Measurement of bone surface strains on the sheep metacarpus in vivo and ex vivo

Abstract

SummaryBone surface strains were measured on the dorsal ovine metacarpus during normal locomotion on a treadmill at different walking speeds to determine physiological strain levels. These measured strains were related to the strains measured in an ex vivo model of the sheep forelimb with two types of load application: loading by two Schanz-screws and loading via the radius. In vivo, the average surface strains were found to be dependent upon body weight as well as the walking speed. The orientation of the peak principal strain corresponded to the longitudinal axis of the bone. Ex vivo, loads applied via Schanz screws in the screw-loading model lead to strains on the dorsal metacarpus that corresponds to strains experienced in vivo during intermittent peak loads. Screw loading imparted primarily a bending load to the metacarpus, with the dorsal aspect in compression and the palmar aspect in tension. Loads, applied via the radius and the hoof in the radius-loading model, resulted in bone surface strains comparable to those measured during slow walking in vivo. In both ex vivo loading situations, peak strain orientation was parallel to the longitudinal axis of the sheep metacarpus. In conclusion, the results show that although the ex vivo loading models do not exactly replicate the load experienced in vivo, the magnitude and orientation of the principal strains on the dorsal metacarpus are within the range of strains occurring during normal physiological loading. These data validate the physiological significance of the ex vivo model and aid in understanding effects of mechanical loading on interstitial fluid flow and mass transport through bone.