Lateral Femoral Cutaneous Nerve

Anatomy and Function

The lateral femoral cutaneous nerve (LFCN) is formed by contributions from the ventral rami of the L2 and L3 spinal nerves (▶ Fig. 5.1 and ▶ Fig. 5.2). It is a cutaneous nerve serving the lateral aspect of the thigh. Along its highly variable course, it initially emerges from beneath the lateral border of the psoas muscle and traverses the pelvis by running obliquely past the iliacus muscle. It then approaches the anterior superior iliac spine (ASIS) parallel to the iliac crest as it exits the pelvis. At this point, the LFCN supplies sensory innervation to the parietal peritoneum of the iliac fossa. On the left side, it passes behind the lower segment of the descending colon, and on the right side it courses posterolaterally past the cecum. It exits the pelvis and enters the thigh region by piercing through the fascia lata beneath the inguinal ligament. ¹^, ²

Fig. 5.1 Schematic drawing of the right lumbar plexus. Note the course of the lateral femoral cutaneous nerve over the iliacus muscle and under the inguinal ligament to emerge onto the lateral thigh.

Fig. 5.2 Cadaveric dissection of the left lumbar plexus. The two branches of the genitofemoral nerve (purple) are seen exiting the anterior surface of the psoas major muscle and the large femoral nerve (purple) is seen leaving the pelvis on the lateral border of psoas major. The white colored nerve leaving the lateral side of psoas major and traveling over iliacus toward the anterior superior iliac spine is the lateral femoral cutaneous nerve. The obturator nerve (red) is pulled medially to show the L5 ventral ramus (green).

As it travels through the thigh beneath the inguinal ligament, the LFCN courses subcutaneously in a lateral and distal direction. During its descent through the thigh, it divides into anterior and posterior branches. At a point 10 cm distal to the ASIS, its anterior branch becomes superficial and provides sensory innervation to the skin of the anterolateral thigh down to the knee. The anterior branch also connects with cutaneous branches of the anterior femoral nerve and the infrapatellar branch of the saphenous nerve to form the peripatellar plexus. The posterior branch pierces through the fascia lata at a point higher than the anterior branch and further divides to provide innervation to the lateral skin from the greater trochanter to mid-distance along the thigh, and can also supply the gluteal skin. ¹^, ² Hanna described a complete fascial canal surrounding the LFCN in the thigh. ²⁸

An analysis of the LFCN by Ray et al revealed that it is usually flattened at the inguinal ligament, where it is encompassed by a concentrically arranged thick perineurium. ³ Its mean cross-sectional area at this point was recorded as 1.921 ± 0.414 mm². The LFCN was also found to contain three to six fascicles at this point, with a mean of 4.5 fascicles per nerve and a mean fascicular area of 0.647 ±0.176 mm². The cadaveric study by Ray et al also reported that the mean distance from the ASIS to the point at which the LFCN passes the inguinal ligament is 1.87 ± 0.48 cm, and the mean distance from the ASIS to the point at which it crosses the lateral border of the sartorius muscle is 6.15 ± 1.79 cm. ³

5.2 Variations

As mentioned earlier, the exact path taken by the LFCN during its descent through the pelvis and anterolateral thigh can vary greatly. de Ridder et al found some degree of anatomical variation in the LFCN in at least 25% of the patient population. ⁴ This variability could contribute to the occurrence of iatrogenic injury to the nerve during surgical procedures secondary to difficulty in predicting its exact course. ⁵^, ⁶^, ⁷ The first source of variability lies in the nerves that contribute to the formation of the LFCN. Normally, it arises from the posterior divisions of L2 and L3, but it can also arise from L1 and L2 (“high form”) and from L3 and L4 (“low form”). It can also emerge from the femoral nerve or as a distinct branch of the lumbar plexus. ² Sim and Webb found that the LFCN arose from the first two lumbar nerves in 22 of 60 patients, solely from the L2 ventral ramus in 1, and from the femoral nerve in 6, with almost half showing some variation in the nerves from which the LFCN was derived. ⁸ Webber observed at least eight distinct patterns of neural origin and contributions to the LFCN. ⁹ Carai et al found that the LFCN was absent in almost 9% of patients who required operative intervention for meralgia paresthetica. ⁵ Other variations include an absence of the nerve on either side and its replacement by a contribution from the anterior femoral cutaneous nerve. ¹⁰

Another significant area of variability is the point at which the LFCN exits the pelvis and enters the thigh region. Normally, it exits medial to the ASIS and runs underneath the inguinal ligament. ¹¹ Aszmann et al distinguished five categories of anatomical variation in the LFCN’s exit from the pelvis and entry to the thigh during their cadaveric studies, and these findings have been corroborated by other studies. ¹²^, ¹³^, ¹⁴^, ¹⁵

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