Combating frailty: application of a modified skeletal frailty index in modern military and civilian populations.

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Conceptualizing, quantifying, and evaluating frailty in human skeletal remains is critical to understanding and interpreting physiological health and stress among past populations. While many researchers focus on frailty in bioarchaeological samples, developing models for mortality risk and individual- and population-specific indices of stress, no current methods directly address frailty in forensic contexts. This study considers the applicability of a modified index for assessing frailty in forensic anthropology by comparing distributions of 8 biomarkers of stress (linear enamel hypoplasia; periodontal disease; caries; osteoarthritis; intervertebral disc disease; rotator cuff disorder; antemortem fracture; and surgical procedure) using the original skeletal frailty index (SFI) to a modified skeletal frailty index (SFI+) between self-identified military veterans (n=10) and civilians (n=9) from the Bass Donated Skeletal Collection. In this forensic context, the SFI+ reflects both increased levels of skeletal preservation within modern samples and medical interventive care that may mitigate frailty. Further, it implements severity scales, rather than relying on presence/absence binaries, for evaluating frailty biomarkers as low or high. Frailty results were interpreted through a biocultural and embodiment framework with the presence of skeletal frailty in veteran individuals reflective of embodied stressors experienced within the unique culture and lifestyle of the military. Mann-Whitney U tests showed statistically significant differences between SFI and SFI+ distributions overall (p<0.001), with SFI (3.79±1.40) yielding higher average distributions than SFI+ (2.34±1.12). This variation in SFI and SFI+ distributions affected subsequent differences in results comparing military and civilian subsamples, SFI (p=0.243) and SFI+ (p=0.05), with civilian individuals exhibiting higher frailty than the veteran individuals when applied to the SFI+ criterion. The SFI+ also revealed approaching significant differences in fractures, with civilians having higher instances than veterans (p=0.065). While the other biomarkers did not reveal significant differences between veterans and civilians using either frailty index, differences in their distributions were observed and contextually discussed. These results support the applicability of SFI+ to forensic anthropology contexts and present an effective way of quantifying frailty that highlight complexities of modern embodied experiences of military veterans.