 The purpose of this study is to evaluate the effects of the SCS on sensory perceptions of patients with chronic pain CRPS, FBSS. Sensorial perception tests will be carried out in accordance with a standardized procedure Rolke et al. Pain, 2006 at the level of maximum pain area painful leg, and at two non-painful areas contralateral leg and ipsilateral arm. The thermode Thermal Sensory Analyser TSA-II NeuroSensory Analyzer and its complement Vibratory Sensory Analyzer VSA-3000 Medoc will be used to assess warm, cold and vibratory detection thresholds, as well as heat and cold painful thresholds. Von Frey monofilaments Bioseb will be used to evaluate the mechanical detection threshold. The algometer Force Ten TM FDX Digital Wagner will measure the pressure pain threshold. Dynamic mechanical allodynia will be assessed with a standardized brush SENSELab Brush-05, Somedic. The Neuropen Owen Mumford will be used to test the temporal pain summation. Participants will be recruited through the neuromodulation clinic located in Enfant-Jésus Hospital Québec, Canada. 