What usually causes itStrong evidence
The outer (lateral) sprain is the commonest ankle injury. Across 181 prospective studies, mostly in sport, sprains were more common in females (13.6 against 6.94 per 1,000 exposures) and in children, and most common in indoor and court sports. The American Academy of Orthopaedic Surgeons (AAOS) says around 90% of sprains are this kind, where the foot rolls inwards, though it cites no study for the figure.
Most sprains settle, but in a review of 31 studies, 5% to 33% of people still had some pain a year later. A consensus statement links repeated sprains and long-standing instability with doing less activity and with arthritis earlier in life.
Sources 1, 2, 3, 4
Pain months after a sprain: usually something alongside the ligamentEmerging evidence
In 61 ankles operated on for long-standing instability, the ligament was never the only problem: 77% had inflamed peroneal tendons, 67% a scar lesion at the front outer corner of the joint, 25% a split in the peroneus brevis tendon and 23% a cartilage lesion on the talus. In another series of 148 unstable ankles, 40% had an inner ligament injury too. These were people who needed surgery, so the figures show what can be found, not how often it happens after a typical sprain.
Pinching at the front outer corner (anterolateral impingement) causes pain when you squat, lunge or climb, months after sprains; in 22 people, examination found it better than magnetic resonance imaging (MRI). "Sinus tarsi syndrome", pain in the soft hollow in front of the outer ankle bone, is a catch-all label that a review recommends replacing with a precise cause. Most ankle arthritis follows an injury: 78% of 406 painful, worn ankles at one specialist centre.
Sources 5, 6, 7, 8, 9, 10
The peroneal tendonsEmerging evidence
The two peroneal tendons run behind the outer ankle bone and turn the foot outwards. A review calls their problems (inflammation, splits and tendons slipping out of their groove) an under-recognised cause of outer ankle pain that is hard to tell from a ligament injury, and links them with instability and a high arch. After an injury, a clear pop, or a tendon you can see or feel slipping, needs a specialist review, an international consensus of 16 specialists says; otherwise treatment starts without surgery.
Sources 11, 12
Bone: stress fractures and breaks mistaken for sprainsEmerging evidence
A stress fracture of the fibula, the outer leg bone, causes one sore spot a few centimetres above the ankle that builds with running. It's a lower-risk site, and athletes returned to sport after about 8 weeks (56 days) on average across a review of 76 studies; Health New Zealand says the ache can become constant, even at night.
Some breaks are mistaken for sprains: a fracture of the outer edge of the talus (snowboarder's ankle) looks like a severe sprain, and 28 of 36 people in one trauma centre series needed surgery. The bump halfway along the outer edge of the foot is the base of the fifth metatarsal, a foot bone the Ottawa foot rules check after a twist.
Sources 13, 14, 15, 16, 17, 18, 19
Causes that aren't the muscles, tendons and jointsStrong evidence
A sudden, very painful, hot, red, swollen ankle with no injury can be gout, which often starts overnight and can affect the ankle, or a joint infection, which is urgent. In later tibialis posterior tendon problems on the inner side, the heel tips out and can press on the outer ankle bone, so pain moves to the outside. A swollen, throbbing calf after an ankle injury or time in a cast can be a blood clot, and burning or tingling can come from a nerve: see the warning signs.
Sources 20, 21, 22, 23, 24
The Ottawa rules and other testsStrong evidence
After a twist, clinicians check whether you can take four steps and press on the back edge and tip of both ankle bones and, for the foot, the navicular and the base of the fifth metatarsal. The National Institute for Health and Care Excellence (NICE) asks for these Ottawa rules from age 5. If all are fine, a break is very unlikely: in the study that refined them they picked up every fracture, and across 27 studies of 15,581 people they cut X-rays by 30% to 40%. You can still walk on a broken ankle.
An examination 4 to 5 days after a sprain, once the swelling has gone down, judges how bad it is best, a guideline says. The AAOS suggests an MRI if symptoms carry on beyond 6 to 8 weeks or a high ankle sprain is suspected; ultrasound or MRI shows the peroneal tendons. For pinching at the front of the ankle, examination found it in 94% of cases and MRI in 39%.
Sources 19, 25, 26, 27, 2, 11, 7
How it usually goesEmerging evidence
Pain falls fastest in the first 2 weeks after a sprain; in the review of 31 studies, 36% to 85% of people reported a full recovery within 3 years, and 3% to 34% sprained it again. The NHS says most sprains feel better within about 2 weeks, advises avoiding strenuous exercise such as running for up to 8 weeks, and says a severe sprain can take months. In 82 people with a first sprain, being unable to do a single-leg landing at 2 weeks predicted long-term instability. No one can promise a timescale.
Sources 3, 29, 28, 14
