Where it hurts is a clue, not a diagnosisStrong evidence
No study opened for this guide counts how often each cause explains pain on the outer side of the foot. After a twist, the usual stories are a sprain, a break at the base of the fifth metatarsal (the long bone that ends at the bump halfway along the outer edge) or a tendon injury. Without an injury, an imaging review lists the peroneal tendons, a hidden fracture of the cuboid or the heel bone, the joint between the heel bone and the cuboid, a joined pair of bones (a tarsal coalition), a pinch at the front of the ankle, the hollow in front of the outer ankle bone, small extra bones and a nerve.
So this guide says a spot points to a cause rather than proving it, and an examination decides. The NHS says a sprain causes pain, swelling and bruising, and most sprains feel better after 2 weeks; NHS inform expects most new foot problems to begin to settle within 6 weeks.
Sources 1, 2, 3, 4
The tendons behind the outer ankle boneEmerging evidence
Two peroneal tendons run behind the outer ankle bone and along the outer edge of the foot: one to the base of the fifth metatarsal, one under the foot. A specialist review calls their problems an under-appreciated cause of pain on the outer side of the foot and ankle, easily confused with a ligament injury, and says they go with ankles that keep giving way and with high-arched feet whose heels tip inwards. Family-medicine reviews describe tenderness along the outer heel towards the base of the fifth metatarsal.
A tendon that slips out of its groove after an injury, with a pop and swelling behind the ankle bone, is often taken for a sprain, and an international consensus advises a specialist review. Scans often show changes in the tendons of people with no pain, so a scan has to match the examination.
Sources 5, 6, 7, 8
The bump halfway along the outer edge: fifth metatarsal fracturesStrong evidence
The fifth metatarsal most often breaks at its base when the foot and ankle twist downward and inward, and the ligament pulls a fragment of bone away (an avulsion fracture), the American Academy of Orthopaedic Surgeons (AAOS) says. A Jones fracture is a break across the base, just beyond the bump, in an area with a poor blood supply, so it can heal slowly or not at all and is more often treated with surgery, especially in athletes. Breaks at the base of the fifth metatarsal are about 30% of metatarsal fractures, a review says.
A stress fracture there often begins as pain on the outside of the midfoot with no injury, and is especially common in high-level athletes. In 64 elite European football teams over 11 seasons, a team of 25 players might expect one fifth metatarsal fracture every fifth season; only 1 of 38 first fractures was an avulsion, 54% of first X-rays showed stress-type fractures, 45% of players had warning symptoms first, and a third of all the fractures were re-fractures.
Sources 9, 10, 11, 12, 13
After a twist, the Ottawa rules decide who needs an X-rayStrong evidence
The National Institute for Health and Care Excellence (NICE) advises using the Ottawa ankle and foot rules to decide whether someone over 5 needs an X-ray. For the foot, an X-ray is needed if the base of the fifth metatarsal or the navicular (the bump on the inner midfoot) is tender, or you couldn't take 4 steps.
In the study that refined the rules, they picked up all 19 fractures in the midfoot zone. Across 27 studies of 15,581 people, they missed almost no midfoot fractures, and they could cut X-rays by 30% to 40%. They're a guide for clinicians, not a self-test: being able to walk doesn't rule out a break if that bump is tender.
Sources 14, 15, 16
An old sprain that still hurtsEmerging evidence
Across 31 studies of ankle sprains, pain fell quickly in the first 2 weeks, but 5% to 33% of people still had pain a year later, and up to a third felt the ankle was unstable. Ankle sprains are the commonest muscle and joint injury in active people and often recur, and many people go on to have an ankle that keeps giving way (chronic ankle instability). After a first sprain, not being able to jump and land well at 2 weeks went with lasting instability a year later.
A second injury is often there: of 61 people having surgery for an unstable ankle, none had a ligament injury alone; 77% had inflamed peroneal tendon sheaths, 25% a tear in one of the tendons and 23% a damaged patch of cartilage. In 2,577 foot and ankle MRI scans, 14 showed a small fracture at the front of the heel bone, and only 3 of 8 of those had been visible on X-rays.
Sources 17, 18, 19, 20, 21, 22
The outer midfoot: cuboid syndrome, on thin evidenceMixed evidence
Cuboid syndrome is thought to be a subtle disturbance of the joint between the cuboid and the heel bone, with symptoms like a sprain, a review says. There is no definitive test and no evidence-based guideline; X-rays, computed tomography (CT) and MRI scans don't show it, and their job is to rule out a fracture or a coalition. The evidence for treating it is case reports and one series of 7 athletes.
A painful os peroneum is different: a small bone inside the tendon that runs under the foot can crack, or the tendon can tear or catch there, causing pain under the outer side of the foot.
Sources 23, 24, 25, 3
The base of the little toe: a tailor's bunionEmerging evidence
A bunionette, or tailor's bunion, is a bony bump on the outside of the foot at the base of the little toe, much like a bunion, sometimes with an irritated fluid sac or hard skin over it, the AAOS says. In a survey of 2,662 adults in Turkey, 13.8% reported one, most of them with a family history, and tight shoes went with it. Painful bunionettes go with wider angles between the fourth and fifth metatarsals and at the little toe joint.
Sources 26, 27, 28
Children: Iselin's diseaseStrong evidence
In an active child, pain and swelling at the bump halfway along the outer edge, where a tendon attaches to the growth plate of the fifth metatarsal, is usually Iselin's disease. A children's hospital lists growth spurts (especially at 9 to 13), a rolled ankle or a blow to the outer foot, and tight or narrow shoes such as football boots or spikes, among the risks. After a twist, tenderness there still needs an X-ray check for a fracture.
Source 29
A hot foot, a broken toe, or diabetesStrong evidence
A sudden, hot, swollen, painful joint can be gout or a joint infection (septic arthritis), which needs an urgent GP appointment or NHS 111, and red, hot, swollen skin can be a skin infection (cellulitis), the NHS says. A broken smaller toe can usually be treated at home and heals in 4 to 6 weeks, sometimes months, but go to A&E for a suspected broken big toe, a toe at an odd angle, bone through the skin, tingling or numbness, or a child's toe injury.
With diabetes, a hot, swollen foot with a change in colour, painful or not, is an active foot problem that NICE asks to reach a specialist foot service within 1 working day; Diabetes UK says see your foot team within 24 hours.
Sources 30, 31, 32, 33, 34
When a scan or test helpsStrong evidence
After a twist or a fall, the Ottawa rules decide on an X-ray; a foot that looks out of shape or is cold and numb goes straight to A&E. An X-ray shows which kind of fifth metatarsal fracture it is, which decides the treatment. A stress fracture may not show at first, and an MRI or bone scan finds it earlier.
For the peroneal tendons, ultrasound and MRI are both suitable, but a scan has to match the examination. When pain lingers after a sprain, an MRI can find a hidden fracture, a tendon tear or a cartilage injury. Cuboid syndrome doesn't show on scans. X-rays of a tailor's bunion matter when surgery is being considered.
Sources 14, 9, 13, 6, 5, 23, 22, 18, 26
How it usually goesEmerging evidence
Sprains: pain eases fast in the first 2 weeks, but a minority still have pain a year later, and up to a third sprain the ankle again within 3 years. An avulsion fracture of the fifth metatarsal usually heals well, walking as comfort allows, and metatarsal fractures usually heal enough to walk on in 6 to 8 weeks, with swelling for months, the AAOS says. Jones fractures are slower: in elite footballers, those treated with surgery healed faster than those treated without (75% against 33%), with similar time out of football (80 and 74 days).
A stress fracture at the base of the fifth metatarsal usually means at least 6 weeks without weight on it in a cast or boot, and sport not usually before 12 weeks. No one can promise a date.
Sources 17, 11, 10, 9, 12, 13, 35