Feasibility of bone healing measurement with external fixation: experimental study

The measurement of fracture healing is a problem before us now; many techniques are now being developed. One of them is strain gauge measurement, allowing control of the development of the callus stiffness. The mathematical models and the experimental controls always had to deal with "preliminary assumptions." Theoretically, the output of a single strain gauge bonded on the fixation rod drops rapidly accordingly to the quality of the healing. Our aim is to verify experimentally the validity of the method in cases where the "preliminary assumptions" are not strictly true.We investigated the influence of the fixation rod on the loading of the tibia using strain gauges bonded on the bone. The tibial cortex was afterwards weakened by a 1 mm broad saw cut (and later a 5 mm one) in the middle of the bone. We again found the hyperbolic pattern of the theoretical curves.The experiments confirm the theoretical result: the measurement of stress drops rapidly as the degree of healing increases. An asymmetrical healing does not seem to modify significantly the pattern of the curve.