Accelerated Method for Determining the Fatigue Limit of Trabecular Bone

This paper presents an experimental method for estimating the fatigue limit of trabecular bone using a single trabecular bone sample, the microstructural parameters of which were determined by microCT. Fatigue tests were carried out using the Locati method, with stepwise increasing load amplitude. The fatigue limits of the trabecular structures were determined experimentally in accordance with Miner's law of fatigue damage accumulation, based on the parameters of the reference S-N curve taken from the literature. On the basis of the fatigue limits, the S-N curves were determined for the tested samples, and from them the compressive strength US corresponding to the fatigue limit for the N = 1 cycle. Ultimate compressive strength US was determined as a result of compression to failure tests. Computational dependencies combining the BV/TV index with US and the BMD index with US were formulated. To verify the proposed method, two groups of human trabecular bone samples were analysed: n = 42 were tested under monotonic loading, and n = 61 were tested under cyclic loading with stepwise increasing amplitude. The statistical test of the distribution conformity of the calculated US compressive strength to the experimental US ultimate strength was performed. The results of the Kolmogorov-Smirnov statistical test were D = 0.19 (p = 0.314). The agreement of the distributions of BV/TV, as determined experimentally and calculated from the computational dependencies, was also tested statistically, with the result of the Kolmogorov-Smirnov test being D = 0.286 (p = 0.065). A similar analysis performed for BMD yielded D = 0.238 (p = 0.185).