A biomechanical comparison of posterior malleolar fracture fixation using screws and locking plates in Trimalleolar fractures: a finite element study

Abstract

Background: The aim of the study is to compare the mechanical stability of posterior malleolar fractures fixed with different screw types and locking plates in the management of trimalleolar ankle fractures using the finite element (FE) method.

Methods: An FE model containing the distal tibia, fibula, talus, and calcaneus was created based on the computed tomographic images of a healthy man without any musculoskeletal disorders. The medial, lateral, and posterior malleoli were segmented using three virtual planes to create a trimalleolar fracture model, with the posterior malleolar fracture fragment comprising approximately 30% of the articular surface. Four different fixation approaches, including two partial thread cannulated screws (PTS), two full thread cannulated screws (FTS), and L-shaped (LLP) and T-shaped (TLP) locking plates with screws, were used to fix the posterior malleolar fracture. Two partial thread screws and a locking plate along with screws were used to fix the medial and lateral malleolar fractures, respectively. Two different loading conditions, namely static axial load and Achilles tendon force, were considered in the simulation.

Results: Under axial load, the maximum gap opening distance of the posterior malleolar fracture with screws only was obviously larger than that with locking plates. The maximum gap distance was 0.12 mm, 0.08 mm, 0.04 mm, and 0.05 mm in the PTS, FTS, LLP, and TLP, respectively. Under Achilles tendon force, the maximum gap opening distance were 0.12, 0.1, 0.03, and 0.1 mm, in the PTS, FTS, LLP, and TLP, respectively, under Achilles tendon force.

Conclusion: The results suggest that locking plates offer greater stability and reduce the fracture gap opening for posterior malleolar fractures involving 30% of the distal tibial articular surface in the fixation of trimalleolar ankle fractures.

Keywords: Finite element study; Locking plates; Posterior malleolar fracture; Trimalleolar fractures.

Fig. 1

The models of medial, posterior and lateral malleolar fractures

Fig. 2

The models of trimalleolar fractures with different plates

Fig. 3

The boundary conditions used in this study

Fig. 4

Comparisons of the maximum displacement (a) and total strain energy (b) with different nodes, and the comparison of stiffness (c) with the published study

Fig. 5

Total displacement of the entire model (upper row) and the fractured posterior malleolus (lower row) with different fixation approaches under axial compression

Fig. 6

Comparisons of maximum displacement and gap opening distance under axial compression load (a and b) and Achilles tendon force (c and d)

Fig. 7

Equivalent stress of the implants under axial compression load

Fig. 8

Total displacement of the entire model (upper row) and the fractured posterior malleolus (lower row) with different fixation approaches under Achilles tendon force

Fig. 9

Equivalent stress of the implants under Achilles tendon force