Talar Center of Migration Ratio (TCM-R) as a Reliable Ratio-Based Method for Measuring Talar Translation on Noncalibrated Radiographs: A Short Report

Background: Coronal talar translation is an important marker of deformity in ankle arthritis, and its correction is vital in total ankle replacement (TAR). The current method for measuring this deformity is talar center of migration (TCM). We developed a novel method, TCM-Ratio (TCM-R), to measure talar translation accurately across all talus sizes using noncalibrated radiographs. Furthermore, we aimed to describe correlations between TCM-R and concomitant procedures during TAR. Methods: Patients were collected from a single-institution prospective TAR registry from June 2023 to May 2024. Inclusion criteria were preoperative calibrated weight-bearing radiographs. For each patient, 4 raters measured the TCM (distance from center of talus to mechanical axis of tibia) and the TCM-R (talar displacement divided by talar radius). Intraclass correlation coefficients (ICCs) were used to assess inter-rater agreement. Pearson correlations were used to assess agreement between TCM-R and TCM. Results: Fifty-eight patients were included, 60.3% male, with mean age 64.8 ± 9.4 years, and mean BMI 30.0 ± 4.7. Inter-rater agreement was excellent for TCM (ICC = 0.914) and TCM-R (ICC = 0.944). TCM-R was highly correlated with TCM ( R = 0.95, CI 0.91-0.97, P < .001). The mean absolute value of TCM-R was 13.89% ± 11.29% (range, −34.57% to +47.53%). Conclusion: We described a new ratio-based method, TCM-R, to measure coronal talar translation, obviating the need for calibrated radiographs while accounting for variations in talar size. TCM-R had excellent inter-rater reliability and strongly correlated with TCM. Level of Evidence: Level IV, case series.