Patients fulfilling the inclusion criteria will be enrolled in the study and receive electrocatheter implant. Then, they will be observed for a two-weeks trial period in which the efficacy of the stimulation and the compliance of the patient is evaluated. During this trial a Tonic wave stimulation is administered by the external generator. After this trial, the definitive generator will be implanted. Two weeks of Tonic stimulation will follow the surgery to avoid any interference of the pain measurement with the surgical pain. After this two weeks period, the stimulation will be switched into the combined waveform for 15 days. At the end of the study period, the final waveform setting of the SCS will be in accord with the patient's stimulation preference.