Background: Clinical diagnosis of pediatric flexible flatfoot is still a challenging issue for health-care professionals. Clarke’s angle (CA) is frequently used clinically for assessing foot posture; however, there is still debate about its validity and diagnostic accuracy in evaluation of static foot posture especially in the pediatric population, with some previous studies supporting and others refuting its validity. The present study aimed to investigate the validity and diagnostic accuracy of the CA using radiographic findings as a criterion standard measure to determine flexible flatfoot between ages 6 and 18 years.
Methods: A cross-sectional study of 612 participants (1224 feet) with flexible flatfoot aged 6 to 18 years (mean ± SD age, 12.36 ± 3.39 years) was recruited. The clinical measure results were compared with the criterion standard radiographic measures and displayed on the receiver operating characteristic curve, and the area under the curve was computed. Intrarater reliability, sensitivity, specificity, predictive values, and likelihood ratios were calculated for the CA. A Fagan nomogram was used to detect post-test probability.
Results: The CA demonstrated higher intrarater reliability (intraclass correlation coefficient = 0.997), sensitivity (98.4%), specificity (98.8), positive predictive value (97.3), negative predictive value (99.3), positive likelihood ratio (84), and negative likelihood ratio (0.02). The area under the curve was 0.98. The positive likelihood ratio yielded a post-test probability of 97%, and the negative likelihood ratio yielded a post-test probability of 0.02.
Conclusions: The CA is a valid measure with high diagnostic accuracy in the diagnosis of flexible flatfoot between ages 6 and 18 years.