Drain tip cultures do not predict infections in primary total knee arthroplasty.

Background And Aim: The possibility to predict surgical site infections development could be of high prognostic value. We aimed to investigate whether cultures obtained from the tip of the closed passive wound drain may provide early signs of progression towards periprosthetic joint infections.

Materials And Methods: We performed an observational study on consecutive primary total knee arthroplasties performed in our department over 4 years by two high volume surgeons (it means they do a lot of arthroplasties/year; it is orthopedics specific). A total of 284 knees in 257 patients were included. Follow up was available for an average of 18.7 months. There were no simultaneous procedures.

Results: Nineteen (6.69%) drain tips yielded positive cultures, for a mean duration, from surgery to sample collection, of 1.63 (0.5) days. None of the positive drain tip cultures developed clinical signs of infection and all knees were healed at discharge after a mean of 13.78 days (SD= 3.34; range= 8-18). None of the 7 (2.46%) cases who developed deep infections had positive drain tip cultures. A true positive value of 0 led to a positive predictive value of 0, a negative predictive value of 97.34%, sensitivity of 0% and specificity of 93.14.

Conclusions: The diagnostic use of passive drain tip cultures to detect early infections after total knee replacement is therefore absolutely useless.