found that most of these factors are directly or indirectly linked to subjects’ BMI (body mass index). Thus, from a statistical perspective, BMI could be an overall indicator of the probability of femur fracture from a sideways fall. Using a biomechanics approach coupled with statistical data we investigate this relationship with a large cohort of postmenopausal women aged 50-79 from WHI-OS (Women’s Health Initiative Observational Cohort). The cohort is divided into six sub-cohorts by BMI where each fall-related factor is examined and compared with each other. Significant differences are discovered among cohorts in terms of femur size, aBMD (areal bone mineral density), peak fall force based on kinematics, and maximum von Mises stresses induced in the proximal femur. Through a probabilistic margin of safety approach which has been recently applied to orthopedic application, we found the margin of safety predicted probability to be decreasing faster with increasing BMI and better v fitted with medical record of the identical cohort compared to that found using a deterministic risk factor approach. To promote the application in other situations, tumor damaged femur bones are examined and tested for possible stress concentration effect in terms of probability of failure. The influence of tumor lesion turned out to be size and location sensitive. The superior side of the femoral neck has the highest stress concentration effect from tumor lesion where a 4mm diameter lesion could result in a 1.7 times greater maximum von Mises stress and 2.95 times greater probability of failure.