Back of the Leg

Introduction

The back of the leg is called the calf or posterior compartment of the leg. It is similar to the front (anterior compartment) of the forearm. This compartment contains the muscles that flex the foot, including the strong antigravity muscles, gastrocnemius and soleus, which help maintain posture and are important for standing, walking, and running.

Main contents of back of thigh

• Muscles: Gastrocnemius, soleus, plantaris, popliteus, flexor digitorum longus, and tibialis posterior.
• Nerve: Tibial nerve.
• Arteries: Posterior tibial and peroneal (fibular) arteries.
• Other structure: Flexor retinaculum.

Surface Landmarks

• The gastrocnemius and soleus muscles form the fleshy prominence of the calf.
• The calcaneal (Achilles) tendon is the strong common tendon of the gastrocnemius and soleus. It attaches to the middle part of the calcaneus and becomes clearly visible when a person stands on the toes.
• The medial malleolus is the downward projection of the lower end of the tibia, while the lateral malleolus is the downward projection of the fibula. The tip of the lateral malleolus lies about 0.5 cm lower than the medial malleolus. The posterior borders of both malleoli lie in the same coronal plane.
• The sustentaculum tali can be felt about one thumb’s breadth below the medial malleolus.
• The navicular tuberosity can be felt about 3–4 cm in front of and below the medial malleolus.
• The posterior tibial artery pulse can be felt against the calcaneus about 2 cm below and behind the medial malleolus.

Superficial Fascia

The superficial fascia of the back of the leg contains:

1. Parts of the small (short) saphenous vein and great saphenous vein.
2. Cutaneous nerves.

Short (small) saphenous vein

• The small saphenous vein begins at the lateral side of the dorsum of the foot. It is formed by the union of the lateral end of the dorsal venous arch and the lateral dorsal digital vein.
• It passes behind the lateral malleolus and ascends along the lateral side of the calcaneal (Achilles) tendon.
• It then runs upward in the midline of the calf, pierces the deep fascia in the lower part of the popliteal fossa, and finally drains into the popliteal vein.

Tributaries

• Lateral end of the dorsal venous arch
• Lateral dorsal digital vein

Important points

• The small saphenous vein is accompanied by the sural nerve.
• The vein of Giacomini is a communicating vein between the great saphenous vein and the small saphenous vein. It passes from the popliteal fossa to the upper front of the thigh along its posteromedial side.
• The great saphenous vein is accompanied by the saphenous nerve.

Great saphenous vein

1. The great saphenous vein begins at the medial side of the dorsum of the foot. It is formed by the union of the medial end of the dorsal venous arch and the medial marginal vein.
2. In the back of the leg, it is visible only on the posteromedial side of the knee.

Cutaneous nerve

The skin of the back of the leg is supplied by the following nerves:

1. Saphenous nerve
2. Posterior division of the medial cutaneous nerve of the thigh
3. Posterior cutaneous nerve of the thigh
4. Sural nerve
5. Lateral cutaneous nerve of the calf
6. Sural communicating nerve
7. Medial calcaneal branches of the tibial nerve

Key description

Saphenous Nerve (L3, L4)

• The saphenous nerve is a branch of the femoral nerve. It accompanies the great saphenous vein. It contributes to the subsartorial plexus and gives an infrapatellar branch. It supplies the skin of the front and medial side of the leg and the medial border of the foot up to the ball of the great toe.

Posterior Division of the Medial Cutaneous Nerve of the Thigh (L2, L3)

• This nerve supplies the skin of the uppermost part of the medial one-third of the calf.

Posterior Cutaneous Nerve of the Thigh (S1, S2, S3)

• It pierces the deep fascia in the middle of the popliteal fossa and descends with the small saphenous vein. It supplies the gluteal region, upper and medial thigh, most of the back of the thigh, and the upper half of the back of the calf.

Sural Nerve (L5, S1, S2)

• The sural nerve is a branch of the tibial nerve. It begins in the popliteal fossa, passes between the two heads of the gastrocnemius, pierces the deep fascia, and runs with the small saphenous vein. It is joined by the sural communicating nerve in the upper part of the calf. It passes behind the lateral malleolus and continues along the lateral border of the foot. It supplies the skin of the lower back of the leg, lateral border of the foot, and the little toe.

Lateral Cutaneous Nerve of the Calf (L4, L5, S1)

• This nerve is a branch of the common peroneal (fibular) nerve. It begins in the popliteal fossa. It supplies the skin of the upper two-thirds of the lateral side of the leg.

Sural Communicating Nerve (L5, S1, S2)

• This nerve is a branch of the common peroneal (fibular) nerve. It pierces the deep fascia and joins the sural nerve on the back of the calf. It supplies the skin of the posterolateral part of the calf.

Medial Calcaneal Branches of the Tibial Nerve (S1, S2)

• These branches arise from the tibial nerve. They supply the skin of the heel and the medial side of the sole of the foot.

Posterior Compartment of Leg

Boundaries

The posterior compartment of the leg is bounded by:

• Anteriorly: Posterior surfaces of the tibia, fibula, interosseous membrane, and the posterior intermuscular septum.
• Posteriorly: The deep fascia of the leg, which extends from the subcutaneous border of the tibia to the posterior intermuscular septum.

Subdivisions of the Posterior Compartment

• The deep fascia divides the posterior compartment into three parts by two transverse fascial septa.

• Superficial transverse septum: Separates the superficial and middle parts. It is attached to the soleal line of the tibia, medial border of the tibia, and posterior border of the fibula.
• Deep transverse septum: Separates the middle and deep parts. It is attached to the vertical ridge on the posterior surface of the tibia and the medial crest of the fibula.

Contents of the Posterior Compartment

Superficial Part

• Gastrocnemius
• Soleus
• Plantaris

Middle Part

• Flexor digitorum longus
• Flexor hallucis longus
• Posterior tibial artery and veins
• Tibial nerve

Deep Part

• Tibialis posterior

Flexor Retinaculum of Foot

• The flexor retinaculum (also called the laciniate ligament or medial annular ligament) is a strong band of deep fascia on the medial side of the ankle.
• It holds the long flexor tendons close to the ankle and prevents them from bowstringing during movement.
• Width: About 2.5 cm.

Attachments

• Superior (anterior): Posterior border and tip of the medial malleolus.
• Inferior (posterior): Medial process of the calcaneal tuberosity.

Structures Passing Deep to the Flexor Retinaculum

The following structures pass beneath the flexor retinaculum from medial to lateral:

1. Tendon of tibialis posterior
2. Tendon of flexor digitorum longus
3. Posterior tibial artery
4. Tibial nerve
5. Tendon of flexor hallucis longus

• Each structure lies in a separate compartment.
• The three tendons are enclosed in synovial sheaths.

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MUSCLES OF POSTERIOR COMPARTMENT OF LEG

The muscles of the posterior compartment of the leg are divided into superficial and deep groups by a transverse intermuscular septum.

Superficial Muscles

1. Gastrocnemius
2. Soleus
3. Plantaris

Deep Muscles

1. Popliteus
2. Flexor digitorum longus
3. Flexor hallucis longus
4. Tibialis posterior

Superficial Muscles of the Back of Leg

• The superficial muscles of the back of the leg are:
  1. Gastrocnemius
  2. Soleus
  3. Plantaris
• These muscles form the calf and play an important role in maintaining an upright posture and walking on two legs.
• Triceps surae = Gastrocnemius + Soleus

Gastrocnemius

The gastrocnemius is the largest and most prominent muscle of the calf. It has two heads, a medial head and a lateral head.

Origin

Medial head

• Arises from the posterior part of the medial condyle of the femur, behind the adductor tubercle.
• Also arises from the adjacent posterior surface of the femur.

Lateral head

• Arises from the lateral surface of the lateral condyle of the femur.
• Also arises from the lateral supracondylar line.
• A few fibers from both heads arise from the capsule of the knee joint.

Direction of Fibers

• The fibers of both heads pass downward and meet in the middle of the leg.
• They form a broad tendon that joins the tendon of the soleus to form the calcaneal (Achilles) tendon.

Insertion

• The calcaneal tendon inserts into the middle part of the posterior surface of the calcaneus.

Nerve Supply

• Tibial nerve

Actions

• Plantar flexes the foot at the ankle joint.
• Flexes the leg at the knee joint.
• Together with the soleus, it helps maintain posture during standing and is important for walking, running, and jumping.

Soleus

The soleus is a broad, flat muscle located deep to the gastrocnemius. It forms part of the calf and is an important muscle for standing and walking.

Origin

The soleus has a horseshoe-shaped origin from the following structures:

1. Posterior surface of the head and upper one-fourth of the fibula.
2. Soleal line and the middle one-third of the medial border of the tibia.
3. Tendinous arch between the tibia and fibula.

Direction of Fibers

• The muscle fibers run downward and join a flat tendon.
• This tendon unites with the tendon of the gastrocnemius in the middle of the calf to form the calcaneal (Achilles) tendon.

Insertion

• The calcaneal tendon inserts into the middle part of the posterior surface of the calcaneus.

Nerve Supply

• Tibial nerve

Actions

• Plantar flexes the foot at the ankle joint.
• Together with the gastrocnemius, it forms a powerful plantar flexor that is important for standing, walking, running, and jumping.

Plantaris

The plantaris is a small muscle with a short muscle belly and a long, thin tendon. It is considered a vestigial muscle in humans because it has very little functional importance.

Origin

The plantaris arises from:

• The lower one-third of the lateral supracondylar line of the femur.
• The adjacent part of the oblique popliteal ligament.

Direction of Fibers

• The muscle forms a fusiform belly about 7–10 cm long.
• Its long tendon passes downward between the gastrocnemius and soleus, running from the lateral side to the medial side.

Insertion

• The tendon inserts into the posterior surface of the calcaneus, just medial to the calcaneal (Achilles) tendon.

Nerve Supply

• Tibial nerve

Actions

• The plantaris has no significant independent action.
• It assists the gastrocnemius during plantar flexion of the foot and flexion of the knee.

Deep Muscles of Back of Leg

The deep muscles of the posterior compartment of the leg are:

1. Popliteus
2. Flexor digitorum longus
3. Flexor hallucis longus
4. Tibialis posterior

Popliteus

The popliteus is a small, flat, triangular muscle that forms part of the floor of the popliteal fossa.

Origin

The tendon of the popliteus begins inside the fibrous capsule of the knee joint but outside the synovial membrane (intracapsular but extrasynovial).

It arises from:

1. The anterior part of the popliteal groove on the lateral condyle of the femur.
2. The arcuate popliteal ligament.
3. The outer margin of the lateral meniscus.

Direction of Fibers

• The muscle fibers spread downward and medially to form a flat triangular muscle that forms the floor of the popliteal fossa.

Insertion

The popliteus inserts into:

1. The medial two-thirds of the triangular area above the soleal line on the posterior surface of the tibia.
2. The popliteal fascia.

Nerve Supply

• Tibial nerve

Actions

• Unlocks the knee joint at the beginning of knee flexion by rotating the femur laterally on the fixed tibia during weight-bearing.
• When the foot is off the ground, it rotates the tibia medially on the femur.
• Pulls the lateral meniscus backward, preventing it from being trapped during knee movements.
• Assists in flexion of the knee.

Flexor Digitorum Longus (FDL)

The flexor digitorum longus (FDL) is a thin muscle located deep to the gastrocnemius and soleus muscles.

Origin

• It arises from the upper two-thirds of the medial part of the posterior surface of the tibia, below the soleal line.

Direction of Fibers

• The muscle fibers pass downward and form a tendon a few centimeters above the ankle.
• The tendon passes behind the medial malleolus and deep to the flexor retinaculum.
• It then enters the sole of the foot and divides into four tendons, one for each of the lateral four toes.

Insertion

• Each tendon inserts into the plantar surface of the base of the distal phalanx of the second to fifth toes.

Nerve Supply

• Tibial nerve

Actions

The flexor digitorum longus:

1. Flexes the lateral four toes.
2. Plantar flexes the foot at the ankle joint.
3. Helps maintain the longitudinal arches of the foot.

Flexor Hallucis Longus (FHL)

The flexor hallucis longus (FHL) is a powerful muscle in the deep posterior compartment of the leg. It is a unipennate muscle and is the main flexor of the great toe.

Origin

The flexor hallucis longus arises from:

1. The lower two-thirds of the posterior surface of the fibula, behind the medial crest.
2. The adjacent interosseous membrane.

Direction of Fibers

• The muscle fibers run downward and join a long tendon.
• The tendon passes behind the medial malleolus, deep to the flexor retinaculum, and enters the tarsal tunnel.
• It then passes below the sustentaculum tali and continues into the sole of the foot toward the great toe.

Insertion

• The tendon inserts into the plantar surface of the base of the distal phalanx of the great toe.

Nerve Supply

• Tibial nerve

Actions

The flexor hallucis longus:

1. Flexes the great toe.
2. Plantar flexes the foot at the ankle joint.
3. Helps maintain the medial longitudinal arch of the foot.

Tibialis Posterior

The tibialis posterior is the deepest muscle of the posterior compartment of the leg. It is an important muscle for supporting the arch of the foot.

Origin

The tibialis posterior arises from:

1. The upper two-thirds of the lateral part of the posterior surface of the tibia, below the soleal line.
2. The posterior surface of the fibula, in front of the medial crest.
3. The adjacent posterior surface of the interosseous membrane.

Direction of Fibers

• The muscle fibers converge to form a central tendon.
• The tendon passes behind the medial malleolus, deep to the flexor retinaculum, and enters the sole of the foot.

Insertion

The tendon divides into two parts:

1. Superficial division: Inserts into the tuberosity of the navicular bone.
2. Deep (lateral) division: Gives slips to the plantar surfaces of all tarsal bones except the talus and to the bases of the second, third, and fourth metatarsals.

Nerve Supply

• Tibial nerve

Actions

The tibialis posterior:

1. Inverts the foot.
2. Plantar flexes the foot at the ankle joint.
3. Helps maintain the medial longitudinal arch of the foot.

Nerves and Vessels of Back of Leg

Posterior Tibial Artery

The posterior tibial artery is the main artery of the posterior compartment of the leg. It is one of the two terminal branches of the popliteal artery.

Beginning

• It begins at the lower border of the popliteus muscle in the popliteal fossa.

Course

• The artery passes downward beneath the tendinous arch of the soleus.
• It runs through the posterior compartment of the leg to reach the posteromedial side of the ankle.
• At the ankle, it passes midway between the medial malleolus and the medial tubercle of the calcaneus, deep to the flexor retinaculum.

Termination

• Deep to the flexor retinaculum, it divides into the:
  • Medial plantar artery
  • Lateral plantar artery

Relations

Superficial Relations

• In the upper part of the leg, it lies deep to the gastrocnemius and soleus muscles.
• In the lower part of the leg, it lies on the medial side of the calcaneal (Achilles) tendon, covered only by skin and fascia.
• At the ankle, it is covered by the flexor retinaculum and the abductor hallucis muscle.

Deep Relations

The artery is related to:

• Tibialis posterior in the upper part of the leg.
• Flexor digitorum longus and the tibia in the lower part of the leg.
• The capsule of the ankle joint beneath the flexor retinaculum.

Branches

The posterior tibial artery gives the following branches:

1. Peroneal (fibular) artery
2. Muscular branches
3. Nutrient artery to the tibia
4. Circumflex fibular branch
5. Communicating branch to the peroneal artery
6. Medial malleolar branch
7. Medial calcaneal branches
8. Medial plantar artery
9. Lateral plantar artery

Important Branches

• The peroneal (fibular) artery is the largest branch. It arises about 2.5 cm below the origin of the posterior tibial artery and descends along the medial side of the fibula.
• The circumflex fibular branch winds around the neck of the fibula to reach the front of the knee.
• The nutrient artery enters the tibia below the soleal line.
• The communicating branch joins the peroneal artery in the lower part of the leg.
• The medial malleolar branch passes around the medial malleolus.
• The medial calcaneal branches pierce the flexor retinaculum and supply the soft tissues of the heel.

Peroneal Artery

The peroneal (fibular) artery supplies the lateral and posterior compartments of the leg.

Beginning

• It is the largest branch of the posterior tibial artery.
• It begins about 2.5 cm below the lower border of the popliteus muscle.

Course

• The artery runs downward and laterally along the fibula.
• It passes between the tibialis posterior and flexor hallucis longus muscles.
• Throughout most of its course, it is covered by the soleus muscle.

Termination

• Near the calcaneus, it divides into several terminal branches.

Branches

The peroneal artery gives the following branches:

1. Muscular branches
2. Nutrient artery to the fibula
3. Perforating branches
4. Posterior lateral malleolar branch
5. Communicating branch to the posterior tibial artery
6. Calcaneal branches

Tibial Nerve

The tibial nerve is the largest and longest terminal branch of the sciatic nerve.

Root value:L4, L5, S1, S2, S3

Beginning and Course

• The tibial nerve begins at the upper angle of the popliteal fossa as one of the terminal branches of the sciatic nerve.
• It descends vertically through the popliteal fossa and enters the back of the leg.

Course in the Leg

• The nerve passes beneath the tendinous arch of the soleus.
• It descends with the posterior tibial artery and veins and closely follows the course of the posterior tibial artery.
• At the ankle, it passes deep to the flexor retinaculum.

Termination

• Deep to the flexor retinaculum, the tibial nerve divides into:
  • Medial plantar nerve
  • Lateral plantar nerve

Branches

Muscular Branches

These supply:

• Tibialis posterior
• Flexor digitorum longus
• Flexor hallucis longus
• Deep part of the soleus

Cutaneous branches: The medial calcaneal branches pierce the flexor retinaculum and supply the skin of the heel.

Articular branches: Supply the ankle joint.

Terminal branches:

• Medial plantar nerve
• Lateral plantar nerve

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