximal femur, treated with wide resection margins and megaprosthesis reconstruction, found an infection rate in silver-coated prostheses to be 7.9% compared to 16.7% in the uncoated group. The overall infection rate was 11.8%, with an average time to infection of 25 mo after surgery. However, differences between the two groups were not statistically significant because of the small number of patients.[51] Schmolders et al.[52] reported a 10% prosthetic joint infection rate in his case series of 100 patients treated with silver-coated megaprosthesis for lower limb reconstruction in tumor patients. They concluded that the infection rate in patients with silver-coated implants was lower compared to those with standard implants. Hardes et al.[53] documented similar findings with use of MUTARS silver-coated megaprosthesis in patients with bone sarcoma. They reported a significant reduction in infection from 17.6% in titanium to 5.9% in the silver group.[49]

Furthermore, the outcomes after debridement and implant retention (DAIR) for treatment of acute infections are more favorable when a silver-coated implant is in-situ. A case control study by Wafa et al.[8] compared the infection rate of 85 patients treated with an Agluna® silver-coated tumor prosthesis with an identical group treated with an uncoated tumor prosthesis. They found the overall postoperative infection rate of the silver-coated group to be 11.8% compared with 22.4% for uncoated implants. They also noted that debridement with implant retention for patients with acute infections was more successful in patients with silver-coated implants.[8]

In the most recent study by Hardes et al.[53] in 2017, the group compared the infection rates of titanium with those in silver-coated megaprostheses (MUTARS) in proximal tibial endoprosthetic replacement for sarcomas. The rates of infection were 16.7% in the titanium group and 8.9% in the silver group. This resulted in a 5-year prosthesis survival rate of 90% in the silver group and 84% in the titanium group. In the titanium group 37.5% of patients ultimately underwent amputation, but this was only required in one of the patients in the silver group.[53]

Silver-coated implants have been shown to be a viable alternative to above-knee amputation in the treatment of unsalvageable infected total knee replacement. In a series of eight patients with catastrophic knee prosthetic joint infection treated with a silver-coated arthrodesis nail, only one patient experienced recurrent infection and this was then successfully treated with debridement and implant retention. Furthermore, at a mean follow-up of 16 mo there were no amputations, deaths, or implant revisions.[54]

There have been concerns raised regarding the side-effects that can occur after insertion of silver-coated implants. One such side-effect is the development of argyria caused by a exposure to excessive amounts of silver particles.[46] This appears to be rare with implant coatings, with only a single case reported in the literature after the use of a MUTARS prosthesis, which incorporates high amounts of silver in its coating.[55] Numerous other studies of various implants have not reported any evidence of adverse reaction to silver exposure.[48,56–58] A number of studies have investigated the levels of silver ions in blood, urine, and wound drains that are present after silver prosthesis implantation. The plasma levels appear to vary greatly, depending on the type of implant and time points used for evaluation. Hussmann et al.[59] found that after implantation of a silver megaprosthesis the mean silver blood levels were 30 μg/L and 20 μg/L at 7 and 14 days, respectively. Glehr et al.[56] recorded an average level of silver in blood of 15.9 μg/L (range 6.5–40 μg/L). All of these recordings are below toxic level.

Hardes et al.[48] reported the highest single value of 56.4 μg/L in a patient at 15 mo after surgery with a mean silver concentration in the blood of 2.8 μg/L (range, 0.8–9.12 μg/L) at 2 wk after surgery, with subsequent mean silver levels ranging from 1.93 to 12.98 μg/L from the third to the 24th month. The authors concluded that these levels were also nontoxic, with no histological evidence of local inflammation or systemic side-effects. Scoccianti et al.,[58] in their series of 33 patients using a silver layer of titanium alloy (Porag) on a Megasystem-C® (Waldemar Link GmbH & Co. Kg, Hamburg, Germany) megaprosthesis demonstrated a mean level of circulating silver in blood from 2 wk after surgery to 36 mo, ranging from 2.09 to 5.33 μg/L. They also noted the mean blood silver concentration of patients with this prosthesis to be lower than those previously reported for MUTARS prostheses. This can be potentially linked to the differences in manufacturing process and rate of sustained release of silver ions into surrounding tissues. It is clear that the health risks from systemic exposure to silver ion exposure are low.[46]

Further advances continue with regards to silver incorporation into orthopaedic implants. High silver concentrations are toxic to osteoblasts, and as a result the silver coating on implants is confined to the exposed surfaces only. To maximize the available antimicrobial properties of silver while not affecting the osseous fixation of an implant, a small trial was carried out to determine the effects of silver oxide containing hydroxyapatite coatings on hip implants.[57] The early results are promising, with no evidence of early loosening or signs of systemic silver toxicity.

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