Histological variation in modern human robust and gracile femur

Bones respond to mechanical stimuli by altering their internal and external structure. Bioarchaeologists routinely use this knowledge to infer ancient human behaviour. However, the extent to which human bone robusticity reflects its microstructural properties is still largely unexplored. Here, histological variation was examined in an archaeological sample of adult human femora (n = 450) dating to the medieval period in the UK. Femoral midshaft circumference (Mid.C) and posterior cortical thickness (Post.Cort.T) were recorded and used to create five robusticity groups. Histological sections from the posterior aspect of each femur were prepared following standard methods. Osteon population density (OPD), Haversian canal area (H.Ar) and diameter (H.Dm), osteon area (On.Ar) and osteocyte lacunae density (Ot.Dn) were compared between the groups. Histology values differed significantly between the five robusticity groups, though variation with age and between sexes was not consistent. A multivariate discriminant function analysis revealed that Ot.Dn, On.Ar, Ot.Dn, and H.Dm were the best predictors of Mid.C and Post.Cort.T in each of the five groups. Results indicate increased remodeling activity in larger and thicker bone. Small osteons and Haversian canals imply a highly strenuous loading history in robust femora. It is suggested that studies which infer ancient human behaviour from comparisons of femoral bone microstructure should account for histological variation that occurs with increased bone robusticity.