Lower Limb Plexi and Sciatica

Question 1

What is a plexus?

Answer 1

Collection of nerve fibres from one source that form ‘new’ nerves with specific targets/destinations

Question 2

2 plexuses of the lumbosacral plexus

Answer 2

• Lumbar plexus
• Sacral plexus

Question 3

Where is the lumbosacral plexus located?

Answer 3

Posterior wall of abdomen and pelvis

Question 4

Where does the lumbar plexus receive input from?

Answer 4

• Anterior rami of nerve roots L1-4
• T12 (subcostal nerve)

Question 5

In what muscle does the lumbar plexus form?

Answer 5

Psoas

Question 6

6 branches of lumbar plexus

Answer 6

• I (twice) get late on Fridays:
  > Iliohypogastric
  > Ilioinguinal
  > Genitofemoral
  > Lateral cutaneous nerve of thigh
  > Obturator
  > Femoral

Question 7

Where does the iliohypogastric nerve emerge in relation to psoas major, and what nerve root supplies it?

Answer 7

• Lateral to psoas major
• Nerve root L1

Question 8

Where does the ilioinguinal nerve emerge in relation to psoas major, and what nerve root supplies it?

Answer 8

• Lateral to psoas major
• Nerve root L1

Question 9

Where does the genitofemoral nerve emerge in relation to psoas major, and what nerve root supplies it?

Answer 9

• Anterior to psoas
• Nerve roots L1-2

Question 10

Where does the lateral cutaneous nerve of the thigh emerge in relation to psoas major, and what nerve root supplies it?

Answer 10

• Lateral to psoas major
• Nerve roots L2-3

Question 11

Where does the obturator nerve emerge in relation to psoas major, and what nerve root supplies it?

Answer 11

• Medial to psoas
• Nerve roots L2-4

Question 12

Where does the femoral nerve emerge in relation to psoas major, and what nerve root supplies it?

Answer 12

• Lateral to psoas major
• Nerve roots L2-4

Question 13

Is each branch of the lumbar plexus sensory only or mixed motor and sensory?

Answer 13

• Iliohypogastric = mixed
• Ilioinguinal = mixed
• Genitofemoral = mixed
• Lateral cutaneous nerve of thigh = sensory only
• Obturator = mixed
• Femoral = mixed

Question 14

Motor target of each branch of lumbar plexus

Answer 14

• Iliohypogastric = internal oblique, transversus abdominis
• Ilioinguinal = internal oblique, transversus abdominis
• Genitofemoral = male cremasteric muscle
• LCNOT = N/A
• Obturator = obturator externus, pectineus, muscles in medial compartment of thigh
• Femoral = iliacus, pectineus, muscles in anterior compartment of thigh

Question 15

Where does the sacral plexus receive input from?

Answer 15

• Ventral rami of nerve roots S1-4
• Lumbosacral trunk L4-5

Question 16

Where is the sacral plexus located?

Answer 16

Superior to piriformis

Question 17

5 major branches of sacral plexus

Answer 17

• Superior gluteal nerve
• Inferior gluteal nerve
• Sciatic nerve
• Posterior femoral cutaneous nerve
• Pudendal nerve

Question 18

Where does the superior gluteal nerve receive input from, exit the pelvis, lie and innervate?

Answer 18

• Nerve roots L4-S1
• Greater sciatic foramen above piriformis
• Gluteus minimus
• Gluteus medius, gluteus minimus, tensor fascia lata

Question 19

Where does the inferior gluteal nerve receive input from, exit the pelvis and innervate?

Answer 19

• Nerve roots L5-S2
• Greater sciatic foramen below piriformis
• Gluteus maximus

Question 20

Where does the sciatic nerve receive input from and exit the pelvis, and what nerves arise from it?

Answer 20

• Nerve roots L4-S3
• Greater sciatic foramen below piriformis
• Tibial and common peroneal nerves

Question 21

Where does the posterior femoral cutaneous nerve receive input from, exit the pelvis and provide sensory innervation for?

Answer 21

• Nerve roots S1-3
• Greater sciatic foramen below piriformis
• Posterior thigh, posterior leg, part of perineum

Question 22

Where does the pudendal nerve receive input from, exit the pelvis, provide motor innervation for and provide sensory innervation for?

Answer 22

• Nerve roots S2-4
• Greater sciatic foramen below piriformis (then back in via lesser foramen)
• Perineum, external urethra, external anal sphincters, levator ani
• Penis/clitoris, most of perineal skin

Question 23

What does the tibial nerve provide motor innervation to?

Answer 23

• Posterior compartment of thigh (except short head of biceps femoris)
• Adductor magnus
• Posterior compartment of leg
• All muscles in sole of foot

Question 24

What does the tibial nerve provide sensory innervation to?

Answer 24

• Posterolateral leg
• Sole of foot

Question 25

What does the common peroneal nerve provide motor innervation to?

Answer 25

- Short head of biceps femoris - Anterior leg compartment - Lateral leg compartment - Extensor digitorum brevis

Question 26

What does the common peroneal nerve provide sensory innervation to?

Answer 26

- Anterolateral leg - Dorsum of foot

Question 27

What is sciatica?

Answer 27

Term used to describe symptoms that present within the distribution of the sciatic nerve

Question 28

Symptoms of sciatica

Answer 28

- Pain over aspects of thigh or leg - Numbness/tingling of aspects of thigh or leg - Weakness of movement of knee or ankle

Question 29

Causes of sciatica

Answer 29

- Disc prolapse - Muscle entrapment from piriformis muscle - Bony spinal pathology (OA, stenosis, spondylolisthesis)

Question 30

Treatment of sciatica

Answer 30

- Physical therapy - NSAIDs - Local steroid injections - Surgical repair