Optimal biomechanical choice of implant placement in various pilon fracture types: a finite element study

The research on the biomechanical characteristics of individual implant placement for pilon fractures based on the different initial direction of fracture displacement is still insufficient. This study's aim is to compare the stress distribution in bones and implants with various pilon fracture types.

Varus, valgus, dorsiflexion, and plantarflexion type fractures were categorized as type I, II, III, and IV, respectively. The buttress plate was placed medially in subtypes I_A and II_B, whereas it was placed anterolaterally in subtypes I_B and II_A; The anterior or posterior buttress plate was utilized in subtypes III_A and IV_A, the lag screws were applied in subtypes III_B and IV_B. The maximum equivalent stress of tibia (TI-S_max) and implants (IF-S_max), stress of fracture fragments (S_fe), and axial displacement values of the fracture fragments (AD_fe) in each subtype were analyzed when the ankle was in a neutral position, 15° of varus and valgus in types I and II, 15° of dorsiflexion and plantarflexion in types III and IV.

Under the same axial stress loading conditions, TI-S_max, S_fe, AD_fe of subtypes I_A and II_A were significantly lower than subtypes I_B and II_B, while IF-S_max of subtypes I_A and II_A were obviously larger than subtypes I_B and II_B. Additionally, TI-S_max, S_fe, AD_fe of subtypes III_A and IV_A were considerably lower as IF-S_max met expectations compared to subtypes III_B and IV_B.

Based on these results, when making decisions for open reduction and internal fixation in various pilon fractures, the choice and placement of the implant can be recommended as follows: the medial buttress plate for varus types; the anterolateral plate for valgus types; the anterior plate for dorsiflexion types; the posterior plate for plantarflexion types.