The lateral femoral cutaneous nerve is a superficial nerve of the outer thigh. Penetrating the skin from the hip to mid-thigh, it is a sensory nerve that sends signals to the central nervous system (CNS) in response to environmental cues like temperature and intrinsic cues like pain. Arising from the dorsal roots of the nerves exiting the spinal column at the second and third lumbar vertebrae, the lateral femoral cutaneous nerve's neurons fire in one direction only: from the sensory receptors in the skin toward the brain.
A vessel of the peripheral nervous system, the lateral femoral cutaneous nerve is found outside of the CNS, which consists of the brain and spinal cord. It links to the CNS in the lower back at the height of the second and third lumbar vertebrae via vessels known as dorsal nerve roots. Each spinal segment, of which there are 31 in total, features two pairs of nerve roots exiting the spine: the dorsal and ventral nerve roots.
The dorsal nerves, one on either side, are the sensory nerves, carrying the afferent signals from the sensory receptors about such stimuli as pain, temperature, and texture to the brain. Exiting each spinal segment just anterior to the dorsal nerves are the paired ventral nerves, motor nerves that deliver commands from the brain to the muscles so that they may contract in response. As a sensory nerve, the lateral femoral cutaneous nerve is responsible for sending messages to its dorsal roots, up the spinal cord, and to the brain.
From the second and third lumbar vertebrae, the lateral femoral cutaneous nerve follows an oblique course across the posterior aspect of the psoas major muscle and anterior aspect of the iliacus muscle, both flexors of the hip. Exiting to the outside of these muscles about halfway down their length, it approaches the anterior superior iliac spine, which is the topmost protrusion of the ilium or hipbone that is palpated on the front of the hip. Crossing the front of the hip just beneath the inguinal ligament, the ligament that runs from the iliac spine to the pubic bone, tracing the line where the leg meets the torso, the lateral femoral cutaneous nerve passes above the deep sartorius muscle.
This nerve then bifurcates into two branches, an anterior and posterior branch, near the top of the tensor fasciae latae muscle in the top of the anterior outer thigh. The anterior branch approaches the skin a few inches (about 10 centimeters) below, and from here continues to subdivide as it runs down the outer thigh toward the knee, innervating the skin as it goes. As its name suggests, the posterior branch of the lateral femoral cutaneous nerve innervates the skin behind this, on the posterior outer thigh and down toward the knee as well.