LOWER EXTREMITY PERIPHERAL NERVE BLOCKS
Lumbar & Sacral Plexus Anatomy
The lumbosacral plexus provides innervation to the lower extremities (Figure 46–38). The lumbar plexus is formed by the ventral rami of L1–4, with occasional contribution from T12. It lies within the psoas muscle with branches descending into the proximal thigh. Three major nerves from the lumbar plexus make contributions to the lower limb: the femoral (L2–4), lateral femoral cutaneous (L1–3), and obturator (L2–4). These provide motor and sensory innervation to the anterior portion of the thigh and sensory innervation to the medial leg. The sacral plexus arises from L4–5 and S1–4. The posterior thigh and most of the leg and foot are sup-plied by the tibial and peroneal portions of the sci-atic nerve. The posterior femoral cutaneous nerve (S1–3), and not the sciatic nerve, provides sensory innervation to the posterior thigh; it travels with the sciatic nerve as it emerges around the pirifor-mis muscle.