K. Li et al. (Eds.): LSMS 2007, LNBI 4689, pp. 111–119, 2007. © Springer-Verlag Berlin Heidelberg 2007 Effect of the Plantar Ligaments Injury on the Longitudinal Arch Height of the Human Foot Yunfeng Yang 1 , Guangrong Yu 1 , Wenxin Niu 2 , Jiaqian Zhou 1 , Yanxi Chen 1 , Feng Yuan 1 , and Zuquan Ding 2 1 Orthopaedic department of Tongji hospital affiliated to Tongji University, Shanghai, China xichangyang@gmail.com 2 School of Life Science and Technology of Tongji University, Shanghai, China Abstract. Most of the foot deformities relate with the arch collapse or instability, especially the medial longitudinal one. Though the function of the plantar fascia to the arch height has been investigated by some authors, the other plantar ligaments` effects are still unclear. The purpose of this study is to explore the roles of the plantar soft tissues in the foot arch biomechanics, including the plantar fascia, spring ligament complex, short plantar ligament and long plantar ligament through normal adult fresh frozen specimens in different injured condition. Also, a three-dimensional finite element model of a normal left foot was developed, which was comprising most joints of the foot and consisted of bone segments, major ligaments and plantar soft tissue. The validity of the three-dimensional finite element model was verified by comparing results with experimentally measured data via the displacements and Von-mise stress of each bone segments. These intrinsic ligaments of the foot arch were sectioned in different sequences in the cadaveric experiment, which simulated the different pathologic situations of the plantar ligaments injury and described the bone segments displacement and stress distribution. 1 Introduction The main factors that contribute to an acquired flat foot deformity are excessive tension in the triceps surae, obesity, PTT dysfunction, or ligamentous laxity in the spring ligament, plantar fascia, or other supporting plantar ligaments. Too little support for the arch or too much arch flattening effect will lead to collapse of the arch. The plantar fascia, or plantar aponeurosis, is the investing fascial layer of the plantar aspect of the foot. It is part of the retinacular system, which consists of a network of connective and adipose tissues whose main functions are to support and protect underlying vital structures of the body. The anatomy and functions of the plantar fascia has been well described by Sarrafianand [1] and others [2],[3],[4] . The spring ligament has been reported to be composed of the inferior calcaneonavicular and superomedial calcaneonavicular ligaments and an important stabilizer of the longitudinal arch of the human foot [5] .