A Simulation Study Of Marrow Fat Effect On Osteoporotic Biomechanics

Osteoporosis is a bone metabolism disease characterized by the reduction of bone mass and deterioration of bone microstructure, which has been a serious health problem in human society. Clinical reports suggest that osteoporotic patients are suffering a decrease of bone strength and an increased probability of bone fragility. Bone fracture is a key problem in osteoporosis, understanding bone fragility is hampered by the inaccessibility of bone investigation. Bone strength is one of bone mechanical properties reflect bone material composition and structure, which have a strong correlation to bone fracture. Researchers are motivated to look for methods to investigate bone strength for its great clinical and research value in helping understand the mechanism of bone fragility. A number of common methods have been developed for measuring or predicting bone strength, especially cancellous bone strength, but all this methods are focusing on hard tissues of cancellous bone, ignoring the soft tissue—bone marrow. Whether bone marrow does any contribution to bone biomechanics remains unknown yet.Previous studies reported that marrow fat was increased in osteoporotic patients, but studies on the relationship between bone strength and the increased marrow fat were still lacking. This study was proposed to investigate the marrow fat effect on trabecular bone biomechanics by simulation. Subjects were recruited from normal community and a quantitative computer tomography(QCT) scan on the L3 lumbar spine was applied on each subject. Finite element(FE) models of vertebra bone were established based on QCT images, where trabecular structures with and without marrow fat were investigated respectively. Anni-static compressive test was applied on the proposed models until to the appearance of fracture,simulation results were analyzed to investigate marrow fat effect.Simulation results show that trabecular bone with marrow fat had about 3%-9% less maximum stress in volume in trabeculae, but its average stress in volume was about 9%-56% larger than the model with only trabeculae. Larger average stress in volume and less maximum stress in volume may indicate a more uniform stress and energy distribution in trabecular subjects, which may reduce the risk of micro crack and bone fracture. We also investigate that models filled with marrow fat have a significant small strain energy density(SED) comparing to those with only trabeculae, this difference may indicate trabecular bone filled with marrow fat may suffer less stress or less deformation. This study also investigates the difference of marrow fat effect in different bone mineral density(BMD) groups people, results show that marrow fat have a larger contribution in low BMD groups and its contribution are varied with trabecular bone structure, marrow fat has a larger effect on models with less trabeculae. As a conclusion, marrow fat may enhance trabecular bone strength by balancing its stress and reducing its deformation when it was subject to a loading.