U01.11.009 Lower extremity nerves

Written by

in

Learning Objectives

  • Identify the nerve roots and sensory/motor distributions of the lower extremity.
  • Correlate specific surgical and traumatic injuries with clinical presentations (e.g., foot drop, Trendelenburg).
  • Apply the PED and TIP mnemonics to distinguish peroneal and tibial nerve functions.
  • Recognize the anatomical landmarks for pudendal nerve blocks and intramuscular injections.

1. Nerves of the Pelvis and Thigh

These nerves are frequently injured during abdominal or pelvic procedures.

  • Iliohypogastric (T12-L1): Often injured during inguinal hernia repair. Leads to burning pain radiating to the suprapubic region.
  • Genitofemoral (L1-L2): Injured in laparoscopic surgery. Results in an absent cremasteric reflex and decreased sensation on the upper medial thigh.
  • Lateral Femoral Cutaneous (L2-L3): Compressed by tight clothing or obesity (Meralgia Paresthetica). Causes burning pain in the anterolateral thigh; no motor deficit.
  • Obturator (L2-L4): Injured in pelvic surgery. Leads to decreased thigh adduction and medial thigh sensation.
  • Femoral (L2-L4): Injured by pelvic fractures or psoas abscesses. Results in loss of knee extension and a decreased patellar reflex.

Activity:

2. The Sciatic Branches: PED and TIP

The sciatic nerve (L4-S3) splits into the common peroneal and tibial nerves. Their deficits are high-yield for gait analysis.

Nerve Injury Site Clinical Presentation
Common Peroneal (L4-S2) Fibular neck fracture or compression. Foot Drop; loss of eversion/dorsiflexion; “steppage gait.” (PED)
Tibial (L4-S3) Knee trauma or Baker cyst. Inability to curl toes; loss of sensation on sole; cannot stand on TIPtoes. (TIP)

3. Gluteal and Pudendal Nerves

These nerves control the “power” movements of the hip and pelvic floor functions.

  • Superior Gluteal (L4-S1): Injured by injections in the superomedial gluteal quadrant.
    • Trendelenburg Sign: The pelvis tilts because the weight-bearing leg cannot abduct. The lesion is contralateral to the side of the hip drop.
  • Inferior Gluteal (L5-S2): Injured by posterior hip dislocation. Causes difficulty climbing stairs or rising from a seat (loss of hip extension).
  • Pudendal (S2-S4): Injured by childbirth or prolonged cycling.
    • Clinical: Perineal anesthesia; fecal/urinary incontinence. The ischial spine is the landmark for a pudendal block.

 

Clinical Notes & Corrections:

  • Safe Injection Site: To avoid the superior gluteal and sciatic nerves, use the superolateral quadrant of the gluteus.
  • Meralgia Paresthetica: This condition only affects sensation. If a patient presents with thigh pain and weakness, look toward the femoral nerve instead.
  • Sciatic Nerve: Posterior hip dislocations are a classic board question for both Sciatic and Inferior Gluteal nerve injuries.

Activity: Lower Extremity Nerve

Activity: