Shoe inversion does not represent ankle inversion: A dynamic x-ray analysis of barefoot and shod cutting

Ankle injuries are common. These injuries are often the result of excessive inversion at the subtalar joint. Previous research measuring shoe motion suggests that inversion at the ankle during cutting is as high as 40 degrees. However, this does not seem possible without injury. Some researchers have cut holes in shoes to view foot motion directly; however, this compromises the integrity of the shoe and potentially changes ankle kinematics. During barefoot cutting, ankle inversion has been measured directly showing that there is little or no ankle inversion. It is not known how footwear affects ankle inversion inside the shoe during cutting. The purpose of this study was to determine the effect of footwear on ankle inversion during aggressive lateral cutting without compromising shoe integrity. This was done using a dynamic x-ray imaging technique to measure ankle and shoe inversion while barefoot and shod. It was hypothesised that during aggressive cutting: 1) maximum ankle inversion would be the same in the barefoot and shod conditions, and 2) maximum shoe inversion would be significantly greater than maximum ankle inversion in the shod condition. During aggressive cutting, the maximum ankle inversion angle was 4.2 +/- 3.5 degrees while barefoot and 11.7 +/- 7.4 degrees while shod (p = 0.009), suggesting that the shoe does affect ankle inversion. Shoe inversion (38.3 perpendicular to 5.2 degrees) greatly overestimated ankle inversion inside the shoe (p = 0.00003). Therefore, shoe inversion measurements should not be used to represent ankle inversion during cutting movements. Ideally, the effect of specific footwear on ankle inversion should be assessed based on direct measurements of ankle inversion inside the shoe.