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Lower Extremity Peripheral Nerve Blocks. Yefim Bogomolny, M.D . General Considerations for Lower Extremity Blocks. LE blocks are not difficult to perform.
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Lower Extremity Peripheral Nerve Blocks Yefim Bogomolny, M.D.
General Considerations for Lower Extremity Blocks • LE blocks are not difficult to perform. • Alternative to GA, Spinal, and Epidural. Examples – intubation might represent a problem, or unilateral anesthesia is indicated, or NA anesthesia is contraindicated. • Can be used in combination with GA and NA. • The nerves of LE are often blocked much higher than their terminal divisions (exception – blocks for foot surgery). This produces extended single shot motor and sensory blocks. • Several LE blocks are amendable to catheter insertion which results in superior analgesia when compared to epidural. • There is a clear consensus favoring the use of nerve stimulator versus paresthesia for LE blocks. Also US is used to localize the nerves.
Lumbosacral plexus • Innervates the LE and perineal area. • Its fibers are extensions of ventral rami of L2-L5 and S1-S3. • L2-L4 form the lumbar plexus, which divides into lateral femoral cutaneous, femoral, and obturator nn. Supply the upper leg with the branch of femoral (saphenous n.) extending medially below the knee. • L4-S3 form two major trunks of the sciatic n., the tibial and the common peroneal nn. They provide the bulk of innervation below the knee.
Lumbosacral plexus • The lumbosacral plexus has a broader origin than the brachial plexus. • Roots emerge from their foramina into the fascial plane between quadratus lumborum and psoas m. • The lumbar roots form lateral femoral cutaneous, femoral, and obturator nn. Can be blocked by an injection into the psoas compartment (Lumbar plexus block). • Lower sacral roots form the sciatic n. They lie in a compartment with bony posterior and can be reached by parasacral approach. • Conclusion - separate injections are needed for anterior (lumbar plexus) and posterior (sacral) branches.
Lower extremity innervation • Femoral n. - courses behind the psoas m. and passes under inguinal l. posterior and just lateral to the femoral a. – reliable landmark. • Below or sometimes slightly above the ligament, it branches. The main trunk going medially across the knee, medial calf all the way to the medial ankle and foot – saphenous n. • Lateral femoral cutaneous n. – Leaves the fascial sheath early, migrates laterally and emerges under inguinal l. medial to ASIS. Provide sensory supply to lateral thigh. • Obturator n. – emerges under superior ramus of the pubis and branches. Supply motor and sensory fibers to the hip, knee, medial thigh, adductor mugnus m.
Lower extremity innervation • Sciatic n. – exits the pelvis through sciatic notch, lies below piriformis and gluteus maximus mm., sends a branch to the hip (quadratus femoris m.), travels behind the femur, splits into the commonperoneal and tibial nn. 7-10 cm above popliteal crease. • Common peroneal n. – winds around the neck of the fibula posterior to lateral. Divides into superficial peroneal and deep peroneal nn. • Innervates knee joint. • Stimulation – dorsiflexion of the foot and eversion.
Lower extremity innervation • Tibial n.- lies between semitendineus and biceps femoris mm. lateral to popliteal artery. • Branches – Sural n., medial and lateral plantar nn., calcaneal n. • Plantar flexion, flexion of the toes, inversion. • Innervates ankle joint.
