A Method for Estimating Relative Bone Loads from CT Data with Application to the Radius and the Ulna

The two bones of the forearm, the radius and the ulna, have been shown to bear different proportions of the overall forearm load at the wrist and the elbow. This biomechanical data suggests load transfer between the bones occurs through the soft tissues of the forearm. Load transfer from radius to ulna through passive soft tissues such as the interosseous ligament (IOL) has been experimentally measured. Ex vivo studies of the forearm, however, cannot account for the effect of internal loads generated by the muscles and, in some cases, external forces acting directly on the forearm bones. The objective of this study was to estimate the relative loads in the radius and ulna for a range of proximal-distal levels in the forearm, accounting for all in vivo mechanical stimuli. This objective was accomplished using a computational technique based on bone remodeling theory and computed tomography (CT) data of the bones. The results indicate a monotonic exchange of load from the radius, which was found to carry the majority of the load distally, to the ulna, which was found to carry most of the load proximally. Because the load transfer was distributed along the forearm, instead of concentrated in the region of the IOL, it appears that muscle forces may play an important role in load transfer and the overall loading of the forearm bones.