Validity and diagnostic accuracy of foot posture Index-6 using radiographic findings as the gold standard to determine paediatric flexible flatfoot between ages of 6-18 years: A cross-sectional study.

BACKGROUND

Diagnosis of flexible flatfoot is usually based upon radiographic or clinical measures. Radiographic measures pose a potential risk of radiation exposure especially in Paediatric population. Clinicians need a valid, accurate, easily used, noninvasive and cost effective measure to evaluate static foot posture clinically. Although, foot posture index-6 (FPI-6) are commonly used in clinical practice, its validity and diagnostic accuracy in evaluation of paediatric flexible flatfoot have not been fully proven yet.

OBJECTIVES

To investigate validity and diagnostic accuracy of FPI-6 to determine Paediatric flexible flatfoot between ages of 6-18 years using radiographic findings as the gold standard measure.

STUDY DESIGN

Cross-sectional study.

METHODS

A cross-sectional study conducted on 612 participants (1224 feet) with flexible flatfoot aged 6-18 years (mean age ± standard deviation of 12.36 ± 3.39 years). The results of FPI-6 were compared to the gold standard radiographic measures and displayed on the receiver operating characteristic curve. Intra-rater reliability, sensitivity, specificity, predictive values and likelihood ratios were calculated. Posttest probability was calculated from Fagan nomogram.

RESULTS

FPI-6 demonstrate high intra-rater reliability (ICC = 0.96) with p value < 0.001. FPI-6 showed a sensitivity of 83.7%, a specificity of 80.4, a positive predictive value of 64.7, a negative predictive value of 92, a positive likelihood ratio of 4.62 and a negative likelihood ratio of 0.20. FPI-6 shows moderate diagnostic accuracy [AUC = 0.82; 95%CI (0.78-0.85)].

CONCLUSION

FPI-6 is valid with moderate diagnostic accuracy to determine paediatric flexible flatfoot between ages of 6-18 years.