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The sacral plexus (L4–S4) (Fig. 45.1)
• Origins: it is a terminal branch of the sciatic nerve.
• Origins: from the anterior primary rami of L4–S4.
• Course: it traverses the popliteal fossa over the popliteal vein and
• Course: the sacral nerves emerge through the anterior sacral foram-
artery from the lateral to medial side. It leaves the popliteal fossa by
ina. The nerves unite, and are joined by the lumbosacral trunk (L4,5), The tibial nerve (L4–S3) (Fig. 45.2)
anterior to piriformis. passing under the fibrous arch of soleus and, in the leg, descends with
• Branches: the branches of the sacral plexus include: the posterior tibial artery under the cover of this muscle. The nerve
• The superior gluteal nerve (L4,5,S1)aarises from the roots of the crosses the posterior tibial artery from medial to lateral in the mid-calf
sciatic nerve and passes through the greater sciatic foramen above and, together with the artery, passes behind the medial malleolus and
the upper border of piriformis. In the gluteal region it runs below then under the flexor retinaculum where it divides into its terminal
the middle gluteal line between gluteus medius and minimis (both branches, the medial and lateral plantar nerves.
of which it supplies) before terminating in the substance of tensor • Main branches:
fasciae latae. • Genicular branchesato the knee joint.
• The inferior gluteal nerve (L5,S1,2)aarises from the roots of the • Muscular branchesato plantaris, soleus, gastrocnemius and the
sciatic nerve and passes through the greater sciatic foramen below deep muscles at the back of the leg.
piriformis. In the gluteal region it penetrates and supplies gluteus • Sural nerveaarises in the popliteal fossa and is joined by the sural
maximus. communicating branch of the deep peroneal nerve. It pierces the
• The posterior cutaneous nerve of the thigh (S1, 2, 3)apasses deep fascia in the calf and descends subcutaneously with the small
through the greater sciatic foramen below piriformis. Its branches saphenous vein. It passes behind the lateral malleolus and under the
supply the skin of the scrotum, buttock and back of the thigh up to flexor retinaculum to divide into its cutaneous terminal branches
the knee. which supply the skin of the lower lateral calf, foot and little toe.
• The perforating cutaneous nerve (S2, 3)aperforates gluteus • Medial plantar nerve (L4,5) (Fig. 45.3)aruns with the medial
maximus to supply the skin of the buttock. plantar artery between abductor hallucis and flexor digitorum bre-
• The pudendal nerve (S2, 3, 4)apasses briefly into the gluteal vis. It sends four motor branches and a cutaneous supply to the
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region by passing out of the greater sciatic foramen below pirifor- medial 3 /2 digits.
mis over the sacrospinous ligament and passes back into the pelvis • Lateral plantar nerve (S1,2) (Fig. 45.3)aruns with the lateral
through the lesser sciatic foramen. It runs forwards in the pudendal plantar artery to the base of the 5th metatarsal where it divides into
(Alcock’s) canal and gives off its inferior rectal branch in the superficial and deep branches. These collectively supply the skin of
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ischio-rectal fossa. It continues its course to the perineum and the lateral 1 /2 digits and the remaining muscles of the sole.
divides into dorsal and perineal branches that pass deep and
superficial to the urogenital diaphragm, respectively. The common peroneal nerve (L4–S2) (Fig. 45.2)
• The sciatic nerveasee below. • Origin: a terminal branch of the sciatic nerve.
• Course: it passes along the medial border of the biceps tendon along
The sciatic nerve (L4–S3) (Fig. 45.2) the superolateral margin of the popliteal fossa. The nerve winds around
• Origins: anterior primary rami of L4,5,S1,S2,S3. the neck of the fibula and, in the substance of peroneus longus, it divides
• Course: the sciatic nerve passes through the greater sciatic foramen into its terminal branches, the superficial and deep peroneal nerves.
below piriformis under the cover of gluteus maximus. In the gluteal • Branches:
region it passes over the superior gemellus, obturator internus and in- • Genicular branches to the knee joint.
ferior gemellus and then over quadratus femoris and adductor magnus • Lateral cutaneous nerve of the calf.
in the thigh as it descends in the midline. The sciatic divides into its • A sural communicating branch.
terminal branches, the tibial and common peroneal nerves, usually just • Superficial peroneal nerve (L5,S1,2)athis branch runs in and
below the mid-thigh, although a higher division is not uncommon. supplies the muscles of the lateral (peroneal) compartment of the
• Branches: leg. In addition it supplies the skin over the lateral lower two-thirds
• Muscular branchesato the hamstrings and the ischial part of of the leg and the whole of the dorsum of the foot except for the
adductor magnus. area between the 1st and 2nd toes, which is supplied by the deep
• Nerve to obturator internus (L5,S1,2)asupplies obturator inter- peroneal nerve.
nus and the superior gemellus. • Deep peroneal nerve (L4,5,S1,2)aruns with the anterior tibial
• Nerve to quadratus femoris (L4,5,S1)asupplies quadratus vessels over the interosseous membrane into the anterior compart-
femoris and the inferior gemellus. ment of the leg and then over the ankle to the dorsum of the foot. It
• Tibial nerveasee below. supplies all of the muscles of the anterior compartment as well as
• Common peroneal nerveasee below. providing a cutaneous supply to the area between the 1st and 2nd toes.

The nerves of the lower limb II 101