Deutscher Kongress für Orthopädie und Unfallchirurgie 2025 (DKOU 2025)
Male sex and higher body weight are predisposing factors for reduced concentrations of perioperative antibiotic prophylaxis in knee synovial fluid
2Deutsche Sporthochschule Köln, Institut für Biochemie, Köln, Deutschland
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Objectives and questions: Surgical site infection (SSI) is a devastating complication in orthopedic surgery and perioperative antibiotic prophylaxis (PAP) can reduce the infection rate. The aim of this study was to identify factors that influence the unbound cefazolin concentration in knee synovial fluid at the time of skin incision after PAP with 2 grams of cefazolin.
Material and methods: All consecutive patients undergoing arthroscopic knee surgery within a five-month period were prospectively included. Patients younger than 18 years, current knee infection or under antibiotic therapy, allergy to beta-lactam antibiotics, without indication for PAP, creatinine clearance less than 35 ml/min and insufficient amount of collectable synovial fluid were excluded. 2 grams of cefazolin was administered as a short infusion during anesthesia preparation. Synovial fluid was aspirated after skin incision and immediately frozen at -80°C. Unbound cefazolin concentration was determined by ultra high-performance liquid chromatography-tandem mass spectrometry and ultrafiltration. Documentation included demographic characteristics, peripheral venous catheter size, start and end time of PAP and time of pneumatic torniquet inflation and synovial fluid aspiration. Multiple linear regression analysis was used with significance set at p < .05.
Results: 65 patients (35 males, 30 females, 37.6 ± 13.0 years) were included. Male sex and higher body weight were independently associated with lower synovial fluid cefazolin concentrations (β = -5.29; p = .006 and β = -.268; p = .035 respectively). Overall, unbound target site concentrations were less than four times the epidemiological cut-off value (ECOFF) in 96.9% of the cases for coagulase-negative staphylococci (32 µg/mL) and 29.2% for Staphylococcus aureus (8 µg/mL). 40.0% of men vs. 16.7% of women had target site concentrations less than four times the ECOFF for Staphylococcus aureus. No significant relationship was found between synovial fluid cefazolin concentration and age, smoking status, diabetes mellitus, BMI, creatinine clearance, ASA score, peripheral venous catheter size, and time from PAP administration to torniquet inflation or skin incision in this healthy population. Post-hoc power analysis showed a power of 0.90.
Discussion and conclusions: The results of this study provide an explanation for higher SSI rates after knee surgery in male patients and patients with higher body weight due to lower concentrations of PAP with cefazolin in knee synovial fluid. In addition, inadequate target site concentrations of cefazolin for common SSI pathogens in knee surgery have frequently been observed. Patient-specific dose adjustment may help optimize PAP and may reduce SSI rates.
