Helps Prevent Sports Ankle Injuries Designed to help prevent ankle injuries, the Aircast Sport-Stirrup is based on the Air-Stirrup Ankle Brace but has a narrower design for less bulk in a sneaker or shoe. The Aircast Sport-Stirrup has anatomically designed shells that prevent inversion/eversion. Each shell is lined with the patented Duplex aircell system. This exclusive system incorporates two pre-inflated overlapping aircells, distal and proximal, that provide support and protection during ambulation.