Forces acting in the forefoot during normal gait--an estimate.

OBJECTIVE To estimate forces acting along tendons and across the joints of the first and second rays of the forefoot during gait. DESIGN Using recently published data on force distribution under the forefoot and relevant anthropometrical data, internal forces are calculated. BACKGROUND It is of paramount importance to know the magnitude and direction of the forces acting within the most heavily loaded structures of the forefoot, especially when surgical treatment is envisaged. It can also be of major value in understanding the pathomechanics of certain disorders of the foot. As far as the author is aware, there is no such information presently available. METHODS The ground force distribution during the second force peak of the stance phase was used with anthropometrical data (including lengths of lever arms of the tendons that cross the joints investigated) to determine conditions of equilibrium in the sagittal plane for each joint of the first and second rays. RESULTS The flexor hallucis longus and brevis tendons exert about 52% and 36% body weight, respectively, and the peroneus longus muscle more than 58% body weight. The resultant force on the first metatarsal head amounts to about 119% body weight. The second metatarsal bone is subjected to a high bending moment with a resultant force of about 45% body weight acting on its head. The flexor digitorum longus and brevis forces are about 9% and 13% body weight, respectively. CONCLUSIONS The high forces acting along the flexor tendons of the heavily loaded first ray support the so-called longitudinal arch of the foot. The second metatarsal bone is also heavily loaded, but more in bending. If the first ray with its powerful toe be deprived of its function, be it through muscular fatigue, disease, or trauma, the second metatarsal bone will probably also fail. RELEVANCE Such information is necessary to understand the physiological function of the foot. It might also explain the development and manifestation of certain foot pathologies. Furthermore, it is of importance when considering surgical procedures in the treatment of forefoot disorders.