Open fractures are common, and infection a frequent complication. There is still uncertainty regarding the urgency of initial treatment. The majority of animal studies indicate that early irrigation and debridement reduces infection; unfortunately, these studies often do not involve antibiotics. Clinical studies indicate that the timing of initial debridement does not affect the infection rate. These studies are observational and fraught with confounding variables. The purpose of this study was to control for these variables using an animal model incorporating both systemic antibiotics and surgical treatment.

This study used a segmental defect rat femur model contaminated with Staphylococcus aureus and treated with a 3 day course of systemic cefazolin (5 mg/Kg 12 hourly) and surgical treatments, both of which were initiated independently at 2, 6 and 24 hour time points. After 14 days bone and hardware was harvested for separate microbiological analysis.

These results show that the earlier systemic antibiotic treatment or surgery is initiated. When antibiotics are started at 2 hours, delaying surgical treatment from 2 to 6 hours significantly increases infection (p=0.047). However, delaying surgery to 24 hours increases infection, but not significantly (p=0.054). The timing of antibiotics had a more significant effect on the proportion of positive samples than earlier surgery. At the 2 and 6 hour treatments, the p value was 0.004 and for the 6 and 24 timings it was 0.003.

Surgery and antibiotics at 2 hours completely eradicates the bacteria, but surgical delay for 6 hours appears to allow the bacteria to form non-susceptible colonies. Delaying antibiotics to 6 or 24 hours had a profound detrimental effect on the infection rate regardless of timing of surgery. These findings are consistent with the concept that bacteria progress from a vulnerable planktonic form to a treatment-resistant biofilm.