Chronic pain conditions are some of the most challenging problems upper-extremity surgeons face and often require a multimodal approach including neuromodulation. Peripheral nerve stimulation (PNS) is one of these modalities, delivering electrical stimulation to peripheral axons to modulate the spinal cord and block out nociceptive signals from the extremity. This blockade leads to long-lasting effects in both the peripheral and central nervous systems. Not only does PNS decrease peripheral pain signals but it also decreases the peripheral inflammatory response and assists with central nervous system plasticity for long-term pain control. Although PNS was initially developed in the 1960s, it has been underrepresented in the literature largely due to the advent of spinal cord stimulation and the lack of Food and Drug Administrationeapproved hardware for PNS. However, for upper-extremity pain, PNS provides notable benefits over spinal cord stimulation devices, as PNS allows for safer, more specific, and often more effective pain control. As clinicians attempt to limit narcotic use, therapies such as PNS have been revisited and are gaining popularity. We present a narrative review of PNS; discuss its mechanism of action, indications, and surgical technique; and provide a summary of the available literature for the upper-extremity surgeon. Peripheral nerve stimulation offers a solution for chronic, debilitating pain recalcitrant to other treatment modalities.

Background: Of all the postsurgical pain conditions, thoracotomy pain poses a particular therapeutic challenge in terms of its prevalence, severity, and ensuing postoperative morbidity. Multiple pain generators contribute to the severity of post-thoracotomy pain, and therefore a multimodal analgesic therapy is considered to be a necessary strategy. Along with opioids, thoracic epidural analgesia, and paravertebral blocks, N-Methyl-D-Aspartate (NMDA) receptor antagonists such as ketamine have been used as adjuvants to improve analgesia. Objective: We reviewed the evidence for the efficacy of intravenous and epidural administration of ketamine in acute post-thoracotomy pain management, and its effectiveness in reducing chronic postthoracotomy pain. Study Design: Systematic literature review and an analytic study of a data subset were performed. Methods: We searched PubMed, Embase, and Cochrane reviews using the key terms “ketamine,” “neuropathic pain,” “postoperative,” and “post-thoracotomy pain syndrome.” The search was limited to human trials and included all studies published before January 2015. Data from animal studies, abstracts, and letters were excluded. All studies not available in the English language were excluded. The manuscript bibliographies were reviewed for additional related articles. We included randomized controlled trials and retrospective studies, while excluding individual case reports. Results: This systematic literature search yielded 15 randomized control trials evaluating the efficacy of ketamine in the treatment of acute post-thoracotomy pain; fewer studies assessed its effect on attenuating chronic post-thoracotomy pain. The majority of reviewed studies demonstrated that ketamine has efficacy in reduction of acute pain, but the evidence is limited on the long-term benefits of ketamine to prevent post-thoracotomy pain syndrome, regardless of the route of administration. A nested analytical study found there is a statistically significant reduction in acute post-thoracotomy pain with IV or epidural ketamine. However currently, the evidence for a role of ketamine as a preventative agent for chronic postthoracotomy pain is insufficient due to the heterogeneity of the studies reviewed with regard to the route of administration, dosage, and outcome measures. Limitations: The evidence for a role of ketamine as a preventative agent for chronic post-thoracotomy pain is insufficient due to the heterogeneity of the studies reviewed. Conclusion: The majority of randomized controlled trials reviewed show no role for ketamine in attenuating or preventing post-thoracotomy pain syndrome at variable follow-up lengths. Therefore, additional research is warranted with consideration of risk factors and long-term follow-up for chronic post-thoracotomy pain though the evidence for benefit appears clear for acute post-thoracotomy pain. Key words: Ketamine, postoperative, thoracotomy pain, post thoracotomy pain syndrome, neuropathic pain

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