Smart implants to counter post-operative infection

Implant manufacturers MatOrtho, Leatherhead, and advanced metal coating developer the Wallwork Group, Cambridge, are leading the programme. Significant support with clinical trials and evaluation is being provided by the Royal National Orthopaedic Hospital, University College London and Queen Mary University London.

Infection is a serious and complex complication of Total Knee Replacement (TKR) that is distressing and highly disruptive to the lives of patients. Smart Spacer consists of a purpose-designed TKR prosthesis with a smart innovative surface coating. The patented chromium-nitride silver coating (CrN-Ag) is applied directly to an existing cobalt-chromium TKR implant for use as a temporary spacer device, used during two-stage treatment of periprosthetic infection.

The Smart Spacer will directly treat infection (including MRSA and Staphylococcus Epidermis) which are increasingly resistant to standard antibiotics. This presents significant advantages over current treatments and opens opportunities for the future of coated prosthesis becoming a long term primary treatment.

Wallwork are specialist hard coating developers and applicators providing a coating process service using Physical Vapour Deposition (PVD) machines that are custom built by the company. Operating one of the largest specialist PVD coating facilities in Europe, the company provide nano-composite coatings that improve surface characteristics and performance of metal components used in the medical, aerospace, automotive, nuclear and other technologically advanced industries.

The patented Wallwork CrN-Ag coating to be applied to the Smart Spacer has two initial functions. By the release of silver ions it can actively reduce infection. The coating also provides a barrier to the device, protecting the surface and preventing the leaching of metal ions into the patient. Initial trials have shown ion leakage to be virtually nil at 200 times less than that for uncoated devices. The coating will be engineered to work in two stages with movement and loading of the knee joint triggering an initial boost of silver ions from the sacrificial surface layer to counter infection immediately after implantation. Subsequently, the device will release lower levels of silver ions as recovery progresses.

Initial development work will focus on accelerated life testing of the coated knee joints by mechanical simulation so that the engineering of the coating can be perfected. Only when this phase is complete will clinical trials begin with patients. Spacers are normally fitted for a period of six weeks after the removal of the primary TKR device following post-operative infection. Surgeons currently rely on high levels of antibiotics to eradicate infection and permit the removal of the traditional spacer and fitting of a new TKR prosthesis. The expectation is that the coated Smart Spacer will facilitate speedier stabilisation of the infection and may reduce the reliance on large doses of antibiotics. Success as a spacer will then create a pathway for similarly coated TKR devices to proceed for further trials as a primary knee replacement.

The demand for knee replacement surgery is growing world-wide due to ageing populations. Post-operative infections are common in all countries. The consortium anticipates a high level of interest from around the world.