[Biomechanical effects of three internal fixation modes on femoral subtrochanteric spiral fractures in osteoporotic patients by finite element analysis].

OBJECTIVE

The biomechanical characteristics of three internal fixation modes for femoral subtrochanteric spiral fracture in osteoporotic patients were compared and analyzed by finite element technology, so as to provide the basis for the optimization of fixation methods for femoral subtrochanteric spiral fracture.

METHODS

Ten female patients with osteoporosis and femoral subtrochanteric spiral fractures caused by trauma, aged 65-75 years old, with a height of 160-170 cm and a body weight mass of 60-70 kg, were selected as the study subjects. The femur was scanned by spiral CT and a three-dimensional model of the femur was established by digital technology. The computer aided design models of proximal intramedullary nail (PFN), proximal femoral locking plate (PFLP), and the combination of the two (PFLP+PFN) were constructed under the condition of subtrochanteric fracture. Then the same load of 500 N was applied to the femoral head, and the stress distribution of the internal fixators, the stress distribution of the femur, and the displacement of femur after fracture fixation were compared and analyzed under the three finite element internal fixation modes, so as to evaluate the fixation effect.

RESULTS

In the PFLP fixation mode, the stress of the plate was mainly concentrated in the main screw channel, the stresses of the different part of the plate were not equal, and gradually decreased from the head to the tail. In the PFN fixation mode, the stress was concentrated in the upper part of the lateral middle segment. In the PFLP+PFN fixation mode, the maximum stress appeared between the first and the second screws in the lower segment, and the maximum stress appeared in the lateral part of the middle segment of the PFN. The maximum stress of PFLP+PFN fixation mode was significantly higher than that of PFLP fixation mode, but significantly lower than that of PFN fixation mode ( <0.05). In PFLP and PFN fixation modes, the maximum stress of femur appeared in the medial and lateral cortical bone of the middle femur and the lower side of the lowest screw. In PFLP+PFN fixation mode, the stress of femur concentrated in the medial and lateral of the middle femur. There was no significant difference in the maximum stress of femur among the three finite element fixation modes ( >0.05). The maximum displacement occurred at the femoral head after three finite element fixation modes were used to fix subtrochanteric femoral fractures. The maximum displacement of femur in PFLP fixation mode was the largest, followed by PFN, and PFLP+PFN was the minimum, with significant differences ( <0.05).

CONCLUSION

Under static loading conditions, the PFLP+PFN fixation mode produces the smallest maximum displacement when compared with the single PFN and PFLP fixation modes, but its maximum plate stress is greater than the single PFN and PFLP fixation mode, suggesting that the combination mode has higher stability, but the plate load is greater, and the possibility of fixation failure is higher.