Sesamoids, also known as sesamoid bones, are focal areas of ossification within tendons as they pass over joints . 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 .

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 :

  • 1st metacarpophalangeal joint sesamoid (two)
    • reported incidence of 100%
  • 1 interphalangeal joint sesamoid
  • 2nd metacarpophalangeal joint sesamoid
  • 5th metacarpophalangeal joint sesamoid

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

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 .