PREDICTION OF PROXIMAL FEMORAL FRACTURE IN SIDEWAYS FALLS USING NONLINEAR DYNAMIC FINITE ELEMENT ANALYSIS

Abstract

Hip fracture incidence caused by sideways falls is increasing year by year. The high morbidity and mortality not only cast a gloom over the life, but also increase the medical cost of the country. From a biomechanical perspective, hip fractures are related to different loading directions. The main purpose of this study is to investigate how different hip fracture types are affected by impact directions. The geometry of a proximal femur was obtained from the CT scan data of a 67-year-old Chinese male. Mimics and Ansys softwares were applied to establish the cortical bone and cancellous bone models. Six different loading cases, i.e., SW1 (α = 120°, β = 0°), SW2 (α = 90°, β = 0°), SW3 (α = 60°, β = 0°), SW4 (α = 20°, β = 0°), SW5 (α = 120°, β = 15°), SW6 (α = 120°, β = 45°) were defined as the angle α with reference to the long axis of the femur in the frontal plane, and β with reference to the femoral neck axis in the horizontal plane. They were established to simulate sideways falls by explicit dynamic nonlinear finite element analyses in ANSYS-LS-DYNA software. The impact speed was 3.17 m/s. Stress and strain analyses with time history of the fracture sites were taken to find the relationships between fracture types and impact directions. SW1–SW4 caused femoral neck fractures, and the maximum principal stresses were 4.5, 6, 5 and 4.8 MPa, respectively. SW5 caused compound fractures including neck fracture and trochanteric fracture, and the maximum principal stresses were 6.8 MPa and 6.5 MPa, respectively. SW6 caused trochanteric fracture, and the maximum principal stress was 4.2 MPa. The maximum principal strains of neck fracture (0.075, 0.135, 0.175, 0.092) and trochanteric fracture (0.045) increased to the maximum values in 10 ms after impact, and were much higher than the ultimate compressive strain of cancellous bone. These results were consistent with the clinical findings. This study showed that falling posture was an important factor leading to different types of fracture. Dynamic simulation was more effective in explaining the fracture mechanism and determining the load direction that caused hip fracture. The study also provided a theoretical basis for more targeted preventive measures for different types of hip fracture in clinics.