Updated: 1/13/2020

Lower Extremity Innervation

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Key Images
https://upload.medbullets.com/topic/112016/images/lower_extremity_innervation.jpg
Snapshot
  • A 27-year-old woman gives birth to a healthy baby boy. She had an uncomplicated vaginal delivery and was placed in obstetric stirrups during the delivery. Soon after the birth, she complains of numbness and weakness in her right foot. On exam, she has decreased sensation to light touch along the dorsum of her foot including in the first webspace. Ankle dorsiflexion is 3/5 and ankle plantarflexion is 5/5. She walks with a steppage gait. (A compression neuropathy of the common peroneal nerve)
Overview
 

Introduction
  • Clinically relevant nerves to the lower extremity
    • hip/thigh
      • motor
        • obturator nerve
        • femoral nerve
        • sciatic nerve
        • superior gluteal nerve
        • inferior gluteal nerve
      • sensory
        • lateral femoral cutaneous nerve
        • obturator nerve
        • femoral nerve
    • leg/foot
      • motor
        • tibial nerve
        • common peroneal
          • deep peroneal nerve
          • superficial peroneal nerve
      • sensory
        • sural nerve
        • saphenous nerve
        • deep peroneal nerve
        • superficial peroneal nerve
        • tibial nerve
Obturator Nerve (L2-L4)
  • Motor innervation
    • hip adduction
      • adductor magnus, longus, and brevis
      • gracilis
  • Sensory innervation
    • medial thigh
  • Terminal branches
    • none
  • Injury
    • causes
      • rare
      • anterior hip dislocation
    • motor deficit
      • impaired hip adduction
    • sensory deficit
      • sensory loss over medial thigh
Femoral Nerve (L2-L4)
  • Motor innervation
    • hip flexion
      • iliacus
      • sartorius
      • rectus femoris (part of the quadriceps femoris)
    • knee extension
      • quadriceps femoris
        • rectus femoris
        • vastus medialis, intermedius, and lateralis
  • Sensory innervation
    • anteromedial thigh
    • medial leg and foot (via the saphenous nerve)
  • Terminal branches
    • saphenous nerve
  • Injury
    • causes
      • trauma
        • penetrating pelvic injury
      • compression
        • prolonged hip flexion (e.g., lithotomy position)
      • iatrogenic
        • pelvic, abdominal, or spinal surgery
    • motor deficit
      • impaired hip flexion
      • impaired knee extension
    • sensory deficit
      • sensory loss over the anteromedial thigh
      • sensory loss over the medial leg
Sciatic Nerve (L4-S3)
  • Motor innervation
    • knee flexion
      • hamstrings
        • semimembranosus
        • semitendinosus
        • biceps femoris (long head)
  • Sensory innervation
    • no direct sensory innervation
    • dorsum of the foot and anterolateral leg (via superficial peroneal nerve)
    • plantar aspect of the foot (via tibial nerve)
    • posterolateral leg (via sural nerve)
  • Terminal branches
    • common peroneal nerve
    • tibial nerve
  • Injury
    • causes
      • trauma
        • lumbar intervertebral disc herniation
      • iatrogenic
        • hip surgery
    • motor deficit
      • impaired knee flexion
      • impaired ankle dorsiflexion, plantarflexion, inversion, and eversion
    • sensory deficit
      • sensory loss over dorsal and plantar surfaces of the foot
      • sensory loss over the lateral leg
Common Peroneal Nerve (L4-S2) 
  • Motor innervation
    • knee flexion
      • biceps femoris (short head)
  • Sensory innervation
    • lateral knee
    • anterolateral leg and dorsum of foot (via superficial peroneal nerve)
    • posterolateral leg (via sural nerve, which also receives innervation from the tibial nerve)
  • Terminal branches
    • deep peroneal nerve
    • superficial peroneal nerve
  • Injury
    • causes
      • compression
        • obstetric or anesthesia stirrups
        • lying on side during anesthesia without appropriate padding
        • tight plaster cast of leg
      • trauma
        • fracture of fibular neck
    • motor deficit
      • impaired ankle dorsiflexion
        • presents as a foot drop 
        • patient will compensate with exaggerated hip and knee flexion (steppage gait)
      • impaired ankle eversion
    • sensory deficit
      • sensory loss over anterior and lateral leg
      • sensory loss over dorsum of the foot including first webspace
Deep Peroneal Nerve (L4-L5)
  • Motor innervation
    • ankle dorsiflexion
      • tibialis anterior
    • toe extension
      • extensor digitorum longus
      • extensor hallucis longus
  • Sensory innervation
    • first webspace
  • Terminal branches
    • none
  • Injury
    • causes
      • compression
        • tight laces or ski boots
      • trauma
        • anterior ankle trauma
    • motor deficit
      • impaired ankle dorsiflexion 
        • presents as a foot drop with a steppage gait 
      • impaired ankle inversion
        • tibialis posterior can still invert the foot
    • sensory deficit
      • sensory loss over first webspace
Superficial Peroneal Nerve (L4-S1)
  • Motor innervation
    • ankle eversion
      • peroneus longus and brevis
  • Sensory innervation
    • anterolateral leg
    • dorsum of foot except for the first webspace
  • Terminal branches
    • none
  • Injury  
    • causes
      • trauma
        • fracture of the fibular diaphysis
    • motor deficit
      • impaired ankle eversion
    • sensory deficit
      • sensory loss over the anterolateral leg
      • sensory loss over the dorsum of the foot
Tibial Nerve (L4-S3)
  • Motor innervation
    • ankle plantarflexion
      • gastrocnemius-soleus complex
    • ankle inversion
      • tibialis posterior
    • toe flexion
      • flexor digitorum longus
      • flexor hallucis longus
  • Sensory innervation
    • plantar aspect of the foot (via medial and lateral plantar nerves)
    • posterolateral leg (via sural nerve, which also receives innervation from the common peroneal nerve)
  • Terminal branches
    • medial and lateral plantar nerves
  • Injury
    • causes
      • trauma
        • posterior knee dislocation
    • motor deficit
      • impaired ankle plantarflexion
      • impaired ankle inversion
        • tibialis anterior can still invert the foot
      • impaired toe flexion
    • sensory deficit
      • sensory loss over plantar aspect of the foot
Superior Gluteal Nerve (L4-S1)
  • Motor innervation
    • hip abduction
      • gluteus medius and minimus
      • tensor fascia latae
  • Sensory innervation
    • none
  • Terminal branches
    • none
  • Injury
    • causes 
      • posterior hip dislocation
      • injection to upper medial gluteal region
    • motor deficit
      • impaired hip abduction
        • presents with a positive Trendelenburg test and a Trendelenburg gait  
          • Trendelenburg test   
            • patient is asked to lift one foot off the ground and to stand on one foot
            • normally, the gluteus medius and gluteus minimus muscles contract to abduct the hip and prevent it from tipping to the unsupported side
            • in a patient with an SGN injury, the pelvis will tip to the unsupported side due to impaired hip abduction
          • Trendelenburg gait
            • a patient with an SGN injury will lean away from the unsupported side when walking to indirectly raise the pelvis in order to allow their leg to clear the ground 
    • sensory deficit
      • none
Inferior Gluteal Nerve (L5-S2)
  • Motor innervation
    • hip extension
      • gluteus maximus
  • Sensory innervation
    • none
  • Terminal branches
    • none
  • Injury
    • cause
      • rare
      • hip arthroplasty
    • motor deficit
      • impaired hip extension
        • presents with difficulty climbing stairs, stepping onto a bus, and arising from a chair
    • sensory deficit
      • none
Lateral Femoral Cutaneous Nerve (L2-L3)
  • Motor innervation
    • none
  • Sensory innervation
    • anterolateral thigh
  • Terminal branches
    • none
  • Injury
    • cause
      • compression as the nerve passes under the inguinal ligament (meralgia paresthetica)
        • pregnancy
        • tight clothing
        • obesity
    • motor deficit
      • none
    • sensory deficit
      • sensory loss, numbness, and paresthesias over the anterolateral thigh
Sensory Innervation to the Foot
  • The foot has multiple nerves carrying sensory input
  • Identifying areas of sensory loss can aid in the localization of specific nerve lesions
  • Localization
    • lateral foot
      • sural nerve
        • receives branches from the tibial nerve and common peroneal nerve
    • medial foot
      • saphenous nerve
        • terminal branch of the femoral nerve
    • dorsal aspect of the foot
      • superficial peroneal nerve
        • terminal branch of the common peroneal nerve
    • first webspace
      • deep peroneal nerve
        • terminal branch of the common peroneal nerve
    • plantar aspect of the foot
      • tibial nerve (via lateral plantar, medial plantar, and calcaneal nerves)
        • terminal branch of the sciatic nerve
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(M1.MK.13.8) A 41-year-old male presents to your office with paresthesias on the lateral left calf and the dorsum of the left foot that he reports has been worsening over the past three months. An MRI of the lumbar spine was unremarkable. An MRI of the left knee with a representative axial cut through the proximal tibiofibular joint is shown in Figure A. Which of the following abnormal physical exam findings would you expect to see in this patient? Tested Concept

QID: 101672
FIGURES:
1

Inability to walk on his toes with the heel elevated on the left

23%

(19/82)

2

Decrease Achilles tendon reflex

6%

(5/82)

3

Positive Trendeleberg test

2%

(2/82)

4

Decreased patellar tendon reflex on the left

10%

(8/82)

5

Inability to walk on his heel with the forefoot elevated off the ground on the left

54%

(44/82)

M 2 E

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