Foot asymmetry in healthy adults: elliptic fourier analysis of standardized footprints

The size and shape of paired structures differ in the left and right sides of the body. Shape characteristics should be analyzed separately from size to supply information about the normal variations of human organs. In the present study, the within-subject normal symmetry of footprint shape and size was analyzed from a mathematical standpoint. On the standardized left and right footprints of 46 healthy adults (23 women and 23 men; 19-26 years old), the outline of each foot excluding the toes was identified and its shape was quantified independently from size by the elliptic Fourier analysis. The symmetry in shape was quantified on an intra-subject basis by calculating a morphologic distance D between the mathematical reconstructions of the left and right footprints of each subject. Symmetry in size was assessed by the right-to-left area ratio and found to be very good for all subjects; it ranged from 0.948 to 1.049. The subjects were also grouped by sex, and mean values were calculated. Within-subject symmetry in the footprint shape appeared high, with morphologic distances ranging between 8.94 and 2.66 in men and between 7.15 and 3.09 in women. No consistent associations between footprint symmetry and age, body height and weight, or shoe size were found. On average, women had more symmetric size-standardized footprints than did men (women: mean 4.57, SD 1.14; men: mean 5.46, SD 1.7; p < 0.05). Mean size-independent shapes of male and female left and right footprints were also calculated. Together with the analysis of individual asymmetry, they could be used for the quantitative diagnosis of borderline patients.