Femoral Head Lag Screw Position for PFN: A Biomechanical Analysis

Objective To compare the biomechanical properties of two lag screws proximal femoral nail(PFN) when they are placed in different points of the neck of femur in the treatment of intertrochanteric fracture of femur. Method Three pairs of fresh femora of adults aging from 55 to 65 are taken. They are made into AO type A1.1 intertrochanteric fracture. Fracture specimens are fixed by PFN. The mechanical testing machine loads the fracture model at a speed of 0.5mm/s. The stress distribution of the fracture broken ends, the opening angle of the fracture broken ends, and the relationship between load and displacement are recorded respectively. Result The stress change of the group inferior of the small trochanter is smaller than that of the group superior. The opening angle of the fracture of the group inferior is smaller than that of the group superior. The displacement of the top of the femoral head of the group inferior is smaller than that of the group superior. Conclusion The performance of the group inferior is better than that of the group superior. Thus it can be concluded that when two lag screws of PFN were placed in the middle and below 1/3 part of femoral neck, the biomechanical properties are better, the structure is relatively more stable, and the stress bearing is more reasonable.