Regional - Lower limb/ Pelvis

Question 1

Innervation of the penis

Answer 1

Sensory innervation is by the pudendal nerve (S2-S4), which divides into the right and left dorsal nerves of the penis that pass under the pubis symphysis, just beneath Buck’s fascia.

Question 2

Landmark technique for penile block

Answer 2

palpate symphysis pubis; use 25GA needle at base of shaft of penis. Walk off inferior border of symphysis pubis, feel ‘pop’ as Buck’s fascia is pierced. Inject 5mL 0.5% Bupivacaine each side (0.1mL/kg in children)

Question 3

What plexi supply the leg? Via which nerves?

Answer 3

Lumbar plexus nerves supply the anterior and medial thigh: FEMORAL nerve L2-L4, OBTURATOR NERVE L2-L4.
Sacral plexus nerves supply the posterior thigh, leg, and foot: SCIATIC nerve
The major cutaneous nerves of the lower limb are the femoral, tibial (sciatic) and common fibular (sciatic).

Question 4

Femoral nerve branches and route

Answer 4

Mixed nerve, descends through psoas, and evolves two cutaneous branches, both in the femoral triangle: anterior cutaneous and saphenous

The anterior cutaneous supplies the skin of the anterior and medial thigh.
The saphenous nerve travels down the adductor canal, exits before the adductor hiatus, and passes deep to sartorius tendon.

Question 5

Tibial nerve branches and route

Answer 5

A terminal branch of the sciatic nerve. Arises at the popliteal fossa, and descends through the posterior compartment of the leg, forming the sural, medial plantar, lateral plantar, and calcaneal nerves

Question 6

Common fibular branches and route

Answer 6

A terminal branch of the sciatic nerve, and arises at the apex of the popliteal fossa, travelling in the lateral compartment. Forms 4 cutaneous branches: Superficial fibular, Deep fibular, Sural, and Lateral Sural.

Question 7

Blocks available for analgesia for femoral shaft

Answer 7

• Femoral nerve block in inguinal triangle.
• Lateral cutaneous nerve of thigh block (cutaneous nerve from lumbar plexus) required if incision is lateral. Block 2cm medial and 2cm caudal to ASIS, just through the fascia lata.
• Or, fascia iliacus block to cover femoral nerve and lateral cutaneous nerve of thigh. (Through fascia lata and fascia iliaca at lateral third of line between ASIS and pubic tubercle, lateral to the femoral artery)
  3-in-1 block includes femoral nerve, lateral cutaneous nerve of thigh, and obturator (variable block) – give 25-30mL of LA solution, and apply pressure distally to aid cephalad spread.

Question 8

Blocks available for knee

Answer 8

Requires blocking of femoral nerve.
Obdurator may require blocking also – US guided injection between interfascial space between the pectineus and adductor brevis muscles to block the anterior branch and the adductor brevis and adductor magnus muscles to block the posterior branch. Block of obturator also causes weakness of adduction (ie the muscles of the medial compartment), in addition to skin of medial thigh.

Question 9

Blocks available for ankle/ foot

Answer 9

Requires blocking of femoral and sciatic nerve.
Sciatic nerve block may be performed at level of hip or at the popliteal fossa.
1. Sciatic nerve exits the pelvis through the sciatic foramen, and runs deep to gluteus maximus. Very deep; difficult ultrasound visualisation.
2. At the popliteal fossa it divides into the common peroneal and tibial nerve, at a variable distance above the crease.
a. Find the popliteal artery, which should be between biceps femoris (lateral) and semimembranosus/ semitendinosus (medial)
b. The tibial nerve is shallow and lateral to the artery
c. The CPN is even more shallow and lateral than the tibial nerve.
d. Follow them up with the probe until they join to become the sciatic nerve (usually 5-10cm above the crease)