Finite element analysis of osteoporotic femur with PFNA fixation

Hip fracture happens to the upper segment of femur, known as the thigh bone. Its probability increases when one gets older due to compound effect of osteoporosis or sarcopenia. Fractures occurring in the specific region of the femur, between the intertrochanteric and subtrochanteric regions, are considered unstable and require specific surgical intervention. The two most common methods are sliding hip screw-plate constructs and cephalomedullary nails. Recently, cephalomedullary nails have overtaken the former as the most used implant in the surgical fixation of this type of fracture. Among these, the short cephalomedullary nail serves as the preferred option not only for its multiple mechanical advantages but also for its cost-effectiveness. However, the short proximal femoral nail anti-rotation (PFNA) implant may not be sufficient to provide adequate stability when the distal extension of the fracture increases. This study aims to determine the maximum range of distal extension length of subtrochanteric fractures appropriate for short PFNA implants.
This research used a new model with a slimmer shaft and osteoporotic mechanical properties. In addition, this study starts from a new baseline which is recently refined, excluding the range from the baseline to 30 mm, as it has been previously validated. Simulation was conducted for different lengths of distal extension, with progressively reduced increment to identify the failure range. The trends of stiffness and vertical force show close agreement with previous studies.
The simulation results indicated that the PFNA-II implant may fail at a distal extension length of more than 35 mm. The findings under this new baseline model indicate that bones in different states (healthy or unhealthy) may have different critical value for distal extension, and it demands further investigation.