By the sounds of it this happened during the original injury and is typical when you hear/feel a 'Pop'. Immobilization in a cast at the time sometimes might assist if the ends approximate but really there is no fix for that other than surgical. The result of the injury is that the ligament connection to the brain is reduced and you will be more prone to recurrent sprains. The best thing is to get in to a local physio to learn some proprioceptive retaining exercises for the lower limb as a whole.

Best of luck