Download Lecture 18 - SCIATIC NERVE

Prof. Saeed Abuel Makarem
By Dr Jammila Al- Madany
OBJECTIVES
 By the end of the lecture, the student 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.
ORIGIN
From Sacral
Plexus,
 (L4,5, S1, 2,3).
It is the largest
branch of the
plexus.
It is the largest
nerve of the body.
SACRAL PLEXUS
 Formation:
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 Ventral (anterior)
rami of a part of L4 &
whole L5
(lumbosacral trunk)
+ S1,2,3 and most of
S4.
 Site:
 On the posterior wall
of the pelvis,
 In front of Piriformis
muscle.
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Lumbosacral
trunk
COURSE
The Sciatic nerve:
Leaves the pelvis through
Greater Sciatic foramen,
below the Piriformis.
It passes in the gluteal
region midway between:
Ischial tuberosity &
Greater trochanter)
Then to posterior
compartment of the
thigh.
G
T
P
S
N
COURSE
It descends on the
posterior aspect of
Adductor Magnus.
It is overlapped by:
Biceps femoris &
Semimembranosus
muscles.
DIVISION
In the lower 1/3rd of
back of the thigh, it is
divides into:
Tibial & Common
peroneal nerves.
TIBIAL NERVE
 Course:
 It descends through the
popliteal fossa (bisect the
fossa) to posterior
compartment of leg,
accompanied with
posterior tibial vessels.
 Passes deep to the flexor
retinaculum (through
the tarsal tunnel, behind
medial malleolus) to
reach the sole of foot
where it divides into two
terminal branches, (medial
& lateral planter nerves).
COMMON PERONEAL (FIBULAR) NERVE
 Course:
 Leaves popliteal fossa through
its lateral angle & turns
around the lateral aspect of
neck of fibula, (dangerous
position).
 Then divides into:
 Superficial peroneal or
(musculocutaneous) to
supply the Lateral
compartment of the leg.
 Deep peroneal or
(anterior tibial) :
 to supply the Anterior
compartment of the leg.
BRANCHES OF THE SCIATIC NERVE
CUTANEOUS:
 To all leg & foot
EXCEPT:
 areas supplied by
the Saphenous
nerve (branch of
Femoral nerve).
MUSCULAR
(through Tibial part)
to:
1. Hamstring part of
Adductor Magnus.
2. Long head of Biceps
Femoris.
3. Semitendinosus.
4. Semimembranosus
NB. The short head of
biceps receives its
branch from the
lateral popliteal
nerve.
CAUSES OF SCIATIC NERVE INJURY
•Badly placed
intramuscular injection
•Posterior dislocation
of hip joint.
•Fracture pelvis.
INTRAMUSCULAR INJECTION IN GLUTEAL REGION
 Gluteal region is one
of the sites of choice
for an intramuscular
injection.
 To avoid injury of
the sciatic nerve in
this region, the
safest place to inject
is the upper outer
quadrant of either
gluteal region.
EFFECT OF SCIATIC NERVE INJURY
MOTOR EFFECT
Paralysis of
Movements affected
Hamstrings
Flexion of knee &
Hamstrings
Extension of hip
All muscles of the All movements of the
leg & Foot
Leg & Foot
SENSORY EFFECT
Loss of sensation of the
areas supplied by sciatic
nerve (below knee
EXCEPT area supplied
by the (Saphenous
nerve).
SCIATIC NERVE INJURY
The following clinical features
are present:
Motor:
 The hamstring muscles are
paralyzed, but weak flexion of
the knee is possible. Why?
-Because of the action of the
sartorius (femoral nerve) and
gracilis (obturator nerve).
 All the muscles below the knee
are paralyzed, and the weight of
the foot causes it to assume the
plantar-flexed position, or foot
drop.
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MANIFESTATIONS OF SCIATIC NERVE INJURY
 MOTOR:
 Marked wasting of the muscles
below the knee.
 Weak flexion of the knee
(sartorius & gracilis are intact).
 Weak extension of hip (gluteus
maximus is intact).
 The foot assumes the position of
Foot Drop (planter flexed
position) by its weight.
 SENSORY EFFECT:
 Loss of sensation below the knee
(EXCEPT medial side of leg and
medial side of the foot as far as
the ball of the big toe).
 ( saphenous nerve is intact).
EFFECT OF INJURY OF COMMON PERONEAL NERVE






Usually occurs due to:
Fracture neck of fibula, or
Pressure from a cast or splint.
Paralysis of muscles of:
Anterior &
Lateral compartments of the
leg
 Movements affected:
 Loss of:
1. Dorsiflexion of ankle.
2. Eversion of the foot.
3. Extension of the toes.
 Foot is Planter flexed & Inverted:
 Talipes equinovarus
EFFECT OF INJURY OF TIBIAL NERVE
 Paralysis of muscles of the :
Posterior compartment of leg
 Muscles of the sole of the foot
Movements affected:
1. Planter Flexion of ankle
2. Inversion of foot
3. Flexion of toes
 Foot is Dorsiflexed & Everted:
 Talipes Calcaneovalgus