The arch index: a useful measure from footprints.

Previous methods of measuring footprints for the purpose of classifying foot type are reviewed. A planimetric method is presented for characterizing footprints using the ratio of the area of the middle third of the footprint to the entire footprint area (excluding the toes). This 'arch index' during 50% body weight standing provides an objective measure for comparative purposes with a measured reliability, within day and between day, of 0.96 and 0.94 respectively. Values measured from footprints taken during other activities show variable responses in different subjects. Examples of the arch index taken from static footprints of various feet are presented and data are reported from 107 randomly selected subjects during half body weight stance. Criteria are suggested for the classification of footprints as high, normal, and flat arch.