Irreversible Foot Drop as a Consequence of Neglected Knee Pain in an Adolescent with a Peroneal Intraneural Ganglion Cyst

Background Peroneal intraneural ganglion cysts (IGCs) are nonneoplastic lesions. They are responsible for a small number of footdrop cases, which occur after additional nerve damage. The earliest patient symptom related to IGCs is knee pain. Case Description A 17-year-old boy developed pain in the left knee, which progressively worsened over 14 months. He did not seek any medical assistance during this time. The patient subsequently was involved in a bicycle accident, and 3 months later he was unable to raise his left foot and was referred to our clinic for footdrop. Surgery was performed, but the weakness persisted. We could not detect any functional reinnervation on electromyography 12 months after surgery. Conclusions The most important factors in determining the prognosis of IGCs are the extent of the nerve trauma and the early diagnosis and treatment of the IGC. Detection of almost complete functional denervation on electromyography may indicate that it is too late for surgery.