A subject-specific integrative biomechanical framework of the pelvis for gait analysis

Drying irreversibly affects the elastic behavior of pelvic cortical bone

Various studies have shown that the water content affects the elastic behavior of cortical bone. However, there is disagreement regarding the reversibility of the elastic behavior with rewetting. This study investigates this issue using an intrinsic approach, i.e., moisture manipulation and material testing were always carried out on the same specimen. The test results were then evaluated separately for each of several specimens. In total, 24 specimens of human cortical bone from the ischiopubic ramus were examined. The water content was varied in 11 steps, and the corresponding elastic moduli were determined using three-point bending tests within the elastic range. Moisture adjustment was achieved mainly using desiccators, accelerated by forced convection. Reference samples stored in the same manner were evaluated microscopically. The experiments confirmed the known correlation between water content reduction and stiffness increase of cortical bone. Complete drying increased the elastic modulus by about 83 %. By rewetting, the stiffness was significantly reduced again, though not only to the initial state, but even about 24 % below this. Thus, an irreversible alteration of the elastic behavior was observed. Decay of the reference samples was not observed. Therefore, decay is not the main reason for the significant loss of stiffness. In terms of the storage conditions for cortical bone specimens, an environment with 100 % relative humidity yielded the best match with the initial state. This storage method can therefore be recommended for biomechanical specimens used to determine in-vivo-like material parameters.

An Integrated Method of Biomechanics Modeling for Pelvic Bone and Surrounding Soft Tissues

The pelvis and its surrounding soft tissues create a complicated mechanical environment that greatly affects the success of fixing broken pelvic bones with surgical navigation systems and/or surgical robots. However, the modeling of the pelvic structure with the more complex surrounding soft tissues has not been considered in the current literature. The study developed an integrated finite element model of the pelvis, which includes bone and surrounding soft tissues, and verified it through experiments. Results from the experiments showed that including soft tissue in the model reduced stress and strain on the pelvis compared to when it was not included. The stress and strain distribution during pelvic loading was similar to what is typically seen in research studies and more accurate in modeling the pelvis. Additionally, the correlation with the experimental results from the predecessor's study was strong (R² = 0.9627). The results suggest that the integrated model established in this study, which includes surrounding soft tissues, can enhance the comprehension of the complex biomechanics of the pelvis and potentially advance clinical interventions and treatments for pelvic injuries.