Purpose

Calculating the timing of bruises is crucial in forensic pathology but is a challenging discipline in both human and veterinary medicine. A mechanical device for inflicting bruises in pigs was developed and validated, and the pathological reactions in the bruises were studied over time in order to identify gross and histological parameters that may be useful in determining the age of a bruise.

Methods

The mechanical device was able to apply a single reproducible stroke with a plastic tube that was equivalent to being struck by a man. In each of 10 anesthetized pigs, four strokes that resulted in bruises were inflicted on the back. In addition, 2 control pigs were included in the study. The pigs were euthanized consecutively from 1 to 10 h after the infliction of bruises. Following gross evaluation, skin, and muscle tissues were sampled for histology.

Results

Grossly, the bruises appeared uniform and identical to the tramline bruises seen in humans and pigs subjected to blunt trauma. Histologically, the number of neutrophils in the subcutis, the number of macrophages in the muscle tissue, and the localization of neutrophils and macrophages in muscle tissue showed a time-dependent response. Combining these parameters, bruises could be grouped as being either less than 4 h old or between 4 and 10 h of age. Gross lesions and changes in the epidermis and dermis were inconclusive with respect to time determination.

Conclusions

The model was reproducible and resembled forensic cases of bruises in pigs and humans. Therefore, the histological parameters are suitable for age determination of bruises in pigs and likely also in humans.