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13

The Foot and Ankle

SCOTT T. SAUER and PAUL S. COOPER

An overview of orthopedics would not be complete without an understanding 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 complaints 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 fibula 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 externally 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 transmitted 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

A B

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 hallucis 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: Saunders, 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 subtalar joint (Fig. 13-4). The large posterior facet articulates with the corresponding 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 longitudinal 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

 

A B

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

Navicular

Talus

A

Phalanges

Metatarsals

Cuneiform

bones

Navicular

Lisfranc’s joint

Cuboid

Calcaneus

B

C1

C2 C3

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 metatarsals terminate distally with articulations to the proximal phalanges

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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, proximal 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.

A

Anterior talofibular lig.

 

 

 

 

 

Interosseus membrane

 

Inferior

 

 

transverse lig.

Posterior tibiofibular lig.

 

 

 

Deltoid lig.

Posterior

 

talofibular lig.

 

Posterior

Calcaneofibular lig.

 

 

 

talocalcaneal lig.

 

 

Achilles tendon

 

B

FIGURE 13-6. The tibiofibular syndesmosis. The syndesmosis consists of the interosseous 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 tibiofibular, and interosseous ligaments. Injuries to these ligaments 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 calcaneocuboid 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. (From Mann RA. The great toe. Orthop Clin N Am 1989;20(4):520. Reprinted by permission.)

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no true transverse interosseous ligament between the first and second metatarsal bases. Instead, there is an oblique plantar ligament that connects the first cuneiform bone to the second metatarsal; it is known as Lisfranc’s ligament. Stabilizing the MTP joints are a deep transverse metatarsal ligament as well as medial and lateral collateral ligaments.

Muscles

The muscles of the leg are encased in four leg compartments: the superficial and deep posterior compartments, the lateral compartment, and the anterior compartment. The superficial posterior compartment includes the gastrocnemius, the plantaris, and the soleus muscles. This compartment houses the main plantarflexors of the ankle (Fig. 13-8), which are innervated by the tibial nerve. The tendon fibers of the soleus merge with the gastrocnemius tendon fibers to firm the tendo calcaneus or Achilles tendon. The Achilles tendon rotates 90 degrees to insert on the posterosuperior tuberosity of the calcaneus. The deep posterior compartment contains three muscles that invert the foot and serve as secondary plantarflexors: the tibialis posterior muscle, the flexor digitorum longus muscle, and the flexor hallucis longus muscle. The lateral compartment, innervated by the superficial peroneal nerve, contains the peroneus longus (FDL) and peroneus brevis muscles, the main evertors of the foot. The deep peroneus longus muscle courses distally underneath the cuboid to insert on the base of the first metatarsal and medial cuneiform bone. The peroneus brevis inserts on the base of the fifth metatarsal. The anterior leg compartment contains the tibialis anterior, the extensor hallucis longus (EHL), and the extensor digitorum longus (EDL) muscles. These muscles serve as the primary dorsiflexors of the ankle and foot; they are innervated by the deep peroneal nerve.

The intrinsic muscles of the foot are arranged in four plantar layers. The EDB is innervated by the deep peroneal nerve. The first superficial layer of the intrinsic plantar muscles includes the flexor digitorum brevis (FDB), the abductor hallucis, and the abductor digiti minimi (ADM) muscles. The second layer contains the muscles for toe motion and includes the quadratus plantae and lumbrical muscles as well as the tendons of the FHL and FDL. The third layer includes the flexor hallucis brevis, abductor hallucis, and the adductor hallucis (ADH) tendon. These muscles assist in first and fifth toe function. The fourth and deepest layer of intrinsic muscles contains the seven interosseous muscles and the insertions of the peroneus longus and anterior and posterior tibial tendons. The interossei are divided into two groups with four dorsal interossei and three plantar interossei. The dorsal interossei are involved in toe adduction, and the plantar interossei are involved in toe abduction.

480 S.T. Sauer and P.S. Cooper

Tibial axis

Dorsiflexion

 

 

Internal

External

A

Plantarflexion

B

Rotation

 

 

 

 

 

 

 

C

Eversion

Inversion

D

 

 

Adduction

Abduction

 

 

 

FIGURE 13-8. Motions of the foot and ankle. (A) Plantarflexion and dorsiflexion refer to movement of the foot downward or upward. Supination and pronation refer to rotation of the foot internally or externally around the longitudinal axis of the foot. (B) Internal and external rotation of the foot refer to motion around the vertical axis of the tibia. (C) Eversion directs the sole laterally, whereas inversion refers to rotation of the foot until the sole is directed medially. (D) Adduction and abduction describe motion of the forefoot toward or away from the midline. (From Weissman BNW, Sledge CB. Orthopedic Radiology. Philadelphia: Saunders, 1986. Reprinted with permission.)

Nerves and Vessels

The neurovascular structures of the foot and ankle include five major nerve branches and three arteries. The tibial and common peroneal nerves are terminal branches of the sciatic nerve, which arises from the lumbosacral plexus. The common peroneal nerve from L5 branches into the superficial peroneal nerve and deep peroneal nerve. The superficial peroneal nerve courses through the lateral compartment and exits the lateral compartment

13. The Foot and Ankle

481

approximately 10 to 15 cm above the lateral malleolus through a fascial defect and continues subcutaneously to provide sensory innervation of the dorsal aspect of the foot and toes. The deep peroneal nerve courses through the anterior compartment with the anterior tibial artery, continues into the foot with the dorsalis pedis artery to provide innervation to the intrinsic foot muscles, including the EDB and EHB muscles, and terminates as a cutaneous nerve in the first web space. The tibial nerve, a branch of S1, travels through the popliteal fossa into the deep posterior compartment. It courses medial to the Achilles tendon, enters the tarsal tunnel just posterior to the medial malleolus, and divides into the median and lateral plantar nerves. The medial and lateral plantar nerves supply motor and sensory function to the plantar aspect of the foot. The sural nerve is a sensory branch of the tibial nerve and provides sensation to the posterolateral hindfoot and lateral border of the foot. The saphenous nerve courses along the anteromedial aspect of the lower limb posterior to the greater saphenous vein and provides sensation to the medial side of the ankle.

Vascular supply to the foot and ankle is derived from the anterior and posterior tibial arteries and peroneal arteries. The anterior tibial artery becomes the dorsalis pedis in the foot. The posterior tibial artery divides into the medial plantar artery and lateral plantar artery to supply the plantar structures in the foot. The peroneal artery branches from the posterior tibial artery and travels posterior to the interosseous membrane, deep to the FHL muscle, terminating at the distal tibiofibular joint.

The major structures of the venous system of the leg include the greater saphenous vein and the lesser saphenous vein. The greater saphenous vein courses anteromedial to end in the femoral vein; it drains the dorsum of the foot. The lesser saphenous vein runs posterior to the fibula and drains the lateral foot and arch.

Gait Cycle

The gait cycle consists of one heel strike to the next heel strike of the same foot. It is traditionally divided into a stance phase that comprises 62% of the cycle and the swing phase which constitutes the remaining 38% of the cycle. At initial heel strike, the lower extremity is in internal rotation. The ankle joint is plantarflexed and the subtalar joint is everted. The transverse tarsal joint is unlocked to allow shock absorption. Anterior compartment muscles are active in helping decelerate the limb. At foot flat, the lower extremity externally rotates, the ankle joint dorsiflexes, and the subtalar joint begins to invert; this increases stability throughout the midfoot in anticipation of push-off. Anterior compartment muscles become inactive, intrinsic muscles of the foot become active, and the posterior compartment calf muscles are contracting. At pre-swing, the ankle joint is in plantarflexion.

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