Bone histology for forensic anthropology: a technical review on the advances in microstructural analysis of taphonomically altered buried or subaerially exposed bone.

Microscopy can be used to assess post-mortem bone degradation at a microstructural level. The duration of exposure to the environment may correlate to microstructural changes of the bone, and therefore, provide information about the post-mortem interval (PMI) or burial interval (BI). Through histological examination of thin bone sections, post-mortem microstructural changes can be investigated. The aim of this review is to provide an overview of histological staining methods that are applicable for studying microstructural taphonomical changes within bone, as well as reviewing and discussing the outcomes obtained through the application of these staining techniques in taphonomic research. In total, 45 stains were classified as promising to stain histological features that can undergo taphonomic changes in bone, including collagen and osteocytes. Examples of these stains include Mallory Trichrome staining, Gomori's Trichrome staining, and Weigert's resorcin-fuchsin method. The availability of protocols for use of the 45 stains on undecalcified, embedded and non-embedded bone sections was investigated. Protocols were available for 8 of the 45 stains on embedded bone sections, and for 2 of the 45 stains on non-embedded bone sections. A follow-up systematic literature search was conducted to obtain a comprehensive overview of the histological staining techniques that already have been tested within taphonomic research. Based on the outcome of the systematic literature search, only 3 out of the 45 different stains were tested, namely the Sirius Red/Fast Green staining, Haematoxylin-Eosin staining and Picrosirius red staining. These studies demonstrated that Sirius Red/Fast Green and Picrosirius red staining revealed significant changes in collagen degradation over time, useful for estimating the PMI or BI, while Hematoxylin-Eosin staining effectively portrayed bone morphology and its relation to a bone integrity index. Interestingly, 42 staining techniques have not yet been tested at all, leaving a huge knowledge gap. Therefore, the next step will involve testing the remaining stains on fresh and taphonomically altered, undecalcified bones, subsequently developing and validating a method to potentially relate the extent of degradation to the post-mortem interval or burial interval.