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Lower Extremity Regional Anesthesia - Overview & Anatomy

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Authors

James Mattson, MD

Lower Extremity Neuroanatomy

Lumbosacral Plexus Overview

  • Lumbosacral Plexus
    • The lumbosacral plexus originates from the spinal nerves L1 to S4. It divides into four primary nerves that innervate the lower extremity: sciatic, femoral, obturator, and lateral femoral cutaneous. [1] Rodziewicz TL, Patel S, Garmon EH. Lower Extremity Blocks. StatPearls. 2020.  
      • Sciatic: supplies sensation to the posterior thigh via the posterior cutaneous nerve of the thigh, then divides into the tibial and common peroneal nerves which supply motor function to the lower leg and sensation to the anterior, lateral, and posterior regions of the leg. 
      • Femoral nerve: provides motor and sensory function to the anterior thigh, then continues as the saphenous nerve to provide sensation to the medial leg, foot, and great toe.
      • Obturator: provides sensation to the medial thigh and motor function to the adductors. 
      • Lateral femoral cutaneous: supplies sensation to the lateral thigh
lumbosacral plexus anatomy
Lumbosacral Plexus Anatomy[2], Image courtesy of wikipedia.org, “Lumbar Plexus”

Osteotomes of the lower extremity. [3] Courtesy of NYSORA. Accessed on 12/21/2022. https://www.nysora.com/topics/anatomy/functional-regional-anesthesia-anatomy/

Sciatic Nerve and Derivatives

Sciatic Nerve
  • The sciatic nerve is the largest peripheral nerve in the body, arising from nerve roots L4 to S3. In the gluteal region, this nerve lies lateral to the proximal tendons of semitendinosus-biceps and semimembranosus. 
  • The proximal sciatic nerve is composed of separate nerve fibers for the common peroneal and tibial nerve, which do not mix. They travel together in the same sheath until they bifurcate in the popliteal fossa. [4] Silvestri E, Martino F, Puntillo F. Ultrasound-guided peripheral nerve blocks. In: Silvestri E, Martino F, Puntillo F, eds. Ultrasound-Guided Peripheral Nerve Blocks. ; 2018. doi:10.2199/jjsca.28.103 [5] Gray AT. Lower Extremity Blocks. In: Gray AT, ed. Atlas of Ultrasound-Guided Regional Anesthesia. 3rd editio. ; 2014:144-232. doi:10.1016/B978-0-323-50951-0.00001-3 [6]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: A case series. Am J Emerg Med. … Continue reading
sciatic nerve anatomy
Sciatic Nerve Anatomy[7], Image courtesy of https://teachmeanatomy.info/, “The Sciatic Nerve”
Tibial Nerve
  • The tibial nerve is the largest branch of the sciatic nerve. It continues from the popliteal fossa in a straight course in the deep posterior compartment of the leg and travels posterior to the medial calcaneus with the tendons of posterior tibialis, flexor digitorum longus and flexor hallucis longus. In the foot, it branches into medial and lateral plantar nerves that supply sensory innervation to the heel region, sole of the foot, and all toes including nailbed. [8] Gray AT. Lower Extremity Blocks. In: Gray AT, ed. Atlas of Ultrasound-Guided Regional Anesthesia. 3rd edition. ; 2014:144-232. doi:10.1016/B978-0-323-50951-0.00001-3 [9] Yurgil JL, Hulsopple CD, Leggit JC. Nerve Blocks: Part II. Lower Extremity. Am Fam Physician. 2020;101(11):669-679. doi:10.1016/S1875-5364(20)30046-7
tibial nerve anatomy
Tibial Nerve Anatomy[10]Image courtesy of https://teachmeanatomy.info/,”Tibial Nerve”
Common Peroneal (Fibular) Nerve
  • The common peroneal nerve (L4-S2), also called the common fibular nerve, is one of the two major branches of the sciatic nerve. It bifurcates (along with the tibial nerve) just proximal to the popliteal fossa. It courses deep the biceps femoris and wraps towards the proximal fibular head. 
  • Inferior and lateral to the fibular head it bifurcates to the superficial and deep peroneal nerves [11]Hardin JM, Devendra S. Anatomy, Bony Pelvis and Lower Limb, Calf Common Peroneal (Fibular) Nerve. [Updated 2022 Oct 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 … Continue reading
tibial nerve anatomy

Bifurcation of the sciatic nerve and common peroneal nerve [12]Image courtesy of https://teachmeanatomy.info/,”Tibial Nerve”

Deep Peroneal (Fibular) Nerve
  • The deep peroneal nerve is a branch of the common peroneal nerve that supplies sensory innervation to the web space between the first and second toes. The deep peroneal enters the anterior compartment to travel down the leg with the anterior tibial artery. The deep peroneal nerve lies lateral adjacent to the anterior tibial artery in between the tibial and extensor hallucis longus muscle. [13] Silvestri E, Martino F, Puntillo F. Ultrasound-guided peripheral nerve blocks. In: Silvestri E, Martino F, Puntillo F, eds. Ultrasound-Guided Peripheral Nerve Blocks. ; 2018. doi:10.2199/jjsca.28.103 [14] Gray AT. Lower Extremity Blocks. In: Gray AT, ed. Atlas of Ultrasound-Guided Regional Anesthesia. 3rd edition. ; 2014:144-232. doi:10.1016/B978-0-323-50951-0.00001-3
deep fibular peroneal nerve anatomy
Deep Peroneal (Fibular) Nerve Anatomy (green)[15]Image courtesy of https://teachmeanatomy.info/,”The Deep Fibular Nerve”
Superficial Peroneal (Fibular) Nerve
  • The superficial peroneal nerve is a branch of the common peroneal nerve that arises at the head of the fibula. It provides sensory innervation to the anterior ankle and dorsum of the foot. It emerges from the fibular head in the lateral (70% of the time) or anterior compartment (30%) and travels along the muscular compartment before emerging through the fascia lata into the subcutaneous tissue of the lateral leg. [16] Gray AT. Lower Extremity Blocks. In: Gray AT, ed. Atlas of Ultrasound-Guided Regional Anesthesia. 3rd edition. ; 2014:144-232. doi:10.1016/B978-0-323-50951-0.00001-3
deep fibular peroneal nerve anatomy
Superficial Peroneal (Fibular) Nerve Anatomy (blue)[17]Image courtesy of https://teachmeanatomy.info/,”The Deep Fibular Nerve”
Sural Nerve
  • The sural nerve supplies sensory innervation to the lateral foot and fifth toe. It derives from the medial sural cutaneous nerve, a terminal branch of the tibial nerve, and the lateral sural cutaneous nerve, a terminal branch of the superficial peroneal nerve. They combine in the distal third of the posterior leg, and the combined nerve then travels posterolaterally between the two heads of the gastrocnemius. It joins the small saphenous vein in a fascial compartment in the lateral leg. It then travels posterior to the lateral malleolus to the lateral foot. [18] Gray AT. Lower Extremity Blocks. In: Gray AT, ed. Atlas of Ultrasound-Guided Regional Anesthesia. 3rd edition. ; 2014:144-232. doi:10.1016/B978-0-323-50951-0.00001-3 [19]Cisewski DH, Alerhand S. ‘SCALD-ED’ Block: Superficial Cutaneous Anesthesia in a Lateral Leg Distribution within the Emergency Department – A Case Series. J Emerg Med. 2019;56(3):282-287. … Continue reading

Sural Nerve coverage [20]Image courtesy of https://pivotalmotion.physio/,”WHAT IS THE SURAL NERVE?”

Femoral Nerve and Derivatives

Femoral
  • The femoral nerve is made up from dorsal divisions of anterior rami from L2, L3, and L4. This nerve provides motor innervation to pectineus, sartorius, and quadriceps. Distal sensory nerve branches include the anterior cutaneous nerve of the thigh, the infrapatellar nerve and the saphenous nerve. These provide sensation to the anterior thigh, medial leg, and arch of foot. The femoral nerve travels in between the psoas and iliacus muscles proximal to the inguinal ligament, then anterior to the iliopsoas muscle before passing underneath the inguinal ligament. It lies lateral to the femoral artery and is usually oval or triangular in shape. [21] Silvestri E, Martino F, Puntillo F. Ultrasound-guided peripheral nerve blocks. In: Silvestri E, Martino F, Puntillo F, eds. Ultrasound-Guided Peripheral Nerve Blocks. ; 2018. doi:10.2199/jjsca.28.103 [22] Ghisi D, Delaunay L, Fanelli A. Use of ultrasound for lower extremity. Curr Opin Anaesthesiol. 2014;27(5):528-537. doi:10.1097/ACO.0000000000000119 [23] Gray AT. Lower Extremity Blocks. In: Gray AT, ed. Atlas of Ultrasound-Guided Regional Anesthesia. 3rd edition. ; 2014:144-232. doi:10.1016/B978-0-323-50951-0.00001-3
femoral nerve anatomy
Femoral Nerve Anatomy[24]Image courtesy of https://teachmeanatomy.info/,”The Femoral Nerve”
Saphenous Nerve
  • The saphenous nerve is the terminal branch of the femoral nerve and supplies sensory innervation to the medial leg, medial malleolus, and medial aspect of foot. It travels through the adductor canal and pierces the fascia lata in between the tendons of the sartorius and gracilis of the pes anserinus. The nerve then travels down the medial aspect of the leg along with the saphenous vein, crossing into the foot anterior to the medial malleolus and supplying sensory branches to the ankle joint. [25] Gray AT. Lower Extremity Blocks. In: Gray AT, ed. Atlas of Ultrasound-Guided Regional Anesthesia. 3rd edition. ; 2014:144-232. doi:10.1016/B978-0-323-50951-0.00001-3 [26] Yurgil JL, Hulsopple CD, Leggit JC. Nerve Blocks: Part II. Lower Extremity. Am Fam Physician. 2020;101(11):669-679. doi:10.1016/S1875-5364(20)30046-7
saphenous nerve anatomy and distribution
Saphenous Nerve Anatomy and Distribution[27]Image courtesy of https://emedicine.medscape.com/,”Saphenous Nerve Block”

Obturator

  • The obturator nerve originates from anterior rami of L2, L3, and L4 and travels through the pelvis crossing over the psoas major muscle at the level of the sacroiliac joint, and exits the pelvis through the obturator. It has anterior and posterior divisions that lie superficial and deep to the adductor brevis. The obturator nerve provides motor innervation to the adductor muscles. It has variable cutaneous sensory innervation that includes the medial thigh. [28] Silvestri E, Martino F, Puntillo F. Ultrasound-guided peripheral nerve blocks. In: Silvestri E, Martino F, Puntillo F, eds. Ultrasound-Guided Peripheral Nerve Blocks. ; 2018. doi:10.2199/jjsca.28.103 [29] Gray AT. Lower Extremity Blocks. In: Gray AT, ed. Atlas of Ultrasound-Guided Regional Anesthesia. 3rd edition. ; 2014:144-232. doi:10.1016/B978-0-323-50951-0.00001-3
obturator nerve anatomy
Obturator Nerve Anatomy[30]Image courtesy of https://teachmeanatomy.info/,”The Obturator Nerve”

Lateral Femoral Cutaneous

  • The lateral femoral cutaneous nerve (LFCN) originates from the lumbosacral plexus from L2 and L3 nerve roots. It traverses the iliacus muscle in the pelvis and enters the thigh medial to the anterior superior iliac spine (ASIS). The LFCN crosses over or pierces through the sartorius muscle from medial to lateral. The LFCN may split into several branches before supplying sensory innervation to the lateral thigh. The sensory territory of the LFCN can often extend distal to the knee. [31] Gray AT. Lower Extremity Blocks. In: Gray AT, ed. Atlas of Ultrasound-Guided Regional Anesthesia. 3rd edition. ; 2014:144-232. doi:10.1016/B978-0-323-50951-0.00001-3 [32] Yurgil JL, Hulsopple CD, Leggit JC. Nerve Blocks: Part II. Lower Extremity. Am Fam Physician. 2020;101(11):669-679. doi:10.1016/S1875-5364(20)30046-7
lateral femoral cutaneus nerve anatomy
Lateral Femoral Cutaneous Nerve Anatomy[33]Image courtesy of https://www.painspa.co.uk/,”Lateral Femoral Cutaneous Nerve Block”

Overview of Blocks By Site

*Blocks are listed by anatomic region where they provide anesthesia, not necessarily the region where the block itself is performed

Hip/Femur, Groin, Buttocks

Femoral Nerve Block
Link to Detailed Discussion of Femoral Nerve Block
  • Primary Nerve(s) Blocked – femoral
  • Indications: hip fractures, pelvic fractures

Anatomic block distribution of the femoral nerve block

Image or video of femoral nerve block

Fascia Iliaca Block
Link to Detailed Discussion of Fascia Iliaca Block
  • Primary Nerve(s) Blocked – femoral
  • Indications: hip fractures, pelvic fractures

Anatomic block distribution of the fascia iliaca block

Image or video of fascia iliaca block

Peng Block
Link to Detailed Discussion of PENG Block
  • Primary Nerve(s) Blocked – sensory nerve branches from the femoral and obturator nerves
  • Indications: hip fractures, pelvic fractures

Diagram of PENG block. [34] Image courtesy of Highland Ultrasound. Image Accessed 12/21/2022. http://highlandultrasound.com/peng

US image or video of PENG block

Dorsal Penile Block
Link to Detailed Discussion of Dorsal Penile Block
  • Primary Nerve(s) Blocked – dorsal penile nerves (branches of the pudendal nerve, S2-S4 sacral nerve roots)
  • Indications: paraphimosis/penile skin entrapment, priapism reduction

Cross-sectional anatomy of the penis [35]Image from Weech D, Ameer MA, Ashurst JV. Anatomy, Abdomen and Pelvis, Penis Dorsal Nerve. [Updated 2021 Aug 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. … Continue reading

US image or video of dorsal penile block

Knee & Leg

Femoral Nerve/Fascia Iliaca Block
  • See above (hip)
  • Indications: midshaft and distal femur fractures, large laceration repairs to anteromedial surface of thigh or knee, patellar pathology
Popliteal-Sciatic Block
  • See below (foot/ankle)
  • Indications: proximal/midshaft tibia fractures, calf/lower extremity lacerations & burns
Saphenous Block
  • See below (foot & ankle)
  • Indications: medial ankle analgesia
Genicular Block
Link to Detailed Discussion of Genicular Block
  • Primary Nerve(s) Blocked – 3 branches of the genicular nerve: superior lateral (SL), superior medial (SM), and inferior medial (IM) 
  • Indications: analgesia to the knee joint only, chronic knee OA, acute intra-articular injuries (ACL tear, meniscus injury, etc)

Genicular nerve anatomy [36]Credit to NYSORA, Accessed 12/19/2022. … Continue reading

Video of US-guided genicular nerves (superior-medial, supero-lateral, inferomedial) nerve block

Infiltration of local anesthetic between the Popliteal Artery and Capsule of the Knee (IPACK) Block
Link to Detailed Discussion of IPACK Block
  • Primary Nerve(s) Blocked – popliteal nerve plexus derived from the tibial nerve and obturator nerve
  • Indications: analgesia to the knee joint only, posterior aspect

Genicular nerve anatomy [37]Credit to NYSORA, Accessed 12/19/2022. … Continue reading

Video of US-guided iPACK nerve block

Foot & Ankle

Popliteal-Sciatic Block
Link to Detailed Discussion of Popliteal-Sciatic Nerve Block
  • Primary Nerve(s) Blocked – popliteal and sciatic nerve
  • Indications: lower extremity analgesia except the medial aspect (fractures, dislocations, lacerations, burns)

Popliteal-Sciatic nerve block distribution [38]Credit to NYSORA, Accessed 10/31/2022. … Continue reading

Video of US-guided popliteal sciatic nerve block

Saphenous Block
Link to Detailed Discussion of Saphenous Nerve Block
  • Primary Nerve(s) Blocked – saphenous nerve
  • Indications: analgesia for the medial leg and ankle

Saphenous nerve block distribution [39]Credit to NYSORA, Accessed 10/31/2022. … Continue reading

Video of US-guided saphenous nerve block

Posterior Tibial Block
Link to Detailed Discussion of Posterior Tibial Block
  • Primary Nerve(s) Blocked – posterior tibial nerve
  • Indications: Calcaneal fracture, Lisfranc injury, sole of foot laceration or foreign body requiring exploration or repair

Posterior tibial nerve block distribution [40]Credit to NYSORA, Accessed 10/31/2022. … Continue reading

Video of US-guided posterior tibial nerve block

Deep Peroneal Nerve
Link to Detailed Discussion of Deep Peroneal Block
  • Primary Nerve(s) Blocked – deep peroneal nerve
  • Indications: analgesia to the webspace between the 1st and 2nd toe

Nerve distribution of the lower leg/foot [41]Credit to Orthobullets, Accessed 10/31/2022. … Continue reading

Video of US-guided deep peroneal nerve block

Superficial Peroneal Nerve Block
Link to Detailed Discussion of Superficial Peroneal Nerve Block
  • Primary Nerve(s) Blocked – superficial peroneal nerve
  • Indications: analgesia to the anterior foot, several of the toes

Nerve distribution of the lower leg/foot [42]Credit to Orthobullets, Accessed 10/31/2022. … Continue reading

Video of US-guided superficial peroneal nerve block

Sural Nerve Block
Link to Detailed Discussion of Sural Nerve Block
  • Primary Nerve(s) Blocked – sural nerve
  • Indications: analgesia to the lateral foot

Nerve distribution of the lower leg/foot [43]Credit to Orthobullets, Accessed 10/31/2022. … Continue reading

Video of US-guided sural nerve block

References[+]