With our study, we have shown that a 5 min footbath in alcohol prior to conventional preoperative disinfection of the foot/ankle reduces the bacterial inocula significantly under the nailfold of the first toe and the first webspace. Moreover the number of cultures with heavy growth is lowered under the nailfold. The overall number of positive cultures is not lowered by the preceding footbath. We took swabs only at an early stage to investigate whether or not a reduction in bacterial load was visible due to the difference in the preparation of skin antisepsis. Performing swabs during the procedure would provide information on the quality of maintaining a sterile field and not about the quality of the preoperative disinfection. Most likely re-taking cultures at a later stage would show an increase in bacterial load, which would probably be the same in both feet. Numerous studies have been conducted to identify the optimal method for preoperative skin antisepsis since skin antisepsis became routine in the late 1990s [
20]. Traditionally iodine was used, it is; however, less attractive due to its irritant nature to the skin and it seemed to be less effective compared to chlorhexidine [
17,
21]. Some studies suggest, however, that the advantage of CHG over PVI in these studies could be explained by the fact that PVI was an aqueous solution and CHG was diluted in alcohols [
9,
14,
22]. They suggest that the actual active ingredient was alcohol and most beneficial effects could, therefore, be attributed to the alcohol [
14]. The foot differs from others parts of the body and consists of several areas (i.e., under the nailfold and the webspaces) which are very difficult to disinfect as shown by previous studies [
8,
19,
23‐
25]. Additional measures that are often used to further lower the chance of contamination the surgical site are, for example, covering the toes shows. However, only one small (underpowered) RCT is available on this subject; in this trial no benefit of covering the toes was observed [
26]. Inspired by the study of Keblish et al. [
19] who found good results in foot/ankle skin preparation using a bristled brush and solely alcohol and by the study of Becerro et al. [
8] and Ng et al. [
18] who made use of a footbath, we decided to use the best of both worlds. As alcohol evaporates quickly, we used a closed system footbath to overcome this problem. Despite using two substances, we still have observed high rates of positive cultures following skin antisepsis. These figures are, however, confirmed by earlier studies indicating that decontamination of especially the foot is challenging [
8,
17,
23]. Skin antisepsis is even more important in light of increasing antibiotic resistance of microorganisms. If wound infections can be prevented, less antibiotics are needed and hence, less antibiotic resistance will develop. Different parts of the body naturally host different species of commensal bacteria [
27]. The microorganisms most frequently cultivated from the foot/ankle by several investigators are Staphylococci [
13,
17]. This is important as Gram-positive bacteria are a common source of SSI’s [
7]. Interestingly we did not culture any
S. aureus indicating that adequate skin antisepsis may prevent postoperative wound infections by eliminating important pathogens. Coagulase-negative Staphylococci (CoNS) are also frequently encountered in postoperative wound infections following osteosynthesis [
17] and we did culture this microorganism often (in 30 out of 87 positive cultures); this finding has been observed by others earlier as well [
8,
23]. Interestingly CoNS was almost exclusively cultured under the nailfold and the first webspace in both the intervention as the control group, Indicating that potential pathogens are hard to eliminate from these spots. Again, this has also been noted by other authors [
8,
19,
23].
We contribute our finding that more positive cultures were found on site 4 in the experimental group (control site only disinfected with chlorhexidine paint) to the fact that this site was not covered by the alcohol and may have been less thoroughly disinfected in the testing environment. Furthermore, it must be noted that 4 of the 12 positive cultures on this site contained only one CFU which may indicate a doubtful clinical significance of this finding.
The main weakness of this study is that the direct relation between bacterial inocula and postoperative wound infections is yet to be proven. It is conceivable that reducing the bacterial load is beneficial for preventing wound complications; however, this is to be proven in clinical studies [
15,
16,
26]. A pilot study in patients undergoing foot/ankle surgery should be the next step. With an infection rate of 10% and a reduction of 25%, a total of 6424 patients are needed. For a reduction of 50%, 864 patients would be necessary, both with an alpha of 5% and a power of 80%. Furthermore, the number of surgical site infections should serve as the primary endpoint.
The results of our study confirm our hypothesis that a footbath with alcohol is of additive value in foot/ankle skin preparation. We feel that adding this extra layer of decontamination could be valuable in the future because of the total amount of microorganisms was lower in the areas (i.e., nailfold and webspace) which are notoriously difficult to decontaminate and the number of cultures with heavy growth was also lower on these two locations. The effect in lowering SSI’s, however, needs to be proven in a clinical trial. As several authors suggested that alcohol might actually be the most active agent, the next study could be to investigate the effects of applying solely a footbath of alcohol compared to traditional chlorhexidine in alcohol paint.