The influence of metatarsal support height and longitudinal axis position on plantar foot loading

Abstract Background: Metatarsal supports are effective at decreasing plantar foot pressures at the metatarsal heads, however, little is known about the dependence of this decrease upon height and position. Methods: Barefoot static stance pressure measurements were recorded during standing in single limb support ( n = 22). Two metatarsal support heights (5 mm, 10 mm) were evaluated in six positions at 5 mm increments (0, 5, 10, 15, 20, 25 mm) proximal to the metatarsal heads along the longitudinal axis of the foot. The barefoot condition with no metatarsal support served as the control. Mean force was measured for each test condition. The findings of this study are limited to the barefoot (unshod) condition. Findings: Mean plantar force decreased significantly under the second metatarsal head with both 5 and 10 mm metatarsal supports compared to the control, and 10 mm metatarsal support compared with 5 mm metatarsal support ( P < 0.05) while no statistically significant differences were noted relative to longitudinal axis position. Interpretation: The results of this study suggest that the thickness of a metatarsal support is a determinant factor in regulating plantar loading. Surprisingly, the longitudinal axis location of a metatarsal support does not appear to be as important as clinically presumed since the data showed that the force decrease was similar for all positions from 5 to 25 mm. Thus, the orthotic induced effect of a metatarsal support seems to have a sizable interaction range that has not previously been reported. We speculate that the metatarsal support’s fulcrum and lift effect can be sustained at a more proximal position due to the foot’s rigidity as a lever and the manner in which a metatarsal support interacts with the plantar aponeurosis.