Background: Phantom limb pain is a frequent complication after limb amputation, its pathophysiology is complex and includes changes in the peripheral nerve, dorsal root ganglia, spinal cord, cerebral cortex, and thalamus. At this time, there is not an effective drug for treatment and prevention of phantom limb pain. Perineural local anesthetic infiltration has obtained different results in the prevention of phantom limb pain, so we propose to combine an α2 agonist in peripheral nerve block to assess its effectiveness in preventing postoperative pain. Methods: This was a prospective, double-blind, controlled, and simple randomized study. We included 30 patients undergoing surgery for supracondylar femoral amputation, older than 18 years, ASA I-III, in a sample calculation of 95% in Confidence Interval and 80% of statistical power. We included 15 patients per group managed with subarachnoid neuraxial block, and a perineural infiltration before the sciatical nerve section with 10 ml of 0.5% ropivacaine + 50 mcg dexmedetomidine (RD Group), or 0.5% ropivacaine + 0.9% saline solution (Group RS), in both groups We continued a perineural infusion with 0.15% ropivacaine using an elastomeric pump for 24 hours; We evaluated stump pain and phantom limb pain, upon admission to recovery, 8 hrs, 24 hrs, 30 days and 3 months. The data analysis was carried out using the SPSS version 21 program; In all cases, we defined statistical significance when obtaining p <0.05. Results: This study included a total of 30 patients, 15 patients in the RD group and 15 patients in the RS group. Statistical significance was found in the pain levels of the stump at rest at 24 hours, being lower in the RD group (p = 0.003). This intervention also impacted the opioid requirements at 24 hours, requiring tramadol rescue 27% of the patients in the RD group, against 93% of the patients in the RS group (p = 0.0002). Regarding phantom limb pain, there was no incidence during the three months of follow-up in the RD group, against three patients who report mild phantom limb pain in the RS group. Conclusions: The combination of ropivacaine with dexmedetomidine appears to be an effective intervention with minimal side effects to prevent the occurrence of acute and chronic pain as well as phantom limb pain in patients undergoing femoral supracondylar amputation as well as reducing the postoperative opioid requirements.