Investigators hypothesis that pre-amputation period could be important in eliminating Phantom Limb Pain (PLP) in the patients in whom cortical reorganization is not yet established. The reduction of pre-operative pain and prevention of formation of pain memories may eliminate development of PLP by using dual networks treatment strategy. This Phase III, randomized, double-blind, placebo-controlled study is designed to evaluate the efficacy of pre-operative pregabalin (lyrica) and ketamine in eliminating phantom limb pain in patients undergoing lower limb amputation.