Coronal plane Calcaneal-Talar Orientation in Varus Ankle Osteoarthritis

Abstract

Background: We do not yet fully understand how the subtalar joint position is related to the varus osteoarthritic ankle joint. The purposes of this study were (1) to investigate the coronal orientation of the calcaneus relative to the talus according to the ankle osteoarthritis stage, talar tilt (TT), and (2) to determine if there is TT threshold at which apparent subtalar compensation begins to fade. Methods: We retrospectively reviewed 132 ankles that underwent weightbearing computed tomography (WBCT) for varus ankle osteoarthritis. The TT, subtalar inclination angle (SIA), and calcaneal inclination angle (CIA) were measured using WBCT. Ankles were divided into 5 groups according to Takakura stage and 2 groups according to the apparent compensation status of the subtalar joint and compared the index of the inclination of the subtalar joint relative to the ankle (SIA) or the index of the inclination of the calcaneus relative to the ankle (CIA). Additionally, we explored the relationship between SIA or CIA and the TT. Results: Apparent subtalar compensation (SIA and CIA) was significantly lower in Takakura stages 3b and 4. The SIA and CIA significantly differed according to the apparent compensation status ( P < .001 and P = .030, respectively). The CIA of the noncompensated group varied widely, whereas the SIA was relatively constant. Furthermore, TT was greater than 9.5, which indicated a high probability of a noncompensated heel (sensitivity, 92.6%; specificity, 89.7%). Conclusion: The position of the calcaneus appears compensatory with coronal plane orientation in varus ankle osteoarthritis when the TT is ≤9.5 degrees. Level of Evidence: Level III, retrospective case control study.

Hindfoot motion according to subtalar compensation and ankle osteoarthritis stage analyzed by a multi-segment foot model

“…Even if the hindfoot appears to be in varus on X-ray, the compensation status of the subtalar joint vary when assessed using WBCT. The calcaneus may exhibit both varus and valgus orientations relative to the talus [ 19 ]. Therefore, further research is needed to investigate the relationship between hindfoot alignment assessed by WBCT and MFM analysis in the future.…”

“…To determine the presence of subtalar compensation, the apparent moment arm was measured on hindfoot alignment radiography [ 18 ]. If the perpendicular distance between the longitudinal midaxis of the distal tibia and the lowest point of the calcaneus (i.e., apparent moment arm) was less than 15 mm, the ankle was classified into the compensated group; otherwise, it was classified into the decompensated group [ 19 ]. Twenty ankles were categorized as compensated group, and 34 ankles as decompensated group.…”