The hallucal interphalangeal sesamoids are accessory ossicles of the interphalangeal joint of the hallux. Although they are termed sesamoids, they do not represent true sesamoids and are rather classified as accessory ossicles1.
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Terminology
It is important to note that there is no clear difference in the literature between hallucal interphalangeal sesamoids and os interphalangeus. They could correspond to the same entity.
Epidemiology
The incidence varies widely according to race and population. The reported rates range from 4.3 to 57.8% 2
Pathology
These accessory ossicles are not true sesamoids, since cadaveric studies showed that they are not located within the tendon of the flexor hallucis longus tendon 1.
They are thought to be the remnant of the lost middle phalanx of the Hallux 1.
Radiographic features
Plain radiographs and CT
these ossicles should be bilateral 2
pyramidal-shaped with a variable size, that ranges from 0.5 to 10 mm2
located directly inferior to the hallucal interphalangeal Joint, beneath the head of the proximal phalanx
generally situated in the midline, but may also be medial or lateral2
have osseous oval-shaped base inserted within the dorsal surface of the plantar capsule and above the flexor hallucis longus tendon 3
they may be bipartite
Related pathology
Differential diagnosis
fracture of the head of proximal phalanx / base of distal phalanx