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Measurement of the Relative Motion Between an Implant and Bone under Cyclic Loading

Abstract:  The measurement of the relative motion between a prosthesis and the surrounding bone is important for the pre‐clinical testing of prostheses and implants. A technique that allows measurements to be made over several million loading cycles was developed by Maher et al. (Clin. Biomech. 2001; 16: 307–314). However, the measurement of implant/bone motion is fraught with difficulties because: (i) testing over millions of cycles can take several days and errors because of diurnal temperature variations can occur, (ii) elastic deformations of the stem could have a dominant effect on ‘inducible displacements’, the rate of change of which is hypothesised to be a measure of loosening, and (iii) the use of this method for the analysis of cementless prostheses has yet to be demonstrated. This paper addresses these methodological issues with respect to testing hip prostheses, and concludes with a comparative evaluation of pre‐clinical testing methods.