Subject-specific planning of femoroplasty: A combined evolutionary optimization and particle diffusion model approach

Abstract

A potential effective treatment for prevention of osteoporotic hip fractures is augmentation of the mechanical properties of the femur by injecting it with agents such as (PMMA) bone cement – femoroplasty. The operation, however, is only in research stage and can benefit substantially from computer planning and optimization. We report the results of computational planning and optimization of the procedure for biomechanical evaluation. An evolutionary optimization method was used to optimally place the cement in finite element (FE) models of seven osteoporotic bone specimens. The optimization, with some inter-specimen variations, suggested that areas close to the cortex in the superior and inferior of the neck and supero-lateral aspect of the greater trochanter will benefit from augmentation. We then used a particle-based model for bone cement diffusion simulation to match the optimized pattern, taking into account the limitations of the actual surgery, including limited volume of injection to prevent thermal necrosis. Simulations showed that the yield load can be significantly increased by more than 30%, using only 9ml of bone cement. This increase is comparable to previous literature reports where gross filling of the bone was employed instead, using more than 40ml of cement. These findings, along with the differences in the optimized plans between specimens, emphasize the need for subject-specific models for effective planning of femoral augmentation.

Subject-specific planning of femoroplasty: An experimental verification study

“…BESO simulations generally suggested augmentation of superior and inferior aspects of the neck as well as supero-posterior aspect of the greater trochanter (Basafa & Armand, 2014) to achieve the desired outcome with the least amount of cement. For the simulated augmentation plans (using at most 9ml of cement injection to match the optimally found BESO volume), FE analyses predicted an average yield load of 3101(±718)N for the augmented femora (38% increase compared to the control group, P<0.001).…”

“…We have described in detail our proposed planning strategy of femoroplasty elsewhere (Basafa & Armand, 2014). Briefly, eight pairs of osteoporotic femur specimens, five males and three females, obtained from the Maryland State Anatomy Board, were cleaned of soft tissue, computed tomography (CT) scanned (Aquilion 64 CT System, Toshiba America Medical Systems, Tustin, CA), and subsequently frozen at -20°C.…”

“…In a recent report (Basafa & Armand, 2014), we described our approach to computer-assisted planning of femoroplasty to optimize cement volume and placement. In summary, we showed that by introducing less than 10ml of bone cement into the femur (substantially less than the 40-50ml volumes used in previous experimental studies (Beckmann et al, 2007; Heini et al, 2004; Sutter et al, 2010a)), it is possible to increase the yield load of the femur specimens by greater than 30%.…”

Numerical investigation of the effect of bone cement porosity on osteoporotic femoral augmentation

“…Therefore, there are considerable risks involved in femoral augmentation when using large amounts of PMMA: bone necrosis because of high temperatures, risk of cement leakage into the blood vessels, or development of regions of stress concentration. To this end, computational studies have been conducted to determine the optimum amount of bone cement and injection locations to minimize the aforementioned possible side effects …”

“…Given the volume of the published computational studies, it is clear that results from numerical simulations depend on a variety of factors such as the bone morphology, the degree of osteoporosis, the imposed boundary conditions, and the material properties of the augmented bone . The bone geometry, the degree of osteoporosis, and the respective material properties are often obtained from a computed tomography scan . Similarly, the most commonly used boundary conditions in the experimental and computational study of femoroplasty replicate a lateral fall on the greater trochanter .…”