Two types of cannulated screw fixation based on Letenneur classification for the treatment of Hoffa fracture: A finite element analysis.

Purpose: A finite element analysis was performed to simulate the biomechanical differences between anterior-posterior (AP) direction and posterior-anterior (PA) direction placement of two cannulated screws in Hoffa fractures.

Methods: Computed tomography images of an healthy male volunteer were used to simulate Letenneur Ⅰ, Ⅱa, Ⅱb, Ⅱc, Ⅲ Hoffa fractures, and two groups of screw internal fixation models were constructed. Two 6.5 mm cannulated screws were implanted parallel in the AP direction or the PA direction. The biomechanical test was performed to determine the displacement, stress distribution, and peaks in the distal femur and cannulated screws in 10 models.

Results: The displacement distribution and peak values of the distal femur and cannulated screws in both groups were similar, and displacement increasing as the load increased. The stress distribution in the distal femur was similar between the two groups, with stress mainly concentrated on both sides of the fracture line, the posterolateral and anterior aspects of the femoral shaft. The peak stress in the PA group of the Letenneur type Ⅱb was significantly higher than that in the AP group, and the stress in the distal femur increased with increasing load. The stress distribution in the cannulated screws of Letenneur Ⅰ, Ⅱa, Ⅱb, and Ⅲ, was similar, but differences are observed between the two groups in type Ⅱc. The stress in the cannulated screws increased with increasing load, and the peak values in the PA group are significantly higher than those in the AP group.

Conclusion: The mechanical stability of the two screw insertion methods is similar. Inserting screws from anterior to posterior can reduce the stress on the distal femur and cannulated screws, and also minimize the dissection of the posterior soft tissues. Therefore, inserting screws from anterior to posterior is a more recommended surgical approach for Hoffa fractures.