Eccentric ankle arthritis in the sagittal plane: a novel description of anterior and posterior ankle arthritis.

Background: To report radiographic characteristics of anterior and posterior ankle arthritis, which demonstrates the eccentric narrowing of either aspect of the tibiotalar joint in the sagittal plane.

Methods: Radiographic analysis of 19 ankles with anterior arthritis and 16 ankles with posterior arthritis was performed, which were defined as having both (1) eccentric narrowing of the anterior or posterior tibiotalar joint space on lateral radiographs and (2) talar tilt angle less than 4 degrees on anteroposterior radiographs. Measured radiographic parameters were: Talar tilt angle, medial distal tibial angle (MDTA), talar center migration (TCM), anterior distal tibial angle (ADTA), tibial axis-to-talus ratio (TT ratio), talo-first metatarsal (Meary) angle, hindfoot alignment angle (HAA), hindfoot moment arm, and mechanical axis deviation (MAD). An Intergroup comparison analysis, including a normal control group, was also performed.

Results: The TT ratio was significantly different between each group, indicating a distinct talus position in the sagittal plane. The anterior group had a significantly larger TCM than the control group and lower ADTA compared to other groups, indicating medial translation of the talus and anterior opening of the tibial plafond. The posterior group demonstrated a significantly higher Meary angle and lower HAA compared to other groups and lower MDTA compared to the control group, indicating lower medial longitudinal arch, valgus heel alignment, and varus tibial plafond. The MAD was significantly higher in both the anterior and posterior groups than the control group, indicating varus lower limb alignment.

Conclusion: Anterior ankle arthritis demonstrated anteromedial translation of the talus and anterior opening of the tibial plafond. Posterior ankle arthritis was associated with the lower medial longitudinal arch and hindfoot valgus, indicating an association with flatfoot deformity. Both anterior and posterior ankle arthritis were associated with varus lower limb alignment.