Lower Extremity Nerves

Tip

• The superior gluteal nerve originates from the L4, L5, and S1 roots.
  • Gluteus medius, gluteus minimus, tensor fascia latae
  • thigh/hip abduction
• The inferior gluteal nerve arises from L5, S1, and S2.
  • Gluteus maximus
  • Thigh/hip extension
• The posterior cutaneous nerve comes from S1, S2, and S3.
• The pudendal nerve is derived from S2, S3, and S4.
• The sciatic nerve, being the largest, includes roots from L4 to S3.
• Obturator nerve
  • thigh adduction

Iliohypogastric Nerve (T12-L1)

• Motor: Internal oblique and transversus abdominis muscles (abdominal wall support and compression).
• Sensory: Skin over suprapubic region and lateral gluteal/iliac crest region.
• Clinical: Injury (e.g., during abdominal surgery like appendectomy or hernia repair) → weakness of anterior abdominal wall (predisposing to direct inguinal hernia), altered sensation in suprapubic/inguinal region.

Ilioinguinal Nerve (L1)

• Motor: Internal oblique and transversus abdominis muscles.
• Sensory: Skin of upper medial thigh, root of penis and anterior scrotum (males) or mons pubis and labia majora (females). Travels through inguinal canal.
• Clinical: Injury (e.g., during inguinal hernia repair) → sensory loss in the distribution, pain. Can be entrapped.

Genitofemoral Nerve (L1-L2)

• Motor:
  • Genital branch: Cremaster muscle (males – testicular elevation, cremasteric reflex).
  • Femoral branch: None (sensory only).
• Sensory:
  • Genital branch: Skin of anterior scrotum (males) or mons pubis and labia majora (females).
  • Femoral branch: Skin over femoral triangle/upper anterior thigh.
• Clinical: Injury (e.g., during inguinal or femoral surgery, appendectomy) → loss of cremasteric reflex, sensory loss in distribution.

Lateral Femoral Cutaneous Nerve (L2-L3)

• Motor: None.
• Sensory: Skin on anterolateral aspect of the thigh.
• Clinical: Entrapment under inguinal ligament (common) → Meralgia Paresthetica (pain, burning, numbness over lateral thigh). Risk factors: obesity, pregnancy, tight clothing.

Femoral nerve (L2-L4)

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• Motor: Anterior thigh compartment muscles (quadriceps femoris for knee extension; sartorius, pectineus, iliacus for hip flexion).
• Sensory: Anterior thigh, medial leg and foot (via saphenous nerve).
• Clinical: Injury → impaired knee extension, loss of patellar reflex, sensory loss to anterior thigh & medial leg/foot.

Obturator nerve (L2-L4)

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• Motor: Medial thigh compartment (adductor muscles: adductor longus, brevis, magnus adductor part; gracilis, obturator externus).
• Sensory: Medial thigh.
• Clinical: Injury → weakened thigh adduction, sensory loss to medial thigh.

Sciatic Nerve (L4-S3)

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• General: Largest nerve; bifurcates into Tibial and Common Peroneal nerves (typically in lower thigh/popliteal fossa).
• Motor (direct branches): Posterior thigh compartment (hamstrings: semitendinosus, semimembranosus, biceps femoris long head) for knee flexion & hip extension. Ischial part of adductor magnus.
• Sensory: No direct sensory to skin; supplied via its branches.
• Clinical: Injury (e.g., piriformis syndrome, hip dislocation) → weakness in hamstrings and all muscles below knee; foot drop (if common peroneal component affected significantly).

Tibial Nerve (L4-S3) (branch of Sciatic)

• Motor: Posterior compartment of leg (gastrocnemius, soleus, plantaris for plantarflexion; popliteus; tibialis posterior for inversion & plantarflexion; FHL, FDL for toe flexion). Most intrinsic foot muscles (via medial & lateral plantar nerves).
• Sensory: Posterolateral leg (via sural nerve, often with common peroneal contribution), sole of foot (via medial & lateral plantar nerves), heel (via medial calcaneal branches).
• Clinical: Injury → inability to plantarflex or invert foot, loss of toe flexion, sensory loss to sole. “Tip-toe” if proximal. Tarsal tunnel syndrome (entrapment at ankle).

Common Peroneal (Fibular) Nerve (L4-S2) (branch of Sciatic)

• Motor (direct branch): Short head of biceps femoris.
• Sensory: Lateral sural cutaneous nerve (skin on upper anterolateral leg).
• Divides into: Superficial and Deep Peroneal nerves.
• Clinical: Most frequently injured nerve in lower limb, esp. at fibular neck. Injury → Foot drop (loss of dorsiflexion and eversion), sensory loss over lateral leg & dorsum of foot.
• Superficial Peroneal Nerve:
  • Motor: Lateral compartment of leg (peroneus longus & brevis for eversion).
  • Sensory: Anterolateral distal leg & dorsum of foot (except 1st web space).
• Deep Peroneal Nerve:
  • Motor: Anterior compartment of leg (tibialis anterior for dorsiflexion & inversion; EHL, EDL for toe extension). Extensor digitorum brevis & extensor hallucis brevis in foot.
  • Sensory: First dorsal web space (b/w 1st & 2nd toes).

Feature	Common Peroneal	Deep Peroneal	Superficial Peroneal
Foot Drop	YES	YES	NO
Foot Eversion	Impaired	Spared	Impaired
Foot Inversion	Spared	Spared	Spared
Plantarflexion	Spared	Spared	Spared
Sensory Loss	Anterolateral leg + Dorsum of foot	Webspace between 1st/2nd toes	Dorsum of foot (spares webspace)
Classic Cause	Fibular neck fracture/compression	Anterior compartment syndrome	Trauma to lateral compartment

Superior Gluteal Nerve (L4-S1)

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• Motor: Gluteus medius, gluteus minimus, tensor fascia lata (hip abduction, medial rotation; pelvic stabilization).
• Sensory: Generally considered motor, though some sources note hip joint capsule sensation.
• Clinical: Injury → Trendelenburg gait/sign (pelvis sags on contralateral side when standing on affected leg), waddling gait.
  • Causes
    • Iatrogenic injury from intramuscular injection in the upper medial gluteal region
      • Correct buttock injection site
  • Motor deficits
    • Paralysis of gluteus medius and minimus, tensor fascia lata → impaired hip abduction
    • Positive Trendelenburg sign: lateral pelvic drop towards the opposite (healthy) side

Inferior Gluteal Nerve (L5-S2)

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• Motor: Gluteus maximus (powerful hip extension, e.g., rising from sit, climbing stairs).
• Sensory: None primarily.
• Clinical: Injury → difficulty rising from seated position, climbing stairs, “gluteus maximus lurch” (backward trunk lean during stance phase).

Posterior Cutaneous Nerve of Thigh (S1-S3)

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• Motor: None.
• Sensory: Skin of posterior thigh and popliteal fossa, inferior gluteal region, parts of perineum.

Pudendal nerve

• Motor: Muscles of perineum, external urethral sphincter, external anal sphincter.
• Sensory: Skin of perineum, penis/clitoris, posterior scrotum/labia.
• Clinical: Injury (e.g., childbirth, cycling, pelvic surgery) → fecal/urinary incontinence, sexual dysfunction, perineal pain. Pudendal nerve block used for obstetric analgesia.
• Pudendal nerve block: injection of a local anesthetic into the pudendal canal to block transmission within the pudendal nerve
  • Most commonly used during childbirth prior to an episiotomy or during surgical procedures involving the perineum
  • The ischial spine is used as a landmark for injection.