Lower extremity neuroanatomy Wyndam M. Strodtbeck, MD Section Head, Acute Pain Dept of Anesthesiology and Pain Medicine Virginia Mason Medical Center wyndam.strodtbeck@vmmc.org

Disclosures No financial disclosures No off-label use of medications or devices will be discussed Patient permission was explicitly granted for any pictures used

Objectives for our talk Describe the clinical anatomy of the innervation of the lower extremity Identify surrounding structures and their implications for sonoanatomy and potential variation

Lumbosacral plexus L1-L4 form the lumbar plexus Branches from L4 –S2 from the lateral trunk Other branches from L3-S3 make up the medial trunk S1-S5 make up the sacral plexus Early branching of the lumbar plexus and thick musculature makes identifying a single compartment for lumbosacral blockade difficult

Early Branches of the Lumbar Plexus Ilioinguinal and iliohypogastric nerves From L1 Iliohypogastric supplies anterior and lateral cutaneous innervation in hypogastric and gluteal region Ilioinguinal supplies cutaneous innervation of genital region Genitofemoral nerve From L1 and L2 Genital division supplies cremasteric muscle and sensory over genital region Femoral branch supplies cutaneous innervation over femoral triangle

Early Branches of the Lumbar Plexus Gray, H. Anatomy of the human body, 1918.

Femoral Nerve Origin is dorsal divisions of L2-L4 Divides into anterior and posterior division typically at level of profunda femoris artery Nader, Relationship Between Ultrasound Imaging and Eliciting Motor Response, J Ultrasound Med, 28(3):345-350, 2009

Femoral Nerve Anterior division Origin L2-L4 Anterior division -Medial and intermediate cutaneous nerves -Muscular branches to sartorious -Articular branch to hip joint Posterior Division -Muscular branches to quads -Articular branches to knee joint -Saphenous nerve is terminal cutaneous branch and provides lower leg anteromedial sensation Nader, Relationship Between Ultrasound Imaging and Eliciting Motor Response, J Ultrasound Med, 28(3):345-350, 2009

Femoral Nerve Nader, Relationship Between Ultrasound Imaging and Eliciting Motor Response, J Ultrasound Med, 28(3):345-350, 2009

Femoral Nerve Ultrasound image shows anterior and posterior divisions Keep in mind the variations in location and appearance of the nerve Groups of authors have reported variable splits in the femoral nerve in 2.2-35% of subjects. Nader, Relationship Between Ultrasound Imaging and Eliciting Motor Response, J Ultrasound Med, 28(3):345-350, 2009

Lateral femoral cutaneous nerve Originates from dorsal divisions of L2 and L3 May have a variable course as it emerges from psoas Passes under inguinal ligament and superficial to the sartorious muscle Located between fascia lata and fascia iliaca Responsible for pain transmission in meralgia paresthetica Hurdle, MF et al. Ultrasound-guided blockade of the lateral femoral cutaneous nerve. Arch Phys Med Rehab 88:1362-1364, 2007.

Saphenous Nerve Terminal branch of posterior division of femoral nerve Provides cutaneous sensation around patella, anteromedial lower leg, and medial ankle Travels in adductor canal with femoral artery and vein In distal thigh, the saphenous nerve can be identified deep to the sartorious and between the vastus medialis and the adductor magnus

Saphenous Nerve Image courtesy of FV Salinas, MD

Saphenous Nerve

Obturator nerve Originates from ventral branches of L2-L4 Supplies articular branches to hip and knee Adductors are supplied Similar to femoral nerve in having anterior and posterior divisions

Obturator nerve Anterior division Motor innervation to pectineus (may be an accessory obturator nerve) , adductor longus and brevis, gracilis Articular branch of the hip Posterior division Motor inneravtion to adductor magnus and brevis as well as obturator externus Articular branches to hip and knee

Nerves of the Sacral Plexus Gray, H. Anatomy of the human body, 1918.

Posterior femoral cutaneous nerve Provides sensation for posterior thigh and leg, gluteal region, and perineum Originates from S1-S3

Posterior femoral cutaneous nerve Gray, H. Anatomy of the human body, 1918.

Sciatic Nerve Largest nerve in the body Joining of L4-S3 Two parts: -Tibial (medial) (L4-S2) - Common Peroneal (L4-S3) Provides sensation for posterior leg and foot (except for saphenous distribution) as well as motor for posterior thigh, and all of leg and foot, and articular branches for hip and knee Wikipedia, Feb 10, 2012

Sciatic Nerve At gluteal level, Sciatic is deep to gluteus maximus and passes out below piriformis muscle, located lateral to ischial spine This level is useful due to the close proximity of the posterior femoral cutaneous nerve to the sciatic nerve

Sciatic Nerve At subgluteal level, the sciatic nerve is positioned between the gluteus maximus and the quadratus femoris

Sciatic Nerve Subgluteal ultrasound Image courtesy of FV Salinas, MD

Sciatic Nerve -Shared epineural sheath for tibial and common peroneal nerves separates above popliteal crease -Schwemmer et al (2005) demonstrated high variability for division of sciatic nerve above popliteal crease (1-15 cm with mean of 8 cm) Schwemmer et al. Sonographic imaging of the sciatic nerve division in the popliteal fossa. Ultraschall in Der Medizin, 2005. Wikipedia, Feb 10, 2012

Nerves of the ankle and foot Primarily consists of terminal branches from the sciatic Exception is the saphenous branch of the femoral nerve NYSORA.com, accessed 2-10-2012 Gray, H. Anatomy of the human body, 1918.

Special Thanks Francis V. Salinas, MD