When the ATFL heals in a lax position—which occurs in 20 to 40 per cent of ankle sprains—chronic instability develops: the ankle gives way on stairs and uneven ground, risking post-traumatic arthritis.When the ATFL heals in a lax position—which occurs in 20 to 40 per cent of ankle sprains—chronic instability develops: the ankle gives way on stairs and uneven ground, risking post-traumatic arthritis.