The human body contains numerous bones, but some unique ones, called sesamoid bones, are embedded within soft tissues like tendons rather than connecting directly to other bones. These distinct structures can be found in various locations throughout the body, including the foot.
Understanding Sesamoid Bones
Sesamoid bones are small, rounded bones embedded within a tendon, often compared to a pea or sesame seed. Unlike most bones, they do not directly articulate with other bones but float within the tendon. This unique arrangement allows them to act as a pulley system, providing a smooth surface for the tendon to glide. By altering the tendon’s angle, sesamoid bones increase the associated muscle’s leverage, enhancing its force and efficiency.
Specific Location in the Foot
In the foot, the most prominent sesamoid bones are found beneath the big toe joint. There are typically two small bones located on the underside of the ball of the foot, directly beneath the head of the first metatarsal bone. These two sesamoids are embedded within the flexor hallucis brevis tendon, a tendon responsible for flexing the big toe. One sesamoid is positioned on the medial (inner) side and the other on the lateral (outer) side of the first metatarsophalangeal joint, where the big toe connects to the foot.
While smaller sesamoid bones can occasionally be present in other foot tendons, the pair beneath the big toe is consistently present in most individuals and plays a primary role in foot mechanics. Their precise placement allows them to interact with the joint surface and surrounding tendons and ligaments, facilitating specific movements of the big toe.
Why Foot Sesamoids Matter
The sesamoid bones in the foot serve important functions in foot biomechanics. They provide a smooth, low-friction surface for the flexor hallucis brevis tendon to move across, increasing the big toe’s mechanical advantage and leverage. This leverage is particularly important during the push-off phase of gait, as the big toe bears substantial force when walking, running, or jumping. These bones also help absorb and distribute the significant weight-bearing pressure on the ball of the foot. They protect the flexor hallucis brevis tendon from excessive wear, friction, and compression, contributing to the foot’s overall durability and efficiency.
Common Issues Affecting Foot Sesamoids
Due to their location and high-stress demands, sesamoid bones in the foot are susceptible to problems. Sesamoiditis, inflammation of the bones and surrounding tendons, is a common issue. This condition often develops from repetitive stress or overuse, particularly in activities involving increased pressure on the ball of the foot. Fractures, both acute (sudden break) and chronic (stress fracture), can also occur. Avascular necrosis, where bone tissue dies due to lack of blood supply, is another potential problem.