Biomechanical Study of Screw Fixation and Plate Fixation of a Posterior Malleolar Fracture in a Simulation of the Normal Gait Cycle.

Background: Fixation of posterior malleolar fractures with plates or screws is under debate. A fatigue loading system and a spatial motion capture system were used in this study to evaluate a posterior malleolar fracture model.

Methods: Thirty-six below-knee specimens with a single posterolateral fragment (Haraguchi I) type posterior malleolar fracture models were randomly divided into 2 groups. Two parallel-placed 3.5-mm partially threaded titanium alloy screws were used in Group A to fix the fractures, while anatomical plates were used in Group B. According to the ratio (S) of the area between the fracture and the total articular surface, each group was subdivided into 3 subgroups. In group A1 and B1, S=1/4; in A2 and B2, S=1/3; and in A3 and B3, S=1/2. To simulate the gait cycle, each specimen was subjected to mechanical loading in 4 different ankle positions. A fatigue loading system was used for repeated loading. A spatial motion capture system was used to measure the displacement in the final loading stage.

Results: Despite the limited sample size and relatively low power, no significant difference was observed between A1 and B1, A2 and B2, and A3 and B3 in all 4 ankle positions after repeated loading.

Conclusion: For a Haraguchi type I posterior malleolar fracture with an average height of 19 mm, fixation with a posterior malleolar anatomical plate failed to demonstrate a stronger strength than 2 parallel-placed 3.5-mm partially threaded screws, which indicates that plates may not be absolutely necessary for standard rehabilitation after posterior malleolar internal fixation.

Clinical Relevance: These findings may help guide surgeons with regard to fixation requirements for posterior malleolar fractures.