An ankle injury which will not get better
Most (75-90%) of ankle sprains recover of their own accord. The modern approach is for early return to activity once the initial pain and swelling are subsiding. However, as specialists we tend to see the people whose ankles do not fully recover.
In some patients, pain persists, in others the ankle keeps giving way and some people have both. If there is little pain but the ankle easily twists , the problem might be ligament incompetence where the torn ligaments have not healed. Sometimes the ligaments are fine and the instability is because the muscle strength and control never recovered; so-called functional instability. The tendons running behind the outside edge of the ankle (lateral malleolus) are called the peroneal tendons. They can be damaged by a bad sprain (peroneal tendinopathy) or the straps which hold them in position (peroneal retinaculum) can be torn so they keep slipping around the corner of the lateral malleolus. This can cause pain and weakness. Tendon damage can also occur on the inside aspect of the ankle (posterior tibial tendon) often followed by flattening of the arch. More commonly there is damage inside the ankle joint itself. A catching pain at the front of the ankle (anterior impingement) often means inflammation or scarring just inside the joint. This tissue is intermittently pinched by certain movements. The same pinching effect can happen at the back of the ankle (posterior impingement) in people who spend lots of time with their ankle and toes pointing downwards, such as ballet dancers or windsurfers, even without an injury.
If the ankle twists badly enough, the cartilage lining the surface of the bone within the joint can be fractured, crushed or sheared off . This is called osteochondritis dissecans (OCD). It can also happen spontaneously without any injury. OCDs tend to cause a more constant pain with less "catching" unless the piece comes away and floats inside the joint. These impingement and OCD lesions often produce pain alone but if they can also cause the ankle to give way, simulating incompetent ligaments. Of course more than one problem can result from a single injury. Repeated episodes of giving way with a short period of swelling after each one should be addressed because there is evidence the damage accumulates, possibly progressing to wear and tear arthritis.
Finally, some people have ankles which are simply built to twist in. The normal heel should sit with the ankle slightly tipped in with respect to the skin of the heel in contact with the floor. People who have ankles tipped the other way, espeically with excessively deep arches (cavo-varus foot) have a tendency to twist their ankles and once it starts happening it often continues to do so. Occasionally fractures go undetected and fail to heal. These non-unions often continue to hurt and require surgical fixation to achieve a bony union.
A rare cause for an ankle sprain continuing to hurt despite treatment and time is a tarsal coalition. This means that some of the bones around the ankle area which should be separate are joined together. These joins are present from birth and tend to produce a rather flat stiff foot which becomes painful during teenage years, but the pattern is very variable and sometimes pain only starts after a twisting injury.