lower limb

1. Sciatic Nerve
Dr M Idris Siddiqui

2. LUMBOSACRAL PLEXUS
• The lumbosacral plexus provides the nerve
supply to the pelvis and lower limb, in
addition to part of the autonomic supply to
the pelvic viscera.
• It gives origin to the sciatic, inferior gluteal,
superior gluteal and pudendal nerves.
• In addition, the nerves to quadratus femoris,
obturator internus and the posterior
cutaneous nerve of the thigh also arise from
LUMBOSACRAL PLEXUS .

4. The sciatic nerve
• The sciatic nerve is a major nerve of the lower
limb.
• It is a thick flat band, approximately 2cm wide
–The largest nerve in the body.
• It is composed of 2 parts:
–Tibial and common peroneal nerves.
• Ventral divisions of anterior primary rami of L4, L5;
S1, S2, S3 compose the tibial part.
• Dorsal divisions of anterior primary rami of L4, L5; S1,
S2 compose the common peroneal part.

5. The
sciatic
nerve

6. EXTENT
• It commences in the pelvis.
• It ends at or just above the
superior angle of the popliteal
fossa by dividing into:
–Tibial nerve
–Common peroneal nerve.

9. Origin
• The sciatic nerve originates from lumbosacral
plexus L4-S3
–Tibial division
• Orginates from anterior preaxial
branches of L4,L5,S1,S2,S3
–Peroneal division
• Originates from from postaxial
branches of L4,L5,S1,S2

10. COURSE
• In the pelvis, it is located in front of piriformis under
cover of its fascia.
• It enters the gluteal region via greater sciatic
foramen below the piriformis.
• In gluteal region It lies under cover of gluteus
maximus.
• Here it runs downward with small lateral convexity
and enters between the ischial tuberosity and
greater trochanter.

12. Note
• the sciatic nerve can be described as two
individual nerves bundled together in the
same connective tissue sheath – the tibial
and common peroneal nerves.
• These usually separate at the apex of the
popliteal fossa, however in approximately
12% of people they separate as they leave
the pelvis.
•

14. Variations in the manner of departure
of the sciatic nerve from pelvis
• Normally the sciatic nerve enters the gluteal region
via greater sciatic foramen below the piriformis.
Occasionally sciatic nerve splits into tibial and
common peroneal elements inside the pelvis.
• In such cases, the manner of exit from pelvis
happens as follows:
– The common peroneal nerve goes through the
piriformis and tibial nerve enters below the piriformis
(12%).
– The common peroneal nerve enters above the piriformis
and tibial nerve enters below the piriformis (0.5%).

15. Sciatic
nerve

18. SURFACE MARKINGS
• The sciatic nerve is marked on the back of
thigh by joining the following 3 points:
–The first point is marked 2.5 cm lateral to the
midpoint of the line joining the anterior superior
iliac spine and ischial tuberosity.
–2nd point is marked halfway between the ischial
tuberosity and greater trochanter.
–The third point is indicated in the junction of the
upper 2/3rd and lower 1/3rd of the back of the
thigh.

19. A thick curved line
(about 2 cm wide) with
outward convexity
joining the first and 2nd
points represents the
sciatic nerve in the
gluteal region and a
thick straight line of
exactly the same width
joining the 2nd and
third points represents
the sciatic nerve in the
thigh.

20. RELATIONS
• DEEP RELATIONS (BED OF THE SCIATIC NERVE)
• From above downward the sciatic nerve is related to:
–Body of ischium (posterior surface).
–Tendon of obturator internus
–Gemellus superior
–Gemellus inferior muscles.
–Quadratus femoris.
–Adductor magnus.

22. RELATIONS
• SUPERFICIAL RELATIONS
From above downward, the sciatic nerve
is related to:
–Gluteus maximus (in the gluteal region).
–Long head of biceps femoris (in the thigh).
–The sciatic nerve is reachable on the back of
the thigh, only in the angle between the
gluteus maximus and long head of biceps
femoris.

23. BRANCHES
• Articular branches to the hip joint originate in the
gluteal region.
• Muscular branches to the hamstring muscles
originate in the lower part of the gluteal region or in
the upper part of the thigh from the medial side of
the nerve.
• Muscular branch to the short head of biceps
femoris originates in the lower part of the thigh
from the lateral side of the nerve.

24. BRANCHES
• All the muscular branches of the sciatic
nerve originate from the medial side with
the exception of nerve to short head of
biceps femoris, which originates from the
lateral side.
• Thus, the side lateral to the sciatic nerve
is safe side and the side medial to its
dangerous side/unsafe side.

25. Summary

27. Motor Functions
• Although the sciatic nerve passes through the gluteal
region, it does not innervate any muscles there.
However, the sciatic nerve does directly innervate the
muscles in the posterior compartment of the thigh, and
the hamstring portion of the adductor magnus.
• The sciatic nerve also indirectly innervates
several other muscles, via its two terminal branches:
• Tibial nerve – the muscles of the posterior leg (calf
muscles), and some of the intrinsic muscles of the foot.
• Common fibular nerve – the muscles of the anterior
leg, lateral leg, and the remaining intrinsic foot
muscles.
• In total, the sciatic nerve innervates the muscles of the
posterior thigh, entire leg and entire foot.

28. Sensory Functions
• The sciatic nerve does not have any direct
cutaneous functions. It does provide indirect
sensory innervation via its terminal branches:
• Tibial nerve – Innervates the posterolateral
and anterolateral sides of the leg, and the
plantar surface of the foot (the sole).
• Common peroneal nerve – Innervates the
lateral leg and the dorsal surface of the foot.

29. Clinical Relevance
• Intramuscular Injections
• The anatomical course of the sciatic nerve must be
considered when
administering intramuscular injections into the gluteal
region.
• The region can be divided into quadrants using 2 lines, marked
by bony landmarks:
– One line descends vertically from the highest point on the iliac crest.
– The other horizontal line passes through the vertical line half way
between the highest point on the iliac crest and ischial tuberosity.
• The sciatic nerve passes through the lower medial
quadrant. To avoid damaging the sciatic nerve
therefore, intramuscular injections are given only in the
upper lateral quadrant of the gluteal region.

31. INJURY OF THE SCIATIC NERVE
• The sciatic nerve could possibly be injured by penetrating
wounds, posterior dislocation of the hip, fracture of the pelvis,
surgery . Listed here are the characteristic clinical features:
• Motor Deficits:
• Inability to stretch the thigh and bend the knee, as a result of
paralysis of the hamstring muscles.
• Loss of all movements below the knee with foot drop, because of
paralysis of all the muscles of the leg and foot.
• The motor loss results in flail foot that results in great trouble in
walking. The patient walks with high-stepping gait.
• Sensory loss:
• The sensory loss on the back of the thigh and entire of the leg
and foot with the exception of the area innervated by
the saphenous nerve, because of participation of the cutaneous
nerves originated from the tibial and common peroneal nerves.

32. Sciatic Nerve Neuropathy
• As the sciatic nerve makes the pelvis,
occasionally, it goes through
the piriformis muscle and at that
stage, it might become entrapped
leading to piriformis syndrome. It’s a
common anatomical form but an
incredibly uncommon entrapment
neuropathy.

33. Sciatica
• It is a term applied to a clinical condition defined by
shooting pain felt along the course of distribution of
the sciatic nerve (example, buttock, posterior
aspect of the thigh, lateral aspect of the leg,
and dorsum of the foot).
• It happens because of compression and aggravation
of L4 S3 spinal nerve roots by herniated
intervertebral disc of the lumbar vertebrae.

34. Sleeping Foot
• The sciatic nerve is uncovered on the back of
thigh in the angle between the lower border of
gluteus maximus and long head of biceps
femoris.
• The temporary compression of the sciatic nerve
against femur at the lower border of gluteus
maximus causes paresthesia in the lower limb.
• It is named “sleeping foot, example, when a man
sits on the hard edge of the seat for a long time”.