ANKLE JOINT

The true ankle (talocrural) joint is a saddle-shaped hinge joint between the distal ends of the tibia and fibula and the trochlea of the talus (see Figure 7-2 ). Most of the body weight is transmitted through the tibia to the talus. The medial (tibial) malleolus and the lateral (fibular) malleolus extend distally to form the ankle mortise that stabilizes the talus and prevents rotation. The joint capsule is lax anteriorly and posteriorly but is strengthened medially by the powerful deltoid ligament and laterally by three distinct bands: the anterior and posterior talofibular ligaments and the calcaneofibular ligament . The synovial cavity does not normally communicate with other joints, adjacent tendon sheaths, or bursae. Tendons crossing the ankle region are invested for part of their course in tenosynovial sheaths ( Figures 7-3 and 7-4 ).

In the anterior (extensor) compartment, the tendons of the tibialis anterior (most medial), extensor hallucis longus, extensor digitorum longus, and peroneus tertius (most lateral) muscles are bound down by the superior and inferior extensor retinaculi (see Figure 7-3 ). The dorsalis pedis artery runs between the extensor hallucis longus and extensor digitorum longus tendons.

BURSAE, TENDONS, AND TENDON SHEATHS OF THE ANTERIOR (EXTENSOR) AND PERONEAL COMPARTMENTS OF THE ANKLE.

(From Hochberg H, Silman AJ, Smolen JS, et al., eds. Rheumatology, 3rd ed. Edinburgh, UK: Mosby, 2003.)

In the lateral (peroneal) compartment, the peroneus longus and brevis tendons are enclosed in a single synovial sheath that runs behind and below the lateral malleolus (see Figure 7-3 ). The superior and inferior peroneal retinaculi strap down the peroneal tendons.

In the medial (flexor) compartment, the tendons of the tibialis posterior (most medial), flexor digitorum longus, and flexor hallucis longus (most lateral) muscles are held down by the flexor retinaculum, forming the tarsal tunnel (see Figure 7-4 ). The flexor retinaculum bridges the interval between the medial malleolus and the calcaneus. The posterior tibial artery and nerve lie between the tendons of the flexor digitorum longus and the flexor hallucis longus.

BURSAE, TENDONS, AND TENDON SHEATHS OF THE MEDIAL (FLEXOR) COMPARTMENT OF THE ANKLE.

(From Hochberg H, Silman AJ, Smolen JS, et al., eds. Rheumatology, 3rd ed. Edinburgh, UK: Mosby, 2003.)

Posteriorly, the common tendon of the gastrocnemius and soleus (Achilles tendon or tendocalcaneus) is inserted into the posterior surface of the calcaneus. The tendon does not have a synovial sheath but is surrounded by a loose connective tissue known as paratendon or peritenon. The tendon of the plantaris muscle, which originates from the lateral femoral epicondyle and lateral meniscus, runs obliquely between the soleus and gastrocnemius muscles to insert into the medial aspect of the superior calcaneal tuberosity medial to the Achilles tendon.

Several bursae exist around the ankle ( Figure 7-5 ; also see Figures 7-3 and 7-4 ). The retrocalcaneal bursa, located between the Achilles tendon insertion and the posterior surface of the calcaneus, is surrounded anteriorly by Kager’s fat pad. The bursa serves to protect the distal Achilles tendon from frictional wear against the posterior calcaneus. The retroachilleal bursa lies between the skin and the Achilles tendon and protects the tendon from external pressure. The subcalcaneal bursa lies beneath the skin over the plantar aspect of the calcaneus. The medial and lateral subcutaneous malleolar, or “last” bursae, are located near the medial and lateral malleoli, respectively.

BURSAE AROUND THE ANKLE.

(From Hochberg H, Silman AJ, Smolen JS, et al., eds. Rheumatology, 3rd ed. Edinburgh, UK: Mosby, 2003.)

Movements of the ankle include dorsiflexion and plantar flexion ( Figure 7-6 ). The axis of movement passes approximately through the malleoli. The gastrocnemius and soleus muscles are the prime plantar flexors of the ankle. The tibialis anterior and extensor digitorum longus muscles are the prime dorsiflexors.

ANKLE JOINT: NORMAL RANGE OF DORSIFLEXION AND PLANTAR FLEXION.

(From Hochberg H, Silman AJ, Smolen JS, et al., eds. Rheumatology, 3rd ed. Edinburgh, UK: Mosby, 2003.)

SUBTALAR JOINT

The subtalar (talocalcaneal) joint lies between the talus and the calcaneus and has three facets: anterior, middle, and posterior . Its tight capsule permits little synovial expansion, about 30° of inversion (sole of the foot turned inward), and 10° to 20° of eversion (sole turned outward).

MIDTARSAL JOINT

The midtarsal (transverse tarsal) joint comprises the combined talonavicular and calcaneocuboid joints (see Figure 7-1 ). The cuboid and navicular are usually joined by fibrous tissue, but a synovial cavity may exist. The midtarsal joint contributes to inversion (supination) and eversion (pronation) movements at the subtalar joint. It also allows 20° of adduction (foot turned toward the midline) and 10° of abduction (foot turned away from the midline). The axis of rotation of the subtalar and midtarsal joints is such that inversion is invariably accompanied by adduction of the forefoot, called supination, and eversion by abduction of the forefoot, called pronation. The tibialis posterior and tibialis anterior, aided by the gastrocnemius, invert the foot. The peroneus longus, peroneus brevis, and extensor digitorum longus evert the foot, aided by the peroneus tertius.

The intertarsal joints between the navicular, cuneiforms, and cuboid are plane-gliding joints that intercommunicate with one another and with the intermetatarsal and tarsometatarsal joints (see Figure 7-1 ).

METATARSOPHALANGEAL JOINTS

The metatarsophalangeal (MTP) joints are ellipsoid synovial joints that lie about 2 cm proximal to the webs of the toes. Their capsule is strengthened by the collateral ligaments on each side and by the plantar ligament (plate) on the plantar surface. The plantar ligaments are fused with the flexor tendon sheaths and are connected together by the transverse metatarsal ligament, which holds the metatarsal heads together to prevent excessive splaying of the forefoot. Small intermetatarsophalangeal bursae are frequently present between the metatarsal heads ( Figure 7-7 ). The long extensor tendons form the extensor expansions (aponeuroses), which overlay the dorsum of the MTP joints and digits. The intrinsic muscles of the foot—including the flexor hallucis brevis, the lumbricals, the interossei, and the flexor digiti minimi brevis—are partly inserted into the extensor expansions and assist in plantar flexion of the MTP joints. The extensor hallucis longus, extensor digitorum longus, and extensor digitorum brevis dorsiflex the MTP joints. Movements at the first MTP joint consist of dorsiflexion (70° to 90°) and plantar flexion (about 35° to 50°). The other MTP joints permit about 40° dorsiflexion and 40° plantar flexion, as well as a few degrees of abduction (away from the second toe) and adduction (toward the second toe).

PLANTAR SURFACE OF THE FOOT: FLEXOR TENDON SHEATHS AND BURSAE.

(From Hochberg H, Silman AJ, Smolen JS, et al., eds. Rheumatology, 3rd ed. Edinburgh, UK: Mosby, 2003.)

INTERPHALANGEAL JOINTS

The proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints are hinge joints. The plantar flexors are the flexor hallucis longus and brevis (great toe), the flexor digitorum longus (the lateral four toes at the DIP joints), and the flexor digitorum brevis (the lateral four toes at the PIP joints). The dorsiflexors are the extensor hallucis longus and the extensor digitorum longus and brevis, assisted by the interossei and lumbricals. The digital flexor tendon sheaths enclose the long and short flexor tendons, extending along the length of the toes to the distal third of the sole proximally (see Figure 7-7 ). A bunion bursa is commonly located over the medial aspect of the first MTP joint. Less frequently, a bursa is present over the fifth metatarsal head ( bunionette or tailor’s bunion or bursa ; see Figure 7-7 ).

The PIP joints of the toes do not normally hyperextend, and plantar flexion is limited to approximately 50°. The DIP joints allow 10° to 30° dorsiflexion and 40° to 50° plantar flexion.

ARCHES OF THE FOOT

The arches of the foot are the result of the intrinsic mechanical arrangement of the bones supported by ligaments and intrinsic and extrinsic muscles, particularly the tibialis posterior and anterior muscles. The arches of the foot act as shock absorbers during weight bearing. Each foot has two longitudinal and two transverse arches ( Figure 7-8 ). The medial longitudinal arch is high and flexible and comprises the medial three rays digits—cuneiforms, navicular, and talus—and the calcaneus. It provides a resilient spring for weight bearing and forward propulsion in walking. The lateral two rays, cuboid and calcaneus, constitute the low, more rigid lateral longitudinal arch. The anterior transverse metatarsal arch includes the second, third, and fourth metatarsals and the heads of the first and fifth metatarsals. It becomes flattened on weight bearing but returns to its arched position when the weight is removed. The transverse midtarsal arch is more rigid and lies across the midtarsal region.

THE FOOT: MEDIAL LONGITUDINAL ARCH AND LIGAMENTS.

(From Hochberg H, Silman AJ, Smolen JS, et al., eds. Rheumatology, 3rd ed. Edinburgh, UK: Mosby, 2003.)

The longitudinal arches are held together by several layers of ligaments: the spring (calcaneonavicular) ligament; the long and short plantar ligaments that join the calcaneus to the metatarsal bases; and, most superficially, the plantar fascia (aponeurosis; see Figure 7-8 ). The plantar fascia extends anteriorly from the medial calcaneal tuberosity and splits at about the middle of the sole into five bands, one for each toe, to be attached to the transverse metatarsal ligament, the flexor tendon sheaths of the toes, and the proximal phalanges. The plantar fascia acts as a strong mechanical tie for the longitudinal arches by joining the three main weight-bearing points of the foot: the calcaneus, the first metatarsal head (including the two sesamoids), and the fifth metatarsal heads . During “toe off” in the later portion of stance phase, it helps the arch to reform and the foot to become more rigid.