Getting the Shaft?: Investigating Midshaft Location in Immature Femora

Abstract

In skeletal samples, diaphyseal breadths of immature femora have traditionally been measured at 50% of diaphyseal length. However, research on the Denver growth sample suggests that 45.5% of diaphyseal length in younger individuals best represents the most analogous position to the 50% midshaft location in adult femora with fused epiphyses. Currently, direct comparisons have not been made between measures at 45.5% and 50% diaphyseal length. Lack of methodological consistency could affect comparisons across studies of immature skeletal remains.Comparative analysis utilizing modern day radiographs of immature individuals (birth‐12 years) indicated that 50% of diaphyseal length is, on average, located 2.6 mm proximal to true midshaft. This discrepancy is caused by the distal epiphysis contributing more to total bone length than the proximal epiphysis and confirms that mid‐diaphyseal locations approximate, but do not exactly align with, midshaft locations.Additionally, we analyzed immature (birth‐12 years)femora from several archaeological skeletal assemblages (n=170) to determine whether significant differences are present in anterioposterior (AP) and mediolateral (ML) breadths between the two diaphyseal locations. A repeated measures ANOVA indicates significantly wider AP and ML breadths at 45.5% when compared with 50% in all archaeological populations. Additionally, age is positively correlated with increases in AP breadth at 45.5% diaphyseal length. Morphological differences in the two locations support current understanding of shaft development and biomechanical changes with age. This finding, along with results from radiographs, suggests that studies utilizing one location may not be directly comparable to those utilizing the other. Future research will assess the impact of age on midshaft location to determine age‐specific methods for collecting diaphyseal breadths from immature femora.