Sesamoid bone
Also called: sesamoid bones
What it means
A sesamoid bone is a small bone embedded inside a tendon, usually near a joint, that helps reduce friction and improve leverage for muscles pulling across that joint.
Sesamoid bones, like the kneecap or those under the big toe, help your joints move efficiently, so keeping them healthy supports comfortable movement and balance as you age.
A sesamoid bone is a small, rounded bone that forms inside a tendon, usually where that tendon crosses a joint under a lot of pressure. Instead of being connected to other bones directly at a joint surface, it sits embedded in soft tissue like a pulley, changing the angle of pull and reducing friction and wear on the tendon as it moves.
The best-known example is the patella (kneecap), the largest sesamoid bone in the body, which protects the knee joint and improves the mechanical leverage of the quadriceps. Smaller sesamoid bones are found at the base of the big toe and near the thumb, helping distribute load during walking, running, and gripping.
Like other bones, sesamoids respond to mechanical stress, remodel over time, and can be affected by overall bone health, injury, or repetitive strain. Problems such as sesamoiditis or stress fractures in these bones are usually mechanical or overuse issues rather than something linked to osteoporosis, though general bone density and loading habits still matter for how well they hold up.
Small sesamoid bones like the kneecap reduce friction and boost leverage so joints move efficiently.
Where this leads
WordWondering what's inside the bones near your joints. Trabecular bone's spongy structure explains a lot about bone strength beyond just shape.
Related words
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