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Lumbosacral plexus

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Innervation of the leg takes place in the lumbar and sacral plexuses. After exiting the intervertebral foramina (Th 12-L4), the lumbar plexus runs within a fascial sheath between the psoas major muscle and the quadratus lumborum muscle. The lumbar vertebrae and the transverse processes are located mediad. The iliohypogastric nerve (Th12, L1), the ilio-inguinal nerve (L1) and the genitofemoral nerve (L1, L2) are formed from the cranial portion of the lumbar plexus. The lateral femoral cutaneous nerve (L2, L3), the obturator nerve (L2-4) and the femoral nerve arise further caudad to this. The femoral nerve extends along the ventral side of the iliopsoas muscle, beneath the inguinal ligament and through the muscular lacuna approximately 1-2 cm lateral of the femoral artery where it divides into its branches. Its cutaneous branch, the saphenous nerve extends to the medial lower leg. The lateral femoral cutaneous nerve is purely sensory. It passes slightly medially to the anterior superior iliac spine and emerges beneath the inguinal ligament to supply the skin of the lateral part of the thigh. Here, however, there are frequently variations to the point that the lateral skin of the thigh is sometimes principally supplied by the femoral nerve. The obturator nerve proceeds along the medial edge of the psoas major muscle and emerges from the false pelvis through the obturator foramen somewhat mediodorsal to the pubic tubercle towards the medial thigh: although the literature assigns it to a circumscribed sensory area of skin in middle of the medial thigh, it is rarely demonstrable in clinical practice. One must therefore assume that this region is supplied entirely by the branches of the femoral nerve. The lumbosacral trunk emerging from the roots L4 / L5 (the fourth lumber nerve) unites the two plexuses. The sacral plexus extends dorsally, emerging from the lower pelvis through the greater sciatic foramen. The posterior femoral cutaneous nerve develops directly out of the sacral plexus. The sciatic nerve is formed from segments L5 to S3. In the buttocks region, it proceeds beneath the gluteus maximus muscle and passes between the ischial tuberosity and the greater trochanter of the femur to the dorsal thigh. At this point it supplies motor fibres to the dorsal musculature of the thigh. Approximately 10 to 15 cm above the level of the knee joint, is commonly where it diverges into the tibial nerve and common peroneal nerve.

 

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Sensory supply areas

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