++
Selective obturator nerve block was first described by Labat in
1922.1 More interest in obturator nerve block emerged a
few years later when Pauchet, Sourdat, and Labat stated, “obturator nerve
block combined with blocks of the sciatic, femoro-cutaneous nerves,
anesthetized the entire lower limb.” However, a lack of clear anatomic
landmarks, the block complexity, and inconsistent results were the reasons
why this block had been used infrequently. Historically, Labat's classical
technique remained forgotten until 1967, when it was modified by
Parks.2 In 1993, the interadductor approach was described
by Wassef,3 which was further modified by Pinnock in
1996.4 In 1973, Winnie introduced the concept of the
“3-in-1 block,” an anterior approach to the lumbar plexus using a simple
paravascular inguinal injection to anesthetize the femoral, lateral
cutaneous nerve of the thigh and obturator nerves.5 Since
its description however, many studies have refuted the ability of the 3-in-1
block to reliably block the obturator nerve with this technique. However,
with the introduction of modern nerve stimulators, selective blockade of the
obturator nerve has become more reliable and has seen a resurgence of
interest in recent times.
++
Obturator nerve block is used to treat hip joint pain and is used in
the relief of adductor muscle spasm associated with hemiplegia or
paraplegia. Muscle spasticity is a relatively common problem among patients
suffering from central neurologic problems, such as cerebrovascular
pathology, medullar injuries, multiple sclerosis, and infantile cerebral
palsy. Spasticity of the adductor muscle induced via the obturator nerve
plays a major role in associated pain problems and makes patient grooming
and mobilization very difficult. Obturator block, tenotomies, cryotherapy, botulin toxin
infiltration, surgical neurolysis, and muscle interpositions all have been
suggested to remedy this problem.6–9 A number of
diagnostic or therapeutic procedures on the knee and thigh can be performed
by combining obturator nerve block with block of the sciatic, lateral
cutaneous nerve and femoral nerves. Common clinical practice is to combine a
sciatic nerve with the femoral nerve block for surgical procedures distal to
the proximal third of the thigh. When deemed necessary, addition of a
selective obturator nerve block may reduce intraoperative discomfort,
improve tourniquet tolerance, and improve the quality of postoperative
analgesia in these cases.
++
Obturator nerve block is also occasionally used in urologic surgery to
suppress the obturator reflex during transurethral resection of the lateral
bladder wall. Direct stimulation of the obturator nerve by the resector as
it passes in close proximity to the bladder wall results in a sudden,
violent adductor muscle spasm. This is not only distracting to the surgeon,
but also potentially dangerous, increasing the risk of serious complications
such as bladder wall perforation, vessel laceration, incomplete tumor
resection, and obturator hematomas.10,11 Prevention
strategies include muscle relaxation, reduction in the intensity of the
resector, the use of laser resectors, shifting to saline irrigation,
peri-prostate infiltrations, and/or endoscopic transparietal
blocks.12–16 However, a selective obturator nerve block
remains the safest and most effective alternative to this
problem.17–22
++
++
Neurolytic blockades with alcohol or phenol, performed with the help of
a nerve stimulator and/or radioscopy, result in a cost-effective and
effective reduction of muscle spasms.3,9,23–26 The
main drawback to neurolytic blockade is its temporal duration and the need
to repeat the blockade when the previous block wears off. Selective
obturator nerve block has also been used in the diagnosis and treatment of
chronic pain states secondary to knee arthrosis or pelvic tumors resistant
to conventional analgesic approaches.27–31
++
Patient refusal, inguinal lymphadenopathy, perineal infection, or
hematoma at the needle insertion site are typical contraindications to obturator
nerve blockade.
++
Preexisting obturator neuropathy, clinically manifested by groin pain,
pain of the posteromedial aspect at the thigh and occasionally paresis of
the adductor group of muscles, are relative contraindications to this block.
Obturator nerve blocks should be avoided in the presence of a coagulopathy.
++
The obturator nerve is a mixed nerve, which, in most cases, provides
motor function to the adductor muscles and cutaneous sensation to a small
area behind the knee. It is derived from the anterior primary rami of L2, L3
and L4 (Figure 34–1). On its initial course, it runs within the
psoas major muscle. Taking a vertical course, it emerges from the inner
border of the psoas, staying medial and posterior at the pelvis until it
crosses at the level of the sacroiliac joint (L5) under the common iliac
artery and vein and runs anterior/lateral to the ureter (Figure
34–2). At this level, it courses close to the wall of the bladder on its
inferior/lateral portion and then it takes place anterior to the obturator
vessels within the superior part of the obturator foramen, exiting the
pelvis below the pubic superior branch. In its intrapelvic course, the
obturator nerve is separated from the femoral nerve by the iliopsoas muscle
and iliac fascia. It innervates the parietal peritoneum on the lateral
pelvic wall and contributes collateral branches to the obturator externus
muscle and the hip joint. It leaves the pelvis by passing through the
obturator canal before entering the adductor region of the thigh
(Figure 34–3). Here, 2.5–3.5 cm after leaving the obturator
foramen, the obturator nerve divides into its two terminal branches,
anterior and posterior, providing innervation to the hip adductor
compartment (see Figure 34–3).32
++
++
++
++
The anterior branch descends behind the
pectineus and adductor longus and in front of the obturator externus and
adductor brevis. It gives muscular branches to the adductor longus, adductor
brevis, gracilis, and occasionally the pectineus, and it terminates as a
small nerve that innervates the femoral artery (Figure 34–4). In
20% of subjects, it contributes a branch, which anastamoses with branches
of the femoral nerve and forms the subsartorial plexus, from which sensory
branches emerge to supply sensation to posteromedial aspect of the inferior
third of the thigh. The anterior branch contributes articular branches to
anteromedial aspect of the hip joint capsule (Figure 34–5) but
does not innervate the knee joint.
++
++
++
The posterior branch descends between the
adductor brevis in front and the adductor magnus behind. It terminates by
passing through the adductor hiatus to enter the popliteal fossa, supplying
the posterior aspect of the knee joint and the popliteal artery. During its
course, the posterior branch sends muscular branches to the obturator
externus, the adductor magnus, and occasionally the adductor brevis muscles
(see Figure 34–4).
++
Cutaneous innervation by the obturator nerve varies according to the authors
and is illustrated in Figure 34–6.
++
++
++
Numerous variations to the formation, course, and distribution of the
obturator nerve can have clinical implications. For instance, in 75% of
cases, the obturator nerve divides into its two terminal branches as it
passes through the obturator canal. In 10% of cases, this division occurs
before the nerve reaches the obturator canal; in the remaining 15% of
cases, after entering the thigh.
++
Occasionally, the anterior and posterior branches descend through the
thigh behind the adductor brevis. Note that the sensory cutaneous branch of
the obturator nerve is often absent.
++
Up to 20% of subjects possess an accessory obturator nerve that can be
formed from variable combinations of the anterior rami L2-L4 or emanate
directly from the trunk of the obturator nerve.33 It
accompanies the obturator nerve as it emerges from the medial border of the
psoas but unlike the obturator, passes in front of the superior pubic ramus
to supply a muscular branch, the pectineus. It contributes articular branches
to the hip joint and terminates by anastomosing with the obturator nerve
itself.
++
To perform a block, the following equipment is required:
++
-
Nerve stimulator
-
Insulated stimulating needle (5–8 cm, depending on the approach chosen)
-
Local anesthetic: 1% mepivacaine (onset of motor block 15 minutes,
duration 3–4 hours) or 0.75% ropivacaine (onset of motor block 25
minutes, block duration 8–10 hours)
-
Sterile fenestrated drape
-
Marking pen
-
Ruler
-
A 10-mL syringe
-
Disinfectant
- Sterile gloves
++
Anatomic landmarks vary depending on the chosen approach.
The following landmarks are useful regardless of the
approach chosen (Figure 34–7):
++
- Bony landmarks: Anterior and superior iliac spine and pubic tubercle, inguinal ligament
- Vascular landmarks: Femoral artery, femoral crease
- Muscular landmarks: Tendon of the long abductor muscle
++
++
Several methods can accomplish block of the obturator nerve. These
approaches can be grouped into plexus block techniques where the obturator nerve is blocked along
with other components of the lumbosacral plexus and specific single-nerve block techniques for the
obturator nerve.
+++
Plexus Block Techniques
++
Several approaches have been described; however, the lumbar plexus
block via the posterior approach (in the psoas compartment) is the only
technique that ensures an acceptable success rate of obturator nerve
blockade.
+++
3‐in-1 Block Technique
++
Based on the theoretical existence of a suprainguinal compartment, in
1973 Winnie described the lumbar plexus block by an anterior approach or the
3 in 1.5 According to the 3-in-1 concept, a large volume
of local anesthetics is injected over the femoral nerve to spread underneath
the fascia iliaca. When combined with distal compression, the local
anesthetic spreads proximally reaching the lumbar plexus. Unfortunately,
several studies have repeatedly failed to demonstrate the reliability of
this technique to obtain a block of the lumbar plexus or the obturator
nerve.5,34–36 In addition, studies in human cadavers
have documented the absence of a fluid-conducting compartment that would
allow such an extensive proximal spread of the local
anesthetic.37 For these reasons, the 3-in-1 technique
results in anesthesia of the cutaneous branches of the obturator nerve. This
is because the local anesthetic spread laterally or medially, rather than
proximally, as once thought. Of note, increasing the volume of injectate
does not increase the spread toward the lumbar plexus; no differences were
found when local anesthetic injection volumes of 20 or 40 mL were
compared.38 Theoretically, catheters inserted by an
inguinal approach can ascend toward the psoas compartment, however, only a
minor percentage (23%) of catheters can be reliably
positioned.39,40
+++
Iliofascial Block Technique
++
Dalens first described this approach in 1989 for use in pediatric
patients.41 Following Winnie's reasoning for the 3-in-1
block, he took a more lateral approach and reported a 100% success rate
for femoral and femorocutaneous nerve blockade and 88% success rate for
the obturator nerve. However, follow-up studies in adults did not confirm
these results.39,42 In adults, the iliofascial approach
allows more successful blockade of the lateral femorocutaneous nerve when
compared with the 3-in-1 technique. However, the obturator nerve remains
spared.42,43
+++
Psoas Compartment Block
++
Since Winnie's description of the posterior approach to the lumbar
plexus in 1974 (psoas compartment block), numerous modifications of the
technique have been described.43,44–47 The obvious
advantage is the ability to obtain a complete lumbar plexus block with a
single injection. Indeed, studies have demonstrated femoral nerve block
close to 100% plexus block with this technique, whereas femorocutaneous
and obturator nerve blocks are anesthetized 88–93% of the
time.48,49
+++
Parasacral Sciatic Block
++
Mansour initially described this technique in 1993 with the objective
of achieving a more complete sciatic nerve block.50,51
Since this technique is a true plexus block, it provides more consistent
anesthesia of all branches of the sciatic nerve. It successfully blocks the
posterior cutaneous nerve of the thigh, the gluteal superior and inferior
nerves, and the pudendal nerve. In addition, the splanchnic nerves, the
inferior hypogastric plexus, the proximal portion of sympathetic trunks, and
the obturator nerve are located close to the point of injection. Thus, a
blockade of all these nervous structures would be theoretically achievable
with a single injection. However, recent anatomic and clinical studies
suggest that the parietal peritoneum and the pelvic fascia surrounding the
sacral plexus are anatomically separated from the obturator nerve that runs
along the medial border of the psoas. Consequently, although the parasacral
approach to sciatic nerve block should result in a complete block of the
sacral plexus, the obturator nerve may be spared.52
+++
Selective Block Techniques
+++
Labat's Classic Technique
++
Labat's classic approach was the most popular technique before the
development of new approaches that are more easy to perform and less
uncomfortable to patients. Originally described as a paresthesia method, the
advent of nerve stimulation has increased the effectiveness and reduced
patient discomfort, complications, and number of needle insertions. The
procedure sequence consists of five phases, depicted in Figure
34–8.
++
++
Nerve stimulation is begun using a current intensity of 2–3 mA (2 Hz,
0.1–0.3 msec) and reduced to 0.3–0.5 mA before injection of local
anesthetic. The patient lies supine, with the limb to be blocked at 30
degrees abduction. The pubic tubercle is identified by palpation, and a
1.5-cm long line is drawn laterally and caudally; the injection insertion
site is labeled at the tip of the end of the caudal line (Figure
34–9). The classical approach consists of carrying out three consecutive
movements of the needle until the tip of the needle is placed over the top
of the obturator foramen, where the nerve runs before splitting into its two
terminal branches. With a 22-gauge, 8-cm long needle, the skin is penetrated
perpendicularly and the needle is advanced until it makes contact with the
inferior border of the superior pubic branch at a depth of 2–4 cm. During
the second phase, the needle is slightly withdrawn and then slipped along
the anterior pubic wall (another 2–4 cm). After this, it is redirected
anteriorly/posteriorly. Finally, the needle is withdrawn again and slightly
redirected (cephalically and laterally) at an angle of 45 degrees for
another 2–3 cm until contractions of the thigh adductor muscles are
observed.
++
++
This technique can be simplified by eliminating the second movement of the
needle. Hence, after making contact with the pubic branch, the needle can be
redirected 45 degrees laterally to the obturator foramen (see Figure 34–9).
+++
Paravascular Selective Inguinal Block
++
This technique consists of a selective block of the two branches of the
obturator nerve (anterior and posterior), performed at the inguinal level
and slightly more caudad than the previously described
techniques.53 The femoral artery and the tendon of the long
adductor muscle at the pubic tubercle are identified. For tendon
identification, extreme leg abduction is required (Figure 34–10).
A line is drawn over the inguinal fold from the pulse of the femoral artery
to the tendon of the long adductor muscle. The needle is inserted at the
mid-point of this line at an angle of 30 degrees anteriorly/posteriorly and
cephalically (Figure 34–11). By following the needle a few
centimeters in depth via the long adductor muscle, twitching responses from
the long adductor and gracilis muscles are easily detectable on the
posterior and medial aspect of the thigh. Subsequently, the needle is
inserted deeper (0.5–1.5 cm) and slightly laterally over the short adductor
muscle until a response from the major adductor muscle is obtained and can
be visualized on the posterior-medial aspect of the thigh. After needle
insertion, infiltration of 5–7 mL local anesthetic is recommended.
Occasionally, a more caudal division of the obturator nerve is found; hence,
the two branches are located within the same location at the inguinal fold,
and two different motor responses may be observed with a single stimulation
(injection).
++
++
++
+++
Choice of Local Anesthetic
++
Ten to 15 mL of local anesthetic are adequate in patients. The type and
concentration of the local anesthetic depend on the indication for the
block. For diagnostic–therapeutic blockades, highly concentrated neurolytic
solutions are used to achieve long-lasting blocks. In the literature,
combinations of phenol, ethanol, bupivacaine, levobupivacaine, and/or
steroids are well reported.3,9,23–26
++
For lower limb surgeries, the recommended anesthetic technique consists
of the administration of medium- to long-lasting local anesthetics that are
associated with adequate postoperative analgesia, such as bupivacaine
0.25–0.5%; ropivacaine 0.25–0.75%, and levobupivacaine
0.25–0.5%. To avoid adductor muscle spasms during transurethral surgery,
the use of medium to long local anesthetics is not required because the
surgery does not last more than 2 hours. Therefore, mepivacaine 1–2% or
lidocaine 1–2% should be adequate for this
purpose.17,54