Clinical Outcomes of Prophylactic Regenerative Peripheral Nerve Interface (RPNI) Surgery in Pediatric Lower Limb Amputation Patients
Ahneesh J. Mohanty, MD1, Paul S Cederna, M.D.2, Stephen WP Kemp, Ph.D.1 and Theodore A Kung, MD3, 1University of Michigan, Ann Arbor, MI, 2Plastic Surgery, University of Michigan, Ann Arbor, MI, 3Section of Plastic & Reconstructive Surgery, University of Michigan, Ann Arbor, MI
Introduction: Chronic post-amputation pain is a debilitating sequela of limb amputation, leading to disability, decreased quality of life, and dependence on pain medications. The prevalence of post-amputation pain in pediatric patients is estimated to be as high as 83%, similar to the adult population. The standard of care continues to be symptomatic pharmacologic treatment and desensitization therapy. In this study, we postulate that prophylactic Regenerative Peripheral Nerve Interface (RPNI) surgery performed during amputation may decrease incidence of neuroma and phantom limb pain as well as pain medication use among pediatric amputation patients.
Methods: Pediatric patients between the ages of 8 and 21 years who underwent major lower limb amputation with and without RPNI surgery were identified. Retrospective chart review was performed to determine post-operative outcomes including pain scores and medication usage in both the prophylactic and control groups. Neuroma pain was elicited by performing Tinel’s test and the experience of phantom limb pain was recorded during follow up exams. Narcotic usage at last follow-up was quantified by conversion to milligrams morphine equivalents per day (MME/day) using standard conversion protocols. Overall analgesic use was converted to Medication Quantification Scale version III (MQSIII) scores, a verified tool to co-quantify analgesics prescribed for chronic nonmalignant pain, taking into consideration drug class, dosage, and potency. Longitudinal analysis was performed using GraphPad Prism.
Results: Forty-four pediatric patients were identified; 25 patients underwent prophylactic RPNI surgery at the time of lower limb amputation and 19 patients who did not have RPNI surgery served as controls. There were no differences in mean age or follow-up periods between groups. Seventy-nine percent of control patients developed chronic post-amputation pain, while 21% of RPNI patients developed chronic post-amputation pain (Fisher’s exact, p<0.001). Of the patients who developed chronic post-amputation pain, 20% of controls developed neuroma pain, compared to 0% of RPNI patients (Fisher’s exact, p<0.001). Overall, controls had a nearly 5-fold higher risk of developing post-amputation pain compared to RPNI patients (RR=4.93, Fisher’s exact, p<0.0001). Furthermore, RPNI patients demonstrated a lower mean pain score (t-test, p<0.001), decreased narcotic usage (t-test, p<0.01), and decreased analgesic use (t-test, p<0.001) compared to controls.
Conclusions: Prophylactic RPNI surgery shows great promise for pediatric patients undergoing major lower limb amputation, as evidenced by decreased chronic pain, narcotic usage, and analgesic use compared to controls. Future investigation will elucidate potential benefit of RPNI surgery on reducing morbidity and improving quality of life in pediatric amputation patients.
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