Biomechanical efficacy of four different dual screws fixations in treatment of talus neck fracture: a three-dimensional finite element analysis

Background

Current there are different screws fixation methods used for fixation of the talar neck fracture. However, the best method of screws internal fixation is still controversial. Few relevant studies have focused on this issue, especially by finite element analysis. The purpose of this study was to explore the mechanical stability of dual screws internal fixation methods with different approaches and the best biomechanical environment of the fracture section, so as to provide reliable mechanical evidence for the selection of clinical internal fixation.

Methods

The computed tomography (CT) image of the healthy adult male ankle joint was used for three-dimensional reconstruction of the ankle model. Talus neck fracture and screws were constructed by computer-aided design (CAD). Then, 3D model of talar neck fracture which fixed with antero-posterior (AP) parallel dual screws, antero-posterior (AP) cross dual screws, postero-anterior (PA) parallel dual screws, and postero-anterior (PA) cross dual screws were simulated. Finally, under the condition of 2400N vertical load, finite element analysis (FEA) were carried out to compare the outcome of the four different internal fixation methods. The results of Von Mises stress, displacement of four groups which contain talus fracture fragments and screws internal fixations were analyzed.

Results

Compared with the other three groups, postero-anterior (PA) parallel dual screws had better results in the stress peak, stress distribution, and displacement of talus and internal fixation.

Conclusions

To sum up, the Von Mises stress of fracture section was the smallest, the stress distribution of screws were the most scattered, and the peak value was the smallest in posterior to anterior parallel double screws fixation, which was obviously better than that in the other three groups. When using screws internal fixation, the method of posterior to anterior screws fixation is better than that of anterior to posterior screws fixation, and the peak value and stress distribution of parallel double screws fixation is better than that of cross double screws fixation. Thus, for the talar neck fracture, the use of posterior to anterior parallel double screws fixation is recommended in clinical surgery.

Extruded talus treated with reimplantation and primary tibiotalocalcaneal arthrodesis

Extruded talus is a rare serious result from a high-energy injury to a supinated and plantar flexed foot. Treatment remains controversial with a lack of congruent evidence for talar reimplantation. A 34-year-old woman was involved in a road traffic accident at 40 mph. Imaging revealed a left talus extruded anterolaterally with a talar neck fracture. Additional injuries included right acetabular fracture, transverse process fractures and rib fractures, which were treated conservatively. The talus was reimplanted and the talar neck fixed with a cortical screw. A hindfoot nail was used to fuse the calcaneus, talus and tibia. Follow-up at two years showed solid tibiotalocalcaneal fusion, with no evidence of avascular development, and the patient was fully weight bearing without pain. We believe this is the first published case of successful primary tibiotalocalcaneal fusion for extruded talus injuries.