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Abstract:
A standardized experimental impact injury model was developed to produce soft tissue trauma that simulated impact injuries to soft tissue overlying the cranium. An aluminum impact instrument was constructed so as to deliver a measured amount of energy to a finite area of soft tissue over a fixed foundation. Impact injury resulted in readily demonstrable changes in the morphology of the tissue and its blood flow. As measured by the distribution of fluorescein dye, the blood flow to the impact site was considerably less than that to unwounded tissue. The magnitude of this reduction in blood flow to the site of injury was proportional to the level of energy absorbed by the tissue. The injury to skin resulting from the impact was restricted primarily to the subcutaneous tissue and panniculus carnosus. Loss of adipose tissue and necrosis of skeletal muscle fibers in these layers were associated with the development of a dense inflammatory infiltrate. The structural damage to the tissue and its reduced perfusion were correlated with the tissue's increased susceptibility to infection by bacteria delivered either by direct infection or as a result of a bacteremia. The magnitude of this damage to the host's defenses is, again, directly related to the amount of energy absorbed per unit area of soft tissue. Antibiotics did suppress the growth of bacteria in these experimental soft tissue impact wounds, even when treatment was delayed eight hours. While the therapeutic efficacy of antibiotics was readily apparent in soft tissue impact wounds, the degree to which they could suppress bacteria in these wounds was less than that encountered in the treated control wounds not subjected to impact.