In Vivo Assessment of Age- and Loading Configuration-Related Changes in Multiscale Mechanical Behavior of the Human Proximal Femur Using MRI-Based Finite Element Analysis.

ABSTRACT

BACKGROUND: MRI-based finite element analysis (MRI-FEA) is the only method able to assess microstructural and whole-bone mechanical properties of the hip in vivo. PURPOSE: To examine whether MRI-FEA is capable of discriminating age-related changes in whole-bone mechanical performance and micromechanical behavior of the proximal femur, particularly considering the most common hip fracture-related sideways fall loading. STUDY TYPE Retrospective. SUBJECTS: A total of nine younger (27 ± 3.2 years) and nine elderly (61 ± 3.9 years) healthy volunteers. FIELD STRENGTH/SEQUENCE 3T; 3D fast field echo sequence. ASSESSMENT The left proximal femurs were scanned and FE models created. FEA was performed to simulate sideways fall and stance loading for each femoral model. Apparent stiffness and high-risk (90th percentile) tensile and compressive strains of the proximal femur as well as the average strains within cubic regions of the femoral neck and greater trochanter were assessed. STATISTICAL TESTS Paired and unpaired t-tests. RESULTS: Compared to the young group, the femoral stiffness of the elderly decreased by 39% and 40% (both P < 0.05) under the sideways fall and stance conditions, respectively. Accordingly, the high-risk tensile and compressive stains were elevated with aging (40% and 23% for sideways fall, 23% and 11% for stance conditions; all P < 0.05). However, the loading configuration-induced difference was only observed in the elderly group for the high-risk strains (22% for tension and 12% for compression; both P < 0.05). Additionally, compared to the stance condition, the sideways fall increased the average tensile (young 108%, elderly 123%; both P < 0.05) and compressive strains (young 631%, elderly 617%, both P < 0.05) within the greater trochanter rather than the femoral neck region. DATA CONCLUSION: In vivo MRI-FEA is capable of capturing age-related changes in both apparent-level stiffness and tissue-level micromechanical behavior of the proximal femur. However, the effect of sideways fall loading might be better reflected by tissue-level micromechanics rather than apparent stiffness. LEVEL OF EVIDENCE 3 TECHNICAL EFFICACY STAGE 1.