The etiology of the end-stage varus type ankle arthritis evaluated by weight-bearing simulated computed tomography

Abstract

Category: Ankle Arthritis Introduction/Purpose: In the patients with the varus type ankle arthritis, the stage of disease was classified according to the narrowing of tibiotalar joint using the weight-bearing ankle radiography. By the Takakura-Tanaka classification, the stage 4 ankle arthritis indicates more than half of the joint space was disappeared in the tibiotalar joint. Inclination of the surface of tibiotalar joint in the patients with stage 4 ranges from neutral to severely varus, that may confuse the etiology of staged ankle arthritis. The purpose of this study was clarifying the etiology of the stage 4 ankle arthritis combined with evaluating the syndesmotic instability using the weight-bearing simulated computed tomography(CT). Methods: Forty nine ankles with stage 4 varus type ankle arthritis were investigated. A weight-bearing simulated CT scan was taken in the neutral position of the ankle with a 300 N pressure from plantar side. In the axial view of the CT at 1 cm proximal to the tibial plafond, the distance between the fibula and the tibia was measured as the fibular clear space (FCS-CT). In the anteroposterior view of the weight-bearing radiography of the ankle, the angle between the tibial shaft and the joint surface of the distal end of the tibia was measured as the tibial anterior surface angle(TAS-Xp). The Pearson correlation coefficient was obtained to identify the correlations between the FCS-CT and the TAS-Xp. P values <0.05 were considered statistically significant. Results: The FCS-CT was 4.3±1.2 mm. The TAS-Xp was 81±4.9°. According to the Pearson correlation coefficient between the FCS-CT and the TAS-Xp, positive correlations were identified (r=0.45; p=0.0011). Conclusion: This study revealed the correlation between the inclination of the distal joint surface of the tibia and distance of the tibiofibular syndesmosis. In the patients with larger FCS-CT, syndesmotic instability may exist, that may lead to the distributed share stress in the tibiotalar joint without the inclination of the joint surface. In the patients with smaller FCS-CT, the varus stress directly transfer to the ankle joint, that may cause to the varus inclination of the distal joint surface of the tibia.