The document details the anatomy of the sciatic nerve, including its origin, course, branches, and clinical significance related to injuries and conditions like sciatica. Key points include the structure being the largest nerve in the body, its role in motor and sensory innervation of the lower limb, and considerations for preventing injury during intramuscular injections. Additionally, it outlines specific case studies of sciatic nerve injury and their manifestations.

1. Anatomy of Sciatic Nerve
Dr Mathew Joseph
MBBS, MD(AIIMS), BCC(Palliative Medicine)
Assistant Professor
Department of Anatomy
Amala Institute of Medical Sciences, Thrissur

2. Learning Objectives:
By the end of the lecture, the students should be able to:
 Describe the anatomy (origin, course & distribution) of
the sciatic nerve.
 List the branches of the sciatic nerve.
 Describe briefly the main motor and sensory
manifestations in case of injury of the sciatic nerve or
its main branches.

3. Self Assesment
A patient presented with severe chronic lower back pain in
the sacral region with radiation to the back of the left leg,
producing a strong pain throbbing and burning behind the
knee. Pain was aggravated when bending forward or in
reaching out position. He gave history of an accident that
resulted in fracture of the lumbar vertebrae. His MRI two
months prior to this severely increasing pain, revealed disc
degeneration, and protrusion of the disc at the S1 level.
Which anatomical structure is likely to be involved ?

9. Lumbo-Sacral Plexus
• Povides the nerve supply to the pelvis and lower limb -
in addition to part of the autonomic supply to the
pelvic viscera.
• Sciatic nerve
• Inferior gluteal nerve
• Superior gluteal nerve
• Pudendal nerve
• Nerve to quadratus femoris
• Nerve to obturator internus
• Posterior cutaneous nerve of the thigh.

10. Let’s Draw
Lumbo-Sacral Plexus....

11. The sciatic nerve
• A major nerve of the lower limb.
• It is a thick flat band, approximately 2cm wide
– The Largest and Thickest nerve in the body.
• It is composed of 2 parts:
– Components: Tibial and Common peroneal
• Ventral divisions of Anterior primary rami of
L4, L5, S1, S2, S3 - Tibial part.
• Dorsal divisions of Anterior primary rami of
L4, L5,S1, S2 - Common peroneal part.

12. The
Sciatic
nerve

13. The Sciatic Nerve : 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

16. The Sciatic Nerve : 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.

18. 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.

20. 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:
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%).

21. Sciatic
nerve

24. Sciatic Nerve: Surface Marking
• 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 posterior 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.

25. 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.

26. The Sciatic Nerve: Relations
• Deep Relations (Bed of Sciatic nerve)
• From above downward the sciatic nerve is related to:
• Body of ischium (posterior surface)
• Tendon of obturator internus
• Gemellus superior
• Gemellus inferior
• Quadratus femoris
• Adductor magnus

28. The Sciatic Nerve: 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.

30. The Sciatic Nerve: 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.

31. Note***
• 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.

32. Summary

34. The Sciatic Nerve: 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.

35. The Sciatic Nerve: 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.

36. The Sciatic Nerve: 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.

38. The Sciatic Nerve : Injury
• Penetrating wounds
• Posterior dislocation of the hip
• Fracture of the pelvis
• Iatrogenic
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 (Foot Drop) 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.

42. The Sciatic Nerve : Neuropathy
• As the sciatic nerve moves outof the pelvis,
occasionally, it goes through the piriformis
muscle.
• It might become entrapped leading to piriformis
syndrome.
• It’s a common anatomical form but an incredibly
uncommon entrapment neuropathy.

43. The Sciatic Nerve: 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.

45. The Sciatic Nerve : 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”.

49. Self Assesment
A patient presented with severe chronic lower back pain in
the sacral region with radiation to the back of the left leg,
producing a strong pain throbbing and burning behind the
knee. Pain was aggravated when bending forward or in
reaching out position. He gave history of an accident that
resulted in fracture of the lumbar vertebrae. His MRI two
months prior to this severely increasing pain, revealed disc
degeneration, and protrusion of the disc at the S1 level.
Which anatomical structure is likely to be involved ?

50. Thank You