The ankle/foot complex is structurally analogous to the wrist/hand complex of the upper extremity but has a number of distinct differences to optimize its primary role to bear weight. The complementing structures of the ankle/foot complex permit both stability and mobility depending on conditions acting on it. The foot is able to sustain large weight-bearing stresses while accommodating to a variety of surfaces and activities. The foot must be stable to provide an adequate base of support and function as a rigid lever for pushing-off when walking, running, or jumping. In contrast, the foot must also be mobile to adapt to uneven terrain, absorb shock as the foot hits the ground, and dampen rotations imposed by the more proximal joints of the lower extremity. The ankle/foot complex meets these diverse requirements through the integrated movements of its 28 bones that form 25 component joints. These joints include the proximal and distal tibiofibular joints, talocrural (ankle) joint, talocalcaneal (subtalar) joint, talonavicular and calcaneocuboid joints (transverse tarsal joints), five tarsometatarsal joints, metatarsophalangeal joints, and nine interphalangeal joints.
To facilitate description and understanding of the ankle/foot complex, the bones of the foot are traditionally divided into three functional segments. These are the hindfoot (posterior segment), composed of the talus and calcaneus; the midfoot (middle segment), composed of the navicular, cuboid, and three cuneiform bones; and the forefoot (anterior segment), composed of the metatarsals and the phalanges (Fig. 12–1). These terms are commonly used in descriptions of ankle/foot dysfunction or deformity and are similarly useful in understanding normal ankle and foot function.
Functional segments and bones of the foot.
Ankle or foot pathology can be related to the integrated multifunctional structures of the ankle/foot complex combined with the demands of stability and mobility placed upon these structures. Additionally, the ankle and foot complex must not only respond to forces from the ground but also imposed forces from the spine, pelvis, hip, and knee. Structural abnormalities can lead to altered movements between joints and contribute to excessive stresses that result in injury to the ankle/foot complex.1
Case 12-1: Patient Case
Arnold Benson is a 63-year-old man seeking intervention for right foot pain. Three weeks ago, at the suggestion of his physician, Mr. Benson (who is quite overweight) started a walking program. Mr. Benson reports that after about a week, he had pain at his right heel that was greatest when he first got out of bed in the morning. He reports that this pain eases after a few steps but increases again when he walks more than two blocks. He says he has "flat feet," which seem to have worsened over the past few years. Despite having a sedentary job, Mr. Benson identifies that his feet often ache at the end of the day. He also reports that ...