Quantitative comparison of plantar foot shapes under different weight-bearing conditions.

Knowledge of the plantar foot shape alteration under weight bearing can offer implications for the design and construction of a comfortable and functional foot support. The purpose of this study was to quantify the change in three-dimensional foot shape under different weight-bearing conditions. The plantar foot shapes of 16 normal feet were collected by an impression casting method under three weight-bearing conditions: non-weight bearing, semi-weight bearing, and full-weight bearing. An optical digitizing system was used to capture the three-dimensional plantar surface shape of the foot cast. Measurements and comparisons from the digitized shapes were conducted for the whole foot and regions of the foot. The data showed that increased weight bearing significantly increased the contact area, foot length, foot width, and rearfoot width, while it decreased average height, arch height, and arch angle. Compared with the non-weight-bearing foot shape, the semi-weight-bearing condition would produce increases in the contact area of 35.1% +/- 21.6 %, foot length of 2.7% +/- 1.2%, foot width of 2.9% +/- 2.4%, and rearfoot width of 5.9% +/- 4.8%, and decreases in the arch height of 15.4% +/- 7.8% and arch angle of 21.7% +/- 17.2%. The full-weight-bearing condition would produce increases in the contact area of 60.4% +/- 33.2%, foot length of 3.4% +/- 1.3%, foot width of 6.0% +/- 2.1%, and rearfoot width of 8.7% +/- 4.9%, and decreases in the arch height of 20.0% +/- 9.2% and arch angle of 41.2% +/- 16.2%. The findings may be useful for considering the change of foot shape in the selection of shoe size and shoe or insole design.