Sesamoid bones

Small, round bones embedded within tendons that help to increase the mechanical advantage of muscles.

Sesamoid bones are specialized bone structures that develop within a tendon. They often form in response to strain and stress placed on the tendon, serving to protect it and enhance the efficiency of muscle function. The most well-known example is the patella, or kneecap, but other sesamoid bones are present in the hands and feet as well.

Terminologia Anatomica

ossa sesamoidea

System

Skeletal system

Function

The primary function of sesamoid bones is to improve the leverage and effectiveness of the muscles that act on the joints. By being situated within tendons, they allow for a change in the angle at which a muscle exerts its force, thereby increasing the mechanical advantage when a movement is performed. This means that movements such as flexing the knee or curling the fingers become more efficient as the sesamoid bones help distribute forces and reduce friction on the tendons. Additionally, these bones can absorb shock and protect the tendons from stress injuries, effectively acting as a shield during high-impact activities.

Location

Sesamoid bones are typically found in areas of the body where there is increased stress and movement involving joints. The most prominent sesamoid bone, the patella, is located at the front of the knee joint. In the hands, sesamoid bones are often present in the tendons of the flexor pollicis longus muscle, situated at the base of the thumb. In the feet, sesamoid bones can be found beneath the first metatarsal head, aiding in the mechanics of walking and running. Their locations may vary between individuals, and some people may have sesamoid bones not commonly present in most anatomical references.

Did You Know?

There can be variations in the number and size of sesamoid bones among individuals; some may have more than the commonly found few.
Sesamoid bones can play a role in conditions like sesamoiditis, where inflammation occurs, leading to pain under the big toe.
While the patella is the largest sesamoid bone, the smallest can be found in the flexor tendons of the hands, often referred to as accessory sesamoids.