Anaes · Applied anatomy

Lumbosacral plexus anatomy

Also known as Lumbar plexus · Sacral plexus · Sciatic nerve anatomy · Femoral nerve · Obturator nerve · Lower limb nerve blocks

The lumbosacral plexus supplies the entire lower limb, the pelvic floor and the perineum, and its branches are the targets of the lower-limb regional blocks used for hip, knee, ankle and foot surgery. The framework rests on six exam-critical ideas. First, the lumbosacral plexus is actually two plexuses: the LUMBAR plexus, formed by the ventral rami of L1-L4 (with T12 and L5 contributions) and lying within the substance of the psoas major muscle; and the SACRAL plexus, formed by the lumbosacral trunk (L4-L5) and the ventral rami of S1-S4, lying on the anterior surface of the piriformis muscle. Second, the principal lumbar-plexus branches are the iliohypogastric and ilioinguinal (L1, the abdominal wall), the genitofemoral (L1-L2, the genital branch and the femoral triangle), the lateral femoral cutaneous nerve (L2-L3, the lateral thigh — compressed in meralgia paraesthetica), the FEMORAL nerve (L2-L4, the anterior thigh quadriceps and the medial leg via the saphenous nerve) and the OBTURATOR nerve (L2-L4, the medial-thigh adductors). Third, the principal sacral-plexus branch is the SCIATIC nerve (L4-S3), the largest nerve in the body, which leaves the pelvis through the greater sciatic foramen below the piriformis and runs down the posterior thigh to the popliteal fossa, where it divides into the TIBIAL nerve (posterior compartment, plantar foot) and the COMMON PERONEAL nerve (lateral/anterior compartment, dorsum of foot). Fourth, other sacral-plexus branches are the superior and inferior gluteal nerves (gluteal muscles), the pudendal nerve (S2-S4, the perineum) and the posterior femoral cutaneous nerve (posterior thigh). Fifth, the lower-limb blocks target these branches: the femoral and fascia-iliaca blocks (anterior thigh and knee), the obturator block (adductor spasm and knee), the pericapsular nerve group (PENG) block (hip capsule), and the sciatic block by posterior, anterior or popliteal approaches (the leg and foot below the knee). Sixth, two injury patterns localise damage: foot drop from a common-peroneal (or L5) lesion, and sciatica from L4-S1 root irritation. Built on the lower-extremity-blocks RCT review (Tran 2007), the inaugural PENG-block report (Giron-Arango 2018), the PENG-plus-LFCN-versus-fascia-iliaca meta-analysis (Cunha 2026), the sciatic-variation-and-bifurcation study (Atoni 2022), the fibular-neck peroneal-release cadaver study (McCool 2019), the interadductor obturator-block trial (Uchino 2026), the piriformis-syndrome ultrasound series (Sudhakar 2026), the CT-guided pudendal-cryoablation series (Battle 2026), and a knee-block peroneal-injury case report (Li 2026).