I. Anatomy
A. Bones and ligaments
1. The ankle joint (
Figure 1)
a. The ankle joint is a ginglymus joint; it includes the tibia, talus, and fibula.
b. The talar dome is biconcave with a central talar sulcus.
c. The radius of curvature is greater laterally.
d. Viewed axially, the joint is trapezoidal and wider anteriorly.
e. The talus is the only tarsal bone without muscular or ligamentous insertions.
f. The medial malleolus and lateral malleolus have osseous grooves for the posterior tibial tendon (PTT) and peroneal tendons, respectively.
g. Lateral ankle ligaments—The lateral ankle ligamentous complex is made up of three ligaments.
i. Anterior talofibular ligament (ATFL)—The ATFL extends from the anterior aspect of the distal fibula to the body of the talus. Strain in the ATFL increases with plantar flexion, inversion, and internal rotation.
ii. Calcaneofibular ligament (CFL)—The CFL extends from the tip of the fibula posterior to its insertion on the lateral wall of the calcaneus. It runs deep to the peroneal tendons and crosses the subtalar joint. The CFL is under increased strain with dorsiflexion and inversion.
iii. Posterior talofibular ligament (PTFL)—The PTFL originates broadly at the posterior fibula and inserts mainly at the posterolateral tubercle of the talus. It is a broad, strong ligament that is congruous with the posterior capsule of the ankle and subtalar joint.
h. Deltoid ligament
i. The deltoid ligament is a triangle-shaped ligament with the apex at the medial malleolus and with fibers extending to the calcaneus, talus, and navicular.
[Figure 1. Lateral ankle and subtalar ligaments viewed laterally (A) and anteriorly (B).]
[
Figure 2. The hallux MTP joint from above (A) and in cross section (B).]
ii. The ligament is divided into superficial and deep components. The superficial component has three parts, extending anteriorly to the navicular, inferiorly to the sustentaculum, and posteriorly on the talar body. The deep deltoid ligament extends in two bands from the medial malleolus to the talar body just inferior to the medial facet.
iii. Syndesmosis—The tibiofibular articulation is made up of the tibial incisura fibularis and its corresponding fibular facet. It has three ligamentous structures that are variably responsible for its support: anterior inferior tibiofibular ligament (AITFL)—35%; interosseous ligament—22%; posterior talofibular ligament—43%.
2. Hindfoot and midfoot
a. The subtalar joint has three facets: one posterior, one middle, and one anterior.
i. The posterior facet is the largest.
ii. The middle facet rests on the sustentaculum of the calcaneus and is located medially.
iii. The anterior facet is often continuous with the talonavicular joint.
b. The transverse tarsal joint, or the Chopart joint, is made up of the talonavicular and calcaneocuboid joints and acts in concert with the subtalar joint to control foot flexibility during gait.
i. The talonavicular joint is supported by the spring ligament complex, which has two separate components: the superior medial calcaneonavicular (SMCN) ligament and the inferior calcaneonavicular (ICN) ligament.
ii. The calcaneocuboid joint is saddle shaped. It is supported plantarly by the inferior calcaneocuboid ligaments (superficial and deep) and superiorly by the lateral limb of the bifurcate ligament.
c. The naviculocuneiform and intercuneiform joints are connected by dense ligamentous structures that allow little motion between the joints.
d. The tarsometatarsal (TMT) joint is made up of the metatarsocuneiform joints 1, 2, and 3, and the metatarsocuboid joints 4 and 5.
i. The osseous anatomy functions as a transverse Roman arch in the axial plane with the dorsal surface wider than the plantar surface.
ii. The second metatarsal base functions as the keystone.
iii. The ligamentous support of the TMT joint is in three layers. The strongest layer is the interosseous layer, which includes the Lisfranc ligament. This ligament originates from the plantar aspect of the medial cuneiform and extends to the base of the second metatarsal. The plantar layer is the next strongest, and the dorsal layer is the weakest.
3. Forefoot
|
a. |
The first metatarsophalangeal (MTP) joint is made up plantarly by the dense phalangeosesamoidal complex, or plantar plate (Figure 2). |
[
Table 1. The Compartments and Muscles of the Leg]
|
b. |
The plantar fascia originates from the medial calcaneal tuberosity and inserts distally on the base of the fifth metatarsal (lateral band), as well as the plantar plate and bases of the five proximal phalanges. |
B. Muscles and tendons
1. Compartments of the leg (Table 1)
a. The anterior compartment contains the tibialis anterior (TA), extensor hallucis longus (EHL), extensor digitorum longus (EDL), and peroneus tertius muscles, as well as the anterior tibial artery and deep peroneal nerve (DPN). Deep to the extensor retinaculum of the ankle, the anterior tibial artery and DPN lie between the TA and EHL tendons.
b. The superficial posterior compartment contains the gastrocnemius-soleus complex and the plantaris muscle.
i. Two heads of the gastrocnemius muscle originate from the medial and lateral femoral condyles and act as knee flexors as well as ankle plantar flexors.
ii. The soleus originates on the tibia and fibula running deep to the gastrocnemius and joining it distally to form the Achilles tendon.
iii. The Achilles tendon fibers twist medially 90° so that the superficial fibers at the myotendinous junction insert laterally on the calcaneus.
iv. The plantaris is absent in 7% of individuals.
c. The deep posterior compartment contains the PTT, flexor digitorum longus (FDL), and flexor hallucis longus (FHL), which become entirely tendinous as they enter the ankle.
i. Posterior to the medial malleolus, the posterior compartment structures enter the fibroosseous tarsal tunnel.
ii. Oriented from anteromedial to posterolateral in the tarsal tunnel are the PTT, FDL tendon, posterior tibial artery, tibial nerve, and FHL tendon.
iii. The FHL and FDL have interconnections at the knot of Henry in the plantar midfoot.
d. The lateral compartment contains the peroneus longus and peroneus brevis muscles, the superficial peroneal nerve (SPN), and the peroneal artery.
i. The tendons enter a system of fibro-osseous tunnels posterior to the fibula to the level of their insertion.
ii. The superior peroneal retinaculum is located at the distal 3 cm of the fibula; the inferior peroneal retinaculum is contiguous with the inferior extensor retinaculum dorsally and inserts on the peroneal tubercle of the calcaneus, which divides the peroneal tendon sheath into separate compartments for the peroneus brevis (dorsal) and peroneus longus (plantar).
iii. The peroneus brevis inserts at the base of the fifth metatarsal.
iv. The peroneus longus curves sharply beneath the cuboid, where it crosses plantarly to insert medially at the base of the first TMT joint. An osseous groove is present at the plantar cuboid, and an os peroneus is present in 5% to 26% of individuals.
v. Accessory peroneals (including the peroneus quartus) are present in 12% of individuals and can contribute to pathology.
2. Muscles of the plantar foot
a. First layer—The first layer is the most superficial of the plantar layers. It contains the flexor digitorum brevis (FDB), abductor hallucis (AbH), and abductor digiti minimi (ADM) muscles.
b. Second layer—This layer contains the quadratus plantae (QP) and lumbrical muscles as well as the FDL and FHL tendons. On the plantar surface of the layer lie the medial and lateral plantar artery and nerves.
c. Third layer—The third layer contains the oblique and transverse heads of the adductor hallucis (AdH), flexor hallucis brevis (FHB), and flexor digiti minimi brevis (FDM) muscles.
d. Fourth layer—This layer is the deepest. It contains the fibro-osseous tunnels for the posterior tibial and peroneus longus tendons to their final insertions. It contains the four dorsal interossei, three plantar interossei, and four lumbrical muscles.
3. Muscles of the dorsal foot
a. Laterally, the extensor digitorum brevis (EDB) arises from the anterior process of the calcaneus.
b. Medially, the extensor hallucis brevis (EHB) is variably present.
c. Each of these muscles contributes tendinous slips to the long extensor tendons or directly to the base of each proximal phalanx.
d. Deep to these muscles course the dorsalis pedis artery and deep peroneal nerve.
C. Arteries
1. Three major arteries typically supply the ankle and foot.
a. Posterior tibial artery—This artery bifurcates into the medial and lateral plantar arteries beneath the sustentaculum.
b. Peroneal artery—The peroneal artery arises from the tibioperoneal trunk and forms a perforating artery that pierces the interosseous membrane at the distal third of the leg.
c. Anterior tibial artery—This artery arises from the popliteal artery below the knee and descends through the anterior compartment of the leg. It combines variably with the perforating branch of the peroneal artery to form the dorsalis pedis artery.
2. Plantar arcades—The medial plantar artery and lateral plantar artery typically branch to give superficial and deep branches, which anastamose distally in the midfoot to give the superficial plantar arcade and deep plantar arch.
3. Osseous vascular supply of interest
a. Talus (
Figure 3)
i. The blood supply to the talus is from five bony regions: the tarsal canal, the sinus tarsi, the superior neck, the medial body, and the posterior tubercle.
ii. The talar neck is well vascularized by an anastomotic ring of vessels that receives blood dorsally from the DPA, laterally from the perforating peroneal artery through the lateral tarsal artery, and inferiorly through the artery of the tarsal canal.
iii. The talar body receives most of its blood supply retrograde through the artery of the tarsal canal, which can be disrupted during talar dislocations and talar neck fractures, making the bone prone to osteonecrosis and nonunion. Lesser contributions to the talar body are from the deltoid branches and posterior tubercle branches of the posterior tibial artery.
[Figure 3. Blood supply of the talus.]
b. Navicular
i. The periphery is well vascularized, but the central third is less vascular.
ii. The navicular is prone to stress fracture in the dorsal third, where the compressive forces are concentrated.
c. Fifth metatarsal
i. Penetrating the fifth metatarsal medially at the junction of its proximal and middle thirds, the main nutrient vessel to the fifth metatarsal then divides into proximal and distal vessels.
ii. The proximal blood supply to the fifth metatarsal is through the tuberosity, creating a watershed area at the proximal metaphyseal/diaphyseal junction, which is prone to stress fractures and nonunion.
D. Nerves of the foot (
Figure 4 and
Table 2)
1. Tibial nerve—The tibial nerve travels in the deep posterior compartment of the leg and has three major branches.
a. Medial calcaneal nerve—This nerve innervates the plantar medial heel.
b. Medial plantar nerve—This nerve supplies sensory innervation to the plantar-medial foot, the plantar aspect of toes 1, 2, and 3, and the medial half of the fourth toe. It provides motor innervation to the FHB, AbH, FDB, and the first lumbrical.
c. Lateral plantar nerve—This nerve provides sensation to the plantar-lateral foot, the lateral fourth toe, and the fifth toe. Motor innervation is provided to the remaining plantar muscles not innervated by the medial plantar nerve.
i. The first branch of the lateral plantar nerve (Baxter's nerve) courses anterior to the medial calcaneal tuberosity between the QP and the FDB, terminally innervating the ADM.
ii. Baxter's nerve is implicated in heel pain but provides no cutaneous innervation.
2. Superficial peroneal nerve (SPN)—The SPN divides into medial and intermediate dorsal cutaneous nerves of the foot proximal to the ankle.
3. Deep peroneal nerve (DPN)—The DPN travels in the anterior compartment, where it innervates the tibialis anterior, extensor digitorum longus (EDL), and extensor hallucis longus (EHL) muscles before traveling distally over the anterior ankle capsule between the tibialis anterior and
[Figure 4. A, Cutaneous innervation of the leg and ankle. 1 = lateral sural cutaneous nerve, 2 = superficial peroneal nerve, 3 = saphenous nerve, 4 = posterior femoral cutaneous nerve, 5 = sural nerve. B,Cutaneous innervation of the dorsal and plantar foot. 1 = peroneal cutaneous nerve, 2 = saphenous nerve, 3 = superficial peroneal nerve, 4 = deep peroneal nerve, 5 = sural nerve, 6 = medial plantar nerve, 7 = lateral plantar nerve, 8 = medial calcaneal nerve, 9 = first calcaneal nerve.]
[Table 2. Nerves at Risk During Surgery of the Foot]
EHL tendons. It innervates the EDB and EHB muscles in the foot and provides sensation to the first dorsal web space.
4. Sural nerve—The sural nerve has a variable origin from confluent branches of the tibial and common peroneal nerve. It provides sensation to the dorsolateral foot and dorsal fourth and fifth toes.
5. Saphenous nerve—The saphenous nerve is the terminal branch of the femoral nerve and supplies sensation to the medial side of the foot.
II. Biomechanics
A. Ankle and syndesmosis
1. The ankle joint is made up of the tibia, fibula, and talus.
a. Its primary motion is dorsiflexion and plantar flexion.
b. With the foot fixed, dorsiflexion is accompanied by internal tibial rotation, and plantar flexion is accompanied by external tibial rotation.
2. The bimalleolar axis runs obliquely at 82° (±4°) in the coronal plane and defines the main motion of the ankle.
a. The talus is wider anteriorly than posteriorly, and the contact area of the dome of the talus increases and moves anteriorly with dorsiflexion.
b. Increased load transmission in the malleoli also occurs with dorsiflexion.
c. The fibula transmits approximately 10% to 15% of the axial load.
3. The tibiofibular syndesmosis allows rotation and proximal and distal migration of the fibula with the tibia but little motion in the sagittal or coronal planes.
B. Hindfoot—Subtalar joint and transverse tarsal (Chopart) joint
1. These joints act through a series of coupled motions to create inversion and eversion of the hindfoot and to lock and unlock the midfoot.
2. The transverse tarsal joint is made up of the talonavicular and calcaneocuboid articulations.
3. Inversion of the subtalar joint locks the transverse tarsal joint, whereas eversion unlocks the joint (
Figure 5).
4. The joints are parallel during heel strike, when the calcaneus is in eversion, allowing the midfoot to be flexible for shock absorption as the foot accepts the body's weight.
[Figure 5. Inversion (A) and eversion (B) of the subtalar joint locks and unlocks the transverse tarsal joint by aligning or deviating the major joint axes of the talonavicular (TN) and calcaneocuboid (CC) joints.]
[
Figure 6. Drawing showing the relationship of the tendons crossing the ankle joint to the axes of the subtalar and tibiotalar articulations. Tendons anterior to the ankle axis create a dorsiflexion moment, whereas tendons posterior to the ankle axis create a plantar flexion moment. Tendons medial to the subtalar axis cause inversion, whereas tendons lateral to the subtalar axis cause eversion. TA = tibialis anterior, TP = tibialis posterior, FDL = flexor digitorum longus, FHL = flexor hallucis longus, AT = Achilles tendon, EHL = extensor hallucis longus, EDL = extensor digitorum longus, PT = peroneus tertius, PL = peroneus longus, PB = peroneus brevis.]
5. The joint axes are deviated as the subtalar joint moves to inversion as during push-off, which makes the foot inflexible so that it provides a rigid lever arm for push-off.
6. The relationships of tendons as they cross the ankle and subtalar joints are shown in Figure 6.
C. Tarsometatarsal and midfoot joints
1. Little motion occurs through the intercuneiform and naviculocuneiform joints.
2. The fourth and fifth TMT joints are the most mobile, with a range of 5° to 20° of motion. The second TMT is the least mobile, with 1° of motion.
D. Metatarsophalangeal joints
1. The hallux MTP joint has a normal range of motion of 30° to 90°.
2. Dorsiflexion of the MTP joints during push-off tightens the plantar fascia through a windlass effect, raising the longitudinal arch and inverting the heel.
III. Gait
A. The phases of the gait cycle are described in chapter 20.
B. Motions and muscle activity at the ankle during the three intervals of stance phase are shown in
Figure 7.
[Figure 7. Summary of kinematics and electromyographic activity during the three intervals of stance phase.]
Top Testing Facts
1. The ATFL is under strain in plantar flexion, inversion, and internal rotation; the CFL is under strain in dorsiflexion and inversion.
2. The spring ligament complex, which supports the talonavicular joint, comprises the superomedial calcaneonavicular ligament and the inferior calcaneonavicular ligaments.
3. The Lisfranc ligament originates at the plantar aspect of the medial cuneiform and continues to the central portion of the lateral base of the second metatarsal metaphysis.
4. The conjoined tendon of the adductor hallucis inserts at the lateral proximal first metatarsal and lateral sesamoid.
5. The Achilles tendon fibers rotate 90° toward their insertion. The superficial fibers of the Achilles tendon at the myotendinous junction insert laterally on the calcaneus.
6. The talar body receives most of its blood supply retrograde from the talar neck, making it prone to non-union and osteonecrosis when the talar neck is fractured.
7. The peroneus brevis tendon lies superior and the peroneus longus tendon lies inferior to the peroneal tubercle in the inferior peroneal retinaculum.
8. The nerves at risk during placement of portals for ankle arthroscopy are: anterolateral—superficial peroneal nerve; anteromedial—saphenous nerve; anterior central—deep peroneal nerve; posterolateral—sural nerve; posteromedial—tibial nerve.
9. Inversion of the subtalar joint causes the talonavicular and calcaneocuboid joint axes of the transverse tarsal (Chopart) joint to deviate, decreasing motion and locking the midfoot.
10. The second TMT joint has the least motion; the fourth and fifth have the most.
Bibliography
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Mann RA: Biomechanics of the foot and ankle, in Mann RA (ed): Surgery of the Foot and Ankle. St Louis, MO, Mosby, 1999.
Resch S: Functional anatomy and topography of the foot and ankle, in Myerson MS (ed): Foot and Ankle Disorders, Philadelphia, PA, WB Saunders, 2000.
Sammarco VJ, Acevedo JI: Clinical biomechanics of the foot and ankle, in Orthopaedic Knowledge Update: Foot and Ankle 3, Rosemont, IL, American Academy of Orthopaedic Surgeons, 2004.
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