Lumbosacral plexus

Question 1

Label the diagram

Answer 1

Question 2

1. Where is the lumbar plexus dervived from?
2. Name the main divisions

Answer 2

1. From ant rami L1-3 and parts of L4.
2. L1 (and a branch of T12 in 50% of cases) divides into an upper and lower division. The upper gives the ILIOINGUINAL (L1) before continuing as the ILIOHYPOGASTRIC (L1+/-T12)

The lower div joins a branch from L2 to form the genitofemoral n

L2,3,4 nerve roots div into dorsal and ventral div:

• Dorsal div of L2 and 3 form LATERAL CUTANEOUS n of thigh
• Dorsal div of L2,3,4 form FEMORAL n
• Ventral div L2,3,4 for OBTURATOR n and the ACCESSORY OBTURATOR (in 1/3 cases)

L4 also contributes to lumbosacral trunk

Question 3

1. Where is the lumbar plexus formed?
2. Where do its branches come and go?

Answer 3

1. The lumbar plexus is formed in the substance of the psoas major muscle.

2.

The obturator and accessory emerge on medial border

The genitofemoral n pierces the muscle to lie on its anterior border

The lat cutaneous n and femoral emerge at the posterolateral edge

The Iliohypogastric and ilioingunial emerge from the upper part of the lateral border

Question 4

FEMORAL n.

1. What is the nerve root of the Femoral n?
2. What does it supply?
3. What are its devisions and what do they supply?

Answer 4

1. L1-4
2. Supplies the skin and muslces of the anterior compartment of the thigh
3. ANTERIOR DIV: supplies sartorius and provide the intermediate and medial cutaneous nerves supplying the anterior and medial thigh

POSTERIOR DIV: innvervates the four quads and the saphenous n. (cutanous branch of the femoral)

Question 5

Saphenous nerve

1. Which nerve does it originate from?
2. Where is it found/course?
3. What does it supply?

Answer 5

1. Posterior division of the femoral nerve
2. From the femoral triangle down the adductor canal. Then along the tibial side of the leg with the great saphenous vein, goes infront of the medial malleolus and reaches the great toe
3. Supplies the skin at the fromt and medial side of the leg and proximal medial side of foot

Question 6

Obturator n.

1. Where does it emerge?
2. What is its course?
3. What does it supply?

Answer 6

1. L2,3,4 (ventral) on the medial border of the psoas
2. Enters thigh through the obturator canal and divideds into ant and post branchs

Ant branch communicates with medial cut n and saphenous to form sub-sartorial plexus suppling the medial thigh.

Post contributes to articular branch of the knee

3. Articular branches to the hip, medial thigh and knee

Question 7

SACRAL PLEXUS

Label the diagram

Answer 7

Question 8

1. What is the lumbosacral trunk comprised of?
2. Where does the sacral plexus originate?
3. Can the sacral plexus be accessed for regional anaesthesia?

Answer 8

1. Formed by all anterior div of L5 and part of L4, emerges from the medial margin the psoas running over the pelvic brim to join S1
2. Anterior rami of all 5 sacral nerves, coccygeal and lumbosacral trunk
3. The sacral plexus cannot be accessed for regional anaesthesia due to its location within the pelvis. It lies on the posterior wall of the pelvic cavity between the piriformis muscle and the pelvic fascia.

Question 9

1. What is the sacral plexus formed from?
2. What are the branches of the sacral plexus?

Answer 9

1. Sacral plexus is formed by the convergence of nerves near the greater sciatic foramen.

2.

• Posterior cutaneous nerve of the thigh
  
  • This is formed from anterior primary rami of S1,2,3 and supplies the skin to the posterior thigh, leg and perineum
• Nerve to quadratus femoris
  
  • ant rami L4.L5 and S1. Runs down in fromt of the sciatic nerve and gives articular branch to hip
• Sciatic nerve
  
  • continuation of sacral plexus through greater sciatic foramen.
  • Divides in the popliteal fossa in to the tibial and common peroneal n. (Sometimes these arise from the plexus seperately)

Question 10

SCIATIC NERVE

1. What are the contents of the sciatic nerve?
2. Where does it run?

Answer 10

1. Tibial and common peroneal n
2. Leaves the pelvis via the greater sciatic foramen below piriformis enters the buttocks under G maximus. It then passes down the posterior aspect of the leg to the popliteal fossa between semitendinous and biceps fem tendons. Here it divides.

Question 11

TIBIAL n.

1. Where is the tibial n in relation to the popliteal a.
2. What does it supply?
3. Do you know where the tibial nerve ends?

Answer 11

1. Lateral to the a. before crossing over to the medial side. Runs between the heads of gastrocnemius with posterior tib a.
2. Supplies the muscles and skin of the calf and sole of the foot and toes.

The med cut sural n (branch of tib n.) receives fibres from the common peroneal to form the sural n. This supplies skin on the back of the leg and joinys on the lat heel and foot

3. The tibial nerve ends behind medial malleolus by dividing into medial and lateral plantar nerves

Question 12

Common peroneal n.

1. Where does it run?
2. What does it divide into?
3. Where do these run?

Answer 12

1. Runs around the head of the fibula into peroneus longus
2. Divides into the deep and superfical
   - deep folows ant tib vessels, lies lateral to the artery at the ankle, supplying muscles of the anterior compartment of the leg
   - superfical pierces the deep fascia in the lower 1/3 of the leg supplies the muscles in the lateral compartment of leg and skin over the anterior lower leg and dorsum of foot.

Question 13

Label the dermatomes of the legs

Answer 13

Question 14

Describe the dermatomes of the foot

Answer 14

Question 15

Describe the nerve supply of the leg (Cutaneous)

Answer 15