Variant Femoral Nerve: The Path Beneath the Iliacus Muscle and Into Neuropathic Symptoms
Authors: Vinson Jacob C. , Pavlovsky Ethan , Loomis Mario 
Published: May 2022

Introduction and Objective

Originating from the lumbar plexus, the femoral nerve has a native course along the anterior surface of the iliacus then travels deep to the inguinal ligament, branching into separate anterior and posterior divisions that provide innervation to the anterior thigh muscles (Figure 1). Clinically, the spatial relationship between the iliopsoas complex and the femoral nerve has been noted for the potential risk of entrapment and compressive neuropathies. Variations in the femoral nerve course following surgical and medical interventions can produce symptoms related to muscle weakness and sensory loss in patients. Relevant literature regarding variant femoral nerve distributions is most often related to aberrant slips of the iliacus muscle and following surgical or medical intervention. In this case study, we describe a variation in the descent of the femoral nerve that travels within the belly of the iliacus muscle without evidence of an aberrant slip or surgical intervention and discuss the clinical implications and appropriate non‐invasive osteopathic treatment options.

Materials

This anatomical variation was revealed in one donor being evaluated at Sam Houston State University College of Osteopathic Medicine’s anatomy lab. The donor was previously dissected by medical students for a first‐year anatomy course. The iliacus and surrounding structures were left intact. Additional dissection necessary for this study was performed from March 2021 to April 2021.

Results

In a 70‐year‐old male cadaver, the right femoral nerve originated from the lumbar plexus, descended, and then bifurcated (Figure 2A). Most of the femoral nerve remained within the Iliacus muscle (Figure 2B) while a small portion of the femoral nerve followed the typical course anterior to the iliacus (Figure 2C). The bulk of the femoral nerve traveled within the iliacus, exiting inferior to the inguinal ligament, then merged with the smaller portion of the nerve (Figure 2D). The left femoral nerve followed a typical course.

Significance/Conclusion

Previous discussions report an aberrant slip of the iliacus splitting the femoral nerve and having the potential for nerve compression, although unlikely due to the smaller muscle belly involved. This highlighted variant is significant because the bulk of the femoral nerve remains beneath the iliacus as it crosses over the pubic eminence. This pathway would be predisposed to a greater degree of compression against the pubic eminence, with potential for certain movements to increase these forces.

This patient presentation is hypothesized to include anterior thigh weakness during hip flexion and knee extension activities, such as stair‐climbing, as well as sensory loss to the anteromedial thigh and medial leg via the saphenous nerve. Sensation to the lateral thigh should remain intact as the lateral femoral cutaneous nerve would be unaffected. conservative treatments, such as osteopathic manipulative techniques, could be an effective form of treatment. Techniques including counterstrain to the psoas and iliacus or muscle energy to the hip flexors could lessen such nerve compression and improve patient symptoms.

Awareness of this variation could provide clinicians with another potential diagnosis to consider when managing femoral neuropathy, as well as rationale for a non‐invasive treatment option.