Tissue stresses and strain in trabeculae of a canine proximal femur can bequantified from computer reconstructions (vol 32, pg 165, 1999)

A quantitative assessment of bone tissue stresses and strains is essential for the understanding of failure mechanisms associated with osteoporosis, o steoarthritis, loosening of implants and cell - mediated adaptive bone-remo deling processes. According to Wolff's trajectorial hypothesis, the trabecu lar architecture is such that minimal tissue stresses are paired with minim al weight. This paradigm at least suggests that, normally, stresses and str ains should be distributed rather evenly over the trabecular architecture. Although bone stresses at the apparent level were determined with finite el ement analysis (FEA), by assuming it to be continuous, there is no data ava ilable on trabecular tissue stresses or strains of bones in situ under phys iological loading conditions. The objectives of this project were to supply reasonable estimates of these quantities for the canine femur, to compare trabecular-tissue to apparent stresses, and to test Wolff's hypothesis in a quantitative sense. For that purpose, the newly developed method of large- scale micro-FEA was applied in conjunction with micro-CT structural measure ments. A three-dimensional high-resolution computer reconstruction of a proximal c anine femur was made using a micro-CT scanner. This was converted to a larg e-scale FE-model with 7.6 million elements, adequately refined to represent individual trabeculae. Using a special-purpose FE-solver, analyses were co nducted for three different orthogonal hip-joint loading cases, one of whic h represented the stance-phase of walking. By superimposing the results, th e tissue stress and strain distributions could also be calculated for other force directions. Further analyses of results were concentrated on a trabe cular volume of interest (VOI) located in the center of the head. For the s tance phase of walking an average tissue principal strain in the VOI of 279 strain was found, with a standard deviation of 212 mu strain. The standard deviation depended not only on the hip-force magnitude, but also on its di rection. In more than 95% of the tissue volume the principal stresses and s trains were in a range from zero to three times the averages, for all hip-f orce directions. This indicates that no single load creates even stress or strain distributions in the trabecular architecture. Nevertheless, excessiv e values occurred at few locations only, and the maximum tissue stress was approximately half the value reported for the tissue fatigue strength. Thes e results thus indicate that trabecular bone tissue has a safety factor of approximately two for hip-joint loads that occur during normal activities. (C) 1999 Elsevier Science Ltd. All rights reserved.