OBJECTIVE: To analyze the principle mechanism of the arcus plantaris and its clinical application. METHODS: The states of forces sustained by the arcus plantaris were analyzed and calculated according to the mechanism of the quadratic parabolic arch. RESULTS: The aponeurosis plantaris corresponded to the pull rod of the arcus plantaris. The medial and lateral longitudinal arches formed by the pedal bones were stable with the rod, but unstable without the rod. In the latter condition, on loading, the force sustained by the parabolic arch became a force sustained by a simple beam, and the arcus plantaris tended to disappear and to be flattened. Clinically, 240 feet with talipes equinus were treated with triple arthrodesis. In 34 out of the reexamined 156 feet, the aponeurosis plantaris was cut in addition to the triple arthrodesis and was immobilized with cast for 3 months. One or two years later, their arcus plantaris disappeared, pain developed when walking, and some of them walked with the midtarsal joint against the ground. Then, the triple arthrodesis and shortening of the aponeurosis plantaris were applied on 18 cases, and osteotomy of the calcaneus and reconstruction of the aponeurosis plantaris were made on 10 cases and satisfactory effects were obtained. CONCLUSIONS: In order to achieve satisfactory therapeutic effects of the triple arthrodesis, we should reestablish the arcus plantaris and accurately treat the aponeurosis plantaris for the balance of the surrounding muscle force.