Tarsal Morphology Differs in Plano Valgus Feet

CATEGORY: Hindfoot INTRODUCTION/PURPOSE: While there are established associated conditions, the intrinsic cause of symptomatic adult flatfoot is not known. There are published data suggesting that the relationship of the hindfoot bones in acquired flatfoot are subluxated. And there is some support in 2 D for the concept that the bones are shaped differently in flatfoot but the complexity of bone shape and human variation makes comparisons difficult. The purpose of this study was to utilize principal component analysis (PCA) to determine whether morphology of the hind- and midfoot bones differs in neutral and plano-valgus feet. METHODS: Forty subjects (23 male and 17 Female, average age 52.6 +/- 8.9) with no history of injury or surgery underwent bilateral foot WB CT scan for another study. The talus, calcaneus, navicular and cuboid were segmented into bone models from these previously acquired CT images. Morphometric Shape analysis software (Geomorph) was used to assess shape variations among foot types using Principal component analysis (PCA). PCA is a statistical modelling technique used to study variation in the shape of structures that are difficult to compare and bring out strong patterns in a dataset objectively. Forty feet had been classified into 4 foot groups prior to this study; neutral, cavus, asymptomatic flatfoot and symptomatic flatfoot. This study included the painful flatfeet and neutral feet. Each bone was compared between the feet that were flat and those that were neutral. Comparisons were made between men and women as well. RESULTS: There were no differences between groups in age or sex. There were 38 principle components identified. The first two PC accounted for 38% of the calcaneal variation and 33% of the talar variation. Subtle differences between men and women were found only at the talus and navicular. The cuboid did not exhibit any differences between foot types. The navicular in symptomatic planus had a more posteriorly positioned tuberosity (tuber wrapped around the medial side of the talus) and were wider than neutral feet. The calcaneus showed planus feet to have calcanei that have decreased height and increased length compared to neutrally aligned feet. The cross -sectional area of the calcaneus was reduced compared to neutral feet. The talar shape was not different in the PC. CONCLUSION: A flat foot is present in over 20% of the population and most often not symptomatic. The root cause of symptomatic adult plano valgus foot is not known and is likely multi factorial. The study demonstrates that there is intrinsic difference in the shape of the calcaneus and navicular bones in flat foot. it is possible that the catalyst for collapse is bony rather than soft tissue.