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The safety factor of the human femur during daily activity
DOI:10.1038/bonekey.2015.18
In this study, CT scans from the healthy femur of 116 women and 84 men undergoing investigations for hip arthritis in the opposite leg were analyzed using a model that estimated the loading conditions at the hip during walking and climbing stairs.
The subjects were aged between 23 and 84; as expected, volumetric bone mineral density at the femur decreased significantly with advancing age, reducing almost twice as much in women compared to men. The authors calculated the femoral safety factor for both activities in all subjects; this never reached unity (which would have meant the activity caused fracture) and observed an average safety factor of five across all subjects.
While the safety factor decreased significantly with age in women, with the lowest values apparent in very elderly women with osteoporosis, it remained stable in elderly men. This could help explain why elderly women most frequently experience femoral and hip fractures.
Major limitations of the study were that the model used involved gait data obtained from healthy subjects rather than being subject specific and that the subjects chosen were showing osteoarthritis of the opposing hip.
Editor’s comment: The mean safety factor for the human femur is high, approximately five, and decreased with age in women but not in men. The challenge for future studies will be to interpret the important standard deviation observed for this safety factor in men and women.
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