Working Diagnosis:
Femoral Nerve mononeuropathy from demyelinating injury

Treatment:
The patient was treated with a two week course of high dose (60 mg) oral steroid taper which mildly improved her symptoms. She obtained the EMG about 4 weeks after injury. She was rested from contact activity, high impact activity and open chain exercises until fasciculations resolved and strength returned to 5/5 (total of 10 weeks). She then progressed to strength training, followed by sport specific drills.

Outcome:
The athlete was able to complete her strength training rehab and sport specific drill training without difficulty. At 20 weeks post injury, she felt that her fitness/strength and confidence had returned to baseline. Her physical exam was normal, and she was returned to full contact activity to participate in her lacrosse season.

Author's Comments:
It was determined from this patient’s history, exam, and diagnostic testing that she had a femoral nerve mononeuropathy from an acute demyelinating injury with an unexpected mechanism of injury. Femoral nerve traumatic neuropathy is uncommon due to its location deep within the pelvis, but may occur after trauma to the hip or pelvis. It is generally associated with acute pelvic fractures, pelvic masses or hematomas, or post-surgical after hip replacement surgery or pelvic surgery. The prognosis for recovery depends on the extent of axonal injury and management is generally supportive unless neurotmesis occurs. There have been cases of femoral nerve neuropathy documented in association to the aforementioned mechanisms, however, to my knowledge, no cases have been documented in association with a traumatic spine injury which makes this case unique along with its presentation. We postulate that hyperextension of the spine with a planted lower extremity led to traction of the femoral nerve resulting in axonotmesis. This case highlights the importance of thinking outside of the box with a seemingly common injury and understanding the mechanism of injury sustained.

Editor's Comments:
Prognosis for traumatic mononeuropathies depend greatly on the extent of neural tissue disruption, potential for scar tissue formation, and the mechanism with which the injury occurred.
When assessing traumatic nerve injuries, a Nerve Conduction Study (NCS) can detect focal slowing or block of a nerve conduction, while an Electromyography (EMG) helps assess the pattern of denervation. Changes to the NCS and EMG can be detected within 7-10 days, but most would argue to wait at least 4 weeks from symptom onset for most accurate/useful results.

References:
Compagnoni, L.; et al. Problems of Etiology in Femoral Neuropathies. The Italian Journal of Neurological Sciences. 1985. Volume 6, Issue 1, page 37.

Kalita, Jayantee; et al. Sports Induced Femoral Neuropathy: Review of Literature. Publication of the Neurological Society of India. 2016. Volume 64, Issue 4, Pages 1303-1304.

Meadows, James; et al. Lower Extremity Nerve Entrapments in Athletes. Current Sports Medicine reports. 2014, Volume 13, Issue 5, pages 299-396.

Muellner, T; et al. Isolated femoral mononeuropathy in the athlete. Anatomic considerations and report of two cases. American Journal of Sports Medicine. 2001. Volume 29, Issue 6.

Rathbun, Elle. A Case of Idiopathic Femoral Neuropathy With Subsequent Quadriceps Atrophy. Journal of Clinical Neuromuscular Disease. 2017. Volume 18, Issue 3, Pages 161-162.

Robinson, Lawrence. Traumatic injury to peripheral nerves. Muscle and Nerve. 2000, Volume 23, Issue 6, pages 863-873.

Stephen, Fealy; et al. Femoral Nerve Palsy Secondary to Traumatic Iliacus Muscle Hematoma: Course after Nonoperative Management. The Journal of Trauma: Injury, Infection, and Critical Care. 1999. Volume 47, Issue 6.

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