Forensic wound age estimation in dog tissue correlated with newly formed collagen fibres: a retrospective study

Parameters for wound age estimation are essential in forensic pathology but difficult to assess. With this retrospective study, wound age parameters in canine skin wounds were assessed with archive material of known age. Haematoxylin and eosin (HE) staining as standard, Prussian blue, Van Gieson (VG) and multiple other special stains were used as well as various immunohistochemistry (IHC) tests. Collagen fibre formation examination included HE staining but also immunolabelling for elastin and collagen I. Collagen fibre formation was further assessed by polarization in HE and VG. HE staining, erythrophagocytosis and presence of haemoglobin decay products in the Prussian blue stained-slides proved to be useful tools in wound age estimation in the early phase of wound repair of less than 5 days. The earliest detection of newly formed collagen was possible in 5-day-old wounds with HE and VG staining. Collagen I reactivity by IHC was weak at this time point, moderate to strong in the lesions older than 10 days and up to 30 days and strong in the lesions older than 3 months. Very slight polarization of collagen fibres was observed at 6 days, becoming stronger in wound lesions of 10-14 days and up to 30 days and reaching the same intensity as normal tissue in a 3-month-old lesion. The morphology of newly formed collagen fibres, utilizing HE and VG staining and polarization as well as collagen I IHC, which proved to be the most important parameters, correlated with distinguishable time points in the available cases of known wound age.