A New Method for Whole Bone Analysis of Bilateral Asymmetry.

Postcranial asymmetry of bones has been mostly studied with linear or angular measurements. Although conclusive, these measurements fail to capture the differences of the entire bone surface. Here, we develop a methodology to measure whole bone bilateral asymmetry from 3D models. We demonstrate the method using the humerus and the second metacarpal. We compare right and left bones of the same individual (bilateral variation) to that of different scans of the same bone (interscan variation) and of the same bone from different individuals (interindividual variation) to show that the method functions and is able to segregate different degrees of variation. The interscan variation is the lowest, while the interindividual variation is the greatest, and the bilateral variation falls between the other two. Visual comparisons, using color maps, illustrate on the bone where the asymmetry is most marked. As expected, the interscan comparisons show very little variation in shape, while the interindividual comparisons reveal extensive variation. In bilateral comparisons, some patterns were observed. In the humerus, the radial groove, the deltoid tuberosity, and the olecranon fossa were usually the most asymmetrical regions. The epiphyses are also more asymmetrical than the diaphysis. For the MC2, the attachments for the palmar interossei muscles and the articular facets with the MC3 were the most asymmetrical regions. These results demonstrate that this new method helps identify areas of asymmetry that would otherwise be difficult to observe.