Sideways fall-induced hip fracture is a major worldwide health problem among the elderly population. Biomechanical modeling is a practical way to study hip fracture risk. However, all existing biomechanical models for assessing hip fracture risk mainly consider the femur-related parameters. Their accuracy is limited as hip fracture is significantly affected by loading conditions as well. The objective of this study is to introduce a two-level subject-specific model to improve the assessment of hip fracture risk. The proposed biomechanical model consists of a whole-body dynamics model and a proximal femur finite element model, which are constructed from the subject’s whole-body and hip DXA (dual energy X-ray absorptiometry) scan. The whole-body dynamics model is used to determine the impact force onto the hip during a sideways fall. Obtained load/constraint conditions are applied to the finite element model in order to determine the stress/strain distribution in the proximal femur. Fracture risk index is then defined over the critical locations of the femur using the finite element solutions. It is found that hip fracture risk is significantly affected by the subject’s body configuration during the fall, body anthropometric parameters, trochanteric soft tissue thickness, load/constraint conditions, and bone mineral density, which are not effectively taken into account by currently available hip fracture discriminatory tools. Predicted hip fracture risk of 130 clinical cases, including 80 females and 50 males, by the proposed model reveals that biomechanical determinants of hip fracture differ widely from individual to individual. This study presents the first in-depth subject-specific model that provides a comprehensive, fast, accurate, and non-expensive method for assessing the hip fracture risk. The proposed model can be easily adopted in clinical centers to identify patients at high risk of hip fracture who may benefit from the in-time treatment to reduce the fracture risk. / May 2016