Lumbosacral Plexus Lesions

Overview of Lumbosacral Plexopathy

Upper lumbar plexus lesions demonstrate various combinations of deficits in the iliohypogastric, ilioin- guinal, genitofemoral, femoral and obturator nerve distributions. Weakness is seen in hip flexion, knee extension (concomitant inability to lock the leg on standing) and adduction of the thigh. Sensory loss is noted in the lower abdominal wall, inguinal, labial, and scrotal areas as well as the thigh and medial lower leg. An absent or a depressed knee reflex is noted.

            Lower lumbar sacral plexus lesions cause deficits within the innervation territories of the glu- teal, sciatic, tibial, and peroneal nerves. Weakness occurs in hip extension, and abduction, knee flexion, and all intrinsic foot musculature. Sensory loss occurs in the posterior thigh, anterior and posterior as- pects of the lower leg below the knee and most of the foot. There are diminished or absent ankle reflexes. Gluteal and sciatic nerve weakness localizes a lesion to the sacral plexus.

            Plexopathies are recognized when motor, sensory, and reflex deficits occur in multiple nerve and segmental distributions that affect one extremity.

            Localization is often difficult due to the pathologies of the region, but usually in a broad sense can be divided into:

    1. Lumbar plexopathy
    2. Sacral plexopathy
    3. Lumbosacral trunk lesions
    4. Pan-plexopathy

In general, lumbar plexopathies evolve in a stepwise and dissociated manner.

            In localization of lumbosacral plexopathies pathology of the cauda equina and conus medullaris has to be considered. Rarely, motor neuron disease may simulate plexopathy if deficits are without pain or sensory loss. Intraspinal lesions (lower spinal cord) tend to be bilateral with early bowel and bladder dysfunction rather than motor weakness. Cauda equina lesions are painful, and bladder dysfunction is seen early.

Differential points in the history or examination include:

  1. Pain in the following territories define specific sensory roots and nerves:
    1. Hip (sclerotomal radiation of L5)
    2. Buttock (L5-S1 root); often have tenderness in the sciatic notch
    3. Proximal thigh laterally (L5); also may be caused by bursitis of the tensor fascia lata
    4. L1, L2, L3 roots innervate the dorsal thigh; this is also the sclerotomal distribution of the recurrent nerve of Spurling of L5. The usual problem is disc herniation that causes radiation to the dorsal thigh rather than its somatic dermatomal distribution.
    5. The medial thigh is innervated by the ilioinguinal nerve (L1, L2 roots)
    6. The groin is innervated by T12 and L1. It may also have a projected sclerotomal radia- tion from S1. Thus, S1 root irritation may radiate to the groin. This invariably is diag- nosed as hip disease or an inguinal hernia.
    7. The straight leg raising test causes sciatic nerve pain (L5-S1 roots); the reverse SLR test stretches the femoral nerve (L2-L3 sensory roots are involved; often concomitant inguinal pain).
    8. In plexopathy, the Valsalva maneuver does not elicit pain as it frequently does with radic- ulopathy
    9. In peroneal nerve neuropathy with foot drop:

      1. Inversion of the foot is normalli>
      2. Toe flexion and hip abduction are normal
      3. The ankle reflex is preserved
    10. Differential signs to distinguish lumbosacral trunk lesions from an L5 radiculopathy:
      1. The lumbar trunk is formed primarily by the L5 spinal nerve with a contribution from L4; peroneal sensation is normal which favors a trunk lesion.
      2. If the pattern of weakness is hip adductors, iliopsoas, and quadriceps a lumbar plex- opathy rather than femoral or obturator nerve lesions is more likely
    11. Simultaneous involvement of the lumbar and sacral roots is usual with external trauma; iatrogenic injury more often involves individual L5 plexus components.

    Anatomical Relationship of the Lumbar and Sacral Plexus

    1. The L1, L2, L3 ventral rami are the primary components of the lumbar plexus with contri- butions from T11 and T12.
      1. They traverse the posterior portion of the psoas muscle anterior to the vertebral trans- verse processes:
        1. Femoral nerve (L2-L4 primary spinal nerves) also supplies sensation to the thigh and leg by:
          1. Medial and intermediate nerve of the thigh
          2. Saphenous nerve which provides sensation to the medial calf
    2. Obturator nerve (L2-L4 spinal nerves):
      1. Innervates the adductor muscles of the thigh
      2. Provide cutaneous innervations to the medial thigh
    3. Muscular branches that derive directly from the plexus:
      1. Iliopsoas (L1-L3 spinal nerves)
      2. Iliacus (L2-L3 spinal nerves)
    4. Sensory nerves of the lumbar plexus:
      1. Iliohypogastric (L1 spinal root)
      2. Ilioinguinal nerve (L1 root) innervates:

        1. Upper medial thigh
        2. Base of the penis and labia majora
      3. Genitofemoral nerve (L1-L2 root):
        1. Innervates the upper anterior thigh
        2. Scrotum and labia majora
      4. d. Lateral cutaneous nerve of the thigh (L2-L3)
    5. Lesions of the entire lumbosacral plexus
      1. Are rare; most are incomplete
      2. Paralysis or paresis of the entire lower extremity with hypo or areflexia
      3. Sensory abnormalities that involve the entire lower extremity
    6. Lesions of lumbar segments:
      1. Usually are incomplete
      2. Paresis and atrophy in the distribution of the femoral and obturator nerves:
        1. Iliopsoas:
          1. Weakness of thigh flexion
        2. Quadriceps:
          1. Weakness of leg extension
        3. Sartorius:
          1. Weakness of thigh eversion
        4. Adductor muscles:
          1. Weakness of thigh adduction
      3. Sensory signs:
        1. Sensory loss in the inguinal area and over the genitalia
          1. Iliohypogastric, ilioinguinal, and genitofemoral nerves are involved
        2. Lateral thigh:
          1. Lateral femoral cutaneous nerve
        3. Medial thigh:
          1. Obturator nerve
        4. Anterior thigh:
          1. Femoral nerve
        5. Medial part of the lower leg:
          1. Saphenous nerve that is derived from the femoral nerve


  1. Depressed or absent patellar reflex:
    1. Femoral nerve
  2. Loss of cremasteric reflex:
    1. Genitofemoral nerve

Sacral Plexus

General Characteristics

  1. S1-S3 ventral rami are the major roots:
    1. Contribution from L4-L5 and S4-S5 roots
  2. The plexus overlies the lateral sacrum and the posterior lateral pelvic wall
  3. Sciatic nerve (spinal nerves L4, L5, S1-S3):
    1. Innervates the hamstrings; all muscles below the knee
    2. All sensation below the knee except that supplied by the saphenous nerve (medial lower leg):
    3. At the sciatic notch it divides into the common peroneal and tibial nerves
  4. Superior gluteal nerve (L4, L5 S1 spinal nerves):
    1. Innervates the gluteus medius and minimus muscles
  5. Inferior gluteal nerve (L5, S1, S2 spinal nerves):
    1. Innervates the gluteus maximus muscles
  6. Posterior femoral cutaneous nerve (S1, S2, S3):
    1. Innervates the buttocks, perineum, posterior thigh
      1. The cuneal branch innervates the posterior upper thigh and inferior buttock

Lesions of the Sacral Plexus

Complete Lesion

  1. Motor signs:
    1. Paralysis or paresis of muscles innervated by the superior gluteal, inferior gluteal and the sciatic nerves
      1. “Flail foot” from paralysis of both the dorsal and plantar foot musculature
    2. Weakness:
      1. Knee flexion:
        1. Hamstrings
    3. Foot eversion:
      1. Peroneal
    4. Foot inversion (L4-S1 spinal roots):
      1. Tibialis anterior and posterior tibial nerve
    5. Plantar flexion of the toes:
      1. Medial plantar nerves (II – V digits)
      2. Tibial nerve innervates the flexor hallucis longus
    6. Extension of the toes:
      1. i. Peroneal nerve innervates the extensor hallucis longus; L5-S1 roots
      2. ii. Deep fibular nerve (Extensor hallucis longus muscle – EHL)
    7. Abduction and internal rotation of the thigh:
        i. Superior gluteal nerve
    8. Hip extension:
    9. Inferior gluteal nerve

Sensory Signs

    1. Loss of sensation in the sciatic nerve distribution:
      1. Outer leg
      2. Dorsum, sole and inner aspect of the foot
    2. Posterior thigh and popliteal fossa:
      1. Posterior femoral cutaneous nerve


      1. Decreased Achilles reflex:
        1. Sciatic nerve
      2. Depressed bulbocavernosus reflex

Sphincter Signs

    1. Loss or dysfunction of bladder and bowel control:
      1. Pudendal nerve

Differential Diagnosis Features between Root and Lumbosacral Plexus Lesions

  1. Positive mechanical signs favor a root lesion:
    1. Straight leg raising test (sciatic nerve and S1 root)
    2. Reverse SLR (places traction on the femoral nerve); the leg is extended with the patient lying on his stomach
    3. Valsalva maneuver that causes pain:
      1. Root greater than plexus involvement
  2. Warm, dry and red foot:
    1. Indicative of a plexus lesion
    2. Involvement of the retroperitoneal lumbar sympathetic nerves
  3. Proximal > distal leg muscle weakness suggests a plexus lesion
  4. Gluteus muscle innervations arise directly from the plexus
  5. Iliopsoas muscle is not involved in a femoral nerve lesion because its innervation is directly from the plexus

Trauma of the Lumbosacral Plexus

General Characteristics

  1. The lumbosacral plexus is often injured with trauma to the pelvic ring:
    1. Double fracture dislocation
    2. Traction injury from dislocation of the hip joint
  2. Femoral nerve compression due to position:
    1. Occupies the gutter between the psoas and iliopsoas muscle above the inguinal ligament:
      1. Surgical retraction (medially)
      2. Injured laterally by a hematoma between the iliacus fascia and the nerve
  3. The lumbosacral cords are vulnerable to compression at the:
    1. Pelvis brim by the fetal head
    2. Obstetric forceps
  4. Aneurysm of the common iliac or hypogastric arteries in the presacral areas
  5. The femoral nerve is compressed by:
    1. Angulation under the inguinal ligament
    2. Prolonged flexion abduction of the thigh (dorsal lithotomy position under anesthesia)
  6. Fixation points of the common peroneal nerve are at the sciatic notch and fibular neck:
    1. Vulnerable to traction injury

Clinical Manifestations

  1. Fracture:
    1. Double vertical fracture dislocations of the pelvic bony ring:
      1. 50% of patients suffer neurologic deficits
    2. The injury is usually ipsilateral to the iliac joint damage
    3. The lumbosacral plexus cord level is affected by consequent compromise of L5-S1 spinal nerve innervated muscles
  2. Rupture, compression and traction injuries affect:
    1. Lumbosacral trunk:
      1. Primarily L4 and L5 spinal nerves (L5 primarily)
      2. The spinal nerves are contiguous with the sacrum adjacent to the sacroiliac joint.
    2. Obturator and or superior gluteal nerves are often concomitantly injured
    3. L5-S3 anterior rami may be affected
    4. Concomitant vertebral body rupture
  3. Intra-arterial injections:
    1. Injections into the buttock:
      1. Ischemic injury due to vasoactive drugs that are injected into the inferior gluteal artery causing ischemia of the sciatic nerve
        1. Weakness, pain, and sensory loss in the sciatic nerve distribution occur minutes to a few hours after the injection<l/i>
      2. Widespread lumbar plexus injury may occur due to retrograde extension of gluteal artery spasm to branches of the internal iliac artery
      3. Buttock skin may be painfully swollen, cyanotic and develop gangrene
      4. Painless lumbosacral plexopathy may follow cisplatin injection into the iliac artery
  • Obstetric and gynecologic procedures that damage the lumbosacral plexus:
    1. Risk factors:
      1. Short women with large babies
      2. Prima gravida
    2. Postpartum weakness:
      1. Lumbosacral trunk injury (primarily L5 spinal nerve) compression at the pelvic brim over the sacroiliac joint:
        1. Cephalic pelvic disproportion
        2. Protracted labor
        3. Mid pelvic forceps delivery
    3. Involvement of the quadriceps muscles:
      1. Bilateral in 25% of patients
      2. Concomitant with an obturator neuropathy
    4. Causes of peripheral femoral neuropathy:
      1. Lithotomy position under anesthesia during vaginal delivery (compression under the inguinal ligament)
      2. Separation of the symphysis pubis with direct compression of the nerve by the fetal head
      3. Epidural anesthesia:
      4. Paracervical block that affects the posterior femoral nerve (pain may be delayed by several days)
      5. Lumbosacral plexus compressed at the pelvic brim by a uterine leiomyoma (acceler- ated growth during pregnancy)
      6. Intrapelvic Schwannoma

Catamenial Neuroendometriosis

General Characteristics

  1. Usually the sciatic nerve is affected but all components of the lumbosacral plexus may be involved

Clinical Manifestations (sciatic)

  1. Implantation of endometrial tissue either intra-abdominally or at the sciatic notch
  2. Perimenstrual pain in the buttock or posterior thigh (sciatic involvement)
  3. Weakness, sensory loss and reflex changes are dependent on the lumbosacral component or the terminal nerve that is affected


  1. Endometrial deposits in the sciatic notch may be associated with an out-pouching of a pocket of peritoneum
  2. Endometrial perineural spread from the uterus to the sacral plexus along the pelvic autonomic nerves and then distally to the sciatic nerve or proximally to the lumbar plexus

Laboratory Evaluation

  1. MRI:
    1. Delineates perineural spread and retrograde menstruation with peritoneal bleeding

Surgical Trauma of the Lumbosacral Plexus

  1. Laterally placed retractor blades compress the femoral nerve between the iliac and psoas muscle during:
    1. Vaginal hysterectomy
    2. Modified lithotomy position (under anesthesia)
    3. Pelvic procedures (ovarian tumors and cysts)
  2. Hip joint replacement:
    1. Approximately 0.7-1% of hip replacement surgeries are complicated by femoral, obturator or sciatic palsies
    2. Subclinical nerve damage occurs from:
      1. Preoperative stretch injury due to hip dislocation
      2. Retroperitoneal hemorrhage
  3. Other surgical complications:
    1. Heat
    2. Toxicity from methyl methacrylate bone cement
    3. Direct trauma and that from retractor blades
    4. Postoperative aneurysm formation

Aneurysm of the Iliac or Hypogastric Artery (Vascular Injury during Lumbar Disc Surgery)

General Characteristics

  1. Surgical repair has been associated with ischemic plexus lesions

Clinical Manifestations

  1. Motor, sensory and reflex deficits are evident in multiple nerves or segmental distributions in the affected extremity
  2. Rectal examination reveals a firm pulsatile mass
  3. Hemorrhage from an aortic, iliac or a hypogastric aneurysm may compress the femoral nerve
  4. Retroperitoneal hematoma occurs from abdominal aortic aneurysm leakage that may affect the lumbosacral plexus and femoral nerve


  1. Neuropractic and axonometric injury occurs with compression and traction injuries
  2. Neuromeric injury is primary with high impact trauma and some surgical procedures


  1. Ultrasonography of the plexus
  2. MRI (conventional) to evaluate the plexus and soft tissue
  3. CT to evaluate the bone at the site of injury

Neoplasms of the Lumbosacral Plexus

General Characteristics

  1. Occur in less than 1% of patients with neoplasms
  2. Direct extension from an intra-abdominal tumor occurs in 75% of patients while extra-abdominal sites are the source in approximately 25% of patients
  3. The lower sacral plexus is involved in approximately 50% of patients followed by the upper plexus in 30% and panplexopathy in 18%
  4. Bilateral plexopathy occurs in 25% of patients (usually of the upper extremities by breast cancer)
  5. Involvement of the sacral sympathetic nerves occurs in approximately 10% of patients
  6. Less commonly plexus invasion occurs from lymph nodes, metastases or bony structures

Clinical Manifestations

  1. In approximately 15% of patients lumbosacral plexopathy is the initial presentation of an intra-abdominal tumor
  2. The most frequent presentation in >90% of patients is with pain in the low back, buttock, hip or thigh:
    1. In 90% of patients the pain is unilateral in onset and is dull, constant aching and is rarely burning; cramping may occur in a radicular pattern
    2. Exacerbation may occur at night
    3. Patients find difficulty in achieving a comfortable position
    4. Position of comfort is with the legs and hips in flexion if the iliopsoas muscle is involved
    5. Pain is exacerbated by walking or sitting
    6. A warm and dry foot (often red) may be seen if the sympathetic chain is involved
    7. Pain may be present for approximately 3 months prior to the onset of other symptoms and signs
    8. Weakness and sensory loss due to involvement of different plexus components is seen in most patients; sensory loss occurs in between 50-75% of patients and is most severe in patients with concomitant weakness
    9. Progressive muscle weakness is diffuse and interferes with gait
    10. Incontinence and impotence occur in 10% of patients due to bilateral involvement
    11. Involvement of the lumbosacral trunk is associated with foot drop
    12. Sacral involvement causes weakness of foot flexion and hamstring muscle involvement
    13. Sensory deficits are most often unilateral
    14. The patellar reflex is depressed with an upper plexopathy and the ankle jerk is depressed with sacral involvement
    15. Peripheral edema occurs in 80% of patients with pan plexopathy, in 41% of patients with upper plexopathy and in 37% of patients with lower plexus involvement
    16. A rectal mass is found in 43% of patients with lower plexopathy and in 25% of patients with upper plexopathy and 15% with panplexopathy
    17. Straight leg raising test occurs (is positive) in greater than 83% of patients with pan plexopathy
    18. Pain may be increased with Valsalva maneuvers


  1. Intra-abdominal tumor extension to the lumbosacral plexus occurs in approximately 75% of affected patients:
    1. Tumor may invade directly
    2. May grow along the connective tissue, epineurium of nerve trunks or perineural spread
  2. Most prevalent tumors are:
    1. Colorectal tumors (20%)
    2. Sarcomas (16%)
    3. Breast tumors (11%)
    4. Lymphoma (9%)
    5. Cervical tumors (9%)
    6. Other tumors including multiple myeloma account for 37% of intra-abdominal tumors
  3. Metastatic lesions are from:
    1. Breast
    2. Lymphoma
    3. Sarcoma
    4. Lung
    5. Thyroid (rare)
    6. Melanoma
    7. Testicular
    8. Multiple myeloma
  4. Primary pelvic plexus tumors are:
    1. Neurofibroma
    2. Schwannoma
    3. Sarcoma (degeneration of a benign Neurofibroma)
  5. Benign tumors that affect the lumbosacral plexus
    1. Dermoid of the omentum
    2. Uterine leiomyoma

Laboratory Evaluation

  1. Dependent on the type of underlying cancer and the extent of its involvement are increased
  2. Sedimentation rate and C-reactive protein
  3. Alkaline phosphatase
  4. Protein electrophoresis
  5. Prostate specific antigen
  6. Uremia and hydronephrosis are associated with gynecologic malignancies


  1. High resolution dedicated MR neurography
  2. CT scan and conventional MRI are positive >80% of patients by the time of clinical presentation
  3. Sacral bone involvement is often a sign of colorectal cancer

Radiation Therapy (X-RT) of the Lumbosacral Region

General Characteristics

  1. Median time to the onset of symptoms is variable; the usual is five years; in some patient, symptoms may appear 20-30 years after treatment
  2. There is no apparent relationship between the amount of X-RT and the latent period to symptoms
  3. Signs rarely occur with less than 40gy rads

Clinical Manifestations

  1. Bilateral or unilateral slowly progressive leg weakness
  2. Starts distally usually in the L5-S1 roots; muscle wasting and absent reflexes