Measuring arch height is a way to characterize foot shape and foot structure; it is also a means to compare these characteristics between a sitting and a standing position. To measure arch height the patient first sits in a chair and places their feet on the ground. Two boards are placed under the heel and the metatarsal heads to allow for maximum collapse of the arch.
A left and right jig is then used to measure the foot length and truncated foot length (foot length from the heel until the first metatarsophalangeal joint). The arch height is then measured from 1/2 the footlength with a free-falling bar. These measurements are recorded and the patient is then asked to stand.
From a standing position the measurements are taken again.With this data arch height index in sitting and standing, arch rigidity index, and arch drop are measured for each foot. This geometry-based arch height measurement is shown to be repeatable.
Arch Height Index (AHI) = Arch Height at ½ Foot Length / Truncated Foot Length-sitting
Arch Rigidity Index (ARI) = Standing AHI / sitting AHI
Arch Drop (mm) = Arch Height at ½ Foot Length sitting – Arch Height at standing