Femoral nerve compression at the inguinal ligament

Background

This is a rare peripheral nerve compression syndrome, presenting with weakness of the knee extensors, as well as numbness and tingling, depending on the exact location of the compression.

Causes

Compressive fascial bands or crossing vessel branches can lead to compression of the femoral nerve. Other causes are space occupying lesions such as prominent lymph nodes or ganglion cysts, bursitis. A separate category consists of cases of iatrogenic injury, such as during vascular intervention, hernia repairs, hip replacements where one of the components can get dislodged, or cement can extrude around the nerve.

Symptoms

Pain and/or weakness, depending on the severity of the compression and the portion of the nerve that is affected.

Diagnosis

Making an accurate diagnosis can be difficult and requires a thorough physical examination, an EMG, and more likely a high-frequency or ultra-high-frequency ultrasound to look more carefully at the nerve. MRI neurography can also be helpful in assessing nearby structures but is only performed in certain centers.

Treatment

If there is a structural issue that is leading to compression, surgical decompression is almost always indicated, if physical therapy yields no results.

Azuelos, Corò, L., & Alexandre. (2005). Femoral nerve entrapment. Acta Neurochirurgica:, 92, 61–62. https://doi.org/10.1007/3-211-27458-8_13

Piza-Katzer H, Schöller T, Stichelberger M. Iatrogene N. femoralis-Läsionen [Iatrogen femoral nerve lesions]. Handchir Mikrochir Plast Chir. 2009 Aug;41(4):230-7. German. doi: 10.1055/s-2008-1039296. Epub 2009 Mar 2. PMID: 19255949.

Moore AE, Stringer MD. Iatrogenic femoral nerve injury: a systematic review. Surg Radiol Anat. 2011 Oct;33(8):649-58. doi: 10.1007/s00276-011-0791-0. Epub 2011 Feb 17. PMID: 21328076.

This case demonstrates a young athlete with signs of compression on exam, with a clear tinel sign over the course of the femoral nerve, as well as numbness in the dotted area. The x denotes the area of the tinel sign which is a shooting sensation down along the course of the nerve. EMG was normal but ultra high frequency ultrasound revealed changes in the nerve consistent with compression.

During the decompression, all branches of the femoral nerve are carefully dissected out and preserved. Several fascial bands crossing over the course of the nerve were identified and released. In the recovery room, her motor function had already recovered, confirming that this represented a compression of the nerve with an ischemic component. Interestingly the compression was dynamic and only occurred during certain hip positions.