Proximal lower extremity mononeuropathies

Author(s): Anita S.W. Craig, DO

Originally published:10/22/2013

Last updated:10/22/2013



The lower abdominal wall, hip, and knee are affected by neuropathies of the iliohypogastric, ilioinguinal, genitofemoral, femoral, obturator, and lateral femoral cutaneous nerves.


  1. All are vulnerable to injury from pelvic trauma, fractures, and hip dislocation.
  2. Intraabdominal, primarily retroperitoneal, and pelvic masses: neoplasm, hematoma, lymphadenopathy, hernia, aneurysm, and endometriosis.
  3. Iatrogenic injury is common.
    • Inguinal herniorrhaphy: ilioinguinal, iliohypogastric, genitofemoral, or femoral nerves. These nerves can also be injured by appendectomy, Cesarean section, abdominoplasty, and iliac graft harvesting.1 External compression or blunt trauma, particularly at the anterior superior iliac spine (ASIS), can injure the iliohypogastric, ilioinguinal, genitofemoral, and lateral femoral cutaneous nerves.2
    • Abdominal hysterectomy: any proximal nerves, particularly with the use of self-retaining retractors.3
    • Lithotomy positioning in the flexed, abducted, and externally rotated position: femoral and obturator nerves.4
  4. Femoral vessel catheterization procedures can injure the femoral nerve. Hematomas as a result of chronic anticoagulation or blood dyscrasias may cause acute iliacus compartment syndrome. The femoral nerve’s terminal saphenous branch is vulnerable to injury.
    • Saphenous vein harvesting, knee braces, and tourniquet use for knee surgery.
    • Femoral neuropathies reported in .01% to 2.3% of total hip arthroplasties because of retractor placement in anterior or anterolateral approaches.5
  5. Prolonged labor may injure the obturator nerve as a result of fetal head compression against the pelvic wall.6

Epidemiology including risk factors and primary prevention

  1. Increased risk with self-retaining retractors in pelvic surgery.3
  2. Thin body habitus may predispose to injury from retractors or lithotomy positioning.4
  3. Obese individuals have higher risk of nerve injury after high energy pelvic trauma.7
  4. Primary prevention includes caution in the positioning of patients in the lithotomy position for prolonged periods of time and careful attention to the placement of retractors during pelvic procedures.
  5. Compression because of tight clothing or belts, or large body habitus and rapid weight fluctuations, particularly in the case of the lateral femoral cutaneous nerve.2


Ilioinguinal/Iliohypogastric/Genitofemoral Nerves

  1. L1 nerve root with variable contribution from T12 and L2.
  2. Ilioinguinal: supplies the upper inner thigh, root of penis, and upper scrotum/mons pubis and lateral labia.
  3. Iliohypogastric: transversus abdominis and internal oblique muscles; sensation to upper lateral buttock and suprapubic region.
  4. Genitofemoral: sensation to inner thigh, round ligament, and labia majora in women; cremaster muscle and lower scrotum in men.
  5. These nerves can be injured where they pierce the lower abdominal muscles or in relation to the inguinal ligament.

Femoral Nerve

  1. From the L2-4 nerve roots, travels between and innervates the psoas and iliacus; passes under the inguinal ligament lateral to the femoral artery and vein.
    • Terminal muscular branch: supplies the four heads of the quadriceps, sartorius, and pectineus muscles.
    • Medial and intermediate sensory branches to the anterior thigh.
    • Saphenous nerve (subsequently discussed).
  2. Most commonly injured in the retroperitoneal space or under the inguinal ligament.

Saphenous Nerve

  1. Terminal branch, femoral nerve: travels in the subsartorial canal with the femoral artery and exits the canal 10 cm above the knee.
  2. Infrapatellar branch to the knee supplies the anteromedial knee and anterior and inferior joint capsule.
  3. Adjacent to the saphenous vein, provides sensation to the medial lower leg down to the first metatarsophalangeal joint.

Obturator Nerve

  1. From the L2-4 nerve roots, anterior to the sacroiliac joint.
  2. Anterior branch: supplies adductor brevis and longus.
  3. Posterior branch: obturator externus and portion of adductor magnus (with sciatic nerve).

Lateral Femoral Cutaneous Nerve

  1. From L2-3 nerve roots. Emerges from the pelvis medial to the ASIS just under the inguinal ligament.
  2. Sensory only with anterior and posterior branches ramifying across the anterolateral thigh.

Specific secondary or associated conditions and complications

Proximal muscle weakness can cause instability around the hip and knee, resulting in falls. Progression of mobility after a trauma may be delayed because of unrecognized neurologic lesions. Protective postures because of neuropathic pain may lead to hip flexion contractures. Complex regional pain syndrome may develop.



Patients often present with an acute pelvic fracture, blunt trauma around the ASIS or groin, pelvic surgery, or vascular catheterization. Patients may also be anticoagulated. Injury may not initially be identified because of acute injury or surgery.

Patients present with numbness or weakness in the anatomic nerve distribution, as previously described.

Physical examination

Loss of strength and sensoration in nerve distribution:

  1. Ilioinguinal/iliohypogastric/genitofemoral nerves: sensory changes and pain seen in the described sensory distribution. Weakness of lower abdominal wall in ilioinguinal and iliohypogastric injury. The cremasteric reflex is affected in genitofemoral injury. Lumbar extension may aggravate symptoms, and Tinel sign may present along the affected nerve.
  2. Femoral nerve: if retroperitoneal space injury, weak hip flexion, and knee extension. Lesions at or distal to inguinal ligament spare hip flexion. Patellar reflex depressed or absent. Abnormal sensation in anterior thigh and anteromedial leg to the first metatarsophalangeal joint (saphenous). Hip extension can exacerbate pain.
  3. Saphenous nerve: sensory loss with no weakness. Isolated injury of the infrapatellar branch resembles medial knee pain.
  4. Obturator nerve: sensory deficit in groin or medial thigh. Hip abduction and internal rotation weakness present. Pain induced by exercise with entrapment in the adductor canal.8
  5. Lateral femoral cutaneous nerve: sensory loss without weakness in very discrete distribution on the anterolateral thigh. Tinel sign is often present in ASIS. Hip extension, standing, and walking will aggravate pain.

Functional assessment

Pain from traumatic injury, such as fractures and orthopedic restrictions, may initially mask nerve injury symptoms. As recovery ensues, symptoms become apparent. A persistent forward-flexed posture may be observed because of pain from neural tension. Internal hip rotator weakness may cause extremity to externally rotate during ambulation and cause a circumducted gait. Femoral and obturator weakness interferes with transfers, such as lifting the limb in and out with bed, tub, and stair use.


Plain radiographs should be obtained in traumatic injury to assess for fractures of the pelvis or proximal femur, to detect bony exostosis, heterotopic ossification, or tumor that impinges on the course of the nerves. Computerized tomography can show bony lesions in greater detail. Magnetic resonance imaging provides detailed visualization of anatomic structures, such as tumor and hematoma, along with direct visualization of nerves and signal change associated with denervated muscle.9Ultrasonography can visualize nerves and help localize injury location. An injured lateral femoral cutaneous nerve will show significantly larger diameter on ultrasound than on the asymptomatic side.10

Supplemental assessment tools

Electrodiagnostic testing is very useful in identifying the lesion, localizing level of injury, assessing the severity and chronicity, and is critical in evaluating plexus or root lesions in trauma or iatrogenic injury.

  1. Ilioinguinal, iliohypogastric, genitofemoral nerve injury: no reliable nerve conduction studies (NCS). Needle electromyography (EMG) may show denervation in the lower abdominal muscles in ilioinguinal neuropathies. Assessing proximal thigh and paraspinal muscles helps to exclude high lumbar radiculopathy or upper plexus lesion.
  2. Femoral nerve injury: NCS may be uncomfortable and technically challenging because of the depth of the nerve. Comparison should be done with the asymptomatic side. A compound action potential amplitude of at least 50% of the other side, obtained between 10 days to a month after injury, predicts good prognosis for recovery within 1 year.11 EMG including iliopsoas and the quadriceps aids in localizing lesions proximal or distal to the inguinal ligament.
  3. Saphenous nerve injury: saphenous NCS are technically challenging and should be compared with the asymptomatic side. EMG of thigh and paraspinal muscles will be normative.
  4. Obturator nerve injury: no NCS available. EMG abnormal in adductor longus and possibly magnus (partly sciatic innervated).
  5. Lateral femoral cutaneous nerve: NCS technically challenging. Compare with the other side. EMG of thigh and L3-5 muscles normative. The use of ultrasound to localize the nerve can improve the ability to record a response.12

Professional Issues

Iatrogenic injury to proximal nerves is very common in many pelvic and orthopedic procedures. Patients can be reassured that in most cases good recovery can be expected. Discussion of the possiblity of such injuries should be part of routine discussion of operative risks. Recurrent injuries, however, warrant examination of intraoperative procedures, particularly in the employment of self-retaining retractors and patient positioning.


Available or current treatment guidelines

Treatment depends on etiology:

  1. Compressive lesion from tumor/mass: surgical decompression. Hematoma may require correction of anticoagulation and urgent drainage. Correction of hernias can relieve compression.
  2. If painful, medications, such as tricyclic antidepressants, anticonvulsants, and topical agents, such as lidocaine and capsaicin, can be prescribed. Transcutaneous electrical nerve stimulation or acupuncture may be useful.
  3. Nerve blocks can be diagnostic and therapeutic.14
  4. The lateral femoral cutaneous nerve can be blocked near the ASIS.
  5. Surgical exploration and neurolysis should be considered if there is no improvement after 3 to 6 months of conservative managment.13
  6. A knee-ankle-foot orthosis, when quadriceps weakness is severe, with a few degrees of ankle plantar flexion can assist the extension moment at the knee.
  7. To compensate for quadriceps weakness, the patient can be trained to activate the gluteus maximus, hamstring muscles, and the gastroc-soleus muscles during stance phase to assist knee extension.

Translation into practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills

  1. When assessing a patient with a traumatic injury to the pelvis, keep a high index of suspicion for neurologic injury, particularly because such injuries can easily be masked by pain, orthopedic restrictions, and altered mental status or sedation.
  2. Likewise, in patients who have had lower abdominal or pelvic surgeries, any unexpected pain, weakness, or delay in progress should raise suspicion for nerve damage.
  3. EMG can aid in differentiating neurologic injury from deficits because of orthopedic injury. It can also assist in localizing the level of the lesion, severity, and prognosis.





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7. Lazar MA, Plocher EK, Egol KA. Obesity and its relationship with pelvic or lower extremity orthopedic trauma. Am J Orthop. 2010;39:175-182.

8. Bradshaw C, McCrory P, Bell S, Brukner P. Obturator neuropathy: a cause of chronic groin pain in athletes. Am J Sports Med. 1997;25:402-408.

9. Stoller DW, Rosenberg ZS, Cavalcanti C, et al. Entrapment neuropathies of the lower extremity. In: Stoller DW, ed. Magnetic Resonance Imaging in Orthopeaedics and Sports Medicine. Philadelphia, PA: Lippincott Williams & Wilkins; 2007:1051-1098.

10. Aravindakannan T, Wilder-Smith EP. High-resolution ultrasonography in the assessment of merlagia parasthetica. Muscle Nerve. 2011;45:434-435.

11. Kuntzer T, van Melle G, Regli F. Clinical and prognostic features in unilateral femoral neuropathies. Muscle Nerve. 1997;20:205-211.

12. Boon AJ, Bailey PW, Smith J, Sorenson EJ, Harper CM, Hurdle MF. Utility of ultrasound-guided surface electrode placement in lateral femoral cutaneous nerve conduction studies. Muscle Nerve. 2011;44:525-530.

13. Ducic I, Dellon L, Larson EE. Treatment concepts for idiopathic and iatrogenic femoral nerve mononeuropathy. Ann Plast Surg. 2005;55:397-401.

14. Waldman SD. Ilioinguinal, iliohypogastric, and genitofemoral neuralgia. In: Waldman S, ed. Pain Management. 1st ed. Philadelphia, PA: Saunders; 2006:742-748.

Author Disclosure

Anita S.W. Craig, DO
Nothing to Disclose

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