Analysis and Treatment of Orthopaedic Pin Site Infections

Pin site infections are a major complication of external fixation of fractures, and bacterial biofilms are known to form on the pin surface.1 This project, in collaboration with Dr Shobana Dissanayeke (RHUL) and St Peter’s Hospital, Chertsey, will investigate bacterial biofilms that have been obtained from percutaneous pins used in orthopaedic fixation frames. We will aim to:
1) identify the principal infecting organisms on such pins;
2) investigate the causes and development of pin site infections;
3) measure the potential of different antimicrobial pin coatings to minimise pin site infection and biofilm formation.

Aim 1 will involve both classical microbiological phenotypic techniques and 16S rRNA gene sequencing to identify the bacteria cultured from infected pin sites and reach objective criteria to measure the extent of infection. We expect to identify a mix of predominantly staphylococcal species, linking our work with previous investigations.

In aim 2 we will examine patterns and progress in pin site infection, measuring correlations between skin microbiota and infection rates, and examining the effect of conventional antibiotic and topical chlorhexidine treatment on infection development. The development of antibiotic resistance in persistent infections will be a particular subject of interest.

In aim 3 we will investigate various antibiotic pin coatings and the use of silver nanoparticles. We will use electrodeposition techniques to lay down nanocomposite coatings on stainless steel and titanium pins and measure their antimicrobial properties in a realistic in vitro model system. Electrochemistry and scanning electron microscopy will be used to characterize these surfaces physically, and the biochemical basis of their antimicrobial action investigated.

In conclusion, this project will apply a variety of techniques to a pressing problem in clinical microbiology and biochemistry. Our long-term objective is to inform surgical practice and reduce pin site infection rates.