Major Nerves of Lower Limb

Introduction

• The major nerves of the lower limb arise from the ventral (anterior primary) rami of the lumbar and sacral spinal nerves. The lumbar plexus (L1–L4) is formed within the posterior abdominal wall. The sacral plexus (L4–S4) is formed within the pelvis. These two nerve plexuses give rise to the nerves that supply the muscles, joints, and skin of the lower limb.

Main Nerves of the Lower Limb

The important nerves of the lower limb are:

1. Femoral nerve
2. Obturator nerve
3. Sciatic nerve
4. Tibial nerve
5. Common peroneal (common fibular) nerve
6. Superficial peroneal (superficial fibular) nerve
7. Deep peroneal (deep fibular) nerve
8. Medial plantar nerve
9. Lateral plantar nerve

Femoral Nerve

The femoral nerve is the largest branch of the lumbar plexus and is the main nerve of the anterior compartment of the thigh. It supplies most of the muscles that extend the knee and also provides sensation to the front and medial side of the thigh and the medial side of the leg.

Beginning

• The femoral nerve is the largest branch of the lumbar plexus. It is formed by the posterior (dorsal) divisions of the ventral primary rami of the L2, L3, and L4 spinal nerves.
• Root value: L2, L3, L4
• Length in the thigh: About 2.5 cm before dividing into its terminal branches.

Course and Relations

In the Abdomen

• The femoral nerve begins on the posterior abdominal wall. It emerges from the lateral border of the psoas major muscle. It then descends over the iliacus muscle, deep to the fascia iliaca, towards the thigh.

In the Thigh

• The nerve enters the femoral triangle by passing behind the inguinal ligament, just lateral to the femoral artery. It lies outside the femoral sheath because it is located behind the fascia iliaca, which forms the posterior wall of the femoral sheath. About 2.5 cm below the inguinal ligament, it divides into anterior and posterior divisions. The lateral circumflex femoral artery passes between these two divisions.

Branches and Distribution

Branches in the Abdomen

The femoral nerve supplies the following muscles before entering the thigh:

• Iliacus
• Pectineus

Branches in the Thigh

Anterior Division

Muscular branch:

• Sartorius

Cutaneous branches:

• Medial cutaneous nerve of the thigh
• Intermediate cutaneous nerve of the thigh

Posterior Division

Muscular branches:

• Rectus femoris
• Vastus medialis
• Vastus lateralis
• Vastus intermedius
• Articularis genu (through the nerve to vastus intermedius)

Cutaneous branch:

• Saphenous nerve

Articular branches:

• The nerve to rectus femoris supplies the hip joint.
• The nerves to the vasti muscles supply the knee joint.

Note: The lateral cutaneous nerve of the thigh is not a branch of the femoral nerve. It arises separately from the lumbar plexus.

Obturator Nerve

The obturator nerve is the main nerve of the medial (adductor) compartment of the thigh. It supplies most of the adductor muscles and also provides sensory and articular branches to the hip and knee joints.

Formation

• The obturator nerve is a branch of the lumbar plexus.
• It is formed by the anterior (ventral) divisions of the ventral primary rami of the L2, L3, and L4 spinal nerves.

Root value: L2, L3, and L4

Course

In the Pelvic Cavity

• The obturator nerve begins in the lumbar plexus within the abdomen.
• It emerges from the medial border of the psoas major muscle.
• It descends into the pelvis and passes behind the common iliac vessels.
• The nerve then reaches the obturator canal.

In the Thigh

• The obturator nerve enters the thigh through the obturator canal.
• Within the canal, it divides into anterior and posterior divisions.
• The anterior division passes in front of the obturator externus muscle, then descends behind the pectineus and adductor longus muscles, and in front of the adductor magnus.
• The posterior division passes through the obturator externus muscle and then lies behind the adductor brevis.

Branches and Distribution

Anterior Division

The anterior division supplies:

• Adductor longus
• Gracilis
• Pectineus (occasionally)
• Adductor brevis (in some individuals)
• Hip joint
• A branch to the subsartorial plexus in the adductor canal that supplies the femoral artery

Posterior Division

The posterior division pierces the obturator externus muscle and supplies:

• Obturator externus
• Adductor magnus
• Adductor brevis (if not supplied by the anterior division)
• A genicular branch to the popliteal vessels, cruciate ligaments, and capsule of the knee joint

Key description

• The obturator nerve emerges from the medial border of the psoas major muscle in the pelvis. The anterior division lies deep to the adductor longus and pectineus muscles. The posterior division lies behind the adductor brevis muscle.
• The genicular branch is the continuation of the posterior division. It enters the popliteal fossa, supplies the popliteal vessels, pierces the oblique popliteal ligament, and enters the knee joint.
• The pectineus muscle may receive nerve supply from both the obturator nerve and the femoral nerve. Therefore, it is considered to have dual nerve supply.

Sciatic Nerve

The sciatic nerve is the largest and thickest nerve in the human body. It is the largest branch of the sacral plexus and supplies the muscles and skin of most of the lower limb. The nerve begins in the pelvis, passes through the gluteal region and the back of the thigh, and usually ends by dividing into the tibial nerve and the common peroneal (fibular) nerve at the superior angle of the popliteal fossa.

• Width: Approximately 1.5–2 cm

Formation

The sciatic nerve is formed by two components:

Tibial Part

• Formed by the anterior divisions of the ventral primary rami of L4, L5, S1, S2, and S3 spinal nerves.

Common Peroneal (Fibular) Part

• Formed by the posterior divisions of the ventral primary rami of L4, L5, S1, and S2 spinal nerves.

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

Extent

The sciatic nerve passes through the following regions:

• Pelvis
• Gluteal region
• Back of the thigh
• Ends at the superior angle of the popliteal fossa, where it divides into the tibial nerve and the common peroneal (fibular) nerve.

Relations

In the Pelvis

• The sciatic nerve lies on the anterior surface of the piriformis muscle, beneath its fascia.

In the Gluteal Region

• The nerve leaves the pelvis through the greater sciatic foramen, below the piriformis muscle.

Superficial relations:

• Gluteus maximus
• Long head of biceps femoris

Deep relations (from above downward):

• Body of the ischium
• Tendon of obturator internus
• Superior gemellus
• Inferior gemellus
• Quadratus femoris
• Adductor magnus

Medial relations:

• Inferior gluteal nerve
• Inferior gluteal vessels

In the Thigh

Superficial relation:

• Long head of biceps femoris (crosses the nerve from medial to lateral)

Deep relation:

• Adductor magnus

Medial relations:

• Semitendinosus
• Semimembranosus

Lateral relation:

• Biceps femoris (in the middle part of the thigh)

Branches

Articular Branch

• Supplies the hip joint

Muscular Branches

From the tibial part:

• Semitendinosus
• Semimembranosus
• Long head of biceps femoris
• Hamstring (ischial) part of adductor magnus

From the common peroneal (fibular) part:

• Short head of biceps femoris

Terminal Branches

• Tibial nerve
• Common peroneal (common fibular) nerve

Tibial Nerve

The tibial nerve is the larger terminal branch of the sciatic nerve. It is the main nerve of the posterior compartment of the leg and supplies most of the muscles in the back of the leg and the sole of the foot. It also provides sensory supply to the skin of the heel, back of the leg, and the lateral side of the foot.

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

Course

• The tibial nerve is the largest terminal branch of the sciatic nerve.
• It begins at the superior angle of the popliteal fossa and descends vertically to its inferior angle.
• In the popliteal fossa, it crosses the popliteal vessels from the lateral side to the medial side.
• It then enters the posterior compartment of the leg and continues downward towards the foot.

Branches

Muscular Branches

The tibial nerve supplies the following muscles:

• Medial head of gastrocnemius
• Lateral head of gastrocnemius
• Plantaris
• Soleus
• Popliteus
• Tibialis posterior
• Flexor digitorum longus
• Flexor hallucis longus
• Deep part of the soleus

Cutaneous Branches

• Sural nerve supplies the skin of the lower half of the back of the leg and the lateral border of the foot up to the tip of the little toe. Medial calcaneal nerve pierces the flexor retinaculum and supplies the skin over the heel.

Articular Branches

The tibial nerve gives articular branches to:

• Superior medial genicular nerve
• Middle genicular nerve
• Inferior medial genicular nerve
• Ankle joint

Key description

• The nerve to the popliteus muscle winds around the lower border of the muscle and enters its deep (anterior) surface. Almost all muscular branches arise from the lateral side of the tibial nerve, except the nerve to the medial head of the gastrocnemius, which arises from the medial side. Therefore, the lateral side of the tibial nerve is considered surgically unsafe, whereas the medial side is relatively safe.
• The middle genicular nerve pierces the oblique popliteal ligament along with the middle genicular artery to supply the interior of the knee joint.
• The sural nerve leaves the popliteal fossa by piercing the deep fascia at its inferior angle. It supplies the lower half of the back of the leg and the lateral border of the foot up to the tip of the little toe.

Common Peroneal Nerve

The common peroneal (common fibular) nerve is the smaller terminal branch of the sciatic nerve. It supplies the short head of the biceps femoris and divides into the superficial and deep peroneal (fibular) nerves, which supply the muscles and skin of the leg and foot.

Root value: L4, L5, S1, and S2 (posterior divisions of the ventral primary rami)

Course

• The common peroneal nerve begins at the superior angle of the popliteal fossa beneath the long head of the biceps femoris.
• It runs downward and laterally along the medial border of the biceps femoris towards the lateral angle of the popliteal fossa.
• The nerve then winds around the neck of the fibula, where it is superficial and vulnerable to injury.
• It pierces the peroneus (fibularis) longus muscle.
• Within the muscle, it divides into:
  • Superficial peroneal (superficial fibular) nerve
  • Deep peroneal (deep fibular) nerve

Branches

Cutaneous Branches

• Lateral cutaneous nerve of the calf supplies the skin over the upper lateral part of the leg.
• Sural communicating nerve joins the tibial nerve contribution to form the sural nerve, which supplies the skin over the posterolateral leg and lateral side of the foot.

Articular Branches

The common peroneal nerve gives branches to the knee joint:

• Superior lateral genicular nerve
• Inferior lateral genicular nerve
• Recurrent genicular nerve

Muscular Branch

• Short head of the biceps femoris muscle

Deep Peroneal Nerve

The deep peroneal (deep fibular) nerve is one of the terminal branches of the common peroneal nerve. It is the main nerve of the anterior compartment of the leg and also supplies part of the dorsum of the foot.

Root value: L4, L5, S1, and S2

Beginning

• The deep peroneal nerve arises from the common peroneal nerve. It begins near the neck of the fibula, deep to the peroneus (fibularis) longus muscle.

Course and Relations

• The nerve starts on the lateral side of the neck of the fibula. It pierces the anterior intermuscular septum to enter the anterior compartment of the leg. It passes through the extensor digitorum longus muscle and descends with the anterior tibial artery.
• In the middle third of the leg, the nerve attempts to cross in front of the anterior tibial artery, but remains on its lateral side. Because of this characteristic course, it is known as the nervus hesitans (“hesitating nerve”).

Termination

• On the dorsum of the foot, in front of the ankle joint, the deep peroneal nerve divides into:
  • Medial terminal branch
  • Lateral terminal branch

Branches and Distribution

Muscular Branches

The deep peroneal nerve supplies all the muscles of the anterior compartment of the leg:

• Tibialis anterior
• Extensor digitorum longus
• Extensor hallucis longus
• Fibularis (peroneus) tertius

Terminal Branches

Lateral Terminal Branch

• Passes beneath the extensor digitorum brevis muscle.
• Supplies:
  • Extensor digitorum brevis
  • Tarsal joints
  • Metatarsal joints
• Ends in a small enlargement called a pseudoganglion.

Medial Terminal Branch

• Runs forwards on the dorsum of the foot.
• Supplies the skin of the first interdigital cleft (the space between the great toe and the second toe).

Key description

• The deep peroneal nerve is considered the lower limb equivalent of the posterior interosseous nerve in the forearm. At the level of the extensor retinaculum, the nerve lies with the tendons of the anterior compartment muscles and the anterior tibial artery.

Superficial Peroneal Nerve

The superficial peroneal (superficial fibular) nerve is one of the terminal branches of the common peroneal nerve. It is the main nerve of the lateral compartment of the leg. It supplies the muscles responsible for eversion of the foot and provides sensation to most of the dorsum of the foot.

Root value: L5 and S1

Beginning

• The superficial peroneal nerve is the smaller terminal branch of the common peroneal nerve.
• It arises near the neck of the fibula, within the fibularis (peroneus) longus muscle.

Course

• The nerve begins on the lateral side of the neck of the fibula within the fibularis longus muscle. It pierces the fibularis longus and descends between the fibularis longus and fibularis brevis muscles.
• Lower down, it runs between the extensor digitorum longus and fibularis brevis muscles. At the junction of the upper two-thirds and lower one-third of the leg, it pierces the deep fascia and becomes superficial. It then divides into medial and lateral terminal branches.

Branches and Distribution

Muscular Branches

The superficial peroneal nerve supplies:

• Fibularis (peroneus) longus
• Fibularis (peroneus) brevis

Cutaneous Branches

It provides sensation to:

• Lower one-third of the lateral side of the leg
• Most of the dorsum of the foot, except the areas supplied by:
  • Saphenous nerve
  • Sural nerve
  • Deep peroneal nerve
  • Plantar nerves

Terminal Branches

Medial Terminal Branch

This branch divides into two digital nerves that supply:

• Medial side of the great toe
• Adjacent sides of the second and third toes

Lateral Terminal Branch

This branch divides into two digital nerves that supply:

• Adjacent sides of the third and fourth toes
• Adjacent sides of the fourth and fifth toes

Medial Plantar Nerve

The medial plantar nerve is the larger terminal branch of the tibial nerve. It supplies most of the muscles on the medial side of the sole and provides sensation to the medial part of the sole and the medial three and a half toes. It is the preaxial nerve of the foot and is comparable to the median nerve of the hand.

Beginning

• The medial plantar nerve is the larger terminal branch of the tibial nerve. It begins deep to the flexor retinaculum.

Root value: L4, L5, and S1

Course and Relations

• The nerve passes forwards deep to the abductor hallucis muscle. It then runs between the abductor hallucis and the flexor digitorum brevis muscles. Throughout its course, it is accompanied by the medial plantar artery, which lies on its medial side.

Branches and Distribution

Muscular Branches

The medial plantar nerve supplies:

• Abductor hallucis
• Flexor digitorum brevis
• Flexor hallucis brevis
• First lumbrical

Cutaneous Branches

It supplies the skin of the medial part of the sole and the medial three and a half toes through four digital nerves:

• First digital nerve: Medial side of the great toe
• Second digital nerve: Adjacent sides of the first and second toes
• Third digital nerve: Adjacent sides of the second and third toes
• Fourth digital nerve: Adjacent sides of the third and fourth toes

Each digital nerve also supplies the skin over the dorsum of the terminal phalanx of its corresponding toe.

Articular Branches

• Supplies the tarsal and metatarsal joints.

Lateral Plantar Nerve

The lateral plantar nerve is the smaller terminal branch of the tibial nerve. It supplies most of the intrinsic muscles of the foot and provides sensation to the lateral part of the sole. It is the postaxial nerve of the foot and is comparable to the ulnar nerve of the hand.

Beginning

• The lateral plantar nerve is the smaller terminal branch of the tibial nerve.
• It begins deep to the abductor hallucis muscle.

Root value: S1 and S2

Course and Relations

• The nerve passes forward and laterally between the flexor digitorum brevis and the flexor digitorum accessorius (quadratus plantae) muscles.
• It then runs between the first and second muscular layers of the sole.
• Near the head of the fifth metatarsal, it divides into:
  • Superficial branch
  • Deep branch

Branches and Distribution

Branches from the Main Trunk

Muscular Branches

The main trunk supplies:

• Abductor digiti minimi
• Flexor digitorum accessorius (quadratus plantae)

Cutaneous Branch

• Supplies the lateral part of the sole.

Superficial Branch

Lateral Branch

Supplies:

• Flexor digiti minimi brevis
• Third plantar interosseous
• Fourth dorsal interosseous
• Skin on the lateral side of the little toe

Medial Branch

Supplies:

• Skin of the fourth interdigital cleft
• Gives a communicating branch to the medial plantar nerve

Deep Branch

The deep branch supplies the following nine muscles:

• Adductor hallucis
• Second lumbrical
• Third lumbrical
• Fourth lumbrical
• First plantar interosseous
• Second plantar interosseous
• First dorsal interosseous
• Second dorsal interosseous
• Third dorsal interosseous

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