An evolutionary perspective to intramedullary nail fit - comparing present-day data with a historical specimen collection

Manufacturers aim to design implants fitting for the broadest possible population segment. Due to the scarcity of available morphological data of intact long bones, anatomical collections of historical bone specimens may represent valuable additional sources. Previous work on femoral morphology measurements suggests that historical specimens are widely consistent with data from present-day populations. This study aimed to investigate whether this also applies to the anatomical fitting of a clinically used femoral nail. Nail fit was computer-graphically quantified through virtual implantation into CT-based 3D models of 52 femora, comprising a subset representative of the present-day Caucasian population (n = 31), a subset from a historical medieval European bone collection (n = 20), and additionally, a dataset from a natural ice mummy from the Neolithic period. Nail fit was assessed by nail protrusion (area and distance) to the inner cortex surface and the distal nail tip's position in the medullary canal. Assessed measurements and parameters of the present-day Caucasian subset were mostly consistent with those of the medieval European subset. After adjusting for multiple testing, only the distance from lateral nail entry point to shaft axis remained significantly (p = 0.03) different when comparing our modern and medieval subsets. Subsequent bivariate (Spearman) correlation analyses for both subsets (modern and medieval) combined showed that of the three variables representing basic demographic parameters, individual age, biological sex, and femur length, most statistically significant associations to the examined nail fit measurements were found for age (six measurements at a level of p < 0.05), however, with a relatively weak monotonic correlation (rho values ranging between +/- 0.31 and +/- 0.37). The measurements for the Iceman's femur lie within the range of the modern and historical subgroups, but in some cases, differ by more than one standard deviation from the mean. Our results confirm previous findings, suggesting that more recent historical bone specimen collections may indeed be a convenient and easily accessible source of new 3D morphological data and complement existing data to be used for the development of femoral nails.