Background: The radius/length (R/L) ratio was developed to evaluate the convexity of the talar dome in idiopathic clubfoot. However, the index has not been tested for its reliability and reproducibility.
Methods: The R/L ratio was determined by three independent observers on the radiographs of 21 adult patients with idiopathic clubfoot and 30 adult subjects with normal feet. The reproducibility and the reliability of the R/L ratio were calculated.
Results: For the normal feet the reproducibility and the reliability of the R/L ratio was high (correlation coefficient > 0.87). For the patients with clubfoot, the reliability and reproducibility depended on the severity of talar flattening. For a radius of less than 45 mm the mean intraobserver correlation coefficient was 0.74 (range 0.54 to 0.83) and the mean interobserver correlation coefficient was 0.58 (range 0.49 to 0.75). For a radius of more than 45 mm no statistically significant intraobserver and interobserver correlations were found.
Conclusion: The current results indicate that the R/L ratio of talar flattening is reliable and reproducible for mild talar deformity but not for severe flattening (radius of more than 45 mm).