Effect of extrinsic rearfoot post design on the lateral-to-medial position and velocity of the center of pressure.

Findings from investigations of the effects of external forefoot and rearfoot posts added to foot orthoses have been inconclusive. This study was undertaken to examine the effects of rearfoot post design on the lateral-to-medial position and velocity of the center-of-pressure path. Four identical pairs of neutral-cast polypropylene orthotic shells were constructed; three pairs had a rearfoot post of specified design added. The fourth pair, the control, did not have a post added. Stance period data were broken down into four functional phases, and the statistically significant differences between the experimental conditions were calculated and analyzed. The addition of a rearfoot post to an orthotic shell affects center-of-pressure lateral-to-medial position and velocity. Although the effect of the post designs seemed to provide reasonably predictable changes in center-of-pressure position, the effect on center-of-pressure velocity was variable and inconsistent. The effect of the orthotic post was dependent on design and phase of gait. The addition of a rearfoot post and, specifically, the design of the post can probably be used to alter the center-of-pressure position and velocity.