5.2 Lower Limb Flashcards
LumboSacral plexus
The lumbosacral plexus
is not a single plexus;
it comprises two distinct
and separate components:
the lumbar and sacral plexus.
A single injection of the lumbosacral
plexus cannot anaesthetise the whole lower extremity.
The lumbar plexus is derived from
The lumbar plexus is derived from the anterior primary rami (ventral) T12–L4,
The sacral plexus is derived from
The sacral plexus is derived from anterior primary rami
(ventral) L4–S3 spinal nerves
What is the benefit of LL block vs central
The renewed popularity of lower-limb peripheral blocks has been
attributed to techniques such as ultrasound guidance and continuous catheter techniques.
It also avoids the potential risk of epidural
haematoma in orthopaedic patients, where the use of venous
thromboprophylaxis is routine
Is lumbrosacral plexus block effective
Continuous lumbosacral plexus block
has been shown to be superior
to morphine patient-controlled analgesia
and equally effective as
epidural analgesia, for post-operative analgesia
facet joint pain.
the posterior (dorsal)
primary rami produce
lateral and medial branches
which innervate the back.
The medial branch innervates the
facet joint and is often targeted
as a chronic pain procedure to treat facet joint pain.
The lumbar plexus is
main supply
lies in
formed by the anterior primary rami of T12–L4
The lumbar plexus mainly supplies the anterior part of the thigh.
lie with the bulk of the psoas muscle
The lumbar plexus is most important branches:
most important branches:
1
the lateral cutaneous nerve of the thigh (LCN)
(lieslaterally),
2
the femoral nerve (FN)
(lies in between) and
3
the obturator nerve
(ON) (lies medially)
within the psoas muscle
Issue with FIB
evidence that the
LCN and the FN may
be separated from the
ON by a muscular compartment,
hence a fascia iliaca
or femoral three-in-one
block usually spares the obturator nerve.
The branches of the lumbar plexus (T12–L4)
Iliohypogastric
Ilioinguinal
Genitofemoral
LCN
Femoral
Obturator
Iliohypogastric
Iliohypogastric T12–L1 (anterior rami) Abdominal muscles Inferior abdomen and buttock
Ilioinguinal
Ilioinguinal L1 (anterior rami) Abdominal muscles Medial thigh, external genitalia
Genitofemoral
Genitofemoral
L1–L2
(anterior rami)
Cremaster
Medial thigh, external genitalia
LCN
LCN
L2–L3
(posterior rami)
None
Lateral thigh
Femoral
Femoral
L2–L4
(posterior rami)
Anterior thigh muscles
Anterior thigh and medial side of l
eg below knee up to
medial malleolus
Hip and knee joint
Obturator
Obturator
L2–L4
(anterior rami)
Medial thigh muscle
Medial side of thigh,
posterior lower thigh
Hip and knee joint
Femoral nerve innervates
femoral nerve innervates
iliacus,
psoas,
sartorius,
quadriceps
(rectus femoris and three vastus muscles),
and pectinius.
The obturator nerve
motor
The obturator nerve
innervates three adductor muscles, obturator externus, gracilis and pectinius
Lateral cutaneous nerve of the thigh has
Lateral cutaneous nerve of the thigh has a
cutaneous innervation only.
What supply hips
knee
The anterior divisions of both femoral and obturator nerve supply the hip joint, while their posterior branches supply the knee joint.
Hip surgery
Lower-limb blocks are an efficacious way to provide post-operative
analgesia.
lumbar plexus supplies the hip joint and part of the knee joint
Hence a lumbar plexus block offers good analgesia for hip surgery,
while femoral nerve block often proves inadequate for knee surgery
Knee replacement
sacral plexus supplies the posterior part of knee joint and ankle
as well. Hence a combined lumbar plexus–sciatic nerve block is
appropriate for a total knee replacement.
Ankle surgery
Only the medial malleolus of the ankle is supplied by the femoral nerve (via
the saphenous nerve), while the remainder is innervated by the sciatic nerve.
Dermatomes of lower limbs
T12-S5
T12 At inguinal ligament
L1 Pubic area
L2 Anterior medial thigh
L3 At the medial epicondyle of the femur
L4 Over the medial malleolus
L5 On the dorsum of the foot
S1 On the lateral aspect of the calcaneus
S2 At the midpoint of the popliteal fossa
S3 Over the tuberosity of the ischium or infragluteal fold
S4, S5 Perianal area
lumbar plexus block is performed at
L3–L5 level where the
lumbar plexus originates.
The aim is to block the three main branches by depositing a large volume of local anaesthetic within the bulk of psoas muscle
lumbar plexus block aim
The aim is to block the three main branches by depositing a large volume of local anaesthetic within the bulk of psoas muscle
lumbar plexus block - needle passes
The needle pierces skin, subcutaneous fat, erector spinae, quadratus
lumborum and psoas major muscles.
Lumbar plexus block - landarks
The landmarks include
Posterior superior iliac spine
Iliac crest
Spinous processes of lumbar vertebrae
Lumbar plexus block - landmark lines (detail)
Line 1 –
iliac crest and intercristal line/Tuffier’s line (vertical).
Line 2 –
passing through spinous process of L4 and L5 (horizontal).
Line 3 –
parallel to the above line passing through the posterior
superior iliac spine (PSIS) (horizontal)
Various puncture points for lumbar plexus block (detail)
Puncture point:
Winnie’s: junction of lines 1 and 3. Anatomical studies suggest that
the location of this classic site is in fact too lateral.
Capdevila’s: the part of the intercristal line between lines 2 and 3 is
divided into three parts. The puncture point is the junction between
lateral and the middle third (as shown).
Chayen’s: caudal to Capdevila’s puncture point at L5 level
Performing lumbar plexus block:
Position
Needle
The patient in placed in the
lateral position
(side to be blocked uppermost)
and hips and knees flexed at right angles.
A 100–150-mm 22-G needle is inserted perpendicular to the skin at Capdevila’s puncture point.
The PNS is set at 1–2 mA #
and 100 μsec
pulse width.
Needle contact TV process how deep
Then how do you proceed
What is the response
The needle contacts the transverse process at 6–8 cm depth (varies with gender and body mass index).
This depth is noted and the needle
is withdrawn and reinserted by directing it
5° cranially or caudally,
to pass its tip beyond the transverse process until evoked motor response (EMR) for lumbar plexus (patellar twitch) is obtained.
How much further beyond TV process
The needle should
not be advanced more than 2 cm
beyond the transverse process,
as studies indicate the average distance
between transverse process and plexus
is 18 mm regardless of
body mass index
or gender.
What is a successful LP block
A successful lumbar plexus block
will anaesthetise the
FN, LFN and ON, and
the lower abdominal nerves
(iliohypogastric/ilioinguinal) in
70% of cases
Troubleshooting manoeuvres while performing a lumbar plexus block
Twitch of erector
spinae
Twitch of erector
spinae
Superficial muscles Advance needle deeper
Troubleshooting manoeuvres while performing a lumbar plexus block
Needle contacts
transverse process
Needle contacts transverse process
An important landmark that serves as a
guide; mark this distance
Redirect 5° cranially/caudally
to proceed deeper
Troubleshooting manoeuvres while performing a lumbar plexus block
Quadriceps twitch
Quadriceps twitch
(patellar tap)
Appropriate twitch Inject solution in aliquots of
5 mL
Troubleshooting manoeuvres while performing a lumbar plexus block
Obturator twitch
Obturator twitch
(thigh adduction)
Needle too medial
Redirect laterally at the same
level
Troubleshooting manoeuvres while performing a lumbar plexus block
Hamstring twitch
Hamstring twitch
Sacral plexus stimulation caudally or
medially (lumbosacral twig)
Redirect needle cranially and
laterally
Troubleshooting manoeuvres while performing a lumbar plexus block
Psoas twitch
Psoas twitch
(thigh flexion)
Needle is too deep and
is stimulating muscle
directly
Withdraw needle
Precautions while performing lumbar plexus block
Anticoag?
Needle Depth + Direction
1
The patient should not be anticoagulated, since this is a deep block.
2
The needle should not be advanced 2–3 cm beyond the transverse process.
3
The needle should not be directed medially to avoid epidural or intrathecal injection.
Precautions while performing lumbar plexus block
is there much blood supply?
4
Rapid, forceful injections must be avoided,
as this is a vascular area.
5
For the same reason, epinephrine should be added to injectate to permit early recognition of intravascular injections.
Precautions while performing lumbar plexus block
Motor response should be >?
Catheter?
6
Avoid injection of local anaesthetic when a response is produced with a current < 0.5 mA, as this may lead to epidural or intrathecal spread.
7
A continuous catheter should not be threaded beyond 3 cm, as it may migrate away from the plexus.
complications of the lumbar plexus block
common
complications of the lumbar plexus block
include
1
renal and
2retroperitoneal haematomas,
3
intravascular injections
(due to vascularity of this region),
4
nerve damage and
5
catheter placement in
the abdomen or other unintended places.
More serious complications of the lumbar plexus block include
More serious complications include
unintended sympathetic block
(spread to sympathetic chain located anteriorly),
epidural
(15%–30% incidence due to medial injections
or lateral extension of dural sleeves)
or even intrathecal anaesthesia.
In fact, the epidural spread may even
be bilateral.
Femoral nerve is formed by
FN is formed by the
posterior divisions
of the anterior rami of
the L2–L4 spinal nerves
Path of FN
first lies within the bulk of psoas muscle,
emerging from its lateral border
in a fascial compartment
between the psoas and iliacus muscles
and innervating both.
Path of FN regards inguinal
Relations to vascular
fascial relations
It then enters the thigh under the
inguinal ligament.
Here it lies lateral to femoral artery.
The femoral sheath contains the
femoral artery and vein,
which lie beneath the fascia lata but
above the fascia iliaca.
The femoral nerve lies deep to
The femoral nerve lies deep to the fascia iliaca, which forms the iliopectineal ligament to separate the femoral nerve from the femoral vessels medially
FN anterior division
The anterior division of the femoral nerve
supplies the skin of the
medial and anterior surfaces
of the thigh,
innervates sartorius
and pectineus muscles
and
provides articular branches to the hip.
FN Posterior division
posterior division of the
femoral nerve provides
muscular branches
to the quadriceps
and articular branches to the knee;
eventually it becomes the saphenous nerve.
The saphenous nerve lies
within the adductor canal
under the sartorius muscle
above the medial
aspect of the knee.
Various techniques to block femoral nerve
Peripheral nerve stimulator guided
Peripheral nerve stimulator guided femoral
nerve block
Inguinal crease,
1–2 cm lateral
to femoral artery
A 50-mm 22-G needle
is inserted at this
puncture point
directed 60° cephalad
Patellar twitch;
15–20 mL local anaesthetic is injected
Various techniques to block femoral nerve
Femoral three in-one block
Femoral threein-
one block
Inguinal crease,
1–2 cm lateral
to femoral artery
A 50-mm 22-G needle
is inserted at this
puncture point
directed 60° cephalad
Patellar twitch;
15–20 mL local anaesthetic is injected
Same as above Same as above Patellar twitch; higher
volume and distal
pressure applied
femoral three-in-one block does not consistently block obturator nerve
Various techniques to block femoral nerve
Fascia iliaca block
Fascia iliaca block
Line joining
anterior superior iliac spine
and pubic tubercle (inguinal ligament)
is divided into three parts
Needle inserted 1 cm
below the junction of
lateral and middle third
20 mL local anaesthetic
injected after two pops
(signifying fascia lata and fascia iliaca)
Various techniques to block femoral nerve
Ultrasound
guidance
Ultrasound guidance
Inguinal crease Identifying
femoral vessels,
nerve and
fascia iliaca
Patellar twitch if a nerve
stimulator is used
Ultrasound guidance may reduce the volume of local anaesthetic needed and
the onset time of anaesthesia for femoral block, but no study has
demonstrated a reduction in peripheral nerve injury.
Indications for femoral nerve block include:
Single injections:
Indications for femoral nerve block include:
Single injections: quadriceps biopsy, long saphenous vein stripping, knee arthroscopy (along with intra-articular LA), analgesia for primary total knee replacement (TKR) and analgesia for anterior cruciate ligament (ACL) reconstruction.
Indications for femoral nerve block include:
Continuous catheter:
Combined with sciatic block:
Continuous catheter:
analgesia for
femoral shaft/femoral neck fractures
(catheter placed upon initial presentation) and TKR.
Combined with sciatic block:
any surgery below mid-thigh level
Salient features of PNS-guided femoral nerve block are as follows.
performed where
Ideally performed at the inguinal crease, since:
1
The femoral nerve is widest and most superficial.
2
At inguinal ligament, needle directed cephalad can enter pelvis.
3
It is less painful than piercing through the inguinal ligament.
Salient features of PNS-guided femoral nerve block are as follows.
Twitches
initial
final
redirection
Initially,
a sartorial twitch is obtained
(movement of lower medial thigh)
due to stimulation of anterior branch of femoral nerve.
The needle is then redirected
slightly deeper
(and laterally or medially) to
stimulate posterior branch
(supplying quadriceps),
resulting in typical ‘patellar twitch’.
Local anaesthetic (15–20 mL) may be injected at this point
Femoral N catheter
Femoral nerve catheters should
not be passed more than 3–5 cm beyond the tip,
as the chances of migration away from the nerve are
increased (i.e. medial or lateral rather than proximal
Fascia iliaca block
How
It is the simplest way to block the femoral nerve.
A line joining
ASIS and pubic tubercle
(inguinal ligament)
is divided into three parts;
at 1 cm below the junction of the lateral and middle
thirds,
a 50-mm blunt-tipped needle is inserted angled at 60° cephalad
Two clicks or pops are detected as the needle pierces through the
fascia lata and the fascia iliaca, and 20–30 mL local anaesthetic is
injected
Femoral three-in-one block:
detailed
Uses the same landmarks and technique as PNS-guided femoral nerve block,
but a larger volume of local anaesthetic and distal pressure is used to encourage proximal migration block of the three main nerves of the lumbar plexus.
However, studies have shown that this does not
occur and local anaesthetic actually spreads laterally and medially rather than proximally.
The following nerves are inconsistently anaesthetised during a three-in one block:
the LCN of the thigh,
the FN and the
anterior branch of the ON.
Is 3 in 1 fem nerve suitable for inguinal or popliteal surgery
why
However,
the posterior branch
ON and
femoral branch of
genitofemoral nerve are
not blocked and it is unsuitable for surgery
performed in the inguinal or popliteal areas.
Also, because of
inconsistent block of anterior branch of the ON, surgery of medial
aspect of the thigh may also need supplementation in some form
Continuous catheters FN
how
where in reation to fascia
Continuous catheters:
They may be inserted either using the
PNS or ultrasound.
The femoral nerve lies
deep to fascia iliaca,
and therefore the catheter tip
should lie below this layer.
Continuous catheters FN
What axis of insertion
stimulating cateter better?
Catheters may be
inserted along the long axis (using the out-of-plane
approach) or
perpendicular to the long axis of the nerve (using the
in-plane approach).
Catheters may be non-stimulating or stimulating.
Theoretically, stimulating catheters should improve secondary block success rate;
however, recent reviews have only been able to demonstrate a limited benefit.
The saphenous nerve
branch of
supplies
The saphenous nerve is the
terminal branch of the
posterior division
of femoral nerve.
It has no motor supply
and provides sensory innervations
to the
anterior thigh,
medial aspect of knee
and
leg down to the medial malleolus.
The saphenous nerve
may be blocked in the following locations
may be blocked in the following locations
Above the knee:
subcutaneous infiltration above knee
subsartorial injection 5 cm above knee – blind or PNS/ultrasound guided.
Below the knee:
subcutaneous infiltration along the medial tibia and the media popliteal fossa; paravenous technique (along the long saphenous vein) just distal to knee; infiltration above medial malleolus.
The saphenous nerve
Highest success
The highest success rate is achieved by
sub-sartorial injections.
The patient is positioned supine,
with the chosen leg slightly abducted and external
rotated.
The sartorius muscle is identified (above the medial aspect of the
knee) by asking the patient to elevate the leg slightly.
A 50-mm 22-G needle is inserted through the belly of sartorius to enter the subsartorial plane, and
paraesthesia is elicited in the saphenous distribution.
Local anaesthetic (10 mL) may be injected here. Using utrasound guidance, the saphenous nerve
may be identified in the subsartorial plane, sandwiched between the sartorius
and the vastus medialis initially and the sartorius and the gracilis distally.
Distally it lies next to the descending genicular artery, which serves as a
landmark for identification under ultrasound
The obturator nerve originates
The obturator nerve originates
from
ventral (anterior) divisions
of anterior primary rami of
L2–L4 spinal nerve roots.
The obturator nerve runs in
emerges at
It is formed within
the substance of psoas muscle and travels near its medial border, emerging
from the obturator foramen to enter the thigh.
The obturator nerve
anterior division
runs
supplies
cutaneous?
Here it divides into an anterior division,
which lies between the
adductor longus
and pectinius above
and
the adductor brevis below.
ANTERIOR
It supplies these muscles
and gracilis,
articular branch to hip
and a variable
cutaneous branch to the
medial side of the thigh.
The obturator nerve
Posterior division
The posterior division passes
deep or POSTERIOR to adductor brevis
but lies above adductor magnus.
It supplies adductor magnus
and
obturator externus;
and an articular branch to the knee joint.
pg 189
ON variations
an accessory obturator nerve (L3, L4) may occur in a third of
individuals, and innervates the pectinius muscle.
Various techniques for blocking the obturator nerve:
Winnie’s classic approach
Winnie’s classic approach:
2 cm lateral and
2 cm caudal to pubic tubercle,
a stimulating needle is inserted
perpendicular to the skin to
contact the pubic ramus.
Then it is walked off the
inferior edge of ramus to
enter the obturator foramen
until an adductor EMR is observed.
This approach is painful because of periosteal contact
Winnie’s classic approach mcq thing for obturator
painful
Inguinal approach
Various techniques for blocking the obturator nerve:
detailed
Inguinal approach:
a line is drawn from the femoral artery
to the medial border of adductor longus
on the inguinal crease.
At the midpoint of this line, a needle is inserted 30° cephalad in a parasagittal plane to elicit a medial adductor response
(stimulation of adductor longus supplied by anterior branch of the ON) at a depth of about 4
cm, and 5 mL of local anaesthetic is deposited here.
The needle is redirected caudal and lateral towards adductor magnus to elicit a
posterior adductor twitch (stimulating posterior branch of ON) and a further 5 mL of local anaesthetic is injected.
success of obturator block is assessed
success of obturator block is assessed
by loss of motor block only,
since the anterior branch inconsistently
supplies the medial thigh.
In addition, adductor magnus is also innervated by the sciatic nerve; therefore, it is not
completely paralysed with an isolated ON block.
Ultrasound guidance approach: Obturator - benefit
helps to block both branches of ON
Ultrasound guidance approach: a high-frequency ultrasound probe is
placed parallel to the inguinal crease. The anterior branch is identified
between the adductor longus and the brevis, while the posterior branch
can be seen lying between the adductor brevis and the magnus
muscles.
The LCN of the thigh derived from
originates
in
The LCN of the thigh is derived from
the dorsal division of anterior
rami of L2–L3.
It originates within the
body of psoas and emerges
from the lateral border of the
muscle to lie on the iliacus muscle.
Where can the lateral cutaneous nerve be blocked
How
Related to lata and iliaca
The nerve proceeds towards the ASIS,
passing under the inguinal
ligament medial to the ASIS.
The LCN of the thigh may be blocked
here by injecting local anaesthetic
2 cm medial and 2 cm caudal to ASIS.
It lies under the fascia lata, but above the fascia iliaca.
The sacral plexus is derived from
Lumbosacral trunk
(anterior rami of L4, L5)
and
the sacral nerves (anterior rami of S1–S3).
The sacral plexus is formed
bounded by
It is formed within the pelvis
and exits it through the greater sciatic foramen
It is
bounded by piriformis posteriorly
and the iliac vessels anteriorly.
What is terminal branches of sacral plexus
sciatic nerve is the
main terminal branch of the sacral plexus
(the other being the posterior cutaneous femoral nerve (PCFN)).
It is the largest
(2 cm wide)
and
longest nerve of the body (approx 45 cm till division).
Branches of sacral plexus
Gluteal nerves
Gluteal nerves (L4–S2)
Superior gluteal nerve:
gluteus medius and minimus
Inferior gluteal nerve:
gluteus
maximus
Nerve to quadratus femoris
Nerves to the piriformis and
obturator internus muscles
Cutaneous
Upper medial buttock
Branches of sacral plexus
Sciatic nerve
Sciatic nerve (L4–S3)
Common peroneal
tibial
Branches of sacral plexus
Gluteal nerves
Sciatic nerve
Posterior femoral
cutaneous nerve
Pudendal nerve
Branches of sacral plexus
PFCN
Posterior femoral cutaneous nerve
(S1– S3)
No motor
Inferior cluneal nerves and perineal branches:
lower medial buttock and posterior thigh
Pudendal nerve
Pudendal nerve
(S2, S3, S4)
Muscles of the pelvic structures
External genitalia
Sciatic nerve course and branches and relevant blocks
Mansour’s parasacral block
(lateral)
Labat’s classic sciatic nerve block
(lateral decubitus)
Subgluteal approach (lateral
decubitus)
Raj’s approach (lithotomy)
Beck’s anterior approach
(supine)
Sukhani’s infragluteal approach
(prone)
Guardini’s subtrochanteric block
(supine)
Popliteal block
(prone/supine/lateral/lithotomy
Mansour’s parasacral block
(lateral)
Labat’s classic sciatic nerve block
(lateral decubitus)
Sciatic nerve exits the greater sciatic foramen, deep to the
piriformis
Subgluteal approach (lateral
decubitus)
Raj’s approach (lithotomy)
Enters the thigh midway between the greater trochanter and the
ischial tuberosity
Beck’s anterior approach
supine
Passes medial to the lesser trochanter
Sukhani’s infragluteal approach
prone
Upper thigh: lies lateral to the tendon of biceps femoris
Guardini’s subtrochanteric block
supine
Mid-thigh: under the belly of biceps femoris
Popliteal block
(prone/supine/lateral/lithotomy
Popliteal fossa:
divides into a medial tibial nerve and lateral
common peroneal nerve (fibular nerve); bounded by biceps
femoris laterally, and semitendinosus and semimembranosus
medially
tibial and common peroneal nerves are two distinct nerves from the
very start contained within the same common sheath, as shown by
anatomical studies. Sciatic nerve divides into its two main branches generally
at lower thigh level, although this is very variable (0–13 cm from popliteal
crease).
Parasacral block
Parasacral block (Mansour’s approach)
is a relatively easy block to
perform and has a high success rate.
unlikely to cause
hypotension.
Parasacral block effect on BP
As sacral outflow is predominantly parasympathetic, sacral nerve
blockade causes parasympathetic blockade, hence is unlikely to cause
hypotension.
Parasacral block & obturator
Obturator nerve can be reliably blocked either by a lumbar plexus
block or specific obturator block.
It is not reliably and consistently
blocked by either a fascia iliaca or sacral plexus block.
(PCFN) vs parasacral tourniquet below knee
that posterior cutaneous femoral nerve (PCFN) block
provides better tolerance of a thigh tourniquet during below-knee surgery
posterior cutaneous femoral nerve (PCFN)
supply
how can it be blocked
The PCFN has
no motor or articular supply.
It provides sensory innervations to the
lower buttock and posterior thigh and therefore is
important for prevention of thigh tourniquet pain,
in combination with
femoral nerve and LCN of thigh.
The PCFN may be blocked by
proximal approaches only (Mansour’s parasacral block, Labat’s gluteal,
Beck’s anterior approach).
However, a randomised study of proximal
and distal block has not revealed any statistical difference in thigh
tourniquet tolerance for below-knee surgery.
Parasacral and what block for LL surgery
?femoral
Along with lumbar psoas compartment block (not femoral nerve
block) it may be used for unilateral lower-limb anaesthesia
proximal sciatic nerve blockade approaches
Posterior transgluteal (Labat’s) approach:
Subgluteal approach (lateral):
Lithotomy subgluteal (Raj’s) approach
Infragluteal (Sukhani’s) approach:
Anterior (Beck’s) approach:
Subtrochanteric (Guardini’s) approach:
Posterior transgluteal (Labat’s) approach:
Greater Troch (GT) and PSIS (line 1)
and another
between GT and sacral hiatus (line 2).
lateral decubitus
Subgluteal approach (lateral):
lateral decubitus,
GT and the ischial tuberosity (IT)
midpoint
Lithotomy subgluteal (Raj’s) approach
supine,
hip and the knee are flexed at 90
connecting GT and IT
midpoint
Infragluteal (Sukhani’s) approach:
prone,
lateral border of the biceps femoris (BF) muscle is palpated
intersects the infragluteal crease is the point of
BF
twitches should not be accepted
Anterior (Beck’s) approach:
ASIS and pubic tubercle
GT
Subtrochanteric (Guardini’s) approach:
Subtrochanteric (Guardini’s) approach: with patient supine, GT is
palpated.
Mansour’s
parasacra
adv disadv
Mansour’s parasacral Simple landmarks Easy to perform High success rate
Lateral positioning needed
Labat’s posterior
transgluteal
Labat’s posterior
transgluteal
Proximal approach
Lateral positioning needed Difficult landmarks Painful needle insertion Ultrasound guidance difficult since nerve is deeper at this level
Subgluteal
Subgluteal
Sciatic nerve is not covered
by gluteus
Reliable landmarks even in
obese individuals
Ultrasound guidance easier
to do
Lateral positioning needed Anisotropy of sciatic
nerve
Raj’s lithotomy
Raj’s lithotomy
Supine positioning
Reliable landmarks
Procedural difficulty (someone needs to hold the leg, and limb moves with stimulation)
Sukhani’s infragluteal
Sukhani’s
infragluteal
Simple landmarks
Prone positioning needed
Landmarks may be variable (only bony landmarks
are fixed)
Spares the posterior cutaneous femoral nerve
Beck’s anterior
Beck’s anterior
Supine positioning
Resurgence with ultrasound
guidance approach
Deeper insertions, hence painful
Technically challenging
Guardini’s
Guardini’s
subtrochanteric
Supine positioning
Not a favoured approach
sciatic nerve is composed of two components
sciatic nerve is composed of two components,
the tibial and the
common peroneal.
The tibial nerve (TN)
is larger and lies medially,
while the
common peroneal nerve (CPN) is
smaller and lies laterally.
What does TN supply
The TN supplies gastronemius, soleus and plantaris in the leg;
and flexor hallucis longus and flexor digitorum longus in the foot through medial and lateral plantar nerves.
Stimulation of TN causes plantar
flexion.
CPN divides into superficial+Deep
Superficial
The CPN divides into a superficial and a deep branch.
The superficial peroneal nerve supplies
peroneus brevis and longus,
which evert the ankle.
Deep PN
The deep peroneal nerve supplies
branches to muscles of the
anterior leg
(tibialis anterior, extensor digitorum longus, peroneus tertius, and extensor hallucis propius)
and extensors of ankle
(extensor hallucis longus and extensor digitorum longus).
This causes dorsiflexion upon
stimulation
What suggests best chance of success with EMR on sciatic nerve block
inversion of the foot
inversion of the foot & Sciatic N block
inversion of the foot is caused by tibialis anterior
(deep peroneal nerve)
and tibialis posterior (the TN).
Hence, such a response suggests a central needle-tip location and stimulation of both TN and CPN components.
This has been the reason suggested for a higher success
rate and a shorter onset time of anaesthesia with inversion EMR.
Sciatic Nerve block most common approach
Popliteal
most superficially at this level (2–4 cm).
separates into its two components: medial tibial nerve (TN)
and l
ateral common peroneal nerve (CPN)
variably above the popliteal crease from 0 to 13 cm
multistimulation or ultrasound guidance techniques enhance success rates (sparing d/t uneven division)
Two approaches to PNS-guided popliteal block are in vogue
Posterior
Posterior approach:
the patient is positioned prone;
a triangle is
drawn over the posterior aspect
of the knee where the
popliteal crease forms the base,
biceps femoris tendon the lateral border
and
semimembranosus tendon the medial border.
A perpendicular line (P)
is dropped from the apex to the popliteal crease bisecting it.
A point 7– 8 cm above the popliteal crease
on this perpendicular line is chosen,
and a 50-mm 22-G needle is inserted 1 cm lateral to this point.
In most people, the sciatic nerve has not divided at this point.
Inversion
EMR yields best results followed by plantar flexion, dorsiflexion and
eversion.
A volume of 25–40 mL of local anaesthetic may be used.
The same landmark technique may be performed with the patient in
lithotomy position.
Lateral approach
PNS-guided popliteal block
Lateral approach:
the groove between biceps femoris
and vastus lateralis is palpated,
and a 100-mm needle is inserted perpendicularly
7–8 cm above the popliteal crease.
The needle is walked off the
femur at an angle of 30° dorsal
to stimulate the sciatic nerves.
Common peroneal nerve is commonly
stimulated here, and the drug is
injected subsequently.
Ultrasound-guided popliteal block
1 probe
2 issue wiht sciatic
how improved
1
This uses a high-frequency array
(6–13 MHz), as sciatic nerves are
located superficially.
2
The sciatic nerve is anisotropic, hence the beam needs to be aligned
at 90° to obtain the best view.
This can be achieved by a cranial tilt of
the probe at the proximal thigh,
vertical positioning at mid-thigh and a
caudal tilt at the lower-thigh level.
Ultrasound-guided popliteal block
3 how is it located
4 then what after location
5 how to deposit local
3
The probe is placed parallel to popliteal crease, and moved upward until the pulsatile popliteal artery is seen.
The sciatic nerve components can
be seen superficial and lateral to the artery at this
level.
4
They may be traced upwards, where they are seen joining to form a single sciatic nerve.
This is the best location for injection as well as
catheter placement.
5
At this point, local anaesthetic is deposited in a circumferential manner to enclose hyperechoic nerve all around (the doughnut sign).
Cutaneous nerve supply ankles
Cutaneous nerve supply of the ankle is important; it is derived from
five nerves,
Landmark Nerve
Lateral malleolus Sural
Superficial peroneal
Medial malleolus Saphenous
Dorsum of foot Mostly superficial peroneal
Plantar surface of foot Medial and lateral plantar (branches of tibial)
Lateral margin of foot Sural
Medial margin of foot Saphenous
Web space between the first and second toes Deep peroneal
Fifth toe Superficial peroneal
Heel Posterior tibial
Ankle block
which are superficial and deep
The ankle is innervated by five nerves:
three nerves are superficial
(superficial peroneal,
sural
and saphenous),
and
two are located deep
(deep peroneal and posterior tibial).
Remember: S is superficial
Injection landmarks for ankle block
Deep
peroneal
Deep peroneal
Peripheral nervous system:
lateral to the tendon of the extensor hallucis longus
muscle (between extensor hallucis longus and extensor digitorum longus)
Ultrasound: nerve is immediately lateral to the dorsalis pedis artery
Injection landmarks for ankle block
Posterior Tibial
Posterior tibial
Behind medial malleolus, deep to posterior tibial artery
Injection landmarks for ankle block
Saphenous
Saphenous
Subcutaneously at medial malleolus near great saphenous vein
Injection landmarks for ankle block
Sural
Sural
Subcutaneously in the groove between lateral malleolus and calcaneum (behind
short saphenous vein)
Injection landmarks for ankle block
Superficial peroneal
Superficial peroneal
Subcutaneously between anterior tibial and lateral malleolus
The duration of analgesia provided for foot surgerie
Subcut infiltration
ankle block
popliteal block
The duration of analgesia provided for foot surgeries is 6 hours by
subcutaneous infiltration, 11 hours by ankle block and 18 hours by
popliteal block.
Mayo block
Mayo block is an alternative
to ankle block for bunion or hallux
surgery, as it anaesthetises the first metatarsal only.
Adrenaline and ankle blokcs
Adrenaline should ideally be avoided in ankle blocks because of the
risk of vascular compromise.
