Finite element analysis of proximal femoral nail anti-rotation in the treatment of osteoporotic AO3.3 intertrochanteric fracture

Abstract

Background: We aimed to use the finite element method to simulate the biomechanical effects of bone cement on the treatment of unstable intertrochanteric fractures with different degrees of osteoporosis using proximal femoral nail anti-rotation (PFNA) to provide personalized treatment plans for patients with type 31-A3.3 intertrochanteric fractures based on the AO Foundation/Orthopaedic Trauma Association classification. Methods: A finite element model of a normal right femur was created from CT images using related finite element analysis software, and its effectiveness was verified. In the experimental group, 12 types of fracture models with different degrees of osteoporosis were fixed using PFNA, while in the control group, 12 types of osteoporotic fracture models were fixed using bone cement augmented PFNA. A 700 N force was applied to the femoral head in a direction that simulated the direction of load-bearing while standing. The differences in the maximum displacement of the femur, PFNA, femoral stress, and varus angle between the two groups were observed and compared in ANSYS software. Results: Compared with the common PFNA model, the femoral head displacement, PFNA displacement, and varus angle of the femoral head were significantly smaller in the bone cement augmented PFNA model. However, the maximum stress in the femur was significantly increased. Compared with the experimental group, the change rate of femoral head displacement, PFNA displacement, and varus angle decreased from 2.94% to 5.89%, 3.23% to 4.79%, and 0.41% to 8.51% with increase in the degree of femur osteoporosis. The maximum stress change rate of the femur increased from 12.2% to 5.74%. Conclusion: Common PFNA for treatment of A3.3 intertrochanteric fracture is likely to fail in severe osteoporosis, and the varus angle and displacement can be significantly reduced with cement reinforcement. Therefore, PFNA internal fixation with bone cement should be considered for treatment of severe osteoporosis. When used in mild osteoporosis, bone cement increases the stress at the joint between the screw blade and the main nail; therefore, the use of PFNA alone should be considered for treatment in such cases to increase the service life of internal fixation devices.