188宝金博页面版

Volume 91 • Number 9 • October 2001 465The subtalar joint is a functional joint of the humanfoot that acts as a mechanical link between the footand the lower extremity. Transverse plane rotationsof the leg are converted into frontal plane rotations ofthe foot, and vice versa, by the oblique triplanar orien-tation of the subtalar joint axis. Two of the more im-portant functions of the subtalar joint are: 1) to allowthe foot to pronate and act as a mobile adapter whenbearing weight on irregular surfaces; and 2) to allowthe foot to supinate into a position of increased sagit-tal plane stability during the propulsive phase of gait.Other functions of the subtalar joint have been dis-cussed previously by other authors. 1-4The characteristics of the axis of rotation of thesubtalar joint have attracted the attention of re-searchers over the years. Manter, 5 Hicks, 6 Root et al, 7and Isman and Inman 8 all suggested in their experi-mental studies that the subtalar joint axis is a solitaryaxis that passes through the talocalcaneal joint and isdirected obliquely from posterior-lateral-plantar toanterior-medial-dorsal. More current research by VanLangelaan, 9 Benink, 10 and Lundberg and Svensson 11investigated the axis of rotation of the subtalar jointusing more accurate methods of subtalar joint axisspatial location with roentgen stereophotogram-metry. By implanting metallic beads into both thetalus and the calcaneus and then taking standardizedx-rays of the feet in two cardinal planes, these re-searchers all demonstrated that the subtalar jointaxis is not a solitary axis but rather is better de-scribed as a number of discrete axes of rotation that,together, form a bundle of axes passing through thetalocalcaneal joint (Fig. 1). 9-11Therefore, the most accurate research to date hasdemonstrated that the subtalar joint axis no longercan be accurately described as a solitary axis of rota-tion but is best described as a multitude of axes ofrotation that all have different spatial locations. Inturn, each discrete spatial location of the subtalarjoint axis is dependent on the rotational position ofthe subtalar joint axis. 9-11 As such, the results fromthese researchers suggest that the morphology of thearticulating surfaces of the talus and calcaneus,Subtalar Joint Axis Location andRotational Equilibrium Theory of Foot FunctionKevin A. Kirby, DPM, MS*A new theory of foot function based on the spatial location of the subta-lar joint axis in relation to the weightbearing structures of the plantar footis proposed. The theory relies on the concept of subtalar joint rotationalequilibrium to explain how externally generated forces, such as groundreaction force, and internally generated forces, such as ligamentous andtendon tensile forces and joint compression forces, affect the mechani-cal behavior of the foot and lower extremity. The biomechanical effect ofvariations among individuals in the spatial location of the subtalar jointaxis are explored, along with their clinical consequences, to offer an ad-ditional theory of foot function, which may improve on existing podiatric bio-mechanics theory. (J Am Podiatr Med Assoc 91(9): 465-487, 2001)*Diplomate, American Board of Podiatric Orthopedicsand Primary Podiatric Medicine; Assistant Clinical Profes-sor, Department of Podiatric Biomechanics, California Col-lege of Podiatric Medicine, San Francisco, CA. Mailingaddress: 2626 N St, Sacramento, CA 95816.ORIGINAL ARTICLE