[An anatomical study of the interphalangeal sesamoid bone of the hallux].

The existence of sesamoid bone on the interphalangeal joint of the hallux has not been sufficiently recognized. The frequency of this sesamoid bone has been described to be low probability in the orthopaedic and anatomical literature. We have, however, experienced some cases of the interphalangeal joint dislocation giving difficulty to usual manipulative reduction because of the presence of the sesamoid bone. In order to ascertain the existence of sesamoid bone on the interphalangeal joint of the hallux, anatomical and radiographic study have been performed with 144 feet of 73 adult cadavers, 32 feet of 16 fetal cadavers and 958 patients. The following results were obtained: The sesamoid bone was seen in 90.9% by radiographical examination and in 95.9% by macroscopic observation for 144 feet on 73 adult cadavers. Cartilagenous sesamoid bone was found in 93.8%, 32 feet of 16 fetal cadavers using stereoscopic microscope. In the radiographical examination of 958 feet of the patients, the sesamoid bones were approved in 56.3%, but it increased to 93.0% using 1/4 sensitivity intensifying screen. The sesamoid bone of the interphalangeal joint on adult cadavers was located at the central portion in parallel with interphalangeal joint space and buried in the fibrocartilagines plantares. This sesamoid bone had two cartilagenous joint surfaces against the base of distal phalanx and the head of proximal phalanx. The sesamoid bone had the shape of longitudinal ellipse and the length, width and thickness were measured. The size of sesamoid bone on the male cadaver were larger than that of the female on the three parameters and there were no special difference between the right and the left sides.