Finite element analysis applied to 3-T MR imaging of proximal femur microarchitecture: lower bone strength in patients with fragility fractures compared with control subjects

Abstract

Purpose: To determine the feasibility of using finite element analysis applied to 3-T magnetic resonance (MR) images of proximal femur microarchitecture for detection of lower bone strength in subjects with fragility fractures compared with control subjects without fractures.

Materials and methods: This prospective study was institutional review board approved and HIPAA compliant. Written informed consent was obtained. Postmenopausal women with (n = 22) and without (n = 22) fragility fractures were matched for age and body mass index. All subjects underwent standard dual-energy x-ray absorptiometry. Images of proximal femur microarchitecture were obtained by using a high-spatial-resolution three-dimensional fast low-angle shot sequence at 3 T. Finite element analysis was applied to compute elastic modulus as a measure of strength in the femoral head and neck, Ward triangle, greater trochanter, and intertrochanteric region. The Mann-Whitney test was used to compare bone mineral density T scores and elastic moduli between the groups. The relationship (R(2)) between elastic moduli and bone mineral density T scores was assessed.

Results: Patients with fractures showed lower elastic modulus than did control subjects in all proximal femur regions (femoral head, 8.51-8.73 GPa vs 9.32-9.67 GPa; P = .04; femoral neck, 3.11-3.72 GPa vs 4.39-4.82 GPa; P = .04; Ward triangle, 1.85-2.21 GPa vs 3.98-4.13 GPa; P = .04; intertrochanteric region, 1.62-2.18 GPa vs 3.86-4.47 GPa; P = .006-.007; greater trochanter, 0.65-1.21 GPa vs 1.96-2.62 GPa; P = .01-.02), but no differences in bone mineral density T scores. There were weak relationships between elastic moduli and bone mineral density T scores in patients with fractures (R(2) = 0.25-0.31, P = .02-.04), but not in control subjects. CONCLUSION Finite element analysis applied to high-spatial-resolution 3-T MR images of proximal femur microarchitecture can allow detection of lower elastic modulus, a marker of bone strength, in subjects with fragility fractures compared with control subjects. MR assessment of proximal femur strength may provide information about bone quality that is not provided by dual-energy x-ray absorptiometry.

Figure 1:

Image analysis workflow. A, After a bone-volume fraction map was generated from high-spatial-resolution MR images of the proximal femur, five volumes of interest (VOIs) were selected. All were 10 mm³, with the exception of Ward triangle, which was selected as 8 mm³ to fit in the trabecular bone compartment. B, FEA was performed on each VOI by simulating compressive loading along three principle axes.

Figure 2:

Representative coronal high-spatial-resolution 3-T MR images of proximal femur microarchitecture in a subject with osteoporotic fracture (left panel) and a control subject (right panel). Trabeculae are hypointense linear foci. There is deterioration in trabecular microarchitecture in the fracture subject compared with the control subject.

Figure 3:

Volume-rendered bone volume fraction maps (BVF) in a subject with osteoporotic fracture (left panel) and a control subject (right panel). The subject with fracture shows lower regional bone volume and deterioration in trabecular microarchitecture compared with the control subject.