Sesamoid

Last revised by Dr Mostafa El-Feky on 30 Jun 2021

Sesamoids, also known as sesamoid bones, are focal areas of ossification within tendons as they pass over joints 1. They can also occur in ligaments and usually measure a few millimeters in diameter. Their function is purported to be to alter the direction of the tendon and modify pressure, thereby reducing friction 2

Some sesamoids form part of normal human anatomy (e.g. patella), while others are anatomical variants (e.g. fabella). 

Sesamoid bones of the lower limb include:

See the article on ossicles of the lower limb.

Sesamoid bones of the upper limb are usually found in the hand at the following joints 3:

Less commonly, they may also occur at the 3rd and 4th metacarpophalangeal joints 4.

Sesamoid ossicles can also form in the nuchal ligament

History and etymology

Sesamoids get their name because the smallest bones resemble sesame seeds in size and morphology 1,3.

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Cases and figures

  • Case 1: sesamoiditis - hallux sesamoid
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  • Case 2: thumb sesamoid fracture
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