Morphological divergence in the curvature of human femoral diaphyses: Tracing the central mass distributions of cross‐sections

Abstract

The diaphysis of the human femoral bone has a physiological anterior curvature; additionally, there is a curvature to the medial side or lateral side. In addition to compression stress from gravity during standing, walking, and running, these bones are continuously exposed to complex stresses from the traction forces of the various strong muscles attached to them. The femoral diaphysis is subjected to these mechanical stresses, and the direction and size of its curvature are defined according to Wolff's law and the mechanostat theory of Frost. The purpose of this study was to quantitatively evaluate the curvature of the femoral diaphysis in Japanese skeletons by determining the curve connecting the central mass distributions (CMD) of cross‐sectional images. A total of 90 right femora (46 males and 44 females) were randomly selected from modern Japanese skeletal specimens. Full‐length images of these bones were acquired using a clinical computed tomography scanner. The range between the lower end of the lesser trochanter and the adductor tubercle of each femur was divided at regular intervals to obtain ten planes, and nine levels were analyzed. The CMD curve was determined by connecting the CMDs of each of the nine cross‐sections. First, the CMD of a cross‐section in each of the nine slices was calculated, and the nine trajectories were superimposed from above. Then, by converting the shape of the entire CMD curve to superimpose the coordinates of the endpoint on the starting point, a closed arc representing the curvature of the femur was determined. For both males and females, the patterns varied from mostly medial to largely lateral curvature. The size of the curvature also varied for individuals. By analyzing only the coordinates of the vertex of the CMD curve of each femoral bone, the outlines of the diaphyseal curvatures could be recognized. The femora were thereby divided into two groups: medial bending and lateral bending. Considering males and females together, the number in the lateral‐curvature group (n = 51) was larger than that in the medial‐curvature group (n = 39). Moreover, the average age of the lateral‐curvature group was significantly higher than that of the medial‐curvature group (p < 0.05). In males, with an increase in the cortical bone proportion of the cross‐sectional area, the anterior vertex of diaphyseal bending tended to be more prominent. This cortical proportion was significantly higher in the medial‐curvature groups than in the lateral‐curvature group (p < 0.01). The phenomena observed in this study may be related to pathophysiologies such as atypical fractures of the femur and osteoarthritis of the knee joints.

Application of Methods for a Morphological Analysis of the Femoral Diaphysis Based on Clinical CT Images to Prehistoric Human Bone: Comparison of Modern Japanese and Jomon Populations from Hegi Cave, Oita, Japan

“…The curvature of Jomon femurs excavated from Hegi cave was quantified using the method established by Imamura et al [ 10 ]. All of the Jomon femurs were flexed anteriorly, and in comparisons with modern bones, the degree of curvature of Initial/Early Jomon bones was similar to that of modern bones, while Late Jomon bones showed significantly stronger curvature than modern and Initial/Early Jomon bones ( Figure 7 ).…”

“…In the present study, we quantitatively analyzed the morphological features of cross-sections of the femoral diaphysis of Jomon humans excavated from Hegi cave based on CT images using an already established method for skeletal specimens of the modern Japanese population (Imamura et al, [ 9 ]; Imamura et al [ 10 ]). Among the male femurs excavated, 15 with well-preserved diaphyses were selected for analysis.…”

“…The method used to quantify the degree of curvature was reported by Imamura et al [ 10 ]. The central mass distribution (CMD) of cross-sectional images was assessed as the intersection of two line segments dividing any two-dimensional figure into equal areas.…”

“…Previously reported morphological data of modern Japanese people were used to support this study and are available at doi: 10.1111/joa.13399 and doi: 10.1111/joa.13060 . These prior studies are cited at relevant places within the text as references [ 9 , 10 ].…”

“…Although the increased curvature of the diaphysis has been implicated as a risk factor for atypical fractures, there is currently no unified method for a quantitative analysis of anterior and lateral curvatures with high reproducibility. Therefore, we developed methods to quantitatively analyze the morphology of cortical bone using CT images of modern Japanese skeletal specimens, with a threshold value that distinguishes cortical bone from cancellous bone [ 9 , 10 ]. This method may become the standard for a morphological analysis because it is completed in Excel and does not require specific software.…”