Subject-specific ex vivo simulations for hip fracture risk assessment in sideways falls

• Published in: Bone (New York, N.Y.) Vol. 125; pp. 36 - 45
• Main Authors: Fleps, Ingmar, Fung, Anita, Guy, Pierre, Ferguson, Stephen J., Helgason, Benedikt, Cripton, Peter A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.08.2019
• ISSN: 8756-3282; 1873-2763; 1873-2763
• DOI: 10.1016/j.bone.2019.05.004

The risk of hip fracture of a patient due to a fall can be described from a mechanical perspective as the capacity of the femur to withstand the force that it experiences in the event of a fall. So far, impact forces acting on the lateral aspect of the pelvic region and femur strength have been investigated separately. This study used inertia-driven cadaveric impact experiments that mimic falls to the side from standing in order to evaluate the subject-specific force applied to the hip during impact and the fracture outcome in the same experimental model. Eleven fresh-frozen pelvis-femur constructs (6 female, 5 male, age = 77 years (SD = 13 years), BMI = 22.8 kg/m2 (SD = 7.8 kg/m2), total hip aBMD = 0.734 g/cm2 (SD = 0.149 g/cm2)), were embedded into soft tissue surrogate material that matched subject-specific mass and body shape. The specimens were attached to metallic lower-limb constructions with subject-specific masses and subjected to an inverted pendulum motion. Impact forces were recorded with a 6-axis force plate at 10,000 Hz and three dimensional deflections in the pelvic region were tracked with two high-speed cameras at 5000 Hz. Of the 11 specimens, 5 femur fractures and 3 pelvis fractures were observed. Three specimens did not fracture. aBMD alone did not reliably separate femur fractures from non-fractures. However, a mechanical risk ratio, which was calculated as the impact force divided by aBMD, classified specimens reliably into femur fractures and non-fractures. Single degree of freedom models, based on specimen kinetics, were able to predict subject-specific peak impact forces (RMSE = 2.55% for non-fractures). This study provides direct evidence relating subject-specific impact forces and subject-specific strength estimates and improves the assessment of the mechanical risk of hip fracture for a specific femur/pelvis combination in a sideways fall. •Eleven subject-specific post mortem human sideways fall simulations using full femur-pelvis constructs embedded in surrogate soft tissue.•Impact conditions representative of a fall from standing with a greater trochanter impact velocity of 3.1 m/s.•Clinical relevant impact outcomes: five femur fractures, three pelvis fractures, and three non-injurious impacts.•Femoral aBMD alone was not able to discriminate between falls leading to femoral fractures and non-injurious falls.•The Mechanical Risk Ratio (MRR) allowed for discrimination between falls leading to femoral fractures and non-injurious falls.