Validity and Reliability of Digital Navicular Drop Equipment in Young People with and without Pes Planus

Background The navicular drop test (NDT) is clinically useful, but its reliability varies depending on the examiner’s skill. As an alternative, digital navicular drop test equipment (D-NDT) has been developed, but it needs to be validated. Purpose This study investigated the diagnostic validity and inter-rater reliability of D-NDT in adults with and without pes planus. Study design A case–control study. Methods We enrolled 52 participants: 26 with normal feet and 26 with pes planus. To assess the diagnostic validity of the D-NDT, all participants randomly underwent the NDT and used the D-NDT at least three times. Three raters assessed the reliability of the D-NDT based on the data for 10 participants randomly selected from each group. Results The correlation between the NDT and D-NDT grades was good in the normal (p<0.001, r =0.650) and pes planus (p<0.001, r=0.740) groups. The inter-rater reliability of the total D-NDT grade was good (ICC2,1=0.702) in the normal group and excellent (ICC2,1=0.773) in the pes planus group. Conclusions D NDT showed high diagnostic validity, with excellent inter rater reliability for participants with pes planus.