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Hey Doc, What is That on the Foot X-Ray?

This is one of the more frequent questions patients ask podiatrists when they see an x-ray of their foot. Depending on who you ask, you will be told that there are either 26 or 28 bones in the foot. If you ask someone who knows about and recognizes the sesamoids, you will learn that there are actually 28 bones in the foot.

sesamoid in tendon

“Where are they”

A sesamoid (pronounced sez-moyd) is, by definition, a bony structure embedded in a tendon. The most well-known sesamoid is the patella, or kneecap, imbedded in the quadriceps tendon. Everyone also has these two little sesamoid bones in their feet, within the flexor hallucis brevis muscle tendon, as depicted in the picture to the left.




xray w/ questionable spot

What is the purpose of the Sesamoid bones?

Just like the patella, the sesamoids in the foot function to create a mechanical advantage to the tendon. Basically, they provide extra strength and mobility to the big toe joint.

Conditions related to the Sesamoids?

Fracture—The sesamoids can fracture, or break, just like any other bone in the body.

Bipartite sesamoid—if a sesamoid is in two or more separate pieces, but is asymptomatic, meaning it causes no problems or complications, it is considered bipartite. It can develop because of genetics, or can heal that way after trauma.

AVN—or Avascular Necrosis, is when bone dies because it doesn’t get enough blood flowing to it. Because the sesamoid bones in the foot have a limited blood supply to begin with, they are at greater risk to develop AVN due difficulty in healing after trauma, or in receiving inadequate treatment after trauma.

Sesamoiditis—“itis” of any kind refers to swelling/inflammation, so sesamoiditis is when the sesamoids become inflamed and swollen because repetitive trauma or overuse. How do you overuse these little bones? Dancers and other athletes are the usual sufferers of sesamoiditis, which is treated by keeping off the affected foot until it heals.

Subluxation—Just like with the shoulder, the sesamoids can become dislocated, but unlike with the shoulder, a sesamoid out of place may need to be surgically repaired.