Assessment of hip protectors and corresponding hip fracture risk using stress calculation in the femoral neck

Abstract 

As in many countries, a significant increase in the number of hip fractures is predicted due to the demographic changes in the population. To reduce the consequences for the patients and the social costs, hip protectors are considered to be effective in reducing the impact force on the hip and so to reduce the risk of hip fractures. The effectiveness of hip protectors has been investigated as well in experimental impact tests as in clinical studies, but there is still an uncertainty about their mechanical protection effect. Therefore, laboratory tests are an effective way to investigate the mechanical behaviour of hip protectors. A fracture is initiated by exceeding an ultimate compressive or tensile stress. In our model, stresses in the femoral neck are estimated by using the Euler beam formula. A standard femur was defined consisting of all mechanical parameters that have been identified to influence the mechanical resistance to external loads, such as the effective cross-sectional area (CSA), cross-sectional moment of inertia (CSMI), femoral neck width (FNW), centre of mass and other geometric parameters of the femur. In this study the necessary formulae as well as first results of assessing hip protectors on the basis of stresses in the femoral neck are presented. The results show that the methodology facilitates assessment and improvement of hip protectors, as the biomechanical parameters of real femora are the basis of the model.

Keywords: Femoral neck fracture, Femoral neck stresses, Safety factor, Hip protectors