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Clinical Pearls

Saphenous Neuropathy—A Masquerading Cause of Anteromedial Knee Pain

Herman, Daniel C. MD, PhD, FACSM; Vincent, Kevin R. MD, PhD, FACSM

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Current Sports Medicine Reports: June 2018 - Volume 17 - Issue 6 - p 177
doi: 10.1249/JSR.0000000000000488
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Saphenous neuropathy is a known but often overlooked cause of anterior and/or medial knee pain. However, due to its poorly defined presentation and nonspecific physical examination findings, it often masquerades as other more common clinical entities (1,2). Compression of the saphenous nerve typically occurs at the adductor (Hunter) canal or at the infrapatellar branch of the saphenous nerve as it courses near the medial femoral condyle. Patients typically complain of vague dull or achy pain located in the area of the anteromedial knee, with variable reports of burning or other neuropathic qualities. The pain is often reported as worse with stairs, prolonged walking, and sitting (1). Because of the location, quality, and exacerbating conditions of this pain, in our clinical experience, it is very commonly confused as patellofemoral pain syndrome, particularly in young athletes for whom this diagnosis is very common. This condition also may occur as a complication from surgical interventions involving the anterior and/or medial knee.

Pearl: Consider the diagnosis of saphenous neuropathy in athletes with a working diagnosis of patellofemoral pain syndrome that has been refractory to good patient compliance with standard conservative treatment measures.

The physical examination of patients with saphenous neuropathy also can be difficult to discern from more common etiologies of anterior knee pain. Patients will commonly have tenderness to palpation at the medial patellar facet and retinaculum as well as at the medial joint line due to the distributions of the infrapatellar and sartorial branches of the saphenous nerve in these areas; however, palpation of the patient’s reported sites of pain does not typically assist with this diagnosis given the overlap of these areas with more common entities, such as patellofemoral pain syndrome. Despite compression of the nerve commonly occurring at the adductor canal, complaints of altered sensation to light touch are typically restricted to the anteromedial knee area; this finding is atypical in its more distal sensory distribution along the medial leg (1). Positions combining knee flexion and abduction stress can exacerbate the patient’s symptoms via neural tension, resulting in false-positive results for meniscus injury maneuvers such as McMurray or Thessaly test (1).

Pearl: Consider the diagnosis of saphenous neuropathy in athletes with a working diagnosis of a medial meniscus injury without confirmatory findings on advanced imaging, particularly in patients without a history of an appropriate mechanism of injury or for whom exploratory arthroscopy is being considered.

In our clinical experience, we have found the use of manual compression of the nerve to reproduce the patient’s symptoms to be the most helpful with this diagnosis. This assessment should be performed at the distal adductor canal; if this does not reproduce the patient’s pain, then it should be repeated at the site of the infrapatellar branch. Confirmation can be achieved via the use of a diagnostic nerve block, which may on occasion also be therapeutic (3).

Pearl: The location of the distal end of the adductor canal can be reliably found approximately 7 cm proximal and 10 cm medial to the superior pole of the patella (1). The location of the infrapatellar branch is more variable, but can typically be compressed in the area between approximately 3 to 5 cm medial to the medial mid-patellar border with the knee in extension (2).

Conservative treatment options may include nerve glide exercises and transfrictional massage. These should be performed several times daily for maximal efficacy. Capsaicin cream or oral nerve membrane stabilizing agents, such as gabapentin, can be used to assist with pain control. If initial conservative measures are not successful, injection of corticosteroids and/or careful ultrasound guided hydrodissection of the nerve at the site of compression may be considered. Nerve ablation, neuromodulation, or surgical decompression, neurolysis, or neurectomy also have been reported in the literature (1,2); however, in our clinical experience, these are rarely necessary and should be entertained with caution.

References

1. Morganti CM, McFarland EG, Cosgarea AJ. Saphenous neuritis: a poorly understood cause of medial knee pain. J. Am. Acad. Orthop. Surg. 2002; 10:130–7.
2. Trescot A, Brown MN, Karl HW. Infrapatellar saphenous neuralgia—diagnosis and treatment. Pain Physician. 2013; 16:E315–24.
3. Herman DC, Vincent KR. Saphenous nerve block for the assessment of knee pain refractory to conservative treatment. Curr. Sports Med. Rep. 2018; 17:146–7.
Copyright © 2018 by the American College of Sports Medicine.