Saphenous Neuropathy Secondary to Extraneural Ganglion Cyst 15 Years After Reconstruction of the Anterior Cruciate Ligament

This case report describes a 43-year-old woman with a previous anterior cruciate ligament reconstruction and medial meniscectomy who presented with right knee dysesthesias radiating into her medial ankle with associated allodynia. An extensive work-up was pursued, without a definitive diagnosis found or improvement in the patient's symptoms. Eventually, she was referred to Pain Medicine for an ultrasound-guided saphenous nerve (SN) block, where a scan before the injection revealed a large cyst anteromedial to the sartorius in the expected location of the SN. Magnetic resonance imaging and surgical pathology confirmed a juxta-articular ganglion cyst compressing the main SN, just above the take-off of the infrapatellar branch. The cyst was successfully resected, with improvement noted in the patient's neuropathic symptoms postoperatively. Saphenous neuropathy is a rare condition, and to our knowledge this case is the first reported of saphenous neuropathy caused by a knee joint capsule-derived ganglion cyst.