Sciatic Nerve Block

Tiffany Tavernier
L4-S3 spinal nerve roots
Largest nerve trunk in the
human body
Distribution = hamstrings,
long head of biceps
femoris, adductor magnus;
part of hip and knee joint
Blocks skin of posterior
aspect of thigh and entire
leg below knee
exception of skin of medial
aspect of lower leg
Classical Posterior
› Pt lies in lateral
decubitus position
› Landmarks: greater
throchanter and
posterior-superior iliac
› Needle is inserted 4-5
cm distal to midpoint
btw the two
perpendicular to skin
in all planes
Parasacral Approach
› Pt lies in lateral
decubitis position
› Landmarks: posterior
superior iliac spine
and ischial tuberosity
› Needle is inserted
6cm caudal to line
btw the 2 in sagittal
› Pt is supine with hip
flexed and upper leg
perpendicular to torso
› Landmarks: greater
trochanter of femur
and ischial tuberosity
› Needle is inserted 4
cm in claudal
direction midway
between the 2
› Needle is advanced
parallel to horizontal
Anterior approach
› Pt is supine with legs
› Landmarks: femoral
crease and femoral
arterial pulse
› Needle inserted 405
cm distal from pulse
of femoral artery and
perpendicular to line
of femoral crease
100 pts undergoing
minor knee surgery
 Randomly divided by
envelope to receive
anterior or posterior
approaches combined
with femoral and lateral
femoral cutaneous
nerve blocks using US
 1% mepivacaine with
short 1100m, 21 gauge
 Block: 20mL of 1.5%
mepivacaine with
1:400,000 epinephrine
Anterior Approach
 Nerve stimulator was
used @ 2Hz to elicit foot
plantar- or dorsiflexion
Posterior Approach
 Same as anterior, but
without nerve stimulator.
both then placed in supine position with
legs extended and femoral and lateral
femoral cutaneous blocks were performed
 Measurements of depth and size of sciatic
nerve, needle depth, block execution time
for sciatic nerve block, block execution
time for all 3 blocks, time required for onset
of sensory and motor blocks of sciatic nerve
and duration of blockade of sciatic nerve
were measured
Sciatic nerve was located deeper in anterior
Both had similar block execution time for
sciatic nerve block, but anterior approach took
less time to complete all 3 blocks
Onset of sensory block for superficial peroneal,
sural and tibial nerves was similar
Sensory block of posterior femoral cutaneous
nerve was achieved less often with the
anterior approach - less block of posterior
area of thigh
Onset of motor block was similar with both
Although posterior femoral cutaneous
nerve was rarely blocked with anterior
approach, can still be used in knee
surgery where thigh tourniquet is used 
pts who required fentanyl was similar btw
groups  tourniquet pain is not affected
by presence of posterior femoral
cutaneous nerve block
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