Spraino: A novel low-friction device for prevention of lateral ankle sprain injuries in indoor sports

A heightened risk for lateral ankle sprain injuries has been associated with excessive shoe-surface friction. ‘Spraino’ is a novel product specifically designed towards preventing friction-related lateral ankle sprains. In a recent 510-athlete randomized controlled trial, allocation to this “low-friction” shoe-patch resulted in a 53% reduction of severe ankle sprain injuries. Until now, however, a theoretical explanation linking shoe-surface friction and lateral ankle sprain injury mechanism is missing, and the extent to which Spraino reduces shoe-surface friction remains unknown. Therefore, the purpose of this study was to present a theoretical link between lateral edge shoe-surface friction and the mechanism of lateral ankle sprain injuries, and ultimately establish the ability of Spraino to reduce lateral edge shoe-surface friction. In this paper, we present a theory on how ankle sprain mechanics are directly affected by the friction between shoe and surface, and why friction modifications might be a viable preventive strategy. When testing slip resistance in a modified mechanical test-setup, we detected a 63% reduction (0.83–0.31) in friction coefficient between the lateral edge of the outsole and the indoor sports floor when adding Spraino to the side of the shoe. Justified in our theory, and the previously established clinical effectiveness, this reduction in friction can mitigate both the risk and severity of lateral ankle sprain injuries. This suggests that reducing friction on the lateral edge of footwear can be an effective ankle sprain injury prevention strategy.