A common step to revision surgery for infected total knee replacement (TKR) is a thorough debridement. Whilst surgical and mechanical debridement are established as the gold standard, we investigate a novel adjuvant chemical debridement using an Acetic Acid (AA) soak that seeks to create a hostile environment for organisms, further degradation of biofilm and death of the bacteria.

We report the first orthopaedic in vivo series using AA soak as an intra-operative chemical debridement agent for treating infected TKR's. We also investigate the in vitro efficacy of AA against bacteria isolated from infected TKR's.

A prospective single surgeon consecutive series of patients with infected TKR were treated according to a standard debridement protocol. Patients in the series received sequential debridement of surgical, mechanical and finally chemical debridement with a 10 minute 3% AA soak.

In parallel, we isolated, cultured and identified bacteria from infected TKR's and assessed the in vitro efficacy of AA. Susceptibility testing was performed with AA solutions of different concentrations as well as with a control of a gentamicin sulphate disc. The effect of AA on the pH of tryptone soya was also monitored in an attempt to understand its potential mechanism of action.

Physiological responses during the AA soak were unremarkable. Intraoperatively, there were no tachycardic or arrythmic responses, any increase in respiratory rate or changes in blood pressure. This was also the case when the tourniquet was released. In addition, during the post-operative period no increase in analgesic requirements or wound complications was noted. Wound and soft tissue healing was excellent and there have not been any early recurrent infections at mean of 18 months follow up.

In vitro, zones of inhibition were formed on less than 40% of the organisms, demonstrating that AA was not directly bactericidal against the majority of the clinical isolates. However, when cultured in a bacterial suspension, AA completely inhibited the growth of the isolates at concentrations as low as 0.19%v/v.

This study has shown that the use of 3% AA soak, as part of a debridement protocol, is safe. Whilst the exact mechanism of action of acetic acid is yet to be determined, we have demonstrated that concentrations as low as 0.19%v/v in solution in vitro is sufficient to completely inhibit bacterial growth from infected TKR's.