[Experimental deformation in a bone fixation plate: measurement using holographic interferometry].

The minute mechanical properties of the tibia fixed by a metal plate and screws were investigated under various simulated loading conditions. The bracing technique and the design of the osteosynthetic plate are discussed based on the measurement results. The specimens were eight dried human tibias. Four different fixation method were employed using an AO plate system, and also using an Eggers plate system. The bending force, torsion force and axial force were applied to the tibia. Deformation in the tibia and/or metal plate was measured using double exposure holographic interferometry. The mechanical properties were estimated from the fringe pattern and from the deformation curve obtained from the reconstruction image of the holographic interferometry. The fixation capability of the plate systems differed according to the direction of the loading. The reconstruction image of the hologram showed that deformation increased mainly in the plate corresponding to the fracture line of the tibia. Screws nearer the fracture line were more important in increasing the fixation capability of the plate. Twisted deformations in the plate were observed under a simple bending force. The new measurement method of holographic interferometry clearly showed the two dimensional bending and the twisted deformation in detail.