Quantifying relative shape variation in modern human femora and humeri

Abstract

Lower limb bones are thought to be more developmentally stable (more symmetric) than upper limb bones, presumably because of the functional importance of locomotion. However, the relative degree of canalization (limits on between‐individual variation) in the limbs is less clear. Here we assess the 3D shape variation between individuals in a sample of modern human femora and humeri.Femora and humeri from 47 human males were CT scanned and 7002 landmarks were distributed across the surface of the bone using a statistical shape atlas (Merkl and Mahfouz, 2007). Each bone was scaled by its first principal component score to remove size and size‐correlated shape, and then by maximum length so that the femora and humeri were the same size. Bone shape variation was assessed as the average root‐sum‐squared distances of bone vertices from their average positions within each element. Bootstrap samples (1000) were used to create distributions of shape variation for each bone type, and distributions were compared using an ANOVA.The analysis reveals that after accounting for differences in size and size‐correlated shape, the humerus is more variable in 3D shape than the femur (p< 0.0001), indicating that the 3D shape of the femur is more canalized than the humerus.Grant Funding SourceNone