Lower Limb Nerves

The nerves of the lower limb provide motor, sensory, and articular innervation to structures extending from the hip and gluteal region to the toes. Most of these nerves originate from the lumbar and sacral plexuses, which are formed by the anterior rami of spinal nerves in the lumbosacral region.

The major peripheral nerves include the femoral nerve, obturator nerve, sciatic nerve, tibial nerve, common fibular nerve, superior gluteal nerve, and inferior gluteal nerve. Additional branches supply the skin, joints, and smaller muscle groups throughout the limb.

Understanding lower limb nerve anatomy requires following each nerve from its spinal roots through the pelvis or gluteal region and into the muscular compartments of the thigh, leg, and foot.

Organization of Lower Limb Innervation

Lower limb peripheral nerves contain axons derived from multiple spinal nerve levels. These fibers are redistributed within the lumbar plexus and sacral plexus before entering named peripheral nerves.

Major Nerve	Roots	Principal Region Supplied
Femoral nerve	L2-L4	Anterior thigh
Obturator nerve	L2-L4	Medial thigh
Superior gluteal nerve	L4-S1	Gluteus medius, gluteus minimus, tensor fasciae latae
Inferior gluteal nerve	L5-S2	Gluteus maximus
Sciatic nerve	L4-S3	Posterior thigh and, through its branches, most of leg and foot
Tibial nerve	L4-S3	Posterior leg and plantar foot
Common fibular nerve	L4-S2	Anterior and lateral leg through its terminal branches

Lumbosacral Plexus

The nerves supplying the lower limb arise from the lumbosacral plexus, which can be considered in lumbar and sacral components. Fibers originating from several spinal nerve levels combine and redistribute before forming the major peripheral nerves.

This arrangement means that injury to a peripheral nerve usually produces a pattern of weakness and sensory loss different from injury to an individual spinal nerve root.

Lumbar Plexus

The lumbar plexus is formed mainly by the anterior rami of L1-L4, with a possible contribution from T12. It develops within the posterior part of the psoas major muscle.

Important branches supplying the lower limb include the femoral, obturator, and lateral femoral cutaneous nerves. Other branches primarily supply the abdominal wall, inguinal region, and external genital region.

Sacral Plexus

The sacral plexus is formed by the lumbosacral trunk and anterior rami of sacral spinal nerves, principally involving L4-S4. It lies on the posterolateral pelvic wall, anterior to the piriformis muscle.

Major branches include the sciatic, superior gluteal, inferior gluteal, posterior femoral cutaneous, pudendal, and nerves supplying several short muscles of the gluteal region.

Femoral Nerve

The femoral nerve is a major branch of the lumbar plexus and is formed from the posterior divisions of the anterior rami of L2-L4.

It emerges from the lateral border of psoas major, descends between psoas major and iliacus, and passes deep to the inguinal ligament to enter the femoral triangle.

Motor Supply of the Femoral Nerve

The femoral nerve supplies muscles responsible primarily for extension of the knee and contributes to hip flexion.

• Iliacus
• Sartorius
• Quadriceps femoris
• Usually part of pectineus

The quadriceps femoris consists of rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius.

Sensory Supply of the Femoral Nerve

Anterior cutaneous branches of the femoral nerve supply much of the skin of the anterior and medial thigh. Its longest cutaneous branch, the saphenous nerve, supplies skin along the medial side of the leg and foot.

Saphenous Nerve

The saphenous nerve is the largest cutaneous branch of the femoral nerve. It accompanies the femoral vessels through part of the adductor canal but does not pass through the adductor hiatus.

It becomes superficial around the medial aspect of the knee and continues along the medial leg, providing sensory innervation without a motor component.

Obturator Nerve

The obturator nerve arises from the anterior divisions of the anterior rami of L2-L4. It emerges from the medial side of psoas major, travels along the lateral pelvic wall, and enters the thigh through the obturator canal.

Within the medial thigh it typically divides into anterior and posterior branches that pass on opposite sides of adductor brevis.

Motor Supply of the Obturator Nerve

The obturator nerve supplies most muscles of the medial compartment of the thigh and therefore plays an important role in hip adduction.

• Adductor longus
• Adductor brevis
• Adductor part of adductor magnus
• Gracilis
• Obturator externus

Pectineus has variable innervation and may receive a contribution from the obturator or accessory obturator nerve in addition to its usual femoral supply.

Sensory and Articular Supply

The obturator nerve can provide cutaneous sensation to a relatively small and variable region of the medial thigh. It also provides articular branches to the hip and knee joints.

Lateral Femoral Cutaneous Nerve

The lateral femoral cutaneous nerve arises from L2-L3 and is a purely sensory branch of the lumbar plexus. It crosses the iliacus toward the anterior superior iliac spine and passes beneath or through structures associated with the inguinal ligament.

It supplies sensation to the anterolateral aspect of the thigh.

Meralgia Paresthetica

Compression of the lateral femoral cutaneous nerve can produce meralgia paresthetica, characterized by sensory symptoms such as burning, numbness, or paresthesia over the anterolateral thigh.

Because the nerve is purely sensory, isolated injury does not directly produce muscle weakness.

Superior Gluteal Nerve

The superior gluteal nerve arises from L4-S1. It leaves the pelvis through the greater sciatic foramen superior to the piriformis muscle and travels laterally within the gluteal region.

It accompanies the superior gluteal vessels between gluteus medius and gluteus minimus.

Muscles Supplied by the Superior Gluteal Nerve

• Gluteus medius
• Gluteus minimus
• Tensor fasciae latae

These muscles are important for hip abduction and stabilization of the pelvis during walking.

Superior Gluteal Nerve Injury

Injury to the superior gluteal nerve weakens the principal hip abductors. During single-leg stance, this can impair the ability to maintain the pelvis in a relatively level position and produce a Trendelenburg sign.

Inferior Gluteal Nerve

The inferior gluteal nerve arises from L5-S2. It exits the pelvis through the greater sciatic foramen inferior to piriformis and enters the deep surface of gluteus maximus.

Its principal motor target is the gluteus maximus.

Function of the Inferior Gluteal Nerve

Gluteus maximus is a powerful extensor of the hip, particularly during activities requiring substantial force, such as rising from a seated position, climbing stairs, and running.

Inferior gluteal nerve injury therefore produces weakness of powerful hip extension.

Sciatic Nerve

The sciatic nerve is the largest peripheral nerve in the human body. It arises from the sacral plexus and contains fibers from L4-S3.

It is composed functionally of two major components, the tibial component and the common fibular component, which are enclosed together within a common connective tissue sheath for much of their course.

Course of the Sciatic Nerve

The sciatic nerve normally leaves the pelvis through the greater sciatic foramen inferior to piriformis. It descends deep to gluteus maximus and continues into the posterior thigh.

It usually divides into the tibial and common fibular nerves near the superior angle of the popliteal fossa, although the level of division is variable and may occur considerably higher.

Motor Supply in the Thigh

The sciatic nerve supplies the posterior compartment of the thigh. Its tibial component supplies most of the hamstring muscles, while the common fibular component supplies the short head of biceps femoris.

• Semitendinosus
• Semimembranosus
• Biceps femoris
• Hamstring part of adductor magnus

Tibial Nerve

The tibial nerve is the larger terminal component of the sciatic nerve and contains fibers from L4-S3. It descends through the popliteal fossa and enters the posterior compartment of the leg.

It supplies the posterior leg muscles and continues behind the medial malleolus into the foot, where it divides principally into the medial and lateral plantar nerves.

Motor Supply of the Tibial Nerve

In the leg, the tibial nerve supplies the superficial and deep muscles of the posterior compartment.

Superficial Posterior Compartment	Deep Posterior Compartment
Gastrocnemius	Popliteus
Soleus	Tibialis posterior
Plantaris	Flexor digitorum longus
	Flexor hallucis longus

These muscles contribute to plantarflexion, inversion, toe flexion, knee flexion, and stabilization during standing and walking.

Course Behind the Medial Malleolus

At the ankle, the tibial nerve passes posterior to the medial malleolus deep to the flexor retinaculum. It travels through the region commonly referred to as the tarsal tunnel.

The close anatomical relationship between the nerve and the flexor retinaculum is clinically important because compression in this region can produce tarsal tunnel syndrome.

Medial Plantar Nerve

The medial plantar nerve is one of the terminal branches of the tibial nerve. It supplies several intrinsic muscles of the foot and provides cutaneous innervation to a substantial portion of the medial plantar surface.

Its distribution has functional similarities to that of the median nerve in the hand, although the anatomy is not identical.

Lateral Plantar Nerve

The lateral plantar nerve is the other major terminal branch of the tibial nerve. It supplies most of the intrinsic muscles not supplied by the medial plantar nerve and provides sensory innervation to the lateral plantar foot.

Its functional distribution has similarities to that of the ulnar nerve in the hand.

Common Fibular Nerve

The common fibular nerve, also called the common peroneal nerve, is the smaller terminal component of the sciatic nerve and contains fibers primarily from L4-S2.

It follows the medial border of biceps femoris toward the lateral side of the knee and passes around the neck of the fibula, where it lies relatively superficially.

Division of the Common Fibular Nerve

Near the fibular neck, the common fibular nerve divides into two major terminal branches:

• Superficial fibular nerve
• Deep fibular nerve

These branches supply the lateral and anterior compartments of the leg respectively.

Superficial Fibular Nerve

The superficial fibular nerve travels through the lateral compartment of the leg. It provides motor innervation to fibularis longus and fibularis brevis.

These muscles primarily evert the foot and contribute to plantarflexion at the ankle.

Sensory Supply of the Superficial Fibular Nerve

The superficial fibular nerve becomes cutaneous in the distal leg and supplies much of the skin on the dorsum of the foot and distal anterior leg.

Its territory excludes several regions supplied by neighboring nerves, particularly the first dorsal web space, which is supplied by the deep fibular nerve.

Deep Fibular Nerve

The deep fibular nerve enters the anterior compartment of the leg and accompanies the anterior tibial vessels. It supplies muscles responsible primarily for dorsiflexion of the ankle and extension of the toes.

Muscles Supplied by the Deep Fibular Nerve

• Tibialis anterior
• Extensor hallucis longus
• Extensor digitorum longus
• Fibularis tertius
• Extensor digitorum brevis
• Extensor hallucis brevis

Sensory Supply of the Deep Fibular Nerve

The deep fibular nerve supplies a small but clinically useful cutaneous region on the dorsum of the foot, particularly the first interdigital cleft between the great toe and second toe.

Common Fibular Nerve Injury

The common fibular nerve is particularly vulnerable near the neck of the fibula because of its superficial location. Injury can impair both its superficial and deep terminal branches.

Weakness of the anterior compartment muscles produces impaired dorsiflexion and may result in foot drop. Weakness of the lateral compartment also reduces eversion.

Foot Drop

Foot drop describes an inability or marked difficulty in dorsiflexing the ankle during the swing phase of walking. Common fibular nerve injury is an important peripheral cause.

Patients may compensate by lifting the affected limb higher during walking to prevent the toes from dragging against the ground.

Sural Nerve

The sural nerve is primarily a sensory nerve supplying the posterolateral distal leg and lateral side of the foot. It is commonly formed through contributions from the tibial and common fibular nerves, although its exact anatomy varies.

Because of its superficial location and predominantly sensory function, the sural nerve is frequently used for diagnostic nerve studies and may be harvested as a donor nerve graft.

Posterior Femoral Cutaneous Nerve

The posterior femoral cutaneous nerve arises from the sacral plexus, generally from S1-S3. It leaves the pelvis inferior to piriformis and descends deep to gluteus maximus before continuing down the posterior thigh.

It is primarily sensory and supplies much of the skin of the posterior thigh, with additional branches to neighboring gluteal and perineal regions.

Nerve to Obturator Internus

The nerve to obturator internus arises from the sacral plexus and supplies obturator internus and superior gemellus. It exits the pelvis through the greater sciatic foramen and then enters the perineal region through the lesser sciatic foramen to reach obturator internus.

Nerve to Quadratus Femoris

The nerve to quadratus femoris supplies quadratus femoris and inferior gemellus. It also gives an articular branch to the hip joint.

It travels deep within the gluteal region, anterior to the sciatic nerve.

Nerve to Piriformis

The nerve to piriformis arises from the sacral plexus and enters the anterior surface of the piriformis muscle. Its root contributions commonly include S1-S2.

Major Nerves by Lower Limb Compartment

Region or Compartment	Principal Nerve
Gluteal abductors	Superior gluteal nerve
Gluteus maximus	Inferior gluteal nerve
Anterior thigh	Femoral nerve
Medial thigh	Obturator nerve
Posterior thigh	Sciatic nerve
Anterior leg	Deep fibular nerve
Lateral leg	Superficial fibular nerve
Posterior leg	Tibial nerve
Plantar foot	Medial and lateral plantar nerves

Cutaneous Innervation of the Lower Limb

Cutaneous innervation of the lower limb is provided by branches from multiple peripheral nerves. Their territories overlap to varying degrees and should be distinguished from dermatomes, which represent sensory territories associated with spinal nerve roots.

Cutaneous Nerve	General Sensory Territory
Lateral femoral cutaneous	Anterolateral thigh
Femoral anterior cutaneous branches	Anterior thigh
Obturator	Variable small medial thigh region
Posterior femoral cutaneous	Posterior thigh
Saphenous	Medial leg and medial foot
Superficial fibular	Much of dorsum of foot
Deep fibular	First dorsal web space
Sural	Posterolateral distal leg and lateral foot
Plantar nerves	Sole of foot and plantar surfaces of toes

Peripheral Nerves and Dermatomes

A peripheral nerve territory should not be confused with a dermatome. Peripheral nerves contain fibers from multiple spinal nerve roots, while a dermatome represents the cutaneous territory associated primarily with a single spinal nerve level.

This distinction is important when localizing neurological lesions.

Important Lower Limb Dermatomes

Spinal Level	Commonly Tested Region
L1	Inguinal region
L2	Anterior thigh
L3	Medial knee region
L4	Medial leg and medial malleolus
L5	Dorsum of foot and great toe region
S1	Lateral foot
S2	Posterior thigh and proximal posterior leg

Exact dermatome boundaries vary between individuals and between anatomical maps.

Myotomes of the Lower Limb

A myotome represents muscles or movements receiving substantial motor contribution from a particular spinal nerve root. Because most muscles receive fibers from multiple roots, clinical testing commonly focuses on representative movements.

Movement	Important Root Contributions
Hip flexion	L1-L3, particularly L2
Knee extension	L2-L4, particularly L3-L4
Ankle dorsiflexion	L4-L5
Great toe extension	Predominantly L5
Ankle plantarflexion	S1-S2

Femoral Nerve Injury

Damage to the femoral nerve can produce weakness of knee extension because of impaired quadriceps function. Hip flexion may also be weakened depending on the level and extent of injury.

Sensory deficits may involve the anterior thigh and, through the saphenous nerve, the medial leg.

Obturator Nerve Injury

Obturator nerve injury can weaken adduction of the thigh and may produce sensory disturbance in its variable medial thigh territory.

The nerve can be affected by pelvic pathology, surgical procedures, or trauma involving the obturator canal and surrounding structures.

Sciatic Nerve Injury

Injury to the sciatic nerve can produce extensive motor and sensory abnormalities because the nerve ultimately provides much of the innervation below the knee through its tibial and common fibular components.

The exact deficits depend on the level, severity, and fascicular distribution of the lesion.

Sciatica

Sciatica is a clinical term describing pain radiating along a distribution associated with the sciatic nerve or its contributing lumbosacral roots. It commonly results from irritation or compression of spinal nerve roots rather than direct injury to the sciatic nerve itself.

Symptoms may extend from the lower back or buttock into the posterior or lateral lower limb depending on the affected neural structures.

Tibial Nerve Injury

Injury to the tibial nerve can impair plantarflexion and toe flexion when the lesion occurs proximally. It can also affect inversion through loss of tibialis posterior function.

Sensory loss depends on the lesion level and can involve the plantar surface of the foot.

Tarsal Tunnel Syndrome

Tarsal tunnel syndrome involves compression of the tibial nerve or its branches beneath the flexor retinaculum near the medial ankle.

Symptoms can include pain, paresthesia, or altered sensation involving the plantar foot, depending on the site and severity of compression.

Common Fibular Nerve Injury

The common fibular nerve is vulnerable where it winds around the fibular neck. Trauma, compression, fractures, or prolonged external pressure in this region can damage the nerve.

A lesion at this level may weaken both dorsiflexion and eversion and can produce sensory loss over portions of the lateral leg and dorsum of the foot.

Deep Fibular Nerve Injury

Isolated deep fibular nerve injury can weaken dorsiflexion and toe extension depending on the level of injury. Sensory disturbance may involve the small first interdigital web-space territory.

Superficial Fibular Nerve Injury

Damage to the superficial fibular nerve can weaken foot eversion and produce sensory abnormalities over much of the dorsum of the foot.

Reflexes and Lower Limb Nerves

Deep tendon reflexes provide information about the integrity of sensory nerves, spinal cord segments, motor neurons, and peripheral motor nerves.

Reflex	Major Roots	Major Peripheral Nerve
Patellar reflex	L2-L4, especially L4	Femoral nerve
Achilles reflex	S1-S2, especially S1	Tibial nerve

Lower Limb Nerves and Gait

Normal gait depends on coordinated activity across multiple peripheral nerves. The superior gluteal nerve stabilizes the pelvis, the femoral nerve contributes to knee control, the common fibular system provides dorsiflexion and eversion, and the tibial nerve supplies powerful plantarflexors used during propulsion.

Lesions of different nerves therefore produce characteristic gait abnormalities.

Trendelenburg Gait

Weakness of gluteus medius and gluteus minimus from superior gluteal nerve dysfunction can impair pelvic stabilization during the stance phase of gait. The pelvis tends to drop on the unsupported side when the abductors on the stance side cannot generate sufficient force.

Steppage Gait

Loss of effective ankle dorsiflexion can cause the toes to drag during the swing phase. A patient may compensate by flexing the hip and knee more than usual, producing a steppage gait.

This pattern is commonly associated with foot drop but can result from lesions at several levels of the motor pathway.

Peripheral Nerve Injury and Localization

Neurological examination of the lower limb combines assessment of muscle strength, reflexes, cutaneous sensation, and gait. The resulting pattern can help distinguish lesions involving peripheral nerves from those involving nerve roots, plexuses, or more proximal parts of the nervous system.

Root Lesion Versus Peripheral Nerve Lesion

Feature	Nerve Root Lesion	Peripheral Nerve Lesion
Sensory pattern	Approximately dermatomal	Peripheral nerve territory
Motor pattern	Myotomal distribution involving muscles from multiple nerves	Muscles supplied by affected peripheral nerve
Reflex changes	Depend on affected root	Depend on nerve and fibers involved

Relationship to the Major Joints

Peripheral nerves of the lower limb also provide articular branches to joints. The hip, knee, ankle, and foot joints receive innervation from nerves that also supply nearby muscles and skin.

Articular innervation is clinically relevant to joint pain and to understanding referred pain patterns.

Hip Joint Innervation

The hip joint receives articular branches from several nerves, including branches associated with the femoral, obturator, superior gluteal, and nerve to quadratus femoris pathways. The precise contribution varies.

Knee Joint Innervation

The knee receives articular branches from nerves including the femoral, obturator, tibial, and common fibular nerves. These branches contribute sensory fibers from multiple aspects of the joint.

Ankle and Foot Innervation

The ankle and foot receive articular and cutaneous branches from the tibial, deep fibular, superficial fibular, sural, and saphenous nerves. The plantar surface is supplied predominantly through branches of the tibial nerve.

Summary of Major Motor Functions

Nerve	Major Motor Function
Femoral	Knee extension, contribution to hip flexion
Obturator	Thigh adduction
Superior gluteal	Hip abduction and pelvic stabilization
Inferior gluteal	Powerful hip extension
Sciatic	Posterior thigh activity and origin of major motor supply below knee
Tibial	Plantarflexion, toe flexion, inversion contribution, intrinsic plantar muscle activity
Deep fibular	Dorsiflexion and toe extension
Superficial fibular	Foot eversion

Key Anatomical Relationships

Nerve	Important Landmark
Femoral nerve	Passes deep to inguinal ligament
Obturator nerve	Passes through obturator canal
Superior gluteal nerve	Exits greater sciatic foramen superior to piriformis
Sciatic nerve	Usually exits greater sciatic foramen inferior to piriformis
Common fibular nerve	Winds around fibular neck
Tibial nerve	Passes posterior to medial malleolus
Deep fibular nerve	Travels in anterior leg with anterior tibial vessels

Functional Importance

The peripheral nerves of the lower limb connect the lumbosacral nervous system with the muscles, skin, and joints of the hip, thigh, leg, and foot. Their organization closely follows the muscular compartments of the limb, making compartmental anatomy particularly useful for understanding motor innervation.

The femoral and obturator nerves dominate the anterior and medial thigh respectively, while the sciatic nerve supplies the posterior thigh and gives rise to the tibial and common fibular systems responsible for most innervation below the knee.

The superficial course of certain nerves creates predictable sites of vulnerability. The common fibular nerve is particularly exposed around the fibular neck, while the tibial nerve can be compressed near the medial ankle. Knowledge of these relationships allows patterns of weakness and sensory loss to be correlated with specific anatomical lesions.

Understanding lower limb nerves is therefore fundamental to the study of muscle innervation, lower limb compartments, gait, dermatomes, myotomes, peripheral nerve injury, radiculopathy, plexopathy, foot drop, joint innervation, and clinical neurological examination.