The Original ASO Ankle Stabiliser Orthosis featuring the patented figure of 8 stabilising straps. The stabilising straps are now angled to contour above the ankle for increased suport and comfort. To select the correct size, measure the circumference of your ankle from under the heel to around the front of the foot and choose from the following ranges - small - 27.9-30.5cm / medium - 30.5-33cm / large 33-35.6cm.