Ground Reaction Forces in Feet with Morton's Syndrome
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Morton’s syndrome is a foot condition where the 1st metatarsal does not protrude as far distally as the 2nd metatarsal. Clinicians believe that short 1st metatarsal protrusion affects foot mechanics and leads to painful conditions of the foot. Normal protrusion ratio of the 1st and 2nd metatarsal has not been delineated in scientific literature, and little is known about the mechanics of feet with short 1st metatarsal protrusion beyond anecdotal clinical evidence. In the first part of this two-part study, a novel tool was developed to guide metatarsal measurement and reduce measurement error so values for normal metatarsal protrusion ratios could be established. In the second part, subjects were divided into those with shorter and longer than average 1st metatarsal protrusion ratio and we measured if there were any differences in the foot-floor forces between the two groups. In Part 1, the feet of 65 healthy subjects were measured with a novel measurement tool and it was determined that the average ratio (1st metatarsal/2nd metatarsal) was 0.902, suggesting a 1st metatarsal that does not protrude as far distally as the 2nd metatarsal. For Part 2, participants were divided into two groups: the short 1st metatarsal group had a ratio of more than one standard deviation below the mean (0.866 or lower) while the control group had a metatarsal ratio of more than one standard deviation above the mean (0.938 or higher). We hypothesized that short 1st metatarsal protrusion would cause an imbalance across the forefoot because the 1st metatarsal would not be able to carry the required load on the medial side of the foot; however, the results of the gait study did not show this as only forces in the walking direction near toe-off correlated with metatarsal protrusion ratio. We can only speculate as to the relationship between the metatarsal protrusion ratio and increased shear force in the walking direction, but it is possible that to compensate for the diminished stabilizing capacity of the shorter 1st metatarsal, the foot must push off with more force to propel the body forward.