sesamoids

Sesamoids are small bones embedded within tendons at sites where the tendon passes over a joint. The largest and most familiar is the patella, located in the quadriceps tendon in front of the knee. Other sesamoid bones occur in the hands and feet, often within tendons near joints: in the wrist the pisiform is a sesamoid within the tendon of flexor carpi ulnaris, the thumb can have sesamoids at the metacarpophalangeal joint, and in the foot two plantar sesamoids lie beneath the head of the first metatarsal. A bony accessory in some people, the fabella, can appear behind the lateral femoral condyle in the knee. Additional small sesamoid bones may be present in other tendons and are variably expressed among individuals.

Sesamoids serve several functional roles. They protect tendons from compressive forces as they glide over joints, increase the tendon's mechanical advantage by changing the angle of pull, and help distribute weight and load across a joint, reducing wear on the tendon and adjacent structures.

Clinical notes about sesamoids include normal anatomic variation, such as absence or bipartite (split) forms. Pathology can include fractures, nonunions, or inflammatory conditions such as sesamoiditis, common in runners, dancers, and other athletes. Diagnosis is typically by radiographs, with CT or MRI used for detailed evaluation. Treatment ranges from rest and immobilization to surgical excision if pain persists despite conservative management.