Most people have two sesamoid bones in each foot, both located beneath the big toe joint. These two small, pea-sized bones are present in virtually everyone and are considered standard anatomy. Beyond these two constants, additional sesamoid bones can appear at the smaller toe joints, meaning the total count varies from person to person.
The Two Constant Sesamoids
The two sesamoid bones that everyone has sit embedded in the tendons running under the first metatarsophalangeal joint, where your big toe meets the ball of your foot. They’re named by their position: the tibial (inner) sesamoid sits closer to the midline of your body, and the fibular (outer) sesamoid sits on the opposite side. Each is roughly the size and shape of a kernel of corn.
Unlike most bones in your body, sesamoid bones don’t connect to other bones through joints. Instead, they float within tendons, much like the kneecap. Their job is mechanical: they absorb weight-bearing pressure on the ball of the foot, reduce friction where the tendon crosses the joint, and act as a pulley that increases the leverage of the muscles controlling your big toe. That pulley effect is directly comparable to how your kneecap works, giving the muscles more power to push off with each step.
Extra Sesamoids at the Smaller Toes
Sesamoid bones can also develop at the joints of the second through fifth toes, though this is far less common. The fifth toe joint is the most likely location for an extra sesamoid, appearing in about 4% to 15% of people depending on the population studied. One study of 602 feet in Turkish individuals found sesamoids at the second, third, fourth, and fifth toe joints in 2.8%, 0.5%, 1.0%, and 15.1% of feet, respectively. A larger study of nearly 1,000 patients from the same population found lower rates across the board: 0.4%, 0.2%, 0.1%, and 4.3%.
These extra sesamoids are considered normal anatomical variants, not a sign of any problem. Most people who have them never know it unless they happen to get a foot X-ray for another reason. In rare cases, a person can have sesamoid bones at all five toe joints, but this is uncommon enough to warrant a case report when it’s discovered.
Accessory Bones Near the Sesamoids
The foot is also home to several other small accessory bones that sometimes get confused with sesamoids. Roughly 18% to 37% of the general population has at least one accessory ossicle (a small extra bone) somewhere in the foot or ankle. Common ones include the os peroneum on the outer edge of the foot, the os trigonum behind the ankle, and the accessory navicular on the inner arch. These aren’t technically sesamoids because they don’t sit within tendons, but they show up on X-rays and can occasionally cause similar symptoms.
Bipartite Sesamoids: When One Looks Like Two
In about 7% to 30% of people, one of the big toe sesamoids develops as two separate pieces instead of one. This is called a bipartite sesamoid, and it happens when the bone’s growth centers never fully fuse during development. The tibial (inner) sesamoid is the one most likely to be bipartite, occurring in 7% to 31% of cases, while the fibular sesamoid splits in only about 0.6% to 2.5%.
This matters because a bipartite sesamoid can look exactly like a fracture on an X-ray. The key differences: a bipartite sesamoid has smooth, rounded edges and typically appears larger than the neighboring single sesamoid. A fracture, by contrast, has jagged, irregular edges and the pieces fit together like a broken puzzle. One useful diagnostic clue is that 80% to 90% of bipartite sesamoids occur in both feet, so imaging the opposite foot for comparison can help clarify the picture. People with bunions are also more likely to have a bipartite tibial sesamoid.
What Happens When Sesamoids Are Injured
Because the two big toe sesamoids bear so much of your body weight during walking, running, and jumping, they’re vulnerable to overuse injuries. Sesamoiditis, a general inflammation of the bones and surrounding tissue, causes a gradual ache under the ball of the foot that worsens with activity. Stress fractures can also develop, particularly in runners, dancers, and anyone who spends a lot of time on the balls of their feet.
Initial treatment focuses on taking pressure off the area. Soft-soled, low-heeled shoes or stiff-soled clogs can help, along with a dense foam cushioning pad placed under the sesamoids inside the shoe. Taping the big toe in a slightly downward position reduces tension on the joint. For persistent symptoms, a removable short leg brace worn for four to six weeks is a common next step. Full recovery from a sesamoid fracture can take multiple weeks to months of limited weight-bearing, and in some cases a period in a cast.
If pain doesn’t resolve with these approaches, imaging beyond a standard X-ray may be needed. An MRI or CT scan can distinguish between sesamoiditis, a stress fracture, and a bipartite sesamoid that’s become symptomatic, since these conditions require different management strategies.