13 The Foot and Ankle Scott T. Sauer and Paul S. Cooper An overview of orthopedics would not be complete without an understand- ing of the foot and ankle. This area of the body is often forgotten in the scheme of things, and yet it is one of the most common sources of com- plaints in any physician’s office. Painful feet are seen in emergency rooms and family practitioners’ offices. Ankle discomfort is seen in medical clinics and on the sidelines of recreational sporting activities. This chapter is intended familiarize the student of medicine, whether an actual medical student, resident, or practitioner, with the anatomy, diagnostic tools, and some common conditions that affect the foot and ankle. Bones and Joints The bony anatomy of the foot and ankle consists of the distal tibia and fi bula in the leg and the 26 major bones that compose the foot. The tibia distally terminates into the metaphyseal plafond with its medial malleolus. The lateral surface of the distal tibia has a sulcus to accommodate the adjacent fibula, forming the distal tibiofibular joint. The distal fibula, which lies laterally and slightly posterior to the tibia, is held there by the inferior tibiofibular ligaments. The fibula forms the lateral malleolus of the ankle joint. The relationship of the fibula to the tibia is not static. With ankle dorsiflexion, the fibula laterally translates, proximally migrates, and exter- nally rotates. The ankle is a diarthrodial joint (Figs. 13-1, 13-2). It consists of an articulation between the talus and the mortise of the tibia and fibula. Dorsiflexion of the ankle joint is coupled with eversion of the foot, and plantarflexion is combined with inversion. The distal fibula provides a static buttress over the talus laterally and also bears one-sixth of the trans- mitted weight during the stance phase of gait. The foot is composed of 7 tarsals, 5 metatarsals, and 14 phalanges. Three anatomic groupings are defined for descriptive purposes: the hindfoot, the midfoot, and the forefoot (see Fig. 13-3). The hindfoot 472 13. The Foot and Ankle 473 AB C Figure 13-1. (A, B) Photographic, diagrammatic, and radiologic anatomy of the normal ankle in anteroposterior views. (C) Note equal width of cartilage spaces and alignment of lateral talus with posterior cortex (arrow) on mortise view. (From Weissman BNW, Sledge CB. Orthopedic Radiology. Philadelphia: Saunders, 1986. Reprinted with permission.) consists of the talus and calcaneus bones, and the talus consists of a body, neck, and head. Two-thirds of the talus is covered by articular cartilage. There are no muscle or tendon attachments on this bone. The talar dome is the superior portion of the body that forms the mortise with the tibia and fibula. The dome is wider anteriorly, which allows for stability in the mortise during dorsiflexion. Posteriorly, a sulcus is formed between the posterolateral and posteromedial tubercles to accommodate the flexor hal- lucis longus (FHL) tendon. The inferior surface of the talus articulates 474 S.T. Sauer and P.S. Cooper Figure 13-2. Photographic (A) and radiologic (B) anatomy of the normal ankle in lateral projection. (From Weissman BNW, Sledge CB. Orthopedic Radiology. Philadelphia: Saun- ders, 1986. Reprinted with permission.) Forefoot Midfoot Figure 13-3. Anatomic regions of the foot. Hindfoot (From Weissman BNW, Sledge CB. Orthopedic Radi- ology. Philadelphia: Saunders, 1986. Reprinted with permission.) 13. The Foot and Ankle 475 with the corresponding facet of the calcaneus to create a subtalar joint. The calcaneus is the largest bone in the foot, with its longitudinal axis directed dorsally and laterally. Its superior surface articulates with the talus and three facets—anterior, medial, and posterior—to form the sub- talar joint (Fig. 13-4). The large posterior facet articulates with the corre- sponding articular facet on the inferior surface of the talus. The middle facet overlies the sustentaculum tali (a dense, medial projection of the calcaneus that contains a groove to accommodate the FHL tendon sheath) and is often merged with the anterior facet. The middle and anterior facets articulate with the undersurface of the talar head. The midfoot consists of the navicular, cuboid, and three cuneiform bones. The tarsonavicular bone articulates with the talar head and lies medially to the cuboid bone. It functions as a keystone for the medial lon- gitudinal arch of the foot. The distal surface is composed of three facets that articulate with the medial, middle, and lateral cuneiform bones, respectively; this is also the insertion site for the posterior tibial tendon. In 10% of people, an unfused accessory navicular bone may be present. The cuboid bone forms an articulation with the calcaneus proximally and the fourth and fifth metatarsals distally. Laterally, a groove accommodates the peroneus longus tendon as it courses plantarly. Three cuneiform bones have distal articulations with the first, second, and third metatarsals and contribute to the formation of part of the tarsometatarsal, or Lisfranc’s Site of talocalcaneal ligament Talocalcaneo navicular joint Fifth metatarsal Sustentaculum tali Subtalar joint AB Figure 13-4. Photographic (A) and diagrammatic (B) anatomy of the normal ankle in tangential calcaneal (Harris) projection. (From Weissman BNW, Sledge CB. Orthopedic Radiology. Philadelphia: Saunders, 1986. Reprinted with permission.) 476 S.T. Sauer and P.S. Cooper Phalanges Metatarsals Cuneiform bones Lisfranc’s joint Navicular Cuboid Talus Calcaneus A B Phalanges Metatarsals Cuneiform C1 bones C2 C3 Navicular Cuboid Talus Calcaneus D C Figure 13-5. Photographic, diagrammatic, and radiologic anatomy of the normal foot in posteroanterior (A, B) and internal oblique (C, D) projections. (From Weissman BNW, Sledge CB. Orthopedic Radiology. Philadelphia: Saunders, 1986. Reprinted with permission.) joint (Fig. 13-5). The middle cuneiform bone is shorter axially, adding to greater stability in the second tarsometatarsal joint; this is also known as the keystone. The forefoot consists of the metatarsal and phalangeal bones. Five meta- tarsals terminate distally with articulations to the proximal phalanges 13. The Foot and Ankle 477 creating metatarsal phalangeal (MTP) joints. The fifth metatarsal is a prominent styloid process proximally to which the peroneus brevis attaches. Each of the lesser toes, two through five, has three phalanges—a proximal, middle, and distal phalanx—and the hallux has only two phalanges, proxi- mal and distal. Each distal phalanx terminates in a tuft of bone and serves as an anchor for the toe pad. Underlying the first MTP joint are the two sesamoid bones. Tibial (medial) and fibular (lateral) sesamoid bones are encased by the flexor hallucis brevis tendon (FHB), which inserts at the base of the proximal phalanx. Ligaments The ligamentous structures of the ankle joint (Fig. 13-6) include the medial deltoid ligament complex and the lateral ankle ligament complex. The deltoid ligament medially has both superficial and deep components Interosseus membrane Anterior inferior tibiofibular lig. Deltoid lig. Anterior talofibular lig. A Interosseus membrane Inferior transverse lig. Posterior tibiofibular lig. Posterior Deltoid lig. talofibular lig. Calcaneofibular lig. Posterior talocalcaneal lig. Achilles tendon B Figure 13-6. The tibiofibular syndesmosis. The syndesmosis consists of the inter- osseous membrane, the anterior and the posterior inferior tibiofibular ligaments, and the inferior transverse ligament. (A) Anterior view; (B) posterior view. (From Weissman BNW, Sledge CB. Orthopedic Radiology. Philadelphia: Saunders, 1986. Reprinted with permission.) 478 S.T. Sauer and P.S. Cooper and is the primary contributor to medial stability of the ankle joint. The lateral ligament complex consists of three major ligaments including the anterior talofibular ligament (ATFL), the calcaneofibular ligament (CFL), and the posterior talofibular ligament (PTFL); these contribute to lateral stability of the ankle joint. Ligaments of the ankle syndesmosis include the anterior tibiofibular, posterior tibiofi bular, and interosseous ligaments. Injuries to these liga- ments may occur with hyperdorsiflexion and external rotation, creating a “high-ankle sprain” that is seen especially in athletes. Ligamentous support of the subtalar joint is contributed by the CFL, the ligaments of the anterior capsule, the posterior subtalar joint capsule, the interosseous talocalcaneal ligaments, and the ligaments of the tarsal canal. The midfoot joints are stabilized by multiple ligaments as well as the intrinsic bony architecture of the wedge-shaped cuneiform bones. Little motion occurs through the midfoot. Stabilizing ligaments include the bifurcate ligament, a V-shaped structure composed of the lateral calcaneonavicular and medial calcaneo- cuboid ligaments, which insert on the anterior process of the calcaneus, navicular, and cuboid bones, respectively. Superficial and deep plantar ligaments span from the calcaneus to the cuboid bone and metatarsals; these serve as static stabilizers of the longitudinal arch. Another important structure is the plantar aponeurosis (or plantar fascia). This thick fibrous structure runs from the plantar surface of the calcaneus to distally insert into the metatarsals; it stabilizes the arch during gait (Fig. 13-7). There is Figure 13-7. Plantar aponeurosis and windlass mechanism provide stability to the longitudinal arch of the foot when the first metatarsophalangeal joint is forced into dorsiflexion and it secondarily plantarflexes the first metatarsal.