[Biomechanics of the metatarsophalangeal joints]

Koehler-Freiberg's disease is found to most commonly manifest itself in the metatarsal head of the second ray. Occasionally it is observed to occur in the metatarsal head of the third and less commonly it is seen to appear in the other rays of the foot. An investigation into probable causes of the disorder calls for consideration of the biomechanical conditions in the region of the metatarsophalangeal joints. A review of the literature pertaining to this matter has failed to reveal any detailed information in this respect and therefore a series of experiments have been conducted involving determination of a) the ground force under the metatarsophalangeal joints and under the toes in normal barefoot walking b) the direction of the flexor tendons and such others that cross the joint and that might play an important role in exerting force between the toes and the ground, c) the geometry of the articulating surfaces and d) the forces that act between the metatarsal head and the corresponding phalangeal joint surface. It is shown that the specific loading of the MP-II joint (due to forces acting across the joint) could amount to nearly twice that to which MP-I is subjected to. This might explain the more frequent occurrence of osteonecrosis of the second metatarsal head as compared to that observed within the head of the first. Furthermore, the direction of the joint resultant force in the MP-II joint is seen to be more dorsally inclined than that in MP-I, which agrees well with clinical findings regarding the site of localized lesions. Lastly, a hypothesis which still requires closer investigation is presented to explain the development of the bone lesions that are known to occur just below the subchondral cortex.