What it is
The navicular is the boat-shaped bone on the inner side of the midfoot. The tibialis posterior tendon, which helps hold up the arch, attaches to the bump on its inner side. An accessory navicular is an extra bone, or an extra piece of bone, at that bump. It forms when a separate growth centre in the bone doesn't fuse with the rest, and it tends to run in families.
There are three types. Type 1 is a small, round bone inside the tendon. Type 2 is a larger piece joined to the navicular by a bridge of cartilage or fibrous tissue, which the tendon's pull or a twist can strain: in operated feet, the bridge showed tiny cracks and signs of repair. Type 3 has fused to the navicular, leaving a large bump that shoes rub. Type 2 causes most of the pain: 72.7% of 226 painful feet in one US children's hospital, and over 70% of painful cases in a review.
In 27 feet with an accessory navicular and flat feet, MRI (magnetic resonance imaging) showed the tendon attaching straight into the extra bone, with little or no slip carrying on under the foot, in 20. That is why the extra bone, tibialis posterior strength and the arch are discussed together.
Sources 1, 2, 3, 4, 5, 6
How common it is: most never hurtStrong evidence
A 2024 review of 39 studies (11,015 people) found an accessory navicular in 17.5% of people, about 1 in 6, and half of them had one in both feet. Men and women were affected alike. It was commonest in East Asian populations (38.4%) and least common in North Americans (8.0%), with Europeans in between (12.1%). NHS leaflets give 4% to 14%, and single studies range from about 8% of foot and ankle X-rays in Turkey to about half of adults in a Japanese population study, depending on the population and how it was looked for.
Most never cause trouble. In 875 Japanese schoolchildren checked with ultrasound, 20.8% of feet with an accessory navicular (55 of 264) had ever been painful, most often at 10 to 11 in girls and 12 to 13 in boys. In people X-rayed for foot pain, the extra bone was blamed for the pain in 10.6% of those who had one. So an extra bone on an X-ray isn't a diagnosis on its own: a tender bump that matches the story is.
Sources 2, 3, 7, 8, 9, 10
Who gets pain
Mostly active children and teenagers, usually between about 10 and 15, around the growth spurt, when sport loads the bridge harder. Clinic series are mostly girls (78% of 169 children in one, 72% of 71 patients in another), although the school study found boys and girls equally likely to have pain.
It often starts after a sprain, more training or new or tight shoes: 31% of the 169 children linked it to an injury, and in a Korean surgical series, 74% of athletes' feet and 39% of non-athletes' had a history of injury. Professional footballers had more accessory naviculars than other men (35.9% of feet against 24%).
Adults get it too. An NHS foot surgery service notes that pain may only start in adulthood, perhaps after a trip or fall. In older adults it may play a part in tibialis posterior tendon problems, and in a Japanese population study, having a type 2 bone in both feet went with more falls, though walking speed and balance tests were no different.
Sources 9, 4, 12, 13, 14, 11, 8
How it's recognised, and what scans do and don't meanEmerging evidence
A bony bump on the inner side of the midfoot, just in front of and below the inner ankle bone, tender to press, sometimes red or swollen after sport, and rubbed by shoes, football boots, ski boots or skates. It aches with walking, running and jumping, and symptoms often come and go with activity. A clinician presses on the bump itself: tenderness on the bone, rather than along the length of the tendon, points to the accessory navicular. An X-ray confirms it, and an angled (oblique) view shows it best.
MRI is kept for pain that doesn't settle, or before an injection or surgery. Painful type 2 bones show swelling inside the bone (marrow oedema) in the extra bone and the navicular: in all 17 operated feet in one series, and in all 27 athletes and 16 of 20 non-athletes in another. But in 1,988 adults having an ankle MRI for other reasons, 21% of type 1 and 2 bones showed the same swelling. Swelling fits a painful accessory navicular; it doesn't prove the bump is the cause.
Sources 3, 4, 5, 15, 13, 16
How it usually goesEmerging evidence
Children's pain often settles as the foot matures, but the evidence is small. In one small Japanese school study, 15 of 21 painful feet had settled 2 years later; treatment wasn't recorded, so this isn't a general rate. Over those 2 years, about a third of the extra bones in 11 to 13 year olds fused to the navicular, though none of the painful ones did. In 19 US children X-rayed every year, 8 fused, at about 12.5 years in girls and 14 in boys.
In two US children's hospitals, about 3 in 10 children with a painful accessory navicular went on to surgery (30% of 169, and 28.8% of a random sample of 299), at a median of about 5 months in one. In the first, 28% had complete relief with non-surgical care, after an average of 8 months, and about 4 in 10 partial relief. Athletes settled less often: in a Korean series, at least 6 months of non-surgical care helped 17 of 50 non-athletes but only 2 of 29 athletes.
Sources 17, 18, 4, 19, 13
Flat feet, and pains that aren't an accessory navicular
The extra bone doesn't cause flat feet, as far as studies show: arches were the same in 49 people with one and 179 without. But the two often go together (17.6% to 21.5% of the 169 children had flat feet on X-ray measures), and a flatter foot made surgery more likely in one series. A flat foot that doesn't hurt needs nothing, as our flat feet guide explains.
Pain behind and below the inner ankle bone, often in women over 40, with the arch dropping on one side, is more often the tibialis posterior tendon itself. Pain on the top of the midfoot, at one spot, with every step and later at night, can be a stress fracture. A soft, smooth lump on the top of the foot is more often a ganglion cyst. Each has its own guide.
Sources 20, 4, 12, 21, 3
