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Mimics Assists in Understanding Cement – Bone Interface Micromechanics
Case presented by Janssen D., Mann K.A., Verdonschot N. – Radboud University Nijmegen Medical Centre, The Netherlands, SUNY Upstate Medical University, NY, USA
Finite Element Simulation of Cement – Bone Interface Micromechanics; a Comparison to Experimental Results
The researchers in this case were seeking a closer look at the micromechanical behavior in the human femur mantle of bone cement, the adhesive used by orthopaedic surgeons in joint replacement surgery. Their question was whether an FE analysis would yield the same information on the interface’s properties as previously discovered by conducting direct experiments. They turned to Mimics as the perfect partner for the preparation of scanner data for FEA.
The cement-bone interface consists of complex structures of cement penetrating into bone lacunar spaces, creating an interlock between bulk cement and bone. The interface provides the fixation of the cement mantle in the femur. As a result, the stability of the cement mantle and the implant are dependent on the mechanical behavior of the cement-bone interface. In order to improve the longevity of cemented implants and, consequently, patient care, it is therefore vital to understand the micromechanical behavior of the cement-bone interface.
One of the main advantages of FEA is its ability to isolate clinical variables and study their effect on the mechanical behavior of reconstructions in a clean, controlled manner. However, the reliability of FEA studies strongly depends on the accuracy of the experimental and clinical data used as input for the models. Therefore, the researchers turned to Mimics to prepare their cement-bone interface specimens for the final analyses. The specimens used in the experiments were prepared from cemented total hip arthroplasties in fresh-frozen proximal femurs. µCT scans were taken to mirror the real situation as good as possible. These were imported in Mimics, where the scanner data were segmented into cement and bone based on the image grayscale. The researchers needed to investigate the reaction force and local displacements of the different parts of the specimen (cement, bone and interface between the two) separately. Mimics allowed the researchers to make this distinction easily by performing the segmentation based on µCT grayscale. Based on these values, Mimics also allowed the research team to assign material properties to the solid FEA model after optimizing the volume mesh.
The FEA simulation duplicated the data obtained in the clinical experiments in several areas. The predicted stress-strain curves were similar, and the simulations also showed
that the majority of the deformation took place at the cement-bone interface. There was, however, some disparity between the simulated and experimental stiffness values and in the amount of hysteresis found. Still, the researchers considered the models a success in terms of achieving their goal: reproducing and predicting the behavior of the bone cement where it interfaces with the femur mantle. Their discoveries in this area will help orthopaedic surgeons in selecting the best possible techniques for ensuring anchorage of the bone cement in the femur.
Mimics played a crucial role in helping the team to explore potential uses for FEA simulation of clinical trails on solid models created from scan data. Mimics’ imaging and meshing capabilities allowed them to create 3D models of a very complex, little-known phenomenon, the cement-bone interface in hip replacement surgery. It also shed light on ways to improve on the creation of such models, as well as providing suggestions for future innovations in simulating aspects of joint replacement surgery.
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