The prevention of infection in open fractures : an experimental study of the effects of fracture stability and of antibiotic therapy
An experimental model of a contaminated open fracture has been developed in rabbits, using a reproducible midshaft fracture of the tibia. This model has been used to: 1) Test the hypothesis that stable fixation of an open fracture will reduce its susceptibility to infection. 2) Assess the effect of antibiotics on infection rate, with particular reference to the delay in administering the initial dose. The pattern of fracture healing was initially determined for stable and unstable fixation, without inoculation with bacteria. Fractures fixed with a dynamic compression plate ("stable" group) healed by primary bone union, while fractures stabilised with a loose-fitting intramedullary rod ("unstable" group) healed by external callus formation. Forty- one rabbits were used in the definitive study of the effect of stability. All fractures were inoculated with Staphylococcus aureus in a standard concentration. There were twenty rabbits in the stable group (compression plate) and osteomyelitis developed in seven (35%). Of the twenty- one rabbits in the unstable group (loose- fitting intramedullary rod), fifteen (71%) became infected. This difference in infection rate is statistically significant (p<0.02). The "rod- fixed fracture" model had the highest infection rate and was therefore used to study the effect of antibiotics. Fifty-one rabbits were used; a single intramuscular injection of cephradine was given to each animal at varying times in relation to inoculation with bacteria. Although the maximal reduction in infection rate was observed when the antibiotic was given before inoculation with bacteria, a 40% decrease in the infection rate was still seen when the antibiotic was given after bacterial inoculation. This effect persisted even if the initial dose of antibiotic was delayed four hours after inoculation. These findings support the concept of stabilisation of open fractures in man; and suggest that appropriate systemic antibiotics should be routinely used in the management of open fractures in man, even if the treatment is delayed up to four hours after injury.