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

BackgroundThe 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.MethodsVarus, valgus, dorsiflexion, and plantarflexion type fractures were categorized as type I, II, III, and IV, respectively. The buttress plate was placed medially in subtypes IA and IIB, whereas it was placed anterolaterally in subtypes IB and IIA; The anterior or posterior buttress plate was utilized in subtypes IIIA and IVA, the lag screws were applied in subtypes IIIB and IVB. The maximum equivalent stress of tibia (TI-Smax) and implants (IF-Smax), stress of fracture fragments (Sfe), and axial displacement values of the fracture fragments (ADfe) in each subtype were analyzed when the ankle was in a neutral position, 15 degrees of varus and valgus in types I and II, 15 degrees of dorsiflexion and plantarflexion in types III and IV.ResultsUnder the same axial stress loading conditions, TI-Smax, Sfe, ADfe of subtypes IA and IIA were significantly lower than subtypes IB and IIB, while IF-Smax of subtypes IA and IIA were obviously larger than subtypes IB and IIB. Additionally, TI-Smax, Sfe, ADfe of subtypes IIIA and IVA were considerably lower as IF-Smax met expectations compared to subtypes IIIB and IVB.ConclusionBased 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.