Discussion
The efficacy of using Chloraprep before TKA has not been well assessed in orthopedic practice. However, compared with other preoperative solutions, chlorhexidine has been shown to be significantly better in preventing post-TKA infections.4 Other studies have found it far more effective than other commonly used surgical preparations in eliminating microorganisms in hip arthroplasty and foot surgery.5,7 Our study, focused on the efficacy of Chloraprep in killing bacteria, found the solution effective in removing 85% (17/20) of cultured presolution organisms.
Of the bacterial isolates cultured, normal flora were effectively removed from all associated postsolution cultures. Although most of the bacterial isolates were eliminated after solution application, both coagulase-negative S aureus and rare Bacillus species were found both pre- and postsolution, suggesting either inadequate skin preparation or resistant bacteria.
With respect to the secondary variables, our study data showed that BMI was an important predictor for bacterial isolates, significantly so presolution (P < .03). Mean BMI for the overall study was 35, firmly in the obese category. Only when BMI increased to 38 did it become significant as a predictor for postsolution organisms. Mean postsolution BMI was even higher, 40, which is in the morbidly obese category. Interestingly, the percentage of nonobese patients (BMI, <30) with positive presolution cultures was only 9%, versus the 20% with positive presolution cultures overall. In addition, 1 nonobese patient had positive postsolution cultures.
Other studies have linked higher BMI to higher rates of surgical site infection and other complications, but it is unknown if the infections are due to higher bacterial counts in the patients with high BMI or to other factors, such as reduced wound healing or decreased immune response. More research is needed to determine if the number of organisms in patients with high BMI correlates to a higher risk for surgical site infection.8 As expected, along with BMI (>38), presolution organism isolation was an important predictor for postsolution organism isolation. Patients with presolution organism isolation were 24 times more likely to have postsolution isolates.
Even though diabetic status was not significant for predicting bacterial isolation, patients with diabetes were 3.6 times more likely than patients without diabetes to have a positive culture. Other studies have shown that, compared with patients without diabetes, patients with diabetes had a higher chance of postoperative infection.9,10
In this study, 18 of 20 patients with presolution organism isolates reported they had been compliant in taking the recommended preoperative cleanser baths. This finding may indicate that preoperative cleanser baths are ineffective. However, only 20% of our patients had positive presolution cultures, whereas Ostrander and colleagues5 reported 30% positive pre-preparation cultures from the anterior knee. A recent Cochrane Database System Review did not provide clear evidence of benefit for preoperative showering or bathing with chlorhexidine over other wash products.11 Although their benefit may be questionable, we will continue to recommend preoperative cleanser baths.
One limitation of this study is sample size. Although size was sufficient for determining the efficacy of Chloraprep in the intertriginous area of the back of the knee, the lack of statistical significance (eg, effect of diabetes) may not be accurate. In addition, because the nurse who prepared patients’ skin was aware of the study and was supervised in every case, it is possible that the preparation was done more carefully than usual, resulting in more negative cultures than average. Also, compliance in taking preoperative cleanser baths was subjectively determined. Patients may have reported more baths than were actually taken. Still another study limitation is that 2 postsolution isolates did not have an associated presolution isolate. Although we think this may have resulted from laboratory contamination, it is possible the presolution swabs did not accurately determine true bacterial counts in these cases.
Conclusion
A study that showed significant residual bacteria between patients’ toes after chlorhexidine skin preparation5 left us concerned that Chloraprep skin preparation for TKA might not be adequate. The present study showed that this solution was effective in eliminating bacteria from the intertriginous area of the back of the knee in 95% of patients. Skin preparation appears to be less effective in patients with higher BMI.