A Particle Model for Prediction of Cement Infiltration of Cancellous Bone in Osteoporotic Bone Augmentation

Abstract

Femoroplasty is a potential preventive treatment for osteoporotic hip fractures. It involves augmenting mechanical properties of the femur by injecting Polymethylmethacrylate (PMMA) bone cement. To reduce the risks involved and maximize the outcome, however, the procedure needs to be carefully planned and executed. An important part of the planning system is predicting infiltration of cement into the porous medium of cancellous bone. We used the method of Smoothed Particle Hydrodynamics (SPH) to model the flow of PMMA inside porous media. We modified the standard formulation of SPH to incorporate the extreme viscosities associated with bone cement. Darcy creeping flow of fluids through isotropic porous media was simulated and the results were compared with those reported in the literature. Further validation involved injecting PMMA cement inside porous foam blocks - osteoporotic cancellous bone surrogates - and simulating the injections using our proposed SPH model. Millimeter accuracy was obtained in comparing the simulated and actual cement shapes. Also, strong correlations were found between the simulated and the experimental data of spreading distance (R(2) = 0.86) and normalized pressure (R(2) = 0.90). Results suggest that the proposed model is suitable for use in an osteoporotic femoral augmentation planning framework.

Figure 1. Initial particle arrangement for Darcy flow simulation.

Black particles represent the porous medium (porosity of 0.5) and white particles represent the fluid.

Figure 2. Experimental setup.

Figure 3. Sample original (A) and masked (B) CT slice and an example of fixed particles arrangement (C).

Figure 4. Representative steady-state Darcy velocity as a function of body force for various porosities.

Figure 5. Dimensionless permeability vs. porosity.

Figure 6. Effect of particle size on the accuracy of the cement cloud.

Figure 7. Comparison between isosurfaces of post-operative CTs and simulated image volumes.

Figure 8. Simulated vs. experimental mean cement spreading distance.

Figure 9. Normalized outlet cement pressure compared between experiments and simulations.

Figure 10. Normalized pressure over the course of injection for example viscosity extremes.

Figure 11. Sample slices taken at 5-mm intervals from the post-operative and simulated CT volumes.

Figure 12. Segmented X-ray snapshots and the corresponding segmented DRR images for two extreme viscosity injections.

The dark lines represent the cannulae.