Tobramycin and Vancomycin in an In Vitro Model of Anterior Cruciate Ligament Allograft Decontamination

Abstract

Background: Approximately 100,000 anterior cruciate ligament (ACL) reconstructions (ACLRs) occur annually in the United States, and postoperative surgical-site infection is a relatively rare but devastating complication, often leading to graft failure or septic arthritis of the knee, necessitating repeat surgery. Wrapping allografts in vancomycin-soaked gauze has been adopted as a common sterilization technique in the operating room to reduce surgical-site infection; however, identifying effective alternatives to vancomycin has not been extensively pursued. Hypothesis: Tobramycin would be as effective as vancomycin in reducing the concentrations of Staphylococcus epidermidis bacteria on tendon allografts. Study Design: Controlled laboratory study. Methods: S. epidermidis strain ATCC 12228 was inoculated onto the human cadaveric gracilis tendon. The tendons were wrapped in sterile gauze saturated with tobramycin or vancomycin at various experimental concentrations. Bacteria remaining on the tendon were dislodged, serially diluted, and plated for colony counting. Statistical analysis was performed utilizing 2-way analysis of variance testing. Results were considered statistically significant when P < .05. Results: Vancomycin ( P = .0001) and tobramycin ( P < .0001) reduced bacterial concentration. Tobramycin was found to produce a statistically significant reduction in bacterial concentration at concentrations as low as 0.1 mg/mL ( P < .0001 and P = .01 at 10 and 20 minutes), while vancomycin produced a statistically significant reduction at a concentration as low as 2.5 mg/mL ( P < .0001 at both 10 and 20 minutes). Conclusion: This study demonstrates that tobramycin is as effective as vancomycin in bacterial concentration reduction but can achieve this reduction level at lower doses. Further studies clarifying the biomechanical and cytotoxic effects of tobramycin on tendon tissue are indicated to solidify its use as a clinical alternative to vancomycin in ACLR. Clinical Relevance: These results will begin establishing tobramycin as an alternative to vancomycin in ACL graft decontamination. Because of relatively frequent shortages of vancomycin, establishing tobramycin as an alternative agent is a useful option for the orthopaedic surgeon.