Session 5b - Muscles Of The Leg, Neurovaculature Of The Leg And The Foot

Question 1

What are the boundaries of the popliteal fossa?

Answer 1

This is a diamond-shaped depression behind the knee joint. The two superior borders are formed by semimembranosus and semitendinosus medially, and biceps femoris laterally. The inferomedial and inferolateral borders are formed by the two heads of gastrocnemius, a superficial muscle in the posterior leg.

Question 2

What are the boundaries of the popliteal fossa?

Answer 2

This is a diamond-shaped depression behind the knee joint. The two superior borders are formed by semimembranosus and semitendinosus medially, and biceps femoris laterally. The inferomedial and inferolateral borders are formed by the two heads of gastrocnemius, a superficial muscle in the posterior leg.

Question 3

What are the contents of the popliteal fossa?

Answer 3

The popliteal fossa contains important structures:
● Popliteal artery - the continuation of the femoral artery. It traverses the adductor hiatus to enter the popliteal fossa. It is possible to palpate the popliteal pulse in the fossa, but it can be difficult. It bifurcates into the anterior and posterior tibial arteries, which supply the leg.
● Popliteal vein - formed by the deep veins of the leg. It traverses the adductor hiatus and continues proximally as the femoral vein.
● Tibial nerve – this nerve descends through the midline of the fossa and innervates the muscles of the posterior leg.
● Common fibular (peroneal) nerve – this nerve travels along the superolateral border of the popliteal fossa, alongside the tendon of biceps femoris. It wraps around the neck of the fibula and then splits into a superficial and a deep branch. The superficial fibular nerve innervates the muscles of the lateral leg, and the deep fibular nerve innervates the muscles of the anterior leg.

Question 4

What is the common fibular nerve also called?

Answer 4

Note: the common fibular nerve is often called the common ‘peroneal’ nerve in older texts and some online resources. The term ‘fibular’ is preferred here as it is more descriptive, but you will likely see the term ‘peroneal’ used in some other resources.

Question 5

Where is the leg located?

Answer 5

The leg is located between the knee and ankle joints. Deep fascia surrounds the leg like a sleeve. Intermuscular septa extend from the deep fascia and separate the leg into anterior, lateral, and posterior compartments.

Question 6

What does the anterior compartments of the leg contain?

Answer 6

The anterior compartment of the leg contains three muscles which arise from the tibia, fibula, and interosseous membrane. They primarily act as dorsiflexors of the foot at the ankle joint and extensors of the toes and they are innervated by the deep fibular nerve.

Question 7

What are the muscles of the anterior compartment?

Answer 7

The muscles of the anterior compartment are:
● Tibialis anterior
● Extensor hallucis longus (EHL)
● Extensor digitorum longus (EDL).

Question 8

Where are the muscles of the anterior compartment located?

Answer 8

Tibialis anterior crosses the anterior aspect of the ankle and inserts onto the medial cuneiform. It dorsiflexes and inverts the foot.

Extensor hallucis longus extends the great toe. Its tendon crosses the anterior aspect of the ankle and inserts onto the distal phalanx of the great toe. It also dorsiflexes the foot.

Extensor digitorum longus gives rise to four tendons. They cross the anterior aspect of the ankle and insert onto the distal phalanges of toes 2-5, extending them. It also dorsiflexes the foot at the ankle joint. Extensor retinacula cover the extensor tendons at the ankle joint.

Question 9

What is the fourth muscle of the anterior compartment?

Answer 9

There is a fourth muscle in the anterior compartment that is not included on the image of the anterior muscles of the leg. Fibularis tertius extends from the fibula to the base of the 5th metatarsal. Due to its position, it is able to weakly dorsiflex and evert the foot. It is relatively small, weak and is not present in all patients. You may find it on some of the models in the MTU.

Question 10

What does the lateral compartment of the leg contain?

Answer 10

The lateral compartment of the leg contains two muscles that attach to the fibula. They evert the foot at the subtalar joint and are innervated by the superficial fibular nerve. The muscles of the lateral compartment are fibularis longus and fibularis brevis. (In some older textbooks these muscles are called peroneus longus and brevis).

Question 11

What do the muscles lie in the lateral compartment of the leg?

Answer 11

Fibularis longus is the more superficial muscle. It inserts onto the plantar surface of the medial cuneiform bone.

Fibularis brevis is the deeper muscle of the two. It inserts onto the base of the 5th metatarsal.
The tendons of both muscles travel posterior to the lateral malleolus to their insertions in the foot.

Question 12

What lies in the posterior compartment of the leg?

Answer 12

The posterior compartment of the leg contains a superficial and a deep group of muscles. They primarily act as plantarflexors of the foot at the ankle joint and flexors of the toes. They are all innervated by the tibial nerve.

Question 13

What superficial muscles lie in the posterior compartment of the leg?

Answer 13

There are three superficial muscles: gastrocnemius, soleus and plantaris. The tendons of all three muscles insert onto the calcaneus via the calcaneal (Achilles) tendon. The ‘Achilles’ tendon is so called as a reference to the hero of popular Greek mythology whose heel was his only vulnerable part.

Question 14

Where is the gastrocnemius?

Answer 14

Gastrocnemius is the most superficial muscle of the leg. It attaches via two heads to the distal femur. This means it can flex the knee in addition to plantarflexing the ankle.

Question 15

Where does the soleus lie?

Answer 15

Soleus is a large, flat muscle that is deep to gastrocnemius. It is attached to the soleal line of the tibia. Contraction of soleus compresses the deep veins of the leg and is important for venous return. The name ‘soleus’ is derived from the Latin for ‘sandal’. When removed, soleus has a very flat, foot-shaped appearance similar to that of a sandal.

Question 16

Where does the plantaris lie?

Answer 16

Plantaris is a very small muscle that is located close to the popliteal fossa. It gives rise to a very long, thin tendon which merges with the calcaneal tendon. Plantaris, like palmaris longus in the forearm, is a non-essential muscle as its primary function can be carried out by other, stronger muscles. For this reason, the tendon of plantaris can be harvested and used to repair or replace damaged ligaments or tendons as a graft.

Question 17

What are the deep muscles of the posterior compartment of the leg?

Answer 17

There are four deep muscles: popliteus, tibialis posterior, flexor hallucis longus (FHL) and flexor digitorum longus (FDL). The tendons of the latter three muscles all travel posterior to the medial malleolus and insert into the plantar surface of the bones of the foot.

Question 18

What is the popliteus muscle like?

Answer 18

Popliteus is located deep in the popliteal fossa. It is attached to the tibia and the femur. It allows for a small degree of rotation of the knee. As discussed in the last session, to help us to stand for long periods, the femur rotates a very small amount as the knee reaches full extension. This means the knee ‘locks’ in place and becomes very stable. Popliteus is responsible for ‘unlocking’ the knee by rotating the femur back again to permit flexion.

Question 19

Where are the other muscles of the posterior compartment of the leg?

Answer 19

Tibialis posterior plantarflexes and inverts the foot. Its tendon attaches to multiple bones in the foot.

Flexor hallucis longus (FHL) flexes the great toe via its insertion onto the distal phalanx. It also plantarflexes the foot.

Flexor digitorum longus (FDL) gives rise to four tendons that insert onto the distal phalanges of toes 2-5. Its primary action is flexion of the toes, but it also plantarflexes the foot.

Question 20

What is the dorsum of the foot like?

Answer 20

The dorsum of the foot is similar to the hand in that superficial veins and extensor tendons are usually visible under the skin. The dorsum of the foot also contains a small muscle called extensor digitorum brevis. It is located laterally and inserts onto the tendons of EDL that correspond to toes 2 – 4. It is innervated by the deep fibular nerve.

Question 21

What is the sole of the foot like?

Answer 21

The plantar aspect of the foot contains numerous intrinsic muscles, much like the palm of the hand. They are arranged in four layers and mirror those of the palm. They include abductors of the great and smaller toes, flexors of the toes, an adductor of the great toe, lumbricals and interossei. They are innervated by the medial and lateral plantar nerves, which are the terminal branches of the tibial nerve.

Question 22

What are the muscles of the sole like?

Answer 22

The muscles of the sole of the foot will not be named here. It is important to appreciate that the most important function of the muscles is that they work as a group to support the foot. The plantar aponeurosis, which is located superficial to the muscles also supports the foot and provides a layer of protection, like the palmar aponeurosis of the hand.

Question 23

What is the blood supply of the leg?

Answer 23

The popliteal artery bifurcates in the popliteal fossa into anterior and posterior tibial arteries. The anterior tibial artery pierces the interosseous membrane to enter the anterior compartment of the leg, which it supplies. Distally, it crosses the anterior aspect of the ankle joint and enters the dorsum of the foot. Here, the artery is called the dorsalis pedis artery, and is palpable in the foot lateral to the tendon of extensor hallucis longus. The dorsalis pedis artery gives rise to branches that travel between the metatarsals and anastomose with arteries in the plantar aspect of the foot.

The posterior tibial artery supplies the posterior compartment of the leg and sole of the foot. It also gives rise to the fibular artery, which supplies the lateral compartment. The posterior tibial artery travels posterior to the medial malleolus, along with the tendons of tibialis posterior, FHL and FDL to enter the plantar aspect of the foot. The artery is palpable here. In the foot, the posterior tibial artery bifurcates into medial and lateral plantar arteries, which supply the sole.

Branches of the dorsalis pedis artery, which enter the sole of the foot from the dorsum, anastomose with branches of the plantar arteries. The deep plantar arch is an important vessel formed by the lateral plantar artery and a branch of the dorsalis pedis. Metatarsal and digital arteries supply the forefoot and toes.

Question 24

What is the venous drainage of the leg?

Answer 24

The posterior tibial, anterior tibial and fibular arteries are accompanied by deep veins. These veins unite to form the popliteal vein.

There are also two major superficial veins in the leg. These veins drain most of the blood from the foot and can usually be seen over the dorsum of the foot and around the distal leg and ankle. The dorsal venous network of the foot drains medially to the great saphenous vein. The great saphenous vein travels anterior to the medial malleolus and courses all the way up the medial aspect of the lower limb to its termination at the femoral vein in the femoral triangle.
The dorsal venous network of the foot also drains laterally to the small saphenous vein. The small saphenous vein travels posterior to the lateral malleolus and courses up the posterior aspect of the leg to its termination at the popliteal vein in the popliteal fossa.

Question 25

What is the common fibular nerve like?

Answer 25

After leaving the popliteal fossa, the common fibular nerve wraps around the neck of the fibula and divides into two branches – the superficial and deep fibular nerves.
● The superficial fibular nerve innervates the muscles of the lateral leg.
● The deep fibular nerve innervates the muscles of the anterior leg.

The common fibular nerve and its branches provide sensory innervation the skin over the anterolateral leg and dorsum of the foot.

Question 26

What is the tibial nerve like?

Answer 26

After leaving the popliteal fossa, the tibial nerve travels vertically distal into the posterior compartment of the leg and it innervates all the muscles in the posterior compartment of the leg and plantar surface of the foot. At the ankle, it travels posterior to the medial malleolus along with the tendons of tibialis posterior, FHL and FDL.

It enters the sole of the foot and divides into two branches: the medial and lateral plantar nerves, which travel along the medial and lateral aspects of the sole of the foot, respectively, alongside the corresponding arteries of the same name. These nerves innervate all the intrinsic muscles in the plantar aspect of the foot. The digital nerves branch from the plantar nerves and supply the toes.

The tibial nerve innervates most of the skin on the plantar surface of the foot.

Question 27

What is the tarsal tunnel?

Answer 27

Like the carpal tunnel in the wrist, the tendons of the deep posterior compartment of the leg travel into the foot through a tunnel covered by a flexor retinaculum, which, in this case connects the medial malleolus to the calcaneus. The tunnel created is called the ‘tarsal tunnel’

Question 28

What are the contents of the tarsal tunnel?

Answer 28

The contents of the tarsal tunnel are as follows, in order from most anterior and superior to most posterior and inferior:
• Tibialis posterior tendon.
• Flexor digitorum longus tendon.
• Posterior tibial artery.
• Posterior tibial vein.
• Tibial nerve.
• Flexor hallucis longus tendon.

The contents of the tarsal tunnel in this order can be remembered using the mnemonic:
‘Tom, Dick And Very Nervous Harry’.

Question 29

What is the peripheral innervation of the lower limb?

Answer 29

Just as in the upper limb, these are the approximate territories of each nerve and there is some variation between individuals. However, testing sensation over these areas of skin should allow us to assess the integrity of the corresponding nerves.
● Femoral: anterior thigh and anteromedial leg (via the saphenous nerve).
● Obturator: medial thigh.
● Common fibular: anterolateral leg and dorsum of the foot.
● Superficial fibular: lower anterolateral leg, most of the dorsum of the foot.
● Deep fibular: 1st interdigital webspace.
● Tibial nerve: sole of the foot.

Question 30

What is the arrangement of the dermatomes of the lower limb?

Answer 30

Just as in the upper limb, the territories of skin supplied by the peripheral nerves are different to those innervated by spinal nerves due to the ‘shuffling’ of nerve fibres in the lumbar plexus. On the anterior surface of the lower limb the dermatomes are arranged in roughly oblique ‘strips’, running inferiorly from the lateral aspect of the lower limb to the medial aspect. On the posterior aspect of the lower limb, the dermatomes are arranged more vertically.

Question 31

What regions are innervated by L1 to S2?

Answer 31

The approximate regions innervated by L1 to S2 are:
• L1: over the inguinal ligament.
• L2: proximal half of the anterior thigh.
• L3: distal anterior thigh and the medial aspect of the knee.
• L4: lateral thigh, anterior knee, anteromedial leg, medial malleolus, medial foot, and great toe.
• L5: lateral leg, distal anterior leg, dorsal and plantar strip down the middle of the foot, and the dorsal and plantar surfaces of toes 2-4.
• S1: vertical strip of skin in the middle of the posterior thigh and leg, distal lateral leg, lateral malleolus, and little toe.
• S2: vertical strip of skin over the posterior aspect of the thigh and leg, plantar strip of skin on the foot and the heel.

Question 32

Over what areas are dermatomes L1-S1 tested?

Answer 32

To test the dermatomes, sensation is tested over the following areas:
• L1: region over the inguinal ligament
• L2: upper anterior thigh
• L3: medial aspect of the knee
• L4: anteromedial leg
• L5: anterolateral leg
• S1: little toe / lateral side of the foot.

Question 33

What is common fibular nerve injury and foot drop?

Answer 33

The common fibular nerve is located relatively superficially as it wraps around the neck of the fibula. Fractures of the fibular neck, caused by a lateral blow to the leg, can injure the nerve. This leads to weakness of the anterior and lateral leg muscles. The foot cannot be dorsiflexed, and the toes will drag on the ground when walking. This condition is called foot drop. Patients may compensate either by lifting the leg higher when walking (by flexing the hip and knee to a greater degree) or by swinging the affected leg out laterally – both allow the toes to clear the ground without catching.

Question 34

What is common fibular nerve injury and foot drop?

Answer 34

The common fibular nerve is located relatively superficially as it wraps around the neck of the fibula. Fractures of the fibular neck, caused by a lateral blow to the leg, can injure the nerve. This leads to weakness of the anterior and lateral leg muscles. The foot cannot be dorsiflexed, and the toes will drag on the ground when walking. This condition is called foot drop. Patients may compensate either by lifting the leg higher when walking (by flexing the hip and knee to a greater degree) or by swinging the affected leg out laterally – both allow the toes to clear the ground without catching.

Question 35

What is deep vein thrombosis?

Answer 35

Thrombus, or clot, can develop in the deep veins of the leg. If this occurs, venous return from the leg is impaired, causing swelling, pain, redness, and warmth of the affected leg. It is important to recognise and treat DVT, as the clot may migrate proximally and enter the pulmonary circulation, causing pulmonary embolism – a potentially fatal condition.

Question 36

What is compartment syndrome?

Answer 36

Because the deep fascia and intermuscular septa of the leg do not stretch, swelling in one of the compartments of the leg (e.g. caused by oedema or bleeding) increases pressure in the compartment and compresses muscles, nerves, and blood vessels. Once the pressure exceeds capillary perfusion pressure, ischaemia and infarction of the tissues occurs if not treated promptly by releasing the fascia (fasciotomy).

Question 37

What is an Achilles tendon rupture ?

Answer 37

The typical mechanism of this injury is a sudden, forceful plantarflexion of the ankle, such as pushing off from the ground to jump or run, or by sudden, forceful dorsiflexion of the ankle, stretching the calcaneal tendon. Patients present with pain and altered gait, as they cannot plantarflex the foot to push-off from the ground when walking.

Question 38

What is an Achilles tendon rupture ?

Answer 38

The typical mechanism of this injury is a sudden, forceful plantarflexion of the ankle, such as pushing off from the ground to jump or run, or by sudden, forceful dorsiflexion of the ankle, stretching the calcaneal tendon. Patients present with pain and altered gait, as they cannot plantarflex the foot to push-off from the ground when walking.

Question 39

What pulses around the ankle?

Answer 39

The pulsation of the dorsalis pedis artery is usually palpable over the dorsum of the foot, just lateral to the tendon of extensor hallucis longus, between the first and second metatarsals. The pulse of the posterior tibial artery is palpable posterior to the medial malleolus. It is important to be able to palpate both pulses when examining a patient’s vascular system.