Date Published: June 13, 2018
Publisher: Public Library of Science
Author(s): Samuel Jesús Ramos-Infante, Amadeo Ten-Esteve, Angel Alberich-Bayarri, María Angeles Pérez, Martijn van Griensven.
This paper proposes a discrete particle model based on the random-walk theory for simulating cement infiltration within open-cell structures to prevent osteoporotic proximal femur fractures. Model parameters consider the cement viscosity (high and low) and the desired direction of injection (vertical and diagonal). In vitro and in silico characterizations of augmented open-cell structures validated the computational model and quantified the improved mechanical properties (Young’s modulus) of the augmented specimens.
Osteoporosis is a skeletal disease characterized by low bone mineral density (BMD) and micro-architectural deterioration of bone tissue, leading to increased bone fragility and risk of fracture . Osteoporotic proximal femur fractures are associated with high morbidity and dramatically reduce a patient´s quality of life . Although these events account for less than 20% of all osteoporotic fractures, they represent the majority of fracture-related health care expenditure and mortality in men and women over the age of 50 years .
A discrete particle model for cement infiltration based on the random-walk theory  is presented in this section (Fig 1), and in vitro and in silico characterizations of augmented open-cell structures are described (Fig 1). In vitro and in silico characterizations of non-augmented open-cell structures were performed in a previous study .
In general, the augmented specimens exhibited enhanced mechanical properties regardless of the direction of injection, cement viscosity or open-cell structure type (Table 2 and Fig 3). Low-viscosity cement showed better improvements for all the specimens and directions, except for specimen #30 and the diagonal direction (see Table 2 and Fig 3B). As specimen #30 showed the lowest porosity fraction (see Table 1), both cement viscosities were difficult to inject using the commercial injection system because cement was not able to reach neighbour pores as easily as it was in specimens #15 and #20, which had high porosity fractions. Although all the augmented specimens exhibited increased mechanical properties for all cement viscosities, the specimen with the highest porosity fraction (specimen #15), similar to osteoporotic bone, showed considerable improvements in mechanical properties (Fig 3) because the cement was able to infiltrate more fully. In addition, similar mechanical property improvements were achieved regardless of the direction of injection. However, we noted certain differences in specimen #20 (Fig 3), for which the diagonal injection showed better Young’s modulus improvements.
Augmentation of an osteoporotic femur using cement to prevent or reduce the risk of fracture has been suggested as an alternative preventive treatment . The results of the current study support our original hypothesis that femoroplasty increases the mechanical properties compared with non-augmented controls (Table 2 and Fig 3). A few recent studies have reported attempts at restoring the mechanical strength of femur specimens using a relatively small amount of infiltrated cement with limited or no success [12,15,18,24]. The procedure requires precise planning and execution. Effective planning relies on (among other factors) an accurate method for predicting the diffusion of the cement through the porous medium of osteoporotic trabecular bone. A crucial step in the planning process is to determine the optimum volume and filling pattern of the cement such that the best outcome is achieved . A successful planning framework should include a module for predicting the cement infiltration inside trabecular bone. The majority of fragility fractures occur at trabecular-dominant bone sites. Indeed, the trabecular bone plays important roles in the load transmission and energy absorption in major joints.