Purpose: Prophylactic antibiotics are frequently withheld until cultures are obtained in revision TKA. A prospective study was undertaken to determine whether prophylactic pre-operative IV antibiotics would affect the results of cultures obtained intra-operatively.

Method: A consecutive series of 25 TKA’s with a known infecting organism were enrolled over 36 months. Inclusion criteria: clinically infected TKA, a known preoperative infecting organism, and no recent antibiotic therapy. Re-aspiration of the infected TKA was performed following anesthesia and sterile prep. IV antibiotic prophylaxis was then administered and the tourniquet was then inflated. Intra-operative culture swabs and tissue were obtained at arthrotomy. The timing of events was recorded. Pre/post antibiotic culture data were analyzed to determine the effect of IV preoperative prophylactic antibiotics on cultures obtained intra-operatively.

Results: Mean time from end of antibiotic infusion to tourniquet inflation was 15 minutes; to arthrotomy culture was 25 minutes. In all 25 knees the organism(s) cultured at arthrotomy were the same as obtained at pre-operative aspiration. In 24 knees the organism cultured was sensitive to the preoperative prophylactic antibiotics given (Ancef and Vancomycin); one patient grew Candida albicans.

Conclusion: Pre-operative prophylactic antibiotics did not affect the results of intra-operative cultures, and should not be withheld prior to infected TKA surgery when an organism has been identified on aspiration. Based on these results, holding pre-operative antibiotics prior to revision TKA is rarely justified.