Procedure
Supplies:
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Cleaning solution
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Chlorhexidine gluconate or povidone iodine
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Sterile equipment
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Gloves
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Dressing
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Drapes
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Imaging
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Ultrasound machine with a linear transducer (8 to 14 MHz), sterile sleeves, and gel
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Fluoroscopy equipment
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Local anesthetic
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Various percentages of local anesthetic given in a 3, 5, or 10 cc syringe for subcutaneous injection to provide patient comfort
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Regional block test solution
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Local anesthetic +/- steroids
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RFA needle and generator
Procedure Overview:
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Informed consent
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Appropriate positioning
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Cleaning with chlorhexidine and sterile drapes
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Anesthetize the overlying skin with local anesthetic for patient comfort
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RFA needle insertion
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Lesioning needles ranging from 4 mm to 10 mm
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Stimulation testing: Goal is for sensory stimulation without eliciting motor and proprioceptive responses
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Radiofrequency ablation configuration
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There are no universal settings for temperature or duration of traditional RFA.
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Pulsed radiofrequency temperatures can range from 40 to 60°C for 180 s.
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Consider risks and benefits when choosing between RFA or pulsed radiofrequency.
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Lumbar plexus
General: The lumbar plexus extends from T12 to L5 and innervates everything from the trunk to the lower extremities. The L1–4 spinal nerve roots specifically innervate the lower extremity via the femoral, obturator, and lateral femoral cutaneous nerves and are the focus of this chapter. Given the large and critical role of the lumbar plexus, neurolysis is only considered in cases of palliative oncological pain and has only been done with the aid of computed tomography. However, ultrasound-guided blockade of the lumbar plexus for surgical pain is a well-established modality of perioperative pain control, and the usage of ultrasound guidance as a potential adjunct for radiofrequency ablation is possible.
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Nerve Anatomy ( Fig. 14.1 ):
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Function
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Motor
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Psoas major, quadratus lumborum, lumbar transverse muscles (direct innervation)
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Quadriceps femoris, sartorius, pectineus, iliacus, articularis genu (via femoral nerve)
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Adductor longus, adductor brevis, adductor magnus, gracilis and obturator externus (obturator nerve)
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Transversus abdominis, internal oblique muscles (iliohypogastric and ilioinguinal nerves)
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Genitals (genitofemoral nerve)
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Sensory
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Skin on the anteromedial aspect of the thigh, leg, foot, hip, and knee joints (femoral nerve)
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Skin on the anterolateral aspect of the thigh (lateral femoral cutaneous nerve)
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Skin on the superolateral quadrant of the buttock (iliohypogastric nerve)
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Skin over the femoral triangle (proximal and medial aspects of the thigh), anterior part of the scrotum, mons pubis, and labia majora (ilioinguinal nerve)
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Skin over the femoral triangle, scrotum, and labia majora (via genitofemoral nerve)
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Origin: T12–L5 with L1–4 spinal nerve roots specifically innervating the lower extremity
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Pathway :
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L1–4 nerve roots exit their individual intervertebral foramina
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Upon exiting the nerves lie between the anterior and posterior portions of the psoas major muscle.
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A subset of the population may have the nerves run between the posterior border of psoas major and the anterior border of quadratus lumborum.
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Within the psoas major muscle, the ventral rami divide into the anterior and posterior branches which then reunite to give rise to the individual peripheral nerves.
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At the level of the L4–5 transverse process:
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L1–2 make up the genitofemoral nerve.
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L2–3 form the lateral femoral cutaneous nerve located lateral to psoas major.
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The obturator nerve receives fibers from L2–4 and is situated medial to the psoas muscle.
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The femoral nerve receives fibers from L2–4 and is found between the obturator and lateral femoral cutaneous nerve.
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Fig. 14.1
Illustration demonstrating the lumbar plexus and its associated branches.
((courtesy Netter Atlas of Human Anatomy 2006). From: Netter, FH. Atlas of Human Anatomy . Philadelphia, PA: Saunders/Elsevier, 2006. Image 49314.)
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Lumbar Plexus (Shamrock Method)
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Technique
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Patient position ( Fig. 14.2 )
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The patient is placed in the supine position with the legs in the neutral position.
Fig. 14.2
Demonstration of optimal patient position, needle approach, and ultrasound image demonstrating the shamrock configuration. (TR.P = transverse process, V = vertebral body, PS = psoas muscle, ES = erector spinae muscle, QL = quadratus lumborum muscle, AW = abdominal wall, P = peritoneum, n = needle.
(From: Saranteas T, Anagnostopoulos D, Kostroglou A, Souvatzoglou R. The “Shamrock method” for ultrasound-guided lumbar plexus nerve block in the supine position. J Clin Anesth . 2021;71:110249.)
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Transducer position ( Fig. 14.2 )
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A curvilinear transducer is placed at the flank just cranial to the iliac crest to identify the shamrock configuration made up of the psoas muscle, quadratus lumborum, and erector spinae.
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Ultrasound image ( Fig. 14.2 )
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The image demonstrates the needle trajectory as it enters the psoas muscle anterolaterally towards the posteromedial segment of the intrapsoas compartment which is the typical anatomic position of the lumbar plexus. Given difficulty in direct visualization of the nerves electrical nerve stimulation often used to aid in localization.
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Sciatic nerve
General: The sciatic nerve is the primary terminal branch of the sacral plexus and extends from the inferior aspect of the piriformis muscle in the gluteal region until it diverges into the tibial and common peroneal nerve at the apex of the popliteal fossa in the distal posterior thigh. Though rarely a target for ablation, case reports have demonstrated ablation being used to successfully treat intrinsic sciatic neuropathic pain, cancer pain, piriformis syndrome, complex regional pain syndrome, and phantom limb pain. ,
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Nerve Anatomy ( Fig. 14.3 ):
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Nerve roots: S1–3 spinal nerves
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Pathway
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Exits the pelvis via the greater sciatic foramen.
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Descends caudally into the gluteal region on the ventral surface of the piriformis muscle.
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Continues caudally down the dorsal surface of the hip rotator muscles (i.e., superior gemellus, tendon of the obturator internus, inferior gemellus, and quadratus femoris) and ventral to gluteus maximus.
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The sciatic nerve then enters the thigh passing between the lateral border of the ischial tuberosity and the medial border of the posterior surface of the greater trochanter.
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In the thigh the sciatic nerve runs posterior to the adductor magnus muscle and below the biceps femoris muscle.
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The sciatic nerve then enters the popliteal fossa where it branches into the tibial and common peroneal nerves.
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Nerve function
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Motor
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Tibial division
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Long head of biceps femoris, semitendinosis, semimembranosus
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Peroneal division
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Short head of biceps femoris
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Tibial nerve
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Gastrocnemius, soleus, popliteus, flexor digitorum longus, flexor hallucis longus, tibialis posterior
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Superficial peroneal nerve
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Peroneus longus, peroneus brevis
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Deep peroneal nerve
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Extensor digitorum longus, extensor hallucis longus, tibialis anterior, peroneus tertius
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Medial plantar nerve
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Flexor digitorum brevis, abductor hallucis, flexor houses brevis, first lumbrical
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Lateral plantar nerve
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Abductor digiti quinti, quadratus plantae, flexor digitorum minimi brevis, abductor houses, second third fourth lumbricals, dorsal plantar, and dorsal interossei
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Deep peroneal
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Extensor digitorum brevis, extensor pollicis brevis
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Sensory
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Posterior aspect of the knee
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Hamstring muscles
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Entire lower limb below the knee, with exception of the medial leg and foot (supplied by the saphenous nerve)
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Skin of the posterior thighs applied to the posterior femoral cutaneous nerve, which is spared by the sciatic nerve block due to the nerve course
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Fig. 14.3
Illustration demonstrating the sciatic nerve course and cutaneous innervation.
((courtesy Netter Atlas of Human Anatomy 2006). From: Netter, FH. Atlas of Human Anatomy . Philadelphia, PA: Saunders/Elsevier; 2006. Image 49302.)
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Technique
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Sciatic nerve anterior approach
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Patient position ( Fig. 14.4 )
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Supine
Fig. 14.4
Transducer position with surface landmarks and ultrasound image. A. Patient is positioned supine with thigh abducted and externally rotated. Surface landmarks demonstrating the location of the inguinal crease and level of the greater trochanter with an imaginary line connecting the inguinal crease to the center of the thigh at the level of the greater trochanter. B. Ultrasound position on the thigh which can be placed on the cneter point of the line and move medial and lateral until lesser trochanter is visualized. C. Ultrasound image demonstrating the sciatic nerve in between the AMM and GMM just lateral to the lesser trochanter. (ABM – adductor brevis muscle; ALM; adductor longus muscle; AMM – adductor magnus muscle. FV, femoral vessel. GMM, gluteus maximus muscle. SN, Sciatic Nerve).
(From: Benzon H, Raja SN, Fishman S, et al., eds. Essentials of Pain Medicine , 3rd edn. Philadelphia: Saunders; 2011:607–620.)
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Transducer position ( Fig. 14.4 )
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Anterior approach transverse on the proximal medial thigh
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Ultrasound ( Figs. 14.4 )
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With the ultrasound placed in the groin the sciatic nerve can be seen medial to the femur underneath the adductor magnus and generally overlying the adductor magnus muscle. The nerve is very deep in this approach (6 to 8 cm) and requires a 10-cm or greater needle.
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Sciatic nerve posterior approach
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Subgluteal approach
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Patient position ( Fig. 14.5 )
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The lateral position involves putting the patient on their contralateral side with slight flexion of the leg at the hip to extend the gluteus maximus and superficial tissue.
Fig. 14.5
( A) Patient is positioned lateral for the subgluteal approach with anatomic landmarks greater trochanter and ischial tuberosity labelled. (B) Ultrasound image showing the greater trochanter (GT), gluteus maximus (GM), sciatic nerve (SN), and ischial tuberosity (IT). (C) Image demonstrating curvilinear ultrasound probe placement. (D) Needle guidance to the sciatic nerve.
(From: Goldsmith AJ, Liteplo A, Hayes BD, Duggan N, Huang C, Shokoohi H. Ultrasound-guided transgluteal sciatic nerve analgesia for refractory back pain in the ED. Am J Emerg Med . 2020;38(9):1792-1795.)
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Transducer position ( Fig. 14.5 )
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The transducer is placed on the lateral leg between the ischial tuberosity (IT) and greater trochanter (GT).
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Ultrasound image ( Fig. 14.5 )
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The ultrasound reveals the sciatic nerve as the hyperechoic oval below the gluteus maximus muscle, lateral to the ischial tuberosity and medial to the femur.
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Transgluteal
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Patient position ( Fig. 14.6 )
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The patient is placed prone on their stomach.
Fig. 14.6
( A, B) This patient is positioned supine for the subgluteal approach with the linear transducer placed in the gluteal crease. (C) Ultrasound image from a linear probe revealing sciatic nerve between semitendinosus and long head of the biceps femoris muscle, superficial to the adductor magnus muscle.
(From: Gray AT. Sciatic nerve block. In: Gray AT, ed. Atlas of Ultrasound-Guided Regional Anesthesia . 3rd ed. Elsevier; 2019:179-188.)
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Transducer position
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The transducer is placed transversely in the gluteal crease on the posterior thigh proximally; however, the nerve can be identified at any point in the posterior thigh and popliteal crease and followed to the point of planned intervention.
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The sciatic nerve runs deep requiring a 10-cm needle, and the nerve is best approached in-plane.
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Ultrasound image ( Fig. 14.6 )
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Proximally the sciatic nerve can be identified lateral to the ischial tuberosity, however, as it runs distally it descends into the crease between the semitendinosus muscle and long head of the biceps femoris muscle down the leg as it descends towards the leg before splitting above the popliteal fossa.
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Femoral nerve
General: The femoral nerve is the largest terminal branch of the lumbar plexus and is responsible for sensation to the anterior and medial thigh, peripatellar region and medial aspect of the lower leg, and most importantly to the hip, knee, and ankle joints. Unfortunately, the femoral nerve provides motor innervation to a variety of critical motor muscles and is not a candidate for direct ablation outside of extreme circumstances such as terminal cancer or in the treatment of phantom limb pain. RFA is more commonly performed on distal branches such as the articular nerves of the hip for treatment of intractable hip pain, , the genicular nerves that include branches of the femoral nerve, as well as the saphenous nerve.
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Nerve Anatomy ( Fig. 14.7 ):
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Nerve roots: L2–4
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Nerve function
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Motor: innervates anterior thigh muscles
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Hip flexors (pectineus, iliacus, sartorius)
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Knee extensors (quadriceps, rectus femoris, vastus medialis, vastus lateralis, vastus intermedius)
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Sensory
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Anterior cutaneous branches of femoral nerve
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Anteromedial thigh
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Peripatellar region
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Medial aspect of the lower leg
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Saphenous nerve
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Medial aspect of the lower leg and leg and foot
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Anterior knee via the infrapatellar nerve off the saphenous
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Articular branches: hip joint
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Pathway
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Arises from the ventral rami of the lumbar plexus (L2–4)
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Travels inferiorly through the psoas major muscle.
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Gives off branches to the iliacus and pectineus muscles.
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Passes beneath the inguinal ligament and enters the femoral triangle with the femoral artery and vein in the femoral sheath.
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Below the inguinal ligament the nerve divides into the anterior and posterior divisions.
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Anterior
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Anterior cutaneous branches
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Branch to sartorius
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Branch to pectineus
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Posterior branches
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Saphenous nerve
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Branches to quadriceps femoris
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Fig. 14.7
Illustration demonstrating the femoral nerve course, branches, and cutaneous innervation.
(From: Netter, FH. Atlas of Human Anatomy . Philadelphia, PA: Saunders/Elsevier; 2006. Image 4445.)
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Technique:
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Patient position ( Fig. 14.8 )
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Supine with proximal thigh and lateral groin exposed
Fig. 14.8
(A) Demonstration of proper transducer and needle placement over the inguinal crease. (B) Ultrasound image demonstrating location of the femoral nerve below the fascial iliaca and medial to the femoral artery.
(From: Shastri U, Kwofie K, Salviz EA, Xu D, Hadzic A. Lower extremity nerve blocks. In: Benzon HT, Rathmell JP, WU CL, Turk DC, Argoff CE, Hurley RW, eds. Practical Management of Pain . 5th ed. Elsevier; 2014:732-744.e2.)
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Transducer position ( Fig. 14.8 )
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The transducer is placed transversely on the femoral crease over the pulse of the femoral artery and near the femoral ligament.
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Ultrasound image ( Fig. 14.8 )
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The ultrasound image shows the femoral nerve directly lateral to the femoral artery and vein as they traverse below the inguinal ligament.
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Obturator nerve
General: The obturator nerve is responsible for sensory innervation to the posteromedial distal thigh, osseus innervation of the pelvis and femur, as well as sensation of the hip and knee joint via articular branches. Direct ablation of the obturator nerve is not considered outside of extreme circumstances with no proper studies evaluating its efficacy outside of diagnostic blocks in the treatment of hip pain. However, ablation of the obturator nerve can be considered when it is a source of persistent pain in the situations of cancer, trauma, or neuropathy.
Nerve Anatomy ( Fig. 14.9 )
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Nerve roots: L2–4
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Function
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Motor
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Muscular branches to the adductor muscles of the thigh
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Sensation
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Cutaneous sensory innervation of the posteromedial distal thigh
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Sensory innervation of the adductor muscles of the thigh
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Articular branches to the hip joint and posterior capsule of the knee joint
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Osseus innervation of the pelvis and femur
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Pathway
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The obturator arises from the ventral rami of the L2–4 spinal nerves and forms within the psoas muscle.
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It emerges from the posterior border of the psoas major muscle and descends along the lateral wall of the pelvis toward the superior part of the obturator foramen.
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Distally, the nerve courses within the interfascial plane ventral to obturator externus and dorsal to pectineus.
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Obturator enters the adductor compartment of the proximal thigh through the obturator foramen and divides into:
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Anterior division
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Initially courses in the interfascial plane between pectineus and adductor brevis muscle
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Continues between adductor longus and the adductor brevis muscles
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At the inferior border of the adductor longus within the apex of the femoral triangle, the distal continuation of the anterior division typically communicates with the medial cutaneous and saphenous branches of the femoral nerve to form a subsartorial plexus that supplies the skin on the medial side of the thigh.
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Posterior division
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Courses between adductor brevis and adductor magnus
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The posterior branch of the obturator nerve descends between the adductor brevis and adductor magnus and enters the popliteal fossa (as the distal genicular branch) from the posterior surface of the adductor magnus muscle, the adductor hiatus, or through the distal 1 cm of the adductor canal.
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Within the popliteal fossa, the genicular branch anastomoses with branches of the tibial nerve to form the posterior popliteal plexus, which provides sensory innervation to the menisci, perimeniscal and posterior joint capsule, cruciate ligaments, as well as the infrapatellar fat pad.
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Technique ,
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Patient position ( Fig. 14.10 )
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Supine with target leg slightly abducted with proximal thigh and groin exposed
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