A simple personalised prediction model for hip fracture risk based on mechanistic parameters

Fragility hip fractures in older adults are a major burden for the individual and the society, as they result in increased morbidity, mortality and substantial health care expenditure. Most hip fractures are caused by falls, resulting in an impact on the postero-lateral aspect of the hip, inducing a force that exceeds the femoral bone strength. The risk of fracture depends on the rate of falling, the fall-induced impact force, and the femoral bone strength. This article presents the framework of a novel fragility hip fracture risk calculator based on a combined mechanistic and stochastic modelling approach. The model integrates the stochastic aspects of a fall and its dynamics together with a 1D mechanical model predicting the impact force in the hip to calculate a one-year absolute fracture risk. The required input parameters are based on QCT images, but can be substituted with more accessible anthropometric and densitometric data. To demonstrate how the parameters are extracted from clinical data and how the model is calibrated, data from the AFFIRM-CT cohort were used. A sensitivity analysis was conducted, confirming that the fall rate, the trochanteric soft tissue thickness and the bone strength are the dominating parameters influencing the risk of fragility hip fractures. Furthermore, output variables such as the predicted impact velocity and impact force aligned well with experimental data. Thus, the model is able to reflect observations from empirical data, indicating that it can capture the intrinsic aspects that define the risk of fragility hip fractures.