Validity of plantar surface visual assessment as an estimate of foot arch height

Popular running magazines and running shoe companies advise using the shape of the weight-bearing plantar surface of the foot as a basis for selecting a proper type of running shoe to reduce injury risk. The imprint is assumed to reflect the height of the medial longitudinal arch (MLA). This study examined the assumption that plantar surface morphology was a surrogate for height of the MLA.

Recruits (n = 3968) entering US Army Basic Combat Training had their plantar foot surfaces assessed visually as low, normal, or high by two raters who viewed imprints of the plantar foot surface. Actual arch height was measured with calipers as distance from the standing surface to the inferior medial border of the navicular tuberosity. Measured MLA heights were compared with plantar surface imprints to evaluate the effectiveness of visual inspection as a means of arch height classification.

For the right foot, individuals with low, normal, or high plantar shapes had a mean +/- SD arch height of 33.5 +/- 6.8, 40.4 +/- 7.2, and 43.1 +/- 7.3 mm, respectively (ANOVA, P < 0.01); however, the individuals' measured MLA heights fell into the corresponding plantar shape percentiles (low, normal, high) only 65% of the time. Increased body mass index (BMI) decreased correct assessment of the MLA.

Visual assessment of indicating progressively higher plantar shapes corresponded to progressively higher average differences in measured arch heights; nonetheless, there was considerable overlap among the three plantar shapes with 35% of plantar shapes being misclassified compared with measured arch height, especially among individuals with higher BMI.