Numerical analysis of the proximal humeral outline: Bilateral shape differences.

A new method is presented for the numerical analysis of bilateral differences in the size and shape of the proximal humeral outlines using elliptical Fourier functions (EFFs). A skeletal sample of 36 pairs of right and left humeri was used. The proximal superior view in the plane of the proximodistal axis of each humerus was photographed with an 800 mm telephoto lens. The two-dimensional humeral outlines were carefully traced onto acetate sheets and 54 boundary points were located. These points were digitized and used to compute size-standardized EFFs with 27 harmonics. From the EFFs, a set of expected points on the proximal humeral outline was generated using the centroid as an origin. Superimposition of the right and left humeral outlines on this centroid provided a detailed picture of the relative bilateral shape differences with respect to that center. The proximal humeri showed significant bilateral size and shape differences, although the pattern of asymmetry in shape varied with respect to the region on the boundary outline. In particular, one localized aspect, the tubercular region of the proximal humeri showed significant bilateral shape differences. In contrast, the humeral head consistently showed not only a much smaller degree of bilateral shape differences, but also much less variability in size as well as shape. The results suggest that while the overall articular shape changes little with altered mechanical loadings placed on articular surfaces, the changes in the tubercular regions of the proximal humeri may be susceptible to the varying stresses associated with particular physical activities. Am. J. Hum. Biol. 11:343-357, 1999. Copyright 1999 Wiley-Liss, Inc.