[Biomechanical investigation of the sesamoid bones of the hallux]

Extensive research has been done on disorders of the sesamoid bone of the hallux. However, reports on the mechanism of the disorder are few and a comprehensive assessment of the biomechanical role played by the sesamoid bone has not been done. In an effort to elucidate the role of the sesamoid bone, we have developed a force sensor which utilizes the capacitance method, and evaluated the biomechanical aspects of fatigue fracture associated with it. Three frozen stored human limbs were thawed at room temperature. The force between the sesamoid bone and the first metatarsal head was measured using force sensors which were placed on the bilateral sesamoid bones. Measurements were also taken at varying loads and angles of dorsiflexion of the MTP (metatarsophalangeal) joint of the hallux from 0 degrees to 60 degrees at increments of 10 degrees. This was done by applying weights ranging from 0 to 4 kg to the first metatarsal head at increments of 1 kg. Load and angle of dorsiflexion of the MTP joint were found to be correlated with the degree of compression force between the hallux sesamoid bone and the first metatarsal head; the load applied affected the force to a greater extent than did the angle. Dorsiflexion of the MTP joint of the hallux had no effect on the amount of compression force between the medial and lateral sesamoid bones, but the increase in compression force became pronounced when the angle of dorsiflexion exceeded 30 degrees.