Peripheral Nauroanatomy And Focal Neuropathies: Lower Extremities

Question 1

How is the lumbosacral plexus formed?

Answer 1

L1-L4 lumbar portion
L4-L5 gives rise to the lumbosacral trunk
S1-S3 sacral portion

Question 2

Which major motor nerves arise from the LSP?

Answer 2

Femoral
Obturator
Sciatic
Common fibular (peroneal)
Tibial
Superior gluteal
Inferior gluteal
Pudendal

Question 3

Which major sensory nerves arise from the LSP?

Answer 3

Saphenous
Iliohypogastric (continuation of the femoral nerve)
Ilioinguinal
Genitofemoral
Lateral femoral cutaneous

Question 4

Which conditions affect the LSP?

Answer 4

Diabetes
Neoplasms
Retroperitoneal hemorrhage
Postradiation plexopathy

Question 5

How is diabetic lumbosacral radiculoplexus neuropathy (diabetic amyotrophy) manifested?

Answer 5

Pain
Bilateral but usually asymmetric leg weakness
Weight loss

Question 6

Femoral nerve: formation / motor and sensory branches

Answer 6

Formation: posterior divisions of the anterior primary rami of L2-L4

Motor branches:
Psoas
Iliacus
Sartorius
Pectineus
Quadriceps

Sensory branches:
Intermediate and medial femoral cutaneous nerves (innervation of the anterior thigh)

The femoral nerve terminates as the saphenous nerve (sensation from the medial aspect of the lower leg and the medial aspect of the foot)

Question 7

Causes of femoral nerve dysfunction

Answer 7

Pelvic tumors
Psoas abscesses or hematomas
Fractures of the pelvis and upper femur
Aneurysms of the femoral artery
Penetrating wounds
Diabetic mononeuropathy
Iatrogenic (lithotomy position or surgical trauma)
Hip hyperextension (hanging leg syndrome)

Question 8

Clinical findings in femoral nerve dysfunction

Answer 8

Weakness in knee extension (difficulty in climbing stairs or walking forward, walking backwards with ease)
Impaired patellar reflex
Sensory loss over the anterior and medial aspects of the thigh and the medial aspect of the leg

Question 9

Obturator nerve: formation / motor and sensory branches

Answer 9

Formation: anterior divisions of the L2-L4 anterior primary rami
Motor:
Adductor muscles of the thigh
Gracilis muscle
Obturator externus muscle

Sensory:
Small are on the medial aspect of the thigh

Question 10

Clinical findings in obturator nerve dysfunction

Answer 10

Weakness of adduction and external rotation of the thigh

Anesthesia over a small area of the inner surface of the thigh

Question 11

Causes of obturator nerve dysfunction

Answer 11

Surgery or injuries
Obturator hernia
Iliopsoas hemorrhage
Diabetes

Question 12

Lateral femoral cutaneous nerve: formation, function and main differential diagnosis of dysfunction

Answer 12

Formation: posterior divisions of L2-L3 anterior primary rami

Sensation of the anterolateral aspect of the thigh

Dysfunction causes meralgia paresthetica

Differential diagnosis from upper lumbar radiculopathy

Question 13

Sciatic nerve: formation and function

Answer 13

The sciatic nerve is formed from the fusion of lumbosacral trunk with elements of the sacral plexus
From its beginnings the sciatic nerve is made up of the fibular and tibial divisions (they run together in a common sheath forming the sciatic nerve until the level of the knee where they divide)

Function: innervates the hamstring muscles and also sends a twig to the adductor magnus