Seasmoid bone anatomy

The seasamoid bones are small, almost rounded bones located in the tendons at the point where they cross over a joint. A tendon is a thick, tough band of connective tissue fibers that connects the muscle to bone.

A seasamoid bone is the hardest form of cartilage and it protects the tendon and increases its mechanical effect.

There are constant seasmoid bones (always present) and seasmoids that are sometimes present. A constant seasmoid bone occurs on the underside of the joint of the big toe.

In the foot, there are also two pea-shaped, seasamoid bones present in the tendon of flexor hallucis brevis muscle at the point where it crosses over the big toe joint (joint of the first metatarsal bone with the bone of the big toe). The muscle is responsible for flexing or bending the big toe of the foot.

These bones are located on the underside of the joint in the ball of the foot. The medial one is called tibial seasamoid and lateral one is called fibular seasamoid.

Functions:

These bones help in the normal movement of the big toe by serving as a pulley for the tendon. These bones provide leverage as the big toe kicks off the ground during walking.

These bones also support the ball of the foot by absorbing the weight during movements such as running, walking and jumping.

Seasamoiditis is a common foot problem in ballet dancers and sports persons. It refers to the inflammation of seasamoid bones resulting from increased pressure on the ball of the foot. Playing football, tennis or basketball, running, dancing, wearing high heals and high foot arches increase the risk of seasamoiditis.

Bipartite Seasamoid bones are the ones having two parts and are larger than the single seasamoid bones. These are present in about 25% of population and mostly the tibial (medial) seasamoid is involved.