Abstract
Background
Deep infection rates of 1 - 2% following primary hip and knee arthroplasty are mainly due to endogenous contamination of the surgical site from bacteria within the patient's own skin. However surgical skin preparation removes only bacteria from the surface of the skin, leaving viable bacteria in the deeper layers of the skin within hair follicles and sweat and sebaceous glands. The aim of our study was to test the hypothesis that surface skin swabs taken after skin preparation with alcoholic povidone iodine would not grow bacteria, whereas full thickness biopsies taken from the line of surgical incision would grow bacteria.
Methods
Under LREC approval, informed consent was obtained from 22 patients undergoing primary hip (n=9) or knee (n=13) arthroplasty. All patients received intravenous antibiotic prophylaxis at the time of induction of anaesthesia. After surgical skin preparation with alcoholic povidone iodine, a surface skin swab and full thickness skin biopsy, using an 8mm x 4 mm elliptical punch, were taken. The swab culture was incubated aerobically and anaerobically at 37°C. The skin biopsy was cut aseptically in half. One half was crushed using artery forceps, placed in 5mL anaerobe basal broth and incubated anaerobically at 37°C. The other half of the skin biopsy was frozen in isopentane and gram – stained after sectioning.
Results
Seven of 20 surface swabs were positive for bacteria (2 S. epidermidis, 3 P. acnes, 1 S. aureus and 1 with both S. epidermidis and P. acnes). Ten of 22 full thickness skin biopsies were positive for bacteria (4 P. acnes, 3 S. epidermidis, 2 S. aureus and 1 S. capitis). Gram positive bacteria were seen in all gram – stained sections.
Conclusions
This study shows that skin preparation with alcoholic povidone iodine does not completely remove viable bacteria from the skin. Surgeons need to be aware of this and to adapt their surgical technique to avoid coming into contact with the patient's skin when performing surgery involving implants. The continuing importance of appropriate antimicrobial prophylaxis is also emphasised.
