EVALUATION OF LOCAL VANCOMYCIN DELIVERY VIA HIP AND KNEE SPACERS: TOWARDS REDUCING INTRAVENOUS ANTIBIOTICS

Aim Periprosthetic joint infection (PJI) is a serious complication following total arthroplasty of the hip (THA) and knee (TKA). Two-stage revision often involves implantation of an antibiotic-loaded spacer delivering antibiotics to the infected site, but the target site concentration is unclear. This study aims to quantify vancomycin concentrations in plasma, synovial fluid, synovial tissue, and bone following a vancomycin-loaded spacer implantation to evaluate whether adequate local vancomycin concentrations are achieved. Optimizing the use of antibiotic-loaded spacers may reduce the need for intravenous (IV) antibiotics, thereby lowering healthcare costs, decreasing systemic side effects and improving patient convenience. Method Patients with PJI of the hip (N= 13) and knee (N = 12) receiving a vancomycin-loaded spacer during two-stage revision were included in an ongoing prospective cohort study. Plasma, synovial fluid, synovial tissue, and bone samples were collected once during second stage prosthesis reimplantation, without systemic vancomycin administration for at least four weeks prior. Samples were analysed using a validated ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) assay. Bone concentrations were compared to the minimum inhibitory concentration (MIC) by applying a bone density of 1.9 kg/L. Results In knee spacers patients, 72.7% demonstrated vancomycin bone concentrations exceeding their individually determined MIC, compared to 54.5% of hip spacers patients. Thicker knee spacers have higher vancomycin concentrations (mean: 12.0 mg/L), followed by medium (mean: 5.2 mg/L) and thin spacers (mean: 2.8 mg/L). Notably, only two patients exhibited plasma concentrations above the lower limit of quantification. Conclusions This study is an important step towards the potential use of local vancomycin delivery via spacers without concurrent IV therapy. Larger bone cement volume in knee spacers, and thereby higher vancomycin amounts, resulted in a higher proportion of patients achieving adequate target site concentration compared to hip spacer patients. Variability in bone concentrations among knee spacer patients can partly be explained by spacer thickness, implantation duration, and potentially, the cement preparation. Further research is needed to explore concentration variability and evaluate whether increasing vancomycin dosage amounts in hip spacers could improve target site concentrations.