Holographic interferometry: a critique of the technique and its potential for biomedical measurements.

Double-exposure holographic interferometry is a contactless whole-field method. Dimensional changes are visualized as a series of interference fringes overlaid on the holographic image of the femur, where each fringe represents 0.316 micron (half the wavelength of the laser light) of motion. Interferograms for intact femora and for femora with identical geometry prostheses were produced. We have shown that the femur bends as a beam under axial load. The position of maximum deflection is a function of the properties of the composite structure. Under a known load the amount of deflection can be calculated and the effect of the prosthesis's modulus can be ascertained. In addition to bending, rotational effects can be perceived. Although data interpretation is complex and holographic production is costly and time-consuming, the technique holds promise for biomechanical applications as well as other biomedical disciplines.