Implant-related infections : application of PCR-based diagnostics and new antimicrobial strategies in prevention and treatment

Abstract

This thesis focused on different aspects of the diagnosis, prevention and treatment of implant-related infections. Using in vitro laboratory experiments, animal infection studies and retro- and prospective clinical studies, different aims were addressed: Aim: To determine the value of the combined use of broad range 16S rRNA PCR and reverse line blot hybridization (PCR-RLB) in the detection of orthopaedic implant-related infections. This technique was first optimized and validated using clinical samples. It showed good reliability in detecting orthopaedic infections and identifying the bacterial species involved. It showed even higher sensitivity than routine culture. Subsequently, a prospective, multicenter clinical study was performed using this technique to investigate whether many patients with loosening of their total hip arthroplasty are falsely diagnosed as aseptic, instead of low-grade infection. As septic loosenings need a different treatment, this could have substantial implications for these patients. Results showed that between 4 and 13% of patients indeed are infected and that most cases are missed with routine diagnostics, like culture and pathology. In almost all cases low virulent bacteria, like coagulase negative staphylococci and Proprionibacterium acnes, were the pathogens identified. After 1 year, this low-grade infection did not seem to have many consequences. However, longer follow-up might show increased implant failure rates. Aim: To investigate new prophylactic antimicrobial strategies, both for uncemented and cemented implants and new applications. Different antimicrobial strategies, like an antibiotic coating on porous hydroxyapatite coated titanium implants, silver-containing bone cement and the use of platelet-leukocyte gel, made from platelet rich plasma, were investigated. The antibiotic-hydroxyapatite coated titanium proved to be an effective strategy in preventing implant-related infection in vivo and improved osseointegration of these implants as well. Unfortunately, the silver-containing bone cement showed no efficacy in preventing early staphylococcal infections in a rabbit infection model. All rabbits showed abundant signs of infection, whereas tobramycin-containing bone cement was effective in preventing these infections. Platelet-leukocyte gel also showed a good in vitro activity against Staphylococcus aureus as it reduced its presence with almost 99%. This effect is probably related to the growth factors and antimicrobial peptides present in the platelets. Aim: To evaluate the availability of antibiotics from different therapeutic carriers. In the treatment of arthroplasty infections, joint spacers made of antibiotic bone cement are often used instead of chains of small cement beads. As antibiotic release is a surface phenomenon, it is criticized that spacers release too little antibiotics. In vitro release showed that beads release almost 8 times as much antibiotic compared to the spacers used. Although this raises concern about adequate therapeutic effects of spacers, it remains unknown how much antibiotic is necessary to cure implant-related infections in vivo. This thesis answered some questions with respect to orthopaedic implant-related infections. Many more remain to be answered. Hopefully more research will follow, in order to give the orthopaedic patient the most optimal treatment available.