Chapter 78 Sciatic Nerve Block and Ankle Block Flashcards
KEY POINTS 1. The sciatic nerve is the largest nerve in the body and innervates the entire leg below the knee and the foot, except for its medial aspect, which is innervated by the saphenous nerve. Its two divisions, the tibial nerve and the peroneal nerve, while separate entities, are covered by a continuous connective tissue sheath. 2. The sciatic nerve can be blocked at different levels along its entire length as it exits the pelvis at the greater sciatic foramen to its termination in the p
sciatic nerve provides sensory innervation
to the back of the thigh and the entire leg below the knee except for its medial aspect, which is innervated by the saphenous nerve.
sciatic nerve provides motor innervation
to the hamstrings
and all the muscles below the knee.
Sciatic nerve block in conjunction with lumbar plexus block, femoral nerve block, or saphenous nerve block can be used to provide
anesthesia and analgesia for
surgical procedures of the lower extremity and the hip.
Peripheral nerve blocks have the following distinct
advantages over general or central neuraxial anesthesia:
(1) no autonomic blockade, with no risk of hemodynamic
instability and urinary retention; (2) unilateral
block; (3) no risk of spinal hematoma in the anticoagulated patient; (4) prolonged postoperative analgesia provided either by injecting a long-acting local anesthetic or by a
continuous infusion of local anesthetic via an indwelling catheter and infusion pump; (5) decreased need for postoperative nursing due to minimal side effects such as uncontrolled pain, emesis, sedation, and respiratory depression;
(6) early ambulation and discharge.
The sciatic nerve formed by
the ventral rami of L4, L5 and S1, S2, S3 nerve roots, is the largest nerve in the body,
measuring 0.8 to 1.5 cm in width.
Sciatic Nerve course
The roots exit the pelvis as they unite to form the sciatic nerve through the greater sciatic foramen and travel on the anterior surface of the piriformis muscle accompanied by the superior gluteal artery, the largest and shortest branch of the internal iliac artery.
two divisions of the
sciatic nerve
tibial nerve (medial position), and peroneal nerve (lateral position)
Proximally, the scaiatic nerve lies
over the posterior surface of the ischium. In this location the sciatic nerve is accompanied by the posterior cutaneous nerve of the thigh and
further down, the inferior gluteal artery
Distal to the
piriformis muscle the sciatic nerve travels
posterior to the superior gemellus, tendon of obturator internus, the inferior
gemellus, quadratus femoris, and adductor magnus muscles.
In the gluteal area the sciatic nerve is covered by
the gluteus maximus
muscle posteriorly. In the infragluteal location, the sciatic nerve lies in close proximity to the lesser trochanter, over the adductor magnus muscle and is crossed obliquely in a mediolateral direction by the long head of the biceps femoris muscle.
The sciatic nerve continues distally in the thigh
under the biceps femoris muscle. At the cephalad portion of popliteal fossa or distal third of the thigh, the
sciatic nerve divides into its two terminal branches, the posterior tibial and common peroneal nerves.
In the popliteal area the sciatic nerve picks up
more connective tissue, resulting in increased connective tissue to neuronal tissue ratio, which may explain the increased latency of onset seen with the popliteal sciatic blocks compared with more
proximal locations.
SCIATIC NERVE BLOCK
INDICATIONS
used for lower extremity surgery, including hip, tibia and fibula, knee, ankle, and foot surgery, and also for above and below knee amputation. There is evidence to support its use in chronic pain
syndromes of the lower extremity, including complex regional pain syndromes, or to pre-empt phantom limb pain
SCIATIC NERVE BLOCK
PARASACRAL APPROACH (MANSOUR)
The local anesthetic is deposited in the
fascial plane enclosing the L4–S3 nerve roots of sacral plexus, as they unite to form the main trunk of the sciatic nerve under the piriformis muscle.
SCIATIC NERVE BLOCK
PARASACRAL APPROACH (MANSOUR)
This was also associated with blockade of
the obturator nerve in 93% of subjects
SCIATIC NERVE BLOCK
PARASACRAL APPROACH (MANSOUR)
Surface Anatomy and Technique
The patient is placed in the lateral (Sim’s) position with the
operative side up. The posterior superior iliac spine (PSIS) and ischial tuberosity are marked and united by a line. The point of needle entry is approximately 6 cm from the PSIS
along this line. A 100-mm, 22-gauge insulated block needle is inserted and advanced maintaining a parasagittal
orientation, until motor responses are elicited in the foot/ankle at a current of less than 0.5 mA. The nerve roots of the sacral plexus are usually contacted at 5 to 8 cm depth. Twenty to 30 ml of local anesthetic is injected after ensuring that the twitches disappear with currents at 0.2 mA and there is no resistance to injection
It is important
to remember that the superior gluteal artery
curves around the upper lip of the greater sciatic notch, should not be injured, as it is a short branch of the internal iliac
artery and will retract back into the pelvis if severed
SCIATIC NERVE BLOCK
PARASACRAL APPROACH (MANSOUR)
Ultrasound-Guided Technique
A
curved low-frequency (C2-5 MHz) probe is positioned across the gluteal region and slid caudad while watching the linear hyperechoic shadow of the back of the ischium. The sciatic notch looks like a discontinuity in
this line, with the piriformis muscle covering the notch.
Hip adduction and abduction help identify the piriformis.
The sciatic nerve is seen in short axis deeper to the piriformis. Rotation of the probe by 45° will bring about the long axis view of the sciatic nerve as it exits the
greater sciatic notch
SCIATIC NERVE BLOCK PARASACRAL APPROACH (MANSOUR)
complications of the traditional approach
hematoma, rectal perforation, and transient sciatic
neuralgia were not seen with the ultrasound guidance
SCIATIC NERVE BLOCK
CLASSIC POSTERIOR APPROACH
LABAT TECHNIQUE
The sciatic nerve is blocked at the level of the greater
sciatic notch distal to the piriformis muscle
SCIATIC NERVE BLOCK
CLASSIC POSTERIOR APPROACH
(LABAT TECHNIQUE)
Anatomy and Technique
The patient is placed in the lateral Sim’s position with the
thigh and knee flexed 90° and the dependent lower extremity
extended. A line is drawn between the tip of greater trochanter (GT) and the PSIS, line 1. A second line is drawn connecting the GT and sacral hiatus, line 2. A perpendicular line, line 3, is drawn from the midpoint of line 1 to bisect line 2. The point of intersection between lines 2 and 3 is the needle entry site. A 100- to 150-mm 22-gauge insulated block needle is inserted perpendicular to the skin and advanced and redirected as
needed until an appropriate EMR is obtained at less than
0.5 mA. The depth of the nerve from the skin usually ranges from 7 to 15 cm. Twenty to 30 ml of local
anesthetic is injected after negative aspiration and absence
of paresthesia
SCIATIC NERVE BLOCK
CLASSIC POSTERIOR APPROACH
(LABAT TECHNIQUE)
Ultrasound-Guided Technique
After finding the piriformis muscle, the probe is moved further inferiorly. The ischium ends in a spiny protrusion, which is the ischial spine. With color Doppler one often will see the pudendal nerve and internal pudendal vessels close to the ischial spine. Lateral to the spine and superficial to the flat surface of the ischium, the sciatic nerve is seen in short axis with the
superior gemellus muscle underneath it. The easier
approach is to position the probe horizontally at the
level of the greater trochanter, which is a dome-shaped
hyperechoic rim with anechoic shadowing underneath.
More medially one will see the ischial tuberosity as another dome-shaped structure. Between these two shadows will be the sciatic nerve with gluteus maximus superficial and the gemellus deep to it. Moving the probe proximal to distal will bring the ischial spine into view. Inferior gluteal vessels will be seen close to the ischial tuberosity. Deep to the gemellus, one often sees
the capsule of the hip joint and the head of the femur just
outside the acetabular rim.
SCIATIC NERVE BLOCK
SUPINE LITHOTOMY APPROACH
RAJ TECHNIQUE
sciatic nerve is blocked at a more distal level, between
the ischial tuberosity and the greater trochanter
SCIATIC NERVE BLOCK
SUPINE LITHOTOMY APPROACH
(RAJ TECHNIQUE)
Surface Anatomy and Technique
The patient is in supine position with the extremity to be blocked supported by an assistant, in maximal hip flexion
and 90° knee flexion. Maximal flexion at the hip thins out
the gluteus maximus (GM) muscle and decreases redundant tissue on the buttock. If there is no help, alternatively, the foot can be tucked under the contralateral
thigh with some rotation at the knee level. This may reduce
the amount of stretch of the GM. The needle entry point is the midpoint of a line between the tip of the greater trochanter (GT) and ischial tuberosity (IT). A 100-mm insulated 22-gauge block needle is inserted perpendicular to the skin, advanced and redirected as needed
until an appropriate EMR is elicited at less than 0.5 mA.
SCIATIC NERVE BLOCK
SUPINE LITHOTOMY APPROACH
RAJ TECHNIQUE
The block can be done supine or in Sim’s position. A C2-5
MHz ultrasound probe positioned across the buttock will reveal the GT and IT and the sciatic nerve in between
SCIATIC NERVE BLOCK
ANTERIOR APPROACH
The sciatic nerve lies posterior to the muscles of the anterior compartment of the thigh, in the proximity of the lesser trochanter. The posterior cutaneous nerve of the thigh will be missed with this approach
SCIATIC NERVE BLOCK
ANTERIOR APPROACH
Surface Anatomy and Technique
The patient is placed supine with the lower extremities in
neutral position. A line is constructed between the anterior superior iliac spine and the pubic tubercle, marking
the reflection of the inguinal ligament. The second line is
constructed parallel to the first line, at the level of the
greater trochanter. In Beck’s approach, a perpendicular
line is drawn at the junction of the lateral two-thirds and
medial one-third of the first line to contact the second line. The needle entry site for Beck’s approach is the junction of the perpendicular and the second line. The block is performed with a 150-mm, 22-gauge insulated block needle as the nerve lies deep under the anterior thigh muscles. Often one encounters the branches
of the femoral nerve as the needle is advanced posteriorly,
with potential for injury. A nerve stimulator is used during the advancement to avoid injury to the femoral nerve. The sciatic nerve may not be encountered until a depth of 12 to 15 cm. Local anesthetic is injected when an appropriate EMR is obtained at less than 0.5 mA
SCIATIC NERVE BLOCK
ANTERIOR APPROACH
Limitations
Pain with bone contact, insertion via major muscles, and difficult landmarks in obese patients. sciatic nerve at this site lies posterior to the lesser trochanter and is not accessible to the needle using the direct anterior approach. Two strategies to overcome this limitation include the insertion of the needle at a more distal level (4 cm distal to
the lesser trochanter) and internal rotation of the foot
(femur) so the sciatic nerve moves medial to the lesser
trochanter
SCIATIC NERVE BLOCK
ANTERIOR APPROACH
Ultrasound-Guided Technique
positioned the patient supine, with the thigh externally rotated at ~ 45°, the hip and knee flexed, and scanned the proximal thigh approximately 8 cm distal to the inguinal crease.36 A C2-5 MHz probe is positioned at the inguinal crease and gradually moved inferiorly until the lesser trochanter is seen as a widening of the femoral circumference. One would see the femoral vessels and nerves more superficially and laterally. At the level where the adductor muscles meet the femur, the sciatic nerve is seen as a hyperechoic round or oval structure, posterior to the adductor magnus. The needle is inserted from the medial side of the thigh through the adductor muscles. Occasionally
branches of the obturator nerve may be encountered.
SCIATIC NERVE BLOCK
LATERAL APPROACH
The sciatic nerve is blocked in the subgluteal space, dorsal to the plane of the quadratus
femoris muscle, between the femur and ischial tuberosity. The other structures in the subgluteal space are the posterior cutaneous nerve of the thigh, the inferior
gluteal nerve and vessels, and the ascending branch of the
circumflex femoral artery.
SCIATIC NERVE BLOCK
LATERAL APPROACH
Surface Anatomy and Technique
The block is performed with the patient supine and the
hip in neutral position. The needle insertion site is 3 cm
distal to the point of maximum lateral prominence of the greater trochanter. The ischial tuberosity can be palpated with the nondominant hand. The needle is inserted perpendicular to the major axis of the limb and advanced toward the femur. Once it contacts the femur it is withdrawn slightly, redirected 20° under the femur, and advanced toward the ischial tuberosity. The sciatic
nerve is contacted at a depth of 8 to 12 cm. Local anesthetic solution is injected after appropriate EMR is obtained
SCIATIC NERVE BLOCK
POSTERIOR SUBGLUTEUS APPROACH
di BENEDETTO
approach blocks the nerve at a location the nerve overlies the adductor magnus muscle, is posterior to the lesser trochanter, and is~ 3 cm above the lower border of the gluteus maximus muscle
SCIATIC NERVE BLOCK
POSTERIOR SUBGLUTEUS APPROACH
(di BENEDETTO)
Surface Anatomy and Technique
The patient is placed in the lateral (Sim’s) position with
the operated side up. A line is drawn from the greater
trochanter to the ischial tuberosity and a second line is
drawn from the midpoint of this line, extending caudally
for 4 cm. The needle insertion site is the distal point of the second line. A stimulating 100-mm, 22-gauge insulated block needle is inserted perpendicular to the skin and advanced to elicit an appropriate EMR at less than
0.5 mA. In the midgluteal approach, the patient is placed in lateral decubitus with the operating site up and the entry point of the needle is 10 cm from midline, from the midpoint of the intergluteal sulcus. In the subgluteal approach, the entry point of the needle is in the subgluteal fold.
at 10 cm from midline
SCIATIC NERVE BLOCK
POSTERIOR SUBGLUTEUS APPROACH
(di BENEDETTO)
Ultrasound-Guided Technique
the greater trochanter, ischial tuberosity, and the sciatic
nerve in between, is gradually moved caudad on the posterior
thigh. The shadows of the hip joint will disappear and the nerve will move into an intermuscular cleft just medial to the femur. In this location it is covered by the lower end of the gluteus maximus, which is thin
SCIATIC NERVE BLOCK
INFRAGLUTEAL PARABICEPS APPROACH
The sciatic nerve is blocked at a site more distal to the classic Labat approach. Distal to the gluteus maximus, the sciatic nerve lies over the adductor magnus and is crossed obliquely in a mediolateral direction by the long head of the biceps femoris muscle. The sciatic nerve therefore lies further lateral and subsequently deep to the
long head of the biceps femoris. For a short distance of 3 to 4 cm, where the nerve is lateral to the long head of the biceps femoris,
SCIATIC NERVE BLOCK
INFRAGLUTEAL PARABICEPS APPROACH
Surface Anatomy and Technique
The surface landmarks for this approach are the lateral
border of the biceps femoris and the gluteal crease. The
lateral border of the biceps femoris muscle is identified by
asking the patient to flex the knee while resistance is
applied to the calf muscles. The site of needle insertion is
along the lateral border of the biceps femoris 1 cm caudal
to the gluteal crease. A 100-mm, 22-gauge insulated block needle is inserted at an angle of 70° to 80° to the skin with a cephalad and anterior orientation within the parasagittal plane. The femur lies lateral to the nerve and the biceps femoris is medial to the nerve. The needle is moved only in one plane from the lateral to medial, and redirected to elicit the appropriate EMR.
SCIATIC NERVE BLOCK
INFRAGLUTEAL PARABICEPS APPROACH
Ultrasound-Guided Technique
The patient is positioned prone and the biceps tendon is identified by asking the patient to flex the knee. A high frequency ultrasound probe is placed at the level of the gluteal crease or slightly below, and the sciatic nerve is identified at the lateral border of the biceps femoris, posterior to the muscle . An appropriate EMR at less than 0.5 mA may be used if needed
SCIATIC NERVE BLOCK
MID-THIGH APPROACH
ULTRASOUND-GUIDED TECHNIQUE
evaluated the mid-thigh approach under ultrasound guidance in a clinical and anatomic study. Biceps femoris, vastus lateralis, adductor magnus muscles, the lateral intermuscular septum between biceps femoris and vastus lateralis, and linea aspera were among the landmarks on the mid-thigh sonograms
The popliteal fossa
diamond-shaped area bound by
the semitendinosus and semimembranosus muscles medially, the biceps femoris muscle laterally, and by the two
heads of the gastrocnemius muscle inferiorly. The popliteal vessels, with the artery located deeper and anterior to the vein, are medial to the sciatic nerve.
The tibial nerve
immediately gives off the sural nerve and, at the level just above the sole of the foot, gives off the medial calcaneal. The tibial nerve then continues as the posterior tibial nerve that terminates into the medial plantar and lateral plantar nerves. nerve.
