The goal of this observational study is to monitor the eluted antibiotic concentrations of gentamicin and vancomycin by a static knee cement spacer in patients being treated for periprosthetic infections of the knee. The main question aims to answer if eluted antibiotics are in a therapeutic range for treatment at sight of infection. Secondarily, local antibiotic concentrations are compared with systemic blood levels, as are systemically applied antibiotics compared to intra-articular concentrations. Intra-articular samples are collected over a 72 hour postoperative period.

The present study moinitors antibiotic concentrations eluted by a static cement knee spacer as two-stage revision treatment of a knee PJI. The static cement spacer consists of COPAL G+V cement containing 2g of vancomycin and 0.5g of gentamicin. Microdialysis is used as a technique for continuous extra cellular sample collection directly from the knee joint cavity. It is implemented guided by a drainage tube during the surgery to remove the infected prosthesis and implement the spacer. Over a 72 hour period samples directly from the knee joint are generated continiously. These are analyzed for the eluded antibiotic concentrations of gentamicin and vancomycin from the knee spacer. Once every 24 hours venous blood samples were collected as well and analyzed for gentamicin and vancomycin and also systemically applied antibiotics (a.e. cefuroxim, clindamycin).

Inclusion Criteria:

• clinical indication for a two-staged revision of a knee PJI
• approval for surgery by the orthopedic and anesthesiologic departments
• being over 18 years of age
• written, informed consent after detailed patient information about the study protocol and possible study-dependent risks

Exclusion Criteria:

• known allergies to the antibiotics gentamicin and vancomycin contained in the spacer

Ten patients over 18 years with a periprosthetic knee infection after total knee arthorplasty and indication for prosthesis explanation and temporary spacer implantation.