Validity of the Most Common Footprint Indices in Measuring Medial Longitudinal Arch in Comparison with a Radiographic Method as a Gold Standard

Measurement of the medial longitudinal arch (MLA) of the foot is a controversial issue in orthopedics. Using footprint parameters is considered as the most common method to evaluate MLA. Present study aimed to determine validity of footprint indices in measuring medial longitudinal arch in comparison with radiography method. Forty-one subjects were randomly selected. Footprints were recorded in static bipedal standing position using ink and paper. Arch index, footprint index, Chippaux-Smirak index, and Staheli index were calculated from the footprints. Also, calcaneal inclination, calcaneal-first metatarsal, talo-calcaneal angles and navicular height were obtained from lateral feet radiographs as a golden standard method for evaluating the static posture of the foot. All measurements of footprints and radiographs were calculated by a technique in computerized image analysis based on Adobe Photoshop software. Pearson correlation coefficient was used to determine validation. Results showed a strong relationship between the values of footprint indices and calcaneal inclination angle, calcaneal-first metatarsal angle and talo-calcaneal angle obtained from radiography (r=0.56 to 0.72). The highest correlation coefficient (r = 0.72) was observed between Staheli index and calcaneal inclination angle and the lowest correlation coefficient (r=0.56) was between the arch index and calcaneal inclination angle whereas no significant relationship was found between footprint indices and navicular height obtained from radiography. Analysis of footprint indices had an acceptable validity in measuring the medial longitudinal arch. Therefore, this method is recommended to be used as a valid, non-invasive, quick, cost-effective and accurate method for measuring MLA.