Assessing Shape Asymmetry in Human Femora and Humeri

Most humans demonstrate a right side bias in upper limb skeletal dimensions, and a similar but smaller dominance in the left lower limb. Although several studies have documented patterns of asymmetry in long bone linear dimensions, relatively little research has been conducted looking at shape asymmetry among the limb bones. The goal of this study was an initial assessment of three‐dimensional shape asymmetries in human humeri and femora. A secondary goal was to determine if areas of shape asymmetry are associated with muscle attachment sites. Computed tomography scans of 17 human femora and humeri pairs were segmented from image stacks to produce three‐dimensional surface models. Left bones were reflected and were surface aligned with paired right bones. Shape variation was quantified as the root mean square (RMS) value of distances between vertices representing the right bone model and the closest point on the surface of the reflected left bone model. Shape differences between models were visualized using colorized distance maps, and common areas of shape variation were compared for association with muscle attachment sites. When RMS values between paired bones were scaled for size (maximum bone length) the difference between the humerus and femur approaches statistical significance (p = 0.06), suggesting a greater average difference between humeri pairs compared to pairs of femora. If bones within pairs were scaled to the same length, the difference becomes less dramatic (p > 0.10) suggesting that the greater asymmetry in the humerus is largely a function of bone length, a result which corroborates findings by other researchers. Distance maps suggest that shape variation is concentrated around the proximal and distal ends of both bones largely in areas of muscle attachments.