Distal Thigh Pain in a Young Mountain Biker: A Case Report

Case Diagnosis: Saphenous neuralgia diagnosed via ultrasonography and analgesic block

Case Description or Program Description: A 39-year-old male mountain biker without significant past medical history presented to clinic with pain and burning in the distal, anteromedial thigh. Symptoms began after an intense bike ride 6-7 months prior. At the time, activity cessation relieved the symptoms. However, as he returned to sport, he experienced progressive pain even at rest, affecting both cycling and sleep.

On exam, the patient had tenderness at the distal, medial aspect of the right thigh, without erythema or edema. The remainder of the exam was unremarkable. MRI of the right femur revealed no distal abnormalities.

Setting: Outpatient Physiatry clinic at a Veteran's Administration Hospital

Assessment/Results: Despite initial conservative management, the patient's pain persisted. On follow up, bedside ultrasound of the right adductor canal showed focal fusiform swelling of the saphenous nerve.

An ultrasound-guided, perineural diagnostic block with 1% lidocaine relieved nearly all of his pain. Subsequently a 4mL solution of 3.5 ml of 1% lidocaine and 20 mg kenalog was injected perineurally. The patient reported 80-90% improvement in pain with sustained relief at 3-month follow-up.

Discussion (relevance): The saphenous nerve is a purely sensory nerve and longest terminal branch of the posterior division of the femoral nerve. Within the proximal third of the thigh, the nerve enters the adductor canal, formed by a fibrous band spanning between the vastus medialis, adductor magnus, and adductor hiatus, piercing the roof of the canal just proximal to the adductor hiatus. Here, the nerve is most susceptible to entrapment and swelling.

Conclusions: Saphenous neuralgia is a rare and subtle diagnosis that, while often associated with anterior knee pain after surgery, can rarely present as distal thigh pain. However, as we have shown, ultrasonography can be an effective tool for diagnosis and treatment of this condition.