Plantar pressure and sole thickness of the forefoot

Background. Based on earlier observations that the forefoot bears the highest plantar pressure at its center, the existence of a functional distal transverse arch in normal feet was denied, and plantar pressure was defined as merely the outcome of loading, surface area, and soft tissue. Although plantar pressure drives the changes in the foot, neither the position nor the behavior of the metatarsals during loading can be derived from plantar pressure alone. In light of this, our goal was to describe the changes in thickness in the sole and the corresponding plantar pressure during loading of the foot. Methods: We used CT to image the foot of 10 subjects in four postures that were chosen to imitate four phases in the walking cycle. Before imaging we also recorded the plantar pressure with a pressure measuring insole on which the subjects were standing. From the data, he minimal thickness of the sole and the corresponding plantar pressure were derived. Results: With the exception of the sesamoids, the thickness of the sole under the bones of the forefoot increased from lateral to medial. This persisted in all postures. Our pressure readings matched previously reported distributions. Conclusions: Depending on the point of view concerning the sesamoids, the bony prominences were placed in a geometrical arch; but they did not form a functional arch. The soft tissue underneath the heads kept the metatarsals in place; the soft-tissue thickness reflected the principle of adequate cushioning.