Inclusion Criteria:  Patients with neuropathic pain associated with avulsion injuries following traumatic brachial plexus injuries scheduled for brachial plexus exploration and reconstruction by three senior surgeons at Mayo Clinic (AYS, ATB, RJS): Neuropathic pain defined as pain directly related to injury to the somatosensory system, and score >4/10 on the Douleur Neuropathique en 4 Questions (DN4) neuropathic pain questionnaire. Symptoms of neuropathic pain include allodynia, hyperalgesia, burning, needle-like, throbbing, shooting, or electrical-type sensation. Nerve root avulsion on CT myelogram. Traumatic brachial plexus injuries defined as blunt or penetrating trauma resulting in injury and dysfunction along the course of the brachial plexus defined as nerve roots C5-T1, trunks, divisions, cords, and terminal branches.  Exclusion Criteria:  Patients without pain following traumatic brachial plexus injuries. Patients with brachial plexus injuries due to non-traumatic causes such as tumors, infection, radiation, or inflammatory disorders such as Parsonage Turner Syndrome. Patients who do not require surgery for exploration/reconstruction at the brachial plexus. Patients under 18 years of age. Contraindication to ketamine use (severe hepatic dysfunction -cirrhosis, high-risk coronary artery disease, poorly controlled psychiatric condition- schizophrenia.