Abstract: BACKGROUND: At present, the surgical methods for ankle osteoarthritis include joint replacement and joint fusion, but both methods have certain problems. Therefore, ankle preservation therapy has become the first choice for the initial treatment of ankle osteoarthritis. Ankle distraction arthroplasty is an important ankle-preserving procedure, which is beneficial to relieve ankle pain and improve function, and contribute to the self-repair of articular cartilage, but there is still a lack of definite biomechanical evidence.  
OBJECTIVE: To explore the mechanical factors of ankle osteoarthritis without obvious force line change in the early and middle periods using ankle distraction arthroplasty through the finite element modeling to provide mechanical evidence for clinical treatment.
METHODS: The DICOM file of CT scan data of the foot and ankle of a 27-year-old volunteer was imported into the finite element software for three-dimensional reconstruction and curved surface fitting. The mesh was divided to establish a fine foot and ankle finite element model with bones, ligaments, tendons and cartilage. The biomechanical responses of tibiotalar joint surface stress, talus stress, and talus strain under three different working conditions of 0° neutral, 20° plantar flexion, and 20° dorsiflexion were compared between the ankle osteoarthritis and external fixator groups.  
RESULTS AND CONCLUSION: (1) Through the finite element simulation calculation, it was found that the overall stress of the ankle joint was smallest in the two groups of models when the neutral position was 0°. When the neutral position was gradually flexion or dorsiflexion, the stress value gradually increased with the change of ankle joint activity. Under the same flexion condition, the overall stress of dorsiflexion was significantly greater than that of the plantar flexion. (2) In terms of the peak stress of the tibiotalar ankle joint, the peak value of the stress of the talar joint surface in the ankle osteoarthritis group increased significantly than that in the normal group, and the peak value of the stress of the tibiotalar joint surface in the external fixator group decreased significantly. (3) For the overall deformation of the ankle joint, the overall deformation of the ankle osteoarthritis group increased the most in the neutral position, while the overall deformation of the external fixator group decreased the most. (4) For the talar stress, the stress of the talus in the ankle osteoarthritis group increased in different degrees under three working conditions. The stress of the talus in the external fixator group decreased, especially in the neutral position. (5) In terms of the forward distance of the talus, the forward distance of the talus in the ankle osteoarthritis group decreased significantly compared with that in the normal group, while the forward distance of the talus in the external fixator group did not increase significantly. (6) It is concluded that through the finite element simulation analysis of two groups of ankle models under different working conditions, it is confirmed that the clinical application of ankle distraction arthroplasty can alter the mechanical stress of tibiotalar joint surface and talus in patients with ankle osteoarthritis, improve the mechanical distribution of the local joints, and delay the development of ankle osteoarthritis.

Key words: traction arthroplasty, ankle, osteoarthritis, biomechanics, finite element analysis