[Biomechanics test of fixation of star-shaped six-part patellar fractures with petal-shaped poly-axial locking plate].

Objective: To compare the biomechanical difference between petal-shaped poly-axial locking plate and tension band wire cerclage in fixing star-shaped 6-part patellar fractures in cadaver model, and provide the experimental data for clinical use.

Methods: The paired 12 knee specimens from 6 human cadavers were randomly divided into 2 groups (the control group and the test group) after a star-shaped 6-part patellar fracture model was established. The specimens were weighted, and the control group was fixed with tension band wire cerclage and the test group was fixed with petal-shaped poly-axial locking plate. The specimens were connected to CMT5105 biomechanics test machine by a customized fixture, the total fracture gap of patellar fracture blocks was measured before testing. The knee extensor load test was performed to record the extensor load of knees at 90° flexion to extension. Then the anti gravity physiological knee extension process at 90° flexion was stimulated according to the knee extensor load. The cyclic times until failure and the total fracture gap of patellar fracture blocks after failure were recorded.

Results: The specimens weight and the total fracture gap of patellar fracture blocks before testing between 2 groups had no significant difference ( t =0.410, P =0.690; t =0.650, P =0.530). In the biomechanical test, there was no significant difference of knee extension load between 2 groups ( t =0.490, P =0.638). The total fracture gap after failure in test group was significantly smaller than that in control group ( t =3.026, P =0.013), and the cyclic times until failure in test group was significantly more than that in control group ( t =2.277, P =0.046). The failure reasons in control group were all the wires slipped off the Kirschner wires, while the failure reasons in test group were the screws pulled out from the upper pole in 5 cases (83.3%) and from the lower pole in 1 case (16.7%).

Conclusion: The petal-shaped poly-axial locking plate has better biomechanical stiffness to fix the star-shaped 6-part patellar fractures when compared with tension band wire cerclage method. However, this type of fracture is a serious comminuted type, and the early excessive activity still carries the risk of displacement.