4 Leg and Foot

LEG AND FOOT

Learning Objectives:

1. Identify the muscles of the anterior, posterior, and lateral compartments of the leg. Be able to give their functional significance in locomotion.
2. Identify the vascular supply of the anterior and lateral compartments of the leg.
3. Identify the nerves of the anterior and lateral compartments of the leg, the muscles and cutaneous regions supplied by them, so that given a functional and/or cutaneous loss one can predict the nerve and the probable level of injury.
4. Describe the bony structure of the foot; including its arches, subtalar and transverse tarsal joints, and the bones and ligaments contributing to its strength and flexibility.
5. Identify the vascular supply of the foot and give the regions supplied by each.
6. Identify the nerves of the foot, and the muscles and cutaneous regions supplied by them, so that given a functional and/or cutaneous loss one can predict the nerve and the probable level of injury.

Reference: Moore, Clinically Oriented Anatomy, Chapter 5.

Particularly relevant Blue Boxes in Moore:

●Containment and Spread of Compartment Infections in the Leg, p. 605

●Tibialis Anterior Strain (Shin Splints), p. 605

●Deep Fibular Nerve Entrapment, p. 606

●Injury to Common Fibular Nerve and Footdrop, p. 605-6

●Ruptured Calcaneal Tendon, p. 607

●Calcaneal Tendon Reflex, p. 607

●Posterior Tibial Pulse, p. 608

●Palpation of Dorsalis Pedis Pulse, p. 625

To access the Netter Presenter Database click here

Grant’s Dissector, 15th Edition, pp 184 – 198

To access the Gray’s Photograhpic Dissector section on the Leg and Ankle click here

To access the Gray’s Photographic Dissector on the Foot click here

To access the Primal Pictures software click here 

Check out the Primal Pictures model of the Leg and Foot

The Leg 

The leg (Netter 503, 504,505, 507, 508, 506; Moore 595- 596) is anatomically defined as the portion of the lower limb between the knee and the ankle. The tibia and the fibula bones  (Netter 501) provide the leg’s skeletal support. Distally, the tibia forms the medial malleolus and the fibula the lateral malleolus,  which are both prominent bony landmarks. The interosseus membrane is a layer of dense fibrous connective tissue that stretches between the tibia and the fibula.

The leg’s muscles, innervation, and vasculature fall roughly into four compartments (Netter 510):

anterior, lateral, superficial posterior, and deep posterior. Intermuscular septa, the bones, and deep fascia, divide the leg into these four compartments.

Each compartment contains a group of muscles with similar origins, insertions, and actions. The sciatic nerve divides into the tibial and common peroneal nerves just proximal to the popliteal fossa. The tibial nerve remains in the posterior compartment of the leg, supplying all its muscles. As the common peroneal nerve crosses the head of the fibula laterally, it further divides into the deep peroneal nerve for the anterior compartment and the superficial peroneal nerve for the lateral compartment.

The popliteal artery emerges from the popliteal fossa and divides to form the anterior and posterior tibial arteries. The posterior tibial artery further divides to form the peroneal artery.

Anterior Compartment of the Leg (Netter 507, 508; Moore 589-91)

Extensor digitorum longus arises from the fibula and interosseus membrane proximal to extensor hallucis longus. As it extends down the leg it passes superficially over the extensor hallucis longus muscle. Its tendon divides into four slips, which insert onto the bases of the second and terminal phalanges of the lateral four toes. The extensor digitorium longus acts to extend the toes.

Peroneus tertius arises from the fibula and interosseus membrane immediately distal to the extensor digitorum longus muscle. It inserts on the base of the 5^th metatarsal and helps to evert the foot.

The extensor retinacula are transverse strands of connective fibers that hold the extensor tendons of the anterior compartment close to the ankle joint. Without them, the tendons, when contracted, would bowstring away from the joint.

After supplying the muscles of the anterior leg compartment, the deep peroneal nerve emerges as a cutaneous nerve  in the first web space between the big toe and second toe.

Lateral Compartment (Netter 506; Moore 587-594)

Clinical point to note: Because of the superficial location of the common fibular (peroneal) nerve posterior to the head of the fibula and because of its close relationship with the neck of the fibula, the nerve can be injured by a sharp blow to the head of the fibula and during a fracture of the fibular neck. Severing the common peroneal nerve results in paralysis of the muscles of the anterior compartment (dorsiflexors) and lateral compartment (evertors of the foot). This results in a condition known as “foot drop” in which the foot remains in the plantar flexed position. There is also accompanying loss of sensation in the inferolateral half of the leg and most of the dorsum of the feet.  (Moore’s p. 605)
Superficial Posterior Compartment of the Leg (Netter 503, 504; Moore p. 596-600)

This compartment contains three muscles that overlay the deep posterior compartment of the leg (see table 5.13.1 in Moore, p. 597). The tibial nerve and the posterior tibial artery run between the superficial and deep posterior leg compartments.

The gastrocnemius arises from two heads, medial and lateral, from the respective femoral condyles. The soleus muscle arises deep to gastrocnemius from the proximal posterior surfaces of the tibia and fibula. Together, gastrocnemius and soleus insert via the calcaneal tendon into the calcaneus bone.  Both act to strongly plantarflex the foot. The plantaris muscle arises just proximal to the lateral femoral condyle. It travels deep to gastrocnemius, along the medial aspect of the soleus to insert by a long thin tendon on the calcaneus. It weakly flexes the leg and plantarflexes the foot.

Branches of the tibial nerve innervate all the muscles of this compartment. They receive their blood supply from muscular branches of the posterior tibial artery, as well as from the inferior vessels of the genicular anastamosis.

Deep Posterior Compartment of the Leg (Netter 505; Moore p. 598-603)

This compartment contains four muscles (see table 5.13.11 in Moore, p. 598):

• Popliteus
• Flexor Digitorum Longus
• Tibialis Posterior
• Flexor Hallucis Longus

Popliteus arises from the lateral condyle of the femur and inserts onto the posterior aspect of the tibia. This muscle is important in initiating flexion at the knee by medially rotating the leg, thus unlocking the joint. The other three muscles arise from the posterior aspects of the tibia, fibula, and interosseus membrane. The tibialis posterior is the deepest muscle in this compartment and originates largely from the interosseus membrane. It inserts onto the plantar surfaces of many of the tarsal bones and it’s tendon remains deep to the overlying flexor tendons within the sole of the foot.

Flexor digitorum longus arises from the posterior tibia and sends its tendon around the medial malleolus, crossing the flexor hallucis longus tendon superficially. The tendon sends slips to insert onto the bases of the distal phalanges of the lateral 4 toes. The flexor digitorium longus acts to flex the toes. Flexor hallucis longus arises from the fibula and sends its tendon around the sustentaculum tali to insert on the base of the phalanx of the hallux. This muscle acts to flex the hallux. Note that the flexor hallucis longus tendon and flexor digitorum longus tendons cross. In addition to plantarflexing the foot, these muscles also invert the foot.  The tibialis posterior, due to its extensive attachment to the tarsal bones, also has an important role in maintaining the arch of the foot.

Arteries of the Leg

The posterior tibial artery  (Netter 505) arises from the popliteal artery at the lower border of the popliteus, between the tibia and fibula. It gives rise to the peroneal (fibular) artery which descends between the tibialis posterior and flexor hallucis longus muscles and supplies the lateral muscles in the posterior compartment. The posterior tibial artery terminates by dividing into the medial and lateral plantar arteries which supply the foot.

The anterior tibial artery (Netter 508) arises from the popliteal artery and enters the anterior compartment by passing through the gap between the tibia and fibula at the upper end of the interosseous membrane. It descends along with the deep peroneal nerves on the interosseous membrane between the tibialis anterior and extensor digitorum longus muscles.It runs distally and ends at the ankle midway between the lateral and medial malleoli where it becomes the dorsalis pedis artery (Netter 517)

Clinical Corelations:

Anterior tibial compartment syndrome is characterized by ischemic necrosis of the muscles of the anterior compartment of the leg. It occurs, presumably, as a result of compression of arteries (anterior tibial artery and its branches) by swollen muscles following excessive exertion. It is accompanied by extreme tenderness and pain in the anterolateral aspect o fthe leg.

Shin splints is a painful condition of the anterior compartment of the leg along the thin crest of the tibia caused by swollen muscles in the anterior compartment of the leg, particularly the tibialis anterior muscle, following athletic overexertion.

Muscle cramp (Charley horse) is a sudden, involuntary painful contraction of muscles of the lower limb. It is caused by muscle fatigue, overexertion, dehydration and depletion or imbalance of salt and minerals such as calcium, sodium and potassium. A poor blood supply to leg muscles caused by smoking and atherosclerosis can cause a type of pain called claudication. The most commonly affected muscles are the calf muscles (gastrocnemius), hamstrings and quadriceps.

Intermittent claudication is a condition of limping caused by ischemia of the muscles in the lower limbs, chiefly the calf muscles and is seen in occlusive peripheral arterial diseases particularly in the popliteal artery and its branches. The main symptom is leg pain that occurs during walking and intensifies until walking is impossible, but the pain  is relieved by rest. Assessment of peripherial arterial disease may be performed by calculating the Ankle-Brachial Index, which is a measure of the relative pressure in the lower limb (dorsalis pedis or posterior tibial arteries) and the arm (brachial artery) A video demonstrating this procedure may be found here (from the New England Journal of Medicine’s series of Videos in Clinical Medicine).

The Foot

The foot  (Netter 511, 512, 516, 517, 518, 519, 520, 521, 522; Moore p. 609-624)  has a complicated skeleton, diverse insertions of many leg muscles, and its own network of nerves, arteries, and intrinsic muscles.

The  bones  of the foot (Netter 511) fall into three groups: 14 phalanges forming the toes; the 5 metatarsals numbered 1 to 5 from medial to lateral, and 7 irregular tarsal bones that form the heel, ankle joint, and much of the arches of the foot.

There are two large posterior tarsal bones, the calcaneus and the talus. The 5 smaller tarsal bones of the arch include: the navicular, cuboidal, and 3 cuneiform bones.

Muscles in the Sole of the Foot – Dissected in Four Layers (Netter 519, 520, 521, 522)

Note: we will not be performing a dissection of these muscles in lab.  One or two specimens will be dissected for you, but you will not be responsible for identifying these plantar muscles on the exam.

Nerve Supply to the Sole of the Foot (Netter 521, Moore p. 614-619)

As the tibial nerve passes into the sole of the foot, it divides to form the medial and lateral plantar nerves. These nerves carry both motor and sensory.

The medial plantar nerve innervates only 4 muscles in the sole of the foot: abductor hallucis, flexor digitorum brevis, flexor hallucis brevis, and the 1^st lumbrical.

The lateral plantar nerve innervates all other intrinsic muscles in the sole of the foot.

ANKLE JOINT (Also discussed in Joints of the Lower Limb section)

The ankle joint is a hinge-type joint between the tibia and fibula superiorly an dthe trochlea of the talus inferiorly, permitting dorsiflexion and plantarflexion.

Study Netter’s 511, 512 bones of the foot) then
Study Moore’s 6th Ed fig 5.97 pg 649, fig 5.98 pg 650  & table 5.18 pg 652 

The ligaments holding the ankle joint are:

• Deltoid ligament (Netter 514) (medial ligament of ankle) made up of-
  1. Anterior tibiotalar part
  2. Posterior tibiotalar part
  3. Tibionavicular part &
  4. Tibiocalcaneal part.
• Lateral (collateral) ligament of ankle made up of –
•       1. Anterior talofibular ligament
•       2. Posterior talofibular ligament &
•       3. Calcaneofibular ligament
• Interosseous talocalcaneal ligament (carries blood supply to navicular.
• Anterior & posterior tibiofibular ligaments
• Plantar calcaneonavicular (spring) ligament

Leg and Foot quiz click here