Influence of bone lesion location on femoral bone strength assessed by MRI-based finite-element modeling

Abstract

Currently, clinical determination of pathologic fracture risk in the hip is conducted using measures of defect size and shape in the stance loading condition. However, these measures often do not consider how changing lesion locations or how various loading conditions impact bone strength. The goal of this study was to determine the impact of defect location on bone strength parameters in both the sideways fall and stance-loading conditions. We recruited 20 female subjects aged 48-77 years for this study and performed MRI of the proximal femur. Using these images, we simulated 10-mm pathologic defects in greater trochanter, superior, middle, and inferior femoral head, superior, middle, and inferior femoral neck, and lateral, middle, and medial proximal diaphysis to determine the effect of defect location on change in bone strength by performing finite element analysis. We compared the effect of each osteolytic lesion on bone stiffness, strength, resilience, and toughness. For the sideways fall loading, defects in the inferior femoral head (12.21%) and in the greater trochanter (6.43%) resulted in the greatest overall reduction in bone strength. For the stance loading, defects in the mid femoral head (-7.91%) and superior femoral head (-7.82%) resulted in the greatest overall reduction in bone strength. Changes in stiffness, yield force, ultimate force, resilience, and toughness were not found to be significantly correlated between the sideways fall and stance-loading for the majority of defect locations, suggesting that calculations based on the stance-loading condition are not predictive of the change in bone strength experienced in the sideways fall condition. While stiffness was significantly related to yield force (R² > 0.82), overall force (R² > 0.59), and resilience (R² > 0.55), in both, the stance-loading and sideways fall conditions for most defect locations, stiffness was not significantly related to toughness. Therefore, structure-dependent measure such as stiffness may not fully explain the post-yield measures, which depend on material failure properties. The data showed that MRI-based models have the sensitivity to determine the effect of pathologic lesions on bone strength.

Keywords: Lesion location; Proximal femur; Sideways fall; Stance; Stiffness; Strength.

Figure 1:

The element level nonlinear stress-strain relationship used for finite element modeling.

Figure 2:

High-Resolution MRI and simulated defect locations

Figure 3:

Reduction in strength due to defects at each location. The percent reduction in strength is calculated as (strength without lesion – strength with lesion) * 100 / (strength without lesion).

Figure 4:

Strain Distribution of Greater Trochanter Lesion

Figure 5:

Strain Distribution of Proximal Diaphysis Lesions. Arrows point to visible differences in strain.

Figure 6:

Strain Distribution of femoral neck lesions. Arrows point to visible differences in strain.

Figure 7:

Strain Distribution of femoral head lesions. Arrows point to visible differences in strain.