Is EDTA Irrigation Effective in Reducing Bacterial Infection in a Rat Model of Contaminated Intra-articular Knee Implants?

BACKGROUND To mitigate the possibility of infection after arthroplasty, intraoperative irrigation is essential to remove contaminating bacteria. Previous studies have demonstrated that irrigation with an EDTA solution before wound closure is superior to irrigation with normal saline in removing contaminating bacteria in a rat model of open fractures. However, the effectiveness of an EDTA solution in a model with a contaminated intra-articular implant remains unclear. QUESTIONS/PURPOSES (1) Does irrigation with an EDTA solution decrease the proportion of culture-positive joints compared with normal saline, benzalkonium chloride, and povidone iodine? (2) Is an EDTA solution toxic to cells resident in joints including chondrocytes, osteoblasts, and synovial fibroblasts? (3) Does irrigation with an EDTA solution have adverse effects including arthrofibrosis and hypocalcemia? METHODS We first established a model of contaminated intra-articular implants. Female Sprague-Dawley rats (n = 30 for each treatment group) underwent knee arthrotomy and implantation of a femoral intramedullary wire with 1 mm of intra-articular communication. To simulate bacterial contamination, the inserted wire was inoculated with either Staphylococcus aureus or Escherichia coli. After 1 hour, the wound and implant were irrigated with normal saline, benzalkonium chloride, povidone iodine, or an EDTA solution (1 mM). The animals were euthanized 1 week later, and the distal femur, knee capsule, and implanted wire were harvested for bacterial culture using standard techniques. In this study, we used a well-established animal model of an intra-articular implant and inoculated the implant to simulate the clinical setting of intraoperative contamination. The proportion of culture-positive joints in normal saline, benzalkonium chloride, povidone-iodine, and EDTA groups were compared. The viable cell numbers (chondrocytes, osteoblasts, and synovial fibroblasts) were counted and compared after treatment with either solution. Measurement of blood calcium level and histological examination of the joint were performed to rule out hypocalcemia and arthrofibrosis after EDTA irrigation. RESULTS With S. aureus inoculation, EDTA irrigation resulted in fewer culture-positive joints than normal saline (37% [11 of 30] versus 70% [21 of 30]; p = 0.019), benzalkonium chloride (83% [25 of 30]; p < 0.001), and povidone iodine (83% [25 of 30]; p < 0.001) irrigation. Likewise, infection rates for implant inoculation with E. coli were also lower in the EDTA irrigation group (13% [four of 30]) than in the normal saline (60% [18 of 30]; p < 0.001), benzalkonium chloride (77% [23 of 30]; p < 0.001), and povidone iodine (80% [24 of 30]; p < 0.001) groups. Between normal saline control and EDTA, there were no differences in cell viability in chondrocytes (normal saline: 98% ± 18%; EDTA: 105% ± 18%; p = 0.127), osteoblasts (normal saline: 102 ± 19%, EDTA: 103 ± 14%; p = 0.835), and synovial fibroblasts (normal saline: 101% ± 21%, EDTA: 110% ± 13%; p = 0.073). EDTA irrigation did not result in hypocalcemia (before irrigation: 2.21 ± 0.32 mmol/L, after irrigation: 2.23 ± 0.34 mmol/L; p = 0.822); and we observed no arthrofibrosis in 30 histologic samples. CONCLUSIONS In a rat model of a bacteria-contaminated intra-articular implants, intraoperative irrigation with 1 mmol/L of an EDTA solution was superior to normal saline, 0.03% benzalkonium chloride, and 0.3% povidone iodine in preventing surgical-site infection and caused no adverse effects including death of resident cells, arthrofibrosis, and hypocalcemia. Future studies should seek to replicate our findings in other animal models, perhaps such as dog and goat. CLINICAL RELEVANCE If other animal models substantiate the efficacy and safety of the EDTA solution, clinical trials would be warranted to determine whether the use of an EDTA irrigation solution might reduce the risk of periprosthetic joint infections in patients compared with traditional irrigation solutions.