The study of bone remodeling, how bone tissue changes over time due to the activity of bone cells, is fundamental for the better understanding of musculoskeletal diseases and to design new treatments.
Bone adapts to external loading and exercise can be used to stimulate the formation of new tissue in order to strengthen the bones. Animal studies on small rodents, in particular mice and rats, provide a good environment to study bone remodeling related to controlled mechanical stimuli. In these experiments, the mouse is placed under anesthesia for a few minutes and its leg is positioned between two loading plates and small, high rate loads are imposed to the limb between the knee and the ankle. This procedure, that is associated with minimal discomfort for the animals, aims to apply an axial load to the tibia that would stimulate cell activity and increasing the bone mass. Nevertheless, considering the complexity of the mechanical test, it is impossible to control the transverse loading, which could affect dramatically the deformation of the bone, which drives the bone formation.
Therefore, the aim of this study was to combine state of the art experimental and image processing approaches to evaluate the realistic deformation imposed to the mouse tibia during these experiments. We designed a small loading device that replicates the loading conditions imposed during one of the animal experiments. We mechanically tested three hindlimbs dissected from cadaver mice used in previous studies with that jig, which can be placed inside a high-resolution scanning machine. We acquired high-resolution three-dimensional images of the mouse tibia before and after the load was imposed, by using a micro computed tomography. Finally we processed the collected images with a digital volume correlation (DVC) approach developed in the MULTISIM project. This approach allows computing the deformation of the bone under the specific loading condition.
With this workflow we showed for the first time the realistic deformation of the bone in typical loading experiments. Moreover, we have shown that the loading protocol can induce pretty different deformations according to the positioning of the bone in the testing machine.
These results are fundamental for the development of computational models for predicting bone remodeling over time, one of the main objectives of the MULTISIM consortium.
Giorgi, M., Dall’Ara, E. (2018), “Variability in strain distribution in mice tibia loading model: A preliminary study using digital volume correlation”, Medical Engineering & Physics