Comparison of radiological measures for diagnosing flatfoot

Background. In the Taiwanese military, flatfoot is indicated by a calcaneal-fifth metatarsal angle (arch angle) =165 deg . However, the arch angle is not always easily defined. Purpose. To assess correlations between the arch angle and other radiographic measures and thus identify an alternative radiographic measure for diagnosing flatfoot. Material and Methods Eighty-seven male Taiwanese military recruits were studied (median age 22 years, interquartile range 20-23 years). Lateral, weight-bearing radiographs were taken. Five radiographic measurements, including the calcaneal-fifth metatarsal angle (arch angle), medial arch angle (MAA), calcaneal pitch angle (CP), talus angle (TA), and talar-first metatarsal angle (TFM) were made. Correlations between the arch angle and all other measures were determined. A cut-off value for predicting flatfoot (arch angle ≥165 deg ) was determined for each measure using the Youden index and receiver-operating characteristic (ROC) curves were generated for each measure to assess diagnostic accuracy. Results. All measures were significantly correlated with arch angle (P < 0.05); however, the strongest correlation was for CP (ρ = -0.905, P < 0.001). CP was associated with the highest area under the ROC (0.988 vs. 0.711-0.912 for the other measures). Further, CP (cut-off <12.3 deg ) had the highest sensitivity (92.0%), positive predictive value (76.7%), and negative predictive value (96.5%). TFM (>9.5 deg ) had the highest specificity (90.3% vs. 88.75 for CP <12.3 deg ). Conclusion. CP is inversely correlated with arch angle in Taiwanese male military recruits. CP < 12.3 deg is a significant predictor of flatfoot. Assessment of CP may be used as an alternative means of diagnosing flatfoot when the arch angle is not easily defined