LEG14. 05. 2014

Kaan Yücel

M.D., Ph.D.

http://yeditepeanatomy1.org

Dr. Kaan Yücel http://yeditepeanatomy1.org Leg

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The leg region (L. regio cruris) is the part that lies between the knee and and ankle joint. It includes most of the tibia (shin bone) and fibula (calf bone). The leg (L., crus) connects the knee and foot. Often laypersons refer incorrectly to the entire lower limb as “the leg.”

Two intermuscular septa pass from its deep aspect to be attached to the fibula. These, together with the interosseous membrane, divide the leg into three compartments “anterior, lateral, and posterior”; each having its own muscles, blood supply, and nerve supply.

Inferiorly, two band-like thickenings of the fascia form retinacula that bind the tendons of the anterior compartment muscles before and after they cross the ankle joint, preventing them from bowstringing anteriorly during dorsiflexion of the joint.

There are four muscles in the anterior compartment of the leg- tibialis anterior, extensor hallucis longus, extensor digitorum longus, and fibularis tertius. These muscles pass and insert anterior to the transversely oriented axis of the ankle (talocrural) joint and, therefore, are dorsiflexors of the ankle joint, elevating the forefoot and depressing the heel [Collectively they dorsiflex the foot at the ankle joint, extend the toes, and invert the foot].

All the muscles of the anterior compartment of the leg are innervated by the deep fibular nerve, which is a branch of the common fibular nerve.

The artery associated with the anterior compartment of leg is the anterior tibial artery, which passes forward into the anterior compartment of leg. The smaller terminal branch of the popliteal artery, the anterior tibial artery, begins at the inferior border of the popliteus muscle (i.e., as the popliteal artery passes deep to the tendinous arch of the soleus). At the ankle joint, midway between the malleoli, the anterior tibial artery changes names, becoming the dorsalis pedis artery (dorsal artery of the foot).

The nerve associated with the anterior compartment of the leg is the deep fibular (peroneal) nerve. It is one of the two terminal branches of the common fibular nerve, arising between the fibularis longus muscle and the neck of the fibula in the lateral compartment. A lesion of this nerve results in an inability to dorsiflex the ankle (footdrop).

There are two muscles in the lateral compartment of leg (evertor compartment)- fibularis longus and fibularis brevis. Both evert the foot (turn the sole outward) and are innervated by the superficial fibular nerve, which is a branch of the common fibular nerve. The lateral compartment is the smallest (narrowest) leg compartment.

Muscles in the posterior (plantarflexor) compartment of leg, the largest of the three leg compartments, are organized into two groups, superficial and deep, by the transverse intermuscular septum. Generally, the muscles mainly plantarflex and invert the foot and flex the toes. All are innervated by the tibial nerve.

Muscles of the posterior compartment produce plantarflexion at the ankle, inversion at the subtalar and transverse tarsal joints, and flexion of the toes. Plantarflexion is a powerful movement (four times stronger than dorsiflexion) produced over a relatively long range (approximately 50° from neutral) by muscles that pass posterior to the transverse axis of the ankle joint.

The popliteal artery is the major blood supply to the leg and foot and enters the posterior compartment of leg from the popliteal fossa behind the knee. The popliteal artery passes into the posterior compartment of leg between the gastrocnemius and popliteus muscles. As it continues inferiorly it passes under the tendinous arch formed between the fibular and tibial heads of the soleus muscle and enters the deep region of the posterior compartment of leg where it immediately divides into an anterior tibial artery and a posterior tibial artery. The nerve associated with the posterior compartment of leg is the tibial nerve, a major branch of the sciatic nerve that descends into the posterior compartment from the popliteal fossa.The tibial nerve leaves the posterior compartment of leg at the ankle by passing through the tarsal tunnel behind the medial malleolus. It enters the foot to supply most intrinsic muscles and skin. In the leg, the tibial nerve gives rise to: • branches that supply all the muscles in the posterior compartment of leg• two cutaneous branches, the sural nerve and medial calcaneal nerve.

Dr. Kaan Yücel http://yeditepeanatomy1.org Leg

The leg region (L. regio cruris) is the part that lies between the knee and and ankle joint. It includes most of the tibia (shin bone) and fibula (calf bone). The leg (L., crus) connects the knee and foot. Often laypersons refer incorrectly to the entire lower limb as “the leg.” proximally, most major structures pass between the thigh and leg through or in relation to the popliteal fossa behind the knee; distally, structures pass between the leg and foot mainly through the tarsal tunnel on the posteromedial side of the ankle, the exceptions being the anterior tibial artery and the ends of the deep and superficial fibular nerves, which enter the foot anterior to the ankle.

The deep fascia of the leg is called the crural fascia. The deep fascia surrounds the leg and is continuous above with the deep fascia of the thigh. Two intermuscular septa pass from its deep aspect to be attached to the fibula. These, together with the interosseous membrane, divide the leg into three compartments “anterior, lateral, and posterior”; each having its own muscles, blood supply, and nerve supply.Inferiorly, two band-like thickenings of the fascia form retinacula that bind the tendons of the anterior compartment muscles before and after they cross the ankle joint, preventing them from bowstringing anteriorly during dorsiflexion of the joint: The superior extensor retinaculum is a strong, broad band of deep fascia, passing from the fibula to the tibia, proximal to the malleoli. The inferior extensor retinaculum, a Y-shaped band of deep fascia, attaches laterally to the anterosuperior surface of the calcaneus. It forms a strong loop around the tendons of the fibularis tertius and the extensor digitorum longus muscles.Flexor retinaculum; extends from the medial malleolus downward and backward to be attached to the medial surface of the calcaneum. It binds the tendons of the deep muscles of the back of the leg to the back of the medial malleolus as they pass forward to enter the sole. The tendons lie in compartments, each of which is lined by a synovial sheath.Superior peroneal retinaculum; connects the lateral malleolus to the lateral surface of the calcaneum. It binds the tendons of the peroneus longus and brevis to the back of the lateral malleolus. The tendons are provided with a common synovial sheath.Inferior peroneal retinaculum; binds the tendons of the peroneus longus and brevis muscles to the lateral side of the calcaneum. The tendons each possess a synovial sheath, which is continuous above with the common sheath.

The anterior compartment of the leg, or dorsiflexor (extensor) compartment, is located anterior to the interosseous membrane, between the lateral surface of the shaft of the tibia and the medial surface of the shaft of the fibula, and anterior to the intermuscular septum that connects them. The anterior compartment is bounded anteriorly by the deep fascia of the leg and skin.

MUSCLES[ See Table 1 for origins, insertions, innervations and main functions]

There are four muscles in the anterior compartment of the leg- tibialis anterior, extensor hallucis longus, extensor digitorum longus, and fibularis tertius. These muscles pass and insert anterior to the transversely oriented axis of the ankle (talocrural) joint and, therefore, are dorsiflexors of the ankle joint, elevating the forefoot and depressing the heel [Collectively they dorsiflex the foot at the ankle joint, extend the toes, and invert the foot]. All the muscles of the anterior compartment of the leg are innervated by the deep fibular nerve, which is a branch of the common fibular nerve.

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1. LEG

2. FASCIAL COMPARTMENTS OF THE LEG

3. ANTERIOR COMPARTMENT OF THE LEG

Dr. Kaan Yücel http://yeditepeanatomy1.org Leg

Tibialis anteriorThe tibialis anterior muscle is the most anterior and medial (and also the most superficial) of the

muscles in the anterior compartment of leg. The long tendon of the tibialis anterior begins halfway down the leg and descends along the anterior surface of the tibia. Its tendon passes within its own synovial sheath deep to the superior and inferior extensor retinacula to its attachment on the medial side of the foot. In so doing, its tendon is located farthest from the axis of the ankle joint, giving it the most mechanical advantage and making it the strongest dorsiflexor. Although antagonists at the ankle joint, the tibialis anterior and the tibialis posterior (in the posterior compartment) both cross the subtalar and transverse tarsal joints to attach to the medial border of the foot. Thus they act synergistically to invert the foot.

The tibialis anterior dorsiflexes the foot at the ankle joint and inverts the foot at the intertarsal joints. During walking, it provides dynamic support for the medial arch of the foot.

Extensor hallucis longusThe extensor hallucis longus muscle is a thin muscle which lies between the tendons of the tibialis

anterior and extensor digitorum longus in the lower one-half of the leg and descends into the foot. The extensor hallucis longus extends the great toe. As it crosses anterior to the ankle joint, it also dorsiflexes the foot at the ankle joint.

Extensor digitorum longusThe extensor digitorum longus muscle is the most posterior and lateral of the muscles in the anterior

compartment of leg. The muscle becomes tendinous superior to the ankle, forming four tendons that attach to the phalanges of the lateral four toes. A common synovial sheath surrounds the four tendons of the extensor digitorum longus (plus that of the fibularis tertius) as they diverge on the dorsum of the foot and pass to their distal attachments.

Fibularis tertiusThe fibularis tertius muscle is a separated part of extensor digitorum longus, which shares its

synovial sheath. Proximally, the attachments and fleshy parts of the two muscles are continuous; however, distally the fibularis tertius tendon is separate and attaches to the 5th metatarsal, not to a phalanx. Although fibularis tertius contributes (weakly) to dorsiflexion, it also acts at the subtalar and transverse tarsal joints, contributing to eversion of the foot. It may play a special proprioceptive role in sensing sudden inversion and then contracting reflexively to protect the anterior tibiofibular ligament, the most commonly sprained ligament of the body. The fibularis tertius is not always present.

Figures 1 & 2. Muscles of the anterior compartment of the leghttp://biology.clc.uc.edu/fankhauser/labs/anatomy_&_physiology/a&p201/muscles/muscles_legs/muscles_legs.htmhttp://www.getbodysmart.com/ap/muscularsystem/footmuscles/menu/menu.html

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Dr. Kaan Yücel http://yeditepeanatomy1.org Leg

ARTERIES & VEINSAnterior tibial artery

The artery associated with the anterior compartment of leg is the anterior tibial artery, which passes forward into the anterior compartment of leg. The smaller terminal branch of the popliteal artery, the anterior tibial artery, begins at the inferior border of the popliteus muscle (i.e., as the popliteal artery passes deep to the tendinous arch of the soleus). The artery immediately passes anteriorly through a gap in the superior part of the interosseous membrane to descend on the anterior surface of this membrane between the tbialis anterior and extensor digitorum longus muscles. At the ankle joint, midway between the malleoli, the anterior tibial artery changes names, becoming the dorsalis pedis artery (dorsal artery of the foot).

Distally, the anterior tibial artery gives rise to an anterior medial malleolar artery and an anterior lateral malleolar artery, which pass posteriorly around the distal ends of the tibia and fibula, respectively. These vessels connect with vessels from the posterior tibial and fibular arteries to form an anastomotic network around the ankle. Deep veins follow the arteries and have similar names. Figure 3. Anterior tibial artery & posterior tibial arteryhttp://www.gla.ac.uk/ibls/US/fab/tutorial/generic/sapulse.html

Table 1. Muscles of the anterior compartment of the leg.Muscle Origin Insertion Innervation Main ActionTibialis anterior Lateral condyle

Superior half of lateral surface of tibia and interosseous membrane

Medial cuneiform and base of 1st metatarsal

Deep fibular nerve (L4, L5)

Dorsiflexes ankle and inverts foot

Extensor digitorum longus

Lateral condyle of tibia

Superior ¾ of medial surface of fibula and interosseous membrane

Middle and distal phalanges of lateral four digits

Extends lateral four digits and dorsiflexes ankle

Extensor hallucis longus

Middle part of anterior surface of fibula and interosseous membrane

Dorsal aspect of base of distal phalanx of great toe (hallux)

Extends great toe and dorsiflexes ankle

Fibularis tertius Inferior third of anterior surface of fibula and interosseous membrane

Dorsum of base of 5th metatarsal

Dorsiflexes ankle and aids in eversion of foot

NERVES5

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Deep fibular nerveThe nerve associated with the anterior compartment of the leg is the deep fibular (peroneal) nerve. It is one of the two terminal branches of the common fibular nerve, arising between the fibularis

longus muscle and the neck of the fibula in the lateral compartment. The deep fibular nerve passes through the intermuscular septum and then passes deep to the extensor digitorum longus. It reaches the anterior interosseous membrane where it descends with the anterior tibial artery. The deep fibular nerve then exits the anterior compartment, continuing across the ankle joint to supply intrinsic muscles (extensors digitorum and hallucis brevis) and a small area of the skin of the foot. A lesion of this nerve results in an inability to dorsiflex the ankle (footdrop).The deep fibular nerve: innervates all muscles in the anterior compartment; [continues into the dorsal aspect of the foot] innervates the extensor digitorum brevis, first two dorsal

interossei muscles, and supplies the skin between the great and second toes.

MUSCLES[ See Table 2 for origins, insertions, innervations and main functions]

There are two muscles in the lateral compartment of leg (evertor compartment)- fibularis longus and fibularis brevis. Both evert the foot (turn the sole outward) and are innervated by the superficial fibular nerve, which is a branch of the common fibular nerve. The lateral compartment is the smallest (narrowest) leg compartment. It is bounded by the lateral surface of the fibula, the anterior and posterior intermuscular septa, and the deep fascia of the leg. The lateral compartment ends inferiorly at the superior fibular retinaculum, which spans between the distal tip of the fibula and the calcaneus. Here the tendons of the two muscles of the lateral compartment (fibularis longus and brevis) enter a common synovial sheath to accommodate their passage between the superior fibular retinaculum and the lateral malleolus, using the latter as a trochlea as they cross the ankle joint.

The fibularis longus and fibularis brevis muscles have their fleshy bellies in the lateral compartment but are tendinous as they exit the compartment within the common synovial sheath deep to the superior fibular retinaculum. Both muscles are evertors of the foot, elevating the lateral margin of the foot.

Fibularis longusThe fibularis longus muscle arises in the lateral compartment of leg, but its tendon crosses under the

foot to attach to bones on the medial side. The common fibular nerve passes anteriorly around the fibular neck between the attachments of the fibularis longus to the fibular head and shaft. Distal to the superior fibular retinaculum, the common sheath shared by the fibular muscles splits to extend through separate compartments deep to the inferior fibular retinaculum.

The fibularis longus everts and plantarflexes the foot. In addition, the fibularis longus, tibialis anterior, and tibialis posterior muscles, which all insert on the undersurfaces of bones on the medial side of the foot, together act as a stirrup to support the arches of the foot. The fibularis longus supports mainly the lateral and transverse arches. When a person stands on one foot, the fibularis longus helps steady the leg on the foot.

Fibularis brevisThe fibularis brevis is a fusiform muscle that lies deep to the fibularis longus, and, true to its name, it

is shorter than its partner in the lateral compartment. Its broad tendon grooves the posterior aspect of the lateral malleolus and can be palpated inferior to it. The narrower tendon of the fibularis longus lies on that of the fibularis brevis and does not contact the lateral malleolus.

Table 2. Muscles of the lateral compartment of the leg.

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3. LATERAL COMPARTMENT OF THE LEG

Dr. Kaan Yücel http://yeditepeanatomy1.org Leg

Muscle Proximal Attachment

(Origin)

Distal Attachment

(Insertion)

Innervation Main Action

Fibularis longus Head and superior

2/3 of lateral surface

of fibula

Base of 1st

metatarsal and

medial cuneiform

Superficial fibular

nerve (L5, S1, S2)

Everts foot and

weakly plantarflexes

ankle

Fibularis brevis Inferior 2/3 of lateral

surface of fibula

Dorsal surface of

tuberosity on lateral

side of base of 5th

metatarsal

Figure 4. Peroneus (fibularis) longus & brevis muscleshttp://quizlet.com/2514463/lower-appendicaular-musculature-flash-cards

ARTERIES & VEINSNo major artery passes vertically through the lateral compartment of leg. Instead, perforating branches and accompanying veins supply blood to and drain blood from the compartment. Proximally, perforating branches of the anterior tibial artery penetrate the anterior intermuscular septum. Inferiorly, perforating branches of the fibular artery penetrate the posterior intermuscular septum, along with their accompanying veins (L. venae comitantes). Deep veins generally follow the arteries.

NERVESSuperficial fibular nerve

The nerve associated with the lateral compartment of leg is the superficial fibular (peroneal) nerve. This nerve originates as one of the two major branches of the common fibular nerve, which enters the lateral compartment of leg from the popliteal fossa. After supplying the fibularis longus and fibularis brevis, the superficial fibular nerve continues as a cutaneous nerve, supplying the skin on the distal part of the anterior surface of the leg and nearly all the dorsum of the foot.

Figure 5. Nerves in the lateral compartment of the leghttp://upload.wikimedia.org/wikipedia/commons/4/43/Gray835.png

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The common fibular nerve originates from the sciatic nerve in the posterior compartment of thigh or in the popliteal fossa, and follows the medial margin of the biceps femoris tendon over the lateral head of the gastrocnemius muscle and toward the fibula. Here it gives origin to two cutaneous branches, which descend in the leg: Sural communicating nerve, which joins the sural branch of the tibial nerve and contributes to innervation of skin over the lower posterolateral side of the leg; Lateral sural cutaneous nerve, which innervates skin over the upper

lateral leg. The common fibular nerve continues around the neck of the

fibula and enters the lateral compartment by passing between the attachments of the fibularis longus muscle to the head and shaft of fibula. Here the common fibular nerve divides into its two terminal branches: Superficial fibular nerve Deep fibular nerve

The superficial fibular nerve descends in the lateral compartment deep to the fibularis longus and innervates the fibularis longus and fibularis brevis. It then penetrates deep fascia in the lower leg and enters the foot where it divides into medial and lateral branches, which supply dorsal areas of the foot and toes except for: the web space between the great and second toes, which is supplied by the deep fibular nerve; the lateral side of the little toe, which is supplied by the sural branch of the tibial nerve.

The deep fibular nerve passes anteromedially through the intermuscular septum into the anterior compartment of leg, which it supplies.

Dr. Kaan Yücel http://yeditepeanatomy1.org Leg

MUSCLESMuscles in the posterior (plantarflexor) compartment of leg, the largest of the three leg compartments,

are organized into two groups, superficial and deep, by the transverse intermuscular septum. Generally, the muscles mainly plantarflex and invert the foot and flex the toes. All are innervated by the tibial nerve.

Muscles of the posterior compartment produce plantarflexion at the ankle, inversion at the subtalar and transverse tarsal joints, and flexion of the toes. Plantarflexion is a powerful movement (four times stronger than dorsiflexion) produced over a relatively long range (approximately 50° from neutral) by muscles that pass posterior to the transverse axis of the ankle joint. Plantarflexion develops thrust, applied primarily at the ball of the foot, that is used to propel the body forward and upward and is the major component of the forces generated during the push-off (heel off and toe off) parts of the stance phase of walking and running.

Superficial group[ See Table 3 for origins, insertions, innervations and main functions]

The superficial group of calf muscles (muscles forming prominence of “calf” of posterior leg) includes the gastrocnemius, soleus, and plantaris. All of these muscles insert onto the heel (calcaneus) of the foot and plantarflex the foot at the ankle joint.

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4. POSTERIOR COMPARTMENT OF THE LEG

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The gastrocnemius and soleus share a common tendon, the calcaneal tendon, which attaches to the calcaneus. Collectively these two muscles make up the three-headed triceps surae (L. sura, calf). This powerful muscular mass pulls on the lever provided by the calcaneal tuberosity, elevating the heel and depressing the forefoot, generating as much as 93% of the plantarflexion force. As a unit, these muscles are large and powerful because they take the body forward off the planted foot during walking and can elevate the body upward onto the toes when standing. Two of the muscles (gastrocnemius and plantaris) originate on the distal end of the femur and can also flex the knee.

A subcutaneous calcaneal bursa, located between the skin and the calcaneal tendon, allows the skin to move over the taut tendon. A deep bursa of the calcaneal tendon (retrocal-caneal bursa), located between the tendon and the calcaneus, allows the tendon to glide over the bone.

GastrocnemiusThe gastrocnemius muscle is the most superficial of the muscles in the posterior compartment and is

one of the largest muscles in the leg. It originates from two heads, one lateral and one media. At the knee, the facing margins of the two heads of the gastrocnemius form the lateral and medial

borders of the lower end of the popliteal fossa. In the upper leg, the heads of the gastrocnemius combine to form a single elongate muscle belly, which forms much of the soft tissue bulge identified as the calf. In the lower leg, the muscle fibers of the gastrocnemius converge with those of the deeper soleus muscle to form the calcaneal tendon, which attaches to the calcaneus (heel) of the foot. The gastrocnemius plantarflexes the foot at the ankle joint and can also flex the leg at the knee joint.

The large size of the gastrocnemius and soleus muscles is a human characteristic that is directly related to our upright stance. These muscles are strong and heavy because they lift, propel, and accelerate the weight of the body when walking, running, jumping, or standing on the toes.

The calcaneal tendon (L. tendo calcaneus, Achilles tendon) is the most powerful (thickest and strongest) tendon in the body. Approximately 15 cm in length, it is a continuation of the flat aponeurosis formed halfway down the calf where the bellies of the gastrocnemius terminate.

PlantarisThe plantaris has a small muscle belly proximally and a long thin tendon, which descends through the

leg and joins the calcaneal tendon. This vestigial muscle is absent in 5-10% of people and is highly variable in size and form when present. It acts with the gastrocnemius but is insignificant as either a flexor of the knee or a plantarflexor of the ankle. The plantaris has been considered to be an organ of proprioception for the larger plantarflexors. The short spindle-shaped muscle body of the plantaris descends medially between the gastrocnemius and soleus muscles and eventually fuses with the medial side of the calcaneal tendon near its attachment to the calcaneus. The plantaris contributes to plantarflexion of the foot at the ankle joint and flexion of the leg at the knee joint, and is innervated by the tibial nerve.

SoleusThe soleus is a large flat muscle under the gastrocnemius muscle. In the lower leg, the soleus muscle

narrows to join the calcaneal tendon that attaches to the calcaneus. Electromyography (EMG) studies show that during symmetrical standing, the soleus is continuously active.

Figure 6. Calf muscleshttp://www.floota.com/muscles_of_the_calf.html

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Deep group[See Table 4 for origins, insertions, innervations and main functions]

Four muscles make up the deep group in the posterior compartment of the leg: popliteus, flexor digitorum longus, flexor hallucis longus, and tibialis posterior. The popliteus acts on the knee joint, whereas the other muscles plantarflex the ankle with two continuing on to flex the toes. When the calcaneal tendon is ruptured, these muscles cannot generate the power necessary to lift the body's weight (i.e., to stand on the toes).

PopliteusThe popliteus is the smallest and most superior of the deep muscles in the posterior compartment of

the leg. It is a thin, triangular muscle that forms the inferior part of the floor of the popliteal fossa. It unlocks the extended knee at the initiation of flexion and stabilizes the knee. The popliteus muscle ascends laterally across the lower aspect of the knee. When initiating gait from a standing position, contraction of the popliteus laterally rotates the femur on the fixed tibia, unlocking the knee joint.

Flexor hallucis longusThe flexor hallucis longus muscle is a powerful flexor of all of the joints of the great toe. The tendon

of the flexor hallucis longus slips into a distinct groove on the posterior surface of the adjacent tarsal bone (talus) of the foot. The flexor hallucis longus flexes the great toe. It is particularly active during the toe-off phase of walking when the body is propelled forward off the stance leg and the great toe is the last part of the foot to leave the ground. It can also contribute to plantarflexion of the foot at the ankle joint. Table 3. Muscles of the superficial compartment of the leg.

Muscle Origin Insertion Innervation Main ActionGastrocnemius

Lateral head: lateral aspect of lateral

condyle of femur

Medial head: popliteal surface of

femur; superior to medial condyle

Posterior

surface of

calcaneus via

calcaneal

tendon

Tibial nerve

(S1, S2)

Plantarflexes

ankle when knee

is extended;

raises heel during

walking; flexes

leg at knee joint

Soleus Posterior aspect of head and superior

quarter of posterior surface of fibula;

soleal line and middle third of medial

border of tibia; and tendinous arch

extending between the bony

attachments

Plantarflexes

ankle

independent of

position of knee;

steadies leg on

foot

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Plantaris Inferior end of lateral supracondylar line

of femur; oblique popliteal ligament

Weakly assists

gastrocnemius in

plantarflexing

ankle

Flexor digitorum longusThe flexor digitorum longus muscle originates on the medial side of the posterior compartment of

leg. The tendon crosses inferior to the tendon of the flexor hallucis longus muscle to reach the medial side of the foot and then divides into four tendons. The flexor digitorum longus flexes the lateral four toes. It is involved with gripping the ground during walking and propelling the body forward off the toes at the end of the stance phase of gait. The two muscles of the posterior compartment that pass to the toes are crisscrossed. The muscle attaching to the great toe (flexor hallucis longus) arises laterally (from the fibula) in the deep subcompartment, and the muscle attaching to the lateral four toes (flexor digitorum longus) arises medially (from the tibia). Their tendons cross in the sole of the foot.

Tibialis posteriorThe tibialis posterior muscle lies between and is overlapped by the flexor digitorum longus and the

flexor hallucis longus muscles. Near the ankle, the tendon of the tibialis posterior is crossed superficially by the tendon of the flexor digitorum longus muscle and lies medial to this tendon in the groove on the posterior surface of the medial malleolus. The tibialis posterior inverts and plantarflexes the foot, and supports the medial arch of the foot during walking.

Table 4. Muscles of the deep compartment of the leg.Muscle Origin Insertion Innervation Main Action

Popliteus Lateral surface of

lateral condyle of

femur and lateral

meniscus

Posterior surface of tibia,

superior to soleal line

Tibial nerve

(L4, L5, S1)

Weakly flexes knee

and unlocks it by

rotating femur 5° on

fixed tibia; medially

rotates tibia of

unplanted limb

Flexor hallucis

longus

Inferior 2/3 of

posterior surface of

fibula; inferior part of

interosseous

membrane

Base of distal phalanx of great

toe (hallux)

Flexes great toe at all

joints; weakly

plantarflexes ankle;

supports medial

longitudinal arch of

foot

Flexor digitorum

longus

Medial part of

posterior surface of

tibia inferior to soleal

line; by a broad tendon

to fibula

Bases of distal phalanges of

lateral four digits

Flexes lateral four

digits; plantarflexes

ankle; supports

longitudinal arches

of foot

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Tibialis posterior Interosseous

membrane; posterior

surface of tibia inferior

to soleal line; posterior

surface of fibula

Tuberosity of navicular,

cuneiform, cuboid, and

sustentaculum tali of

calcaneus; bases of 2nd, 3rd,

and 4th metatarsals

Plantarflexes ankle;

inverts foot

ARTERIESPOPLITEAL ARTERY

The popliteal artery is the major blood supply to the leg and foot and enters the posterior compartment of leg from the popliteal fossa behind the knee. The popliteal artery passes into the posterior compartment of leg between the gastrocnemius and popliteus muscles. As it continues inferiorly it passes under the tendinous arch formed between the fibular and tibial heads of the soleus muscle and enters the deep region of the posterior compartment of leg where it immediately divides into an anterior tibial artery and a posterior tibial artery.

ANTERIOR TIBIAL ARTERYThe anterior tibial artery passes forward through the aperture in the upper part of the interosseous

membrane and enters the anterior compartment of leg. It continues inferiorly onto the dorsal aspect of the foot.

POSTERIOR TIBIAL ARTERYThe posterior tibial artery descends through the deep region of the posterior compartment of leg on

the superficial surfaces of the tibialis posterior and flexor digitorum longus muscles. It passes through the tarsal tunnel behind the medial malleolus and continues into the sole of the foot. In the leg, the posterior tibial artery has two major branches, the circumflex fibular artery and fibular artery: Circumflex fibular artery passes laterally through the soleus muscle and around the neck of the fibula to connect with the anastomotic network of vessels surrounding the knee; Fibular artery is the largest and most important branch. It arises inferior to the distal border of the popliteus and the tendinous arch of the soleus. It parallels the course of the posterior tibial artery, but descends along the lateral side of the posterior compartment. The fibular artery passes behind the attachment between the distal ends of the tibia and fibula and terminates in a network of vessels over the lateral surface of the calcaneus. The nutrient artery of tibia, the largest nutrient artery in the body, arises from the origin of the anterior or posterior tibial artery. Deep veins in the posterior compartment generally follow the arteries.

NERVESFigure 7. Tibial nervehttp://en.wikipedia.org/wiki/File:Gray832.png

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Tibial nerveThe nerve associated with the posterior compartment of leg is the

tibial nerve, a major branch of the sciatic nerve that descends into the posterior compartment from the popliteal fossa.

The tibial nerve passes under the tendinous arch formed between the fibular and tibial heads of the soleus muscle and passes vertically through the deep region of the posterior compartment of leg on the surface of the tibialis posterior muscle with the posterior tibial vessels. The tibial nerve leaves the posterior compartment of leg at the ankle by passing through the tarsal tunnel behind the medial malleolus. It enters the foot to supply most intrinsic muscles and skin. In the leg, the tibial nerve gives rise to: • branches that supply all the muscles in the posterior compartment of leg• two cutaneous branches, the sural nerve and medial calcaneal nerve.Sural nerveThe sural nerve originates high in the leg between the two heads of the gastrocnemius muscle. It descends superficial to the belly of the gastrocnemius muscle and penetrates through the deep fascia approximately in the middle of the leg where it is joined by a sural communicating branch from the common fibular nerve. It passes down the leg, around the lateral malleolus, and into the foot. The sural nerve supplies skin on the lower posterolateral surface of the leg and the lateral side of the foot and little toe. Medial calcaneal nerveThe medial calcaneal nerve is often multiple and originates from the tibial nerve low in the leg near the ankle and descends onto the medial side of the heel. The medial calcaneal nerve innervates skin on the medial surface and sole of the heel.