Chapter 77 Blocks of the Lumbar Plexus and its Branches Flashcards
he roots of the lumbar
plexus
deeply located, coursing through the substance
of the psoas major muscle in their journey from the lumbar
paravertebral space to the lower extremity
The fasciae of the large psoas major muscle (anteriorly) and
quadratus lumborum muscle (posteriorly) invest the lumbar
plexus from its origin at the
anterior primary rami of
the L1, L2, L3, and L4 nerve roots
The proximal
part of the lumbar plexus supplies
the iliohypogastric and
ilioinguinal nerves, which are in series with the thoracic
nerves and innervate the lower trunk.
The iliohypogastric
nerve supplies
the skin of the buttock and the muscles of
the abdominal wall.
The ilioinguinal nerve supplies
the skin
of the perineum and adjoining inner thigh
The genitofemoral
nerve (from L1 and L2) supplies
the genital area
and adjacent thigh.
The three major components of the
lumbar plexus
(femoral, lateral femoral cutaneous, obturator nerves) soon divide and take widely divergent course down through the pelvis toward their ultimate destinations in the leg.
Of the three nerves, only the largest branch of the lumbar plexus, remains in close
proximity to the psoas muscle as it descends toward the leg
the femoral nerve
The lateral femoral cutaneous nerve leaves the lateral border of the
psoas major muscle at about its midpoint and
enters the lateral thigh at a very superficial level
The obturator
nerve leaves the medial border of the
psoas major muscle and enters the medial thigh at a deeper level, within the adductor muscle compartment.
The femoral nerve derives from the dorsal portions of
L2, L3, and L4,
femoral nerve course
descends from its origin to appear at the lateral margin of the psoas major at approximately the junction of the middle and lower thirds of that muscle. As the nerve continues on its descent toward the leg, it remains between the psoas major and the iliacus muscles so
that, proximal to the inguinal ligament, the femoral nerve is surrounded laterally by the iliacus fascia, medially by the fascia of the psoas major, and anteriorly by the transversalis fascia. Distal to the inguinal ligament, the fused iliopsoas fascia continues to provide a posterior and lateral wall to this compartment
The lumbar plexus
can also be blocked
using an anterior approach distal to the inguinal ligament (the inguinal paravascular technique) that attempts to block the three major nerves using a modification
of the standard femoral nerve block technique (3-in-1 block). The lumbar plexus
can also be blocked with a posterior approach or psoas
compartment block
LUMBAR PLEXUS BLOCK
INDICATIONS
Lumbar plexus block is indicated for surgeries of the thigh or knee, including above-the-knee amputation, as a diagnostic and therapeutic tool for chronic pain disorders, or to provide analgesia for painful conditions of the proximal
leg, including herpes zoster. It can also provide analgesia
following a variety of surgical procedures of the thigh or knee, including femoral shaft surgery, total knee and hip replacements, and open-reduction and internal fixation of
acetabular fractures.
LUMBAR PLEXUS BLOCK ADVANTAGES
reduce opioid
requirements as part of a multimodal analgesic regimen following total hip or knee arthroplasty. Blood loss following total hip arthroplasty is reduced using this
block when compared with general anesthesia
LPB Positioning
A posterior approach or psoas compartment block is typically
performed with the patient in the lateral decubitus position with the intended surgical site uppermost. The
upper thigh is flexed at the hip and the knee is flexed (i.e., Sim’s position).
LUMBAR PLEXUS BLOCK
LANDMARK
A line is drawn between the iliac crests (intercristal line) and another one is drawn through the
lumbar spinous processes. The posterior superior iliac
spine (PSIS) is identified and marked. A line is drawn, parallel
to that connecting the lumbar spinous processes from about L3 inferiorly, bisecting the PSIS. The site of needle insertion is where the parallel spinous line (or paraspinous line) bisects the intercristal line.
LUMBAR PLEXUS BLOCK
TECHNIQUE
a 4-inch, 22-gauge insulated regional block needle is advanced perpendicular
to all planes until the desired transverse process is encountered. The needle is then re-directed in a slightly cephalad direction and advanced slowly beyond the transverse process (not more than 2 cm after bony contact) until a quadriceps contraction is elicited, typically at a current of up to 0.5 mA. The usual volume of local anesthetic is 30 ml.
LUMBAR PLEXUS BLOCK
Complications
systemic local anesthetic toxicity
and retroperitoneal hematoma, unintended
epidural placement
The inguinal paravascular technique of lumbar plexus block (3-in-1 block)
With the patient in the supine position, the
lateral edge of the femoral arterial pulse is palpated about
1 to 2 cm distal to the inguinal ligament. A 22-gauge, 2-inch insulated regional block needle is advanced using
nerve stimulator guidance in a cephalad direction at about a 30º angle to the skin, with the needle entry point 1 cm lateral to the femoral artery. A quadriceps muscle response is sought at a current of up to 0.5 mA. Increasing the volume of LA from 20 to 40 ml (mepivacaine
1%) modestly increases the chances of blockade of the three nerves. Ropivacaine 0.25–0.5% and bupivacaine 0.25% provide similar degrees of analgesia following total knee replacement using a single-injection technique.
3-in-1 block indications
hip fracture
repair and knee arthroscopy
The major difference between 3-in-1 block and femoral nerve block
a larger volume of LA is used, providing a greater degree of muscle relaxation and a longer duration of postoperative analgesia
LUMBAR PLEXUS BLOCK
ULTRASOUND-GUIDED TECHNIQUE
Positioning
The patient is
positioned either in the sitting or lateral decubitus position
with the side to be blocked uppermost.
LUMBAR PLEXUS BLOCK
ULTRASOUND-GUIDED TECHNIQUE
Scanning
A lowfrequency
(4–5 MHz) curved array transducer ensures sufficient depth of imaging. An initial longitudinal paramedian scan allows precise identification of the intervertebral spaces. The probe is initially placed at the upper
end of the sacrum (seen as a continuous hyperechoic line),
just off the midline, in an oblique plane of imaging angulated
toward the midline, and slowly maneuvered in a
cephalad direction. The first “break” in this line represents the L5/S1 junction. The laminas of L5, L4, L3, and L2 are subsequently identified in a similar manner. The lower pole of the kidney can be found as caudally as L3/ L4 on deep inspiration. It is prudent, therefore, to continue to scan higher and laterally until the kidney is identified (hypoechoic oval-shaped structure) to avoid accidental
puncture. The probe is then positioned at the interspinous level where the block is to be placed and rotated 90° from a longitudinal to a transverse orientation
LPB
Important internal bony landmarks that
need to be identified include
the vertebral body, spinous process, articular process, and transverse process
LPB
Important soft tissue structures to be identified include
the erector spinae, quadratus lumborum, and psoas muscles. Deep (anterior) to the psoas muscle, the intraperitoneal
structures can be seen
targeted for LA injection
The roots that form the lumbar plexus are rarely imaged in adults but are known to run
through the posterior or middle third of the psoas muscle.
LUMBAR PLEXUS BLOCK US
Medial needle angulation is
best avoided to prevent
inadvertent subarachnoid injection
help locate the needle tip (the so-called hydrolocation technique).
Injecting 5% dextrose
(D5W) in 0.5 to 1 ml increments
LUMBAR PLEXUS BLOCK US
Needle technique
The needle should be advanced until its tip is positioned in the posterior third of the psoas muscle. A peripheral nerve stimulator can be used to confirm the position
by observing quadriceps contraction. After negative aspiration, the desired LA volume may be administered in divided doses and fluid and tissue expansion can be observed within the psoas muscle.
the lumbar plexus
may be successfully blocked using the “trident” acoustic
window
(the shadows of the transverse processes in the
longitudinal plane) as a landmark
Complications of continuous
techniques are similar to those occurring after single shot
blocks
femoral neuropathy and femoral nerve compression from a subfascial hematoma. Systemic toxic reactions to local anesthetic may also
occur from intravascular injection or from exceeding the
recommended local dosing limits. Arterial puncture and
intravascular catheter placement, although rare, do occur, as does epidural block from advancing the catheter too far in a cephalad direction
femoral nerve course
femoral nerve (L2–L4) courses from the lumbar plexus in the groove between the psoas major and iliacus muscles, where it enters the thigh by passing deep to the inguinal ligament. At the level of the groin crease, the femoral nerve lies anterior to the iliopsoas muscle and slightly lateral to the femoral artery. At or above the inguinal ligament, the femoral nerve divides into anterior and posterior divisions; Both divisions lie deep to the fascia iliaca.
femoral nerve innervations
the anterior division innervates the skin over the anterior thigh and supplies the sartorius muscle, and the posterior division innervates the quadriceps femoris muscle, the knee joint, and its medial ligament, and also is the division from which the saphenous nerve is derived. Therefore posterior division
block is essential for successful femoral nerve block
for procedures of the anterior thigh and knee. The two
divisions may lay one behind the other (as their names suggest, respectively), or side-by-side at the level of
the groin crease
Stimulation of the anterior division results in
muscle contraction of the medial thigh (sartorius twitch).
The branches from the anterior and posterior division are primarily
The branches from the anterior division are primarily sensory and the branches from the posterior division are primarily motor.
