Ankle sprain
What is the Expected Natural History After an Ankle Sprain?
By six weeks following an ankle sprain once should expect a 90% chance of being back to a good level of function. However, it is likely that at this stage following an ankle sprain you are likely still to have some residual symptoms of pain or instability from the ankle joint. Even by six months following an ankle sprain there is still a 20-30% chance of suffering with some level of minor discomfort or instability from the joint. The further away one gets from the index injury the less likely these residual symptoms are likely to improve of their own accord.
If at three months following an ankle sprain, with rehabilitation, your ankle is still painful and/or unstable it would be sensible to obtain an MRI scan of the joint, as a pre-cursor to ankle arthroscopy. This is in particular to exclude an osteo chondral defect as being the source of the ongoing symptoms. The MRI scan will identify in most cases injury to the lateral ankle ligaments. An MRI scan however following an ankle sprain will not give any information as to the stability of the injured ligaments and this is really the key point.
The MRI will also not diagnose the vast majority of soft tissue problems inside the ankle joint which lead to ongoing symptoms once things should have settled. The reason for this is that the soft tissues inside the joint have a high water content which means they are "masked" from the MRI by the joint fluid. It is normal to arthroscope the ankle with a "clear" MRI scan if there are ongoing problematic symptoms. There is almost always pathology within the joint.
What if it doesn't get better?
If at three months with rehabilitation your ankle is still painful and or unstable and not improving our protocol is to MRI the joint to exclude an osteochondral defect as being the source of symptoms. This may still be amenable at this stage for direct fixation. | 
