Abstract
We hypothesize that variations of body anthropometry, conjointly with the bone strength, determine the risk of hip fracture. To test the hypothesis, we compared, in a simulated sideways fall, the hip impact energy to the energy needed to fracture the femur. Ten femurs from elderly donors were tested using a novel drop-tower protocol for replicating the hip fracture dynamics during a fall on the side. The impact energy was varied for each femur according to the donor’s body weight, height and soft-tissue thickness, by adjusting the drop height and mass. The fracture pattern, force, energy, strain in the superior femoral neck, bone morphology and microarchitecture were evaluated. Fracture patterns were consistent with clinically relevant hip fractures, and the superior neck strains and timings were comparable with the literature. The hip impact energy (11 – 95 J) and the fracture energy (11 – 39 J) ranges overlapped and showed comparable variance (CV = 69 and 61%, respectively). The aBMD-based definition of osteoporosis correctly classified 7 (70%) fracture/non-fracture cases. The incorrectly classified cases presented large impact energy variations, morphology variations and large subcortical voids as seen in microcomputed tomography. In conclusion, the risk of osteoporotic hip fracture in a sideways fall depends on both body anthropometry and bone strength.
Highlights
Osteoporotic fractures are a burden for the public health costing 37 billion Euros in EU and 16 billion Dollars in USA every year.[6,24] Hip fractures occur when the hip load generated at the hip while falling exceeds its load bearing capacity, or strength.[5]
According to the World Health Organization (WHO), the diagnosis of osteoporosis and the consequent clinical indication for treatment of patients at risk of fracture is typically based on Dual-Energy Xray Absorptiometry (DXA) measurements of areal Bone Mineral Density, which represents a surrogate of hip strength.[8,26,27,28,51]
The variation of the hip impact energy caused by variation of body anthropometry was compared to that of hip fracture energy
Summary
Osteoporotic fractures are a burden for the public health costing 37 billion Euros in EU and 16 billion Dollars in USA every year.[6,24] Hip fractures occur when the hip load generated at the hip while falling exceeds its load bearing capacity, or strength.[5] Hip strength is a function of femur morphology, bone mineral density (BMD) and bone architecture[43,45,47] whereas the hip load experienced during a fall relates to the dynamics of the fall, the body size and shape, the stiffness of the hip, of its surrounding tissues and of the floor.[4,46,49] Yet, the interdependent role of hip strength and fall dynamics in osteoporotic hip fractures is unclear. Finite-element calculation of hip strength, taking in input the 3D morphology and BMD distribution of the hip from computed tomography (CT) images, showed 6–7% improved accuracy over corresponding aBMD measurements alone.[50]. Other authors developed multivariate statistical models using a variety of parameters, such as BMD, age, history of fragility fracture, pre-
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