title: Comparison of radiological measures for diagnosing flatfoot.
abstract: BACKGROUND
  In the Taiwanese military, flatfoot is indicated by a calcaneal-fifth metatarsal angle (arch angle) ≥165°. However, the arch angle is not always easily defined.
  
  
  OBJECTIVE
  To assess correlations between the arch angle and other radiographic measures and thus identify an alternative radiographic measure for diagnosing flatfoot.
  
  
  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°) 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°) had the highest sensitivity (92.0%), positive predictive value (76.7%), and negative predictive value (96.5%). TFM (>9.5°) had the highest specificity (90.3% vs. 88.75 for CP <12.3°).
  
  
  CONCLUSIONS
  CP is inversely correlated with arch angle in Taiwanese male military recruits. CP < 12.3° 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.
authors.affiliation: Department of Radiology, Taoyuan Armed Forces General Hospital, Taiwan. huanchu_lo@126.com
authors.forename: Huan-Chu
authors.initials: HC
authors.lastname: Lo
authors.forename: Wen-Cheng
authors.initials: WC
authors.lastname: Chu
authors.forename: Wei-Kai
authors.initials: WK
authors.lastname: Wu
authors.forename: Hsin
authors.initials: H
authors.lastname: Hsieh
authors.forename: Chieh-Ping
authors.initials: CP
authors.lastname: Chou
authors.forename: Shao-En
authors.initials: SE
authors.lastname: Sun
authors.forename: Pin-Ya
authors.initials: PY
authors.lastname: Chou
authors.forename: Chen-Hui
authors.initials: CH
authors.lastname: Liao
authors.forename: Xiao-Yun
authors.initials: XY
authors.lastname: Guan
authors.forename: Shu-Chee
authors.initials: SC
authors.lastname: Li
mesh_terms: D000328:Adult; D002111:Calcaneus / Q000000981:diagnostic imaging; D005413:Flatfoot / Q000000981:diagnostic imaging*; D005528:Foot / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D008682:Metatarsal Bones / Q000000981:diagnostic imaging; D011237:Predictive Value of Tests; D012372:ROC Curve; D011859:Radiography; D012680:Sensitivity and Specificity; D013624:Taiwan; D013628:Talus; D055815:Young Adult