Spinal Cord Stimulation (SCS) has been a well-established treatment for chronic neuropathic pain in Failed Back Surgery Syndrome with associated legs and/or low back pain. The waves used in Spinal Cord Stimulation are mainly Tonic or Burst. Both Tonic and Burst stimulation offer neuropathic pain suppression, with slightly superiority of the Burst wave for the FBSS. The aim of our study is to evaluate the efficacy of a new stimulation paradigm with the combination of the two wave forms.

Spinal Cord Stimulation (SCS) has been a well-established treatment for chronic neuropathic pain for decades. One of the most general indication for SCS is Failed Back Surgery Syndrome with associated legs and/or low back pain.

Conventional low frequency neurostimulation is applied with a tonic wave shape (pulse width is usually 300 to 500 μsec, amplitude 2 to 5 mA, and frequency 40 to 50 Hz); this kind of stimulation produces a perceptible paraesthesias in the area of stimulation "covering" the region of pain. Further development in waves of stimulation during the recent years led to new paradigms of sub-perception stimulation like "Burst" stimulation that has characteristics of a cluster of waves with higher frequency.

The efficacy of these two wave forms has been demonstrated by different authors. Both Tonic and Burst stimulation offer neuropathic pain suppression, with slightly superiority of the Burst wave for the FBSS.

Recent advances in technology of the implantable devices for spinal cord stimulation led to the possibility to combine the two stimulation waves described allowing the design of a possible new paradigm of stimulation. The Tonic and Burst wave can be combined to stimulate the same pain area using the same configuration otherwise they can be programmed to stimulate two different pain areas with two different configurations. Both burst and tonic waveforms paradigms can be customized according to patients' need. The characteristics of this combined stimulation wave in terms of efficacy, non inferiority, energy consumption, and patient satisfaction are unknown.

The primary objective of this trial is to compare pain suppressive effect of Low Frequency "Tonic Wave" versus Low Frequency Combined "Burst and Tonic Wave" for Spinal Cord Stimulation in subjects with refractory neuropathic leg and low back pain as result of FBSS.

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.

Inclusion Criteria:

• Chronic, persistent, refractory, low back pain as a result of spinal surgery
• Failed conservative treatments for chronic pain including but not limited to pharmacological therapy, physical therapy and minimally interventional pain procedures for chronic pain
• Pain radiating in the leg, following segments L4 and/or L5 and/or S1 for at least 6 months
• Minimum baseline pain intensity as assessed by VAS of ≥ 50mm on 100mm scale in the primary pain area
• Subject is able and willing to provide informed consent
• Subject is able and willing to comply with the protocol and follow-up schedule

Exclusion Criteria:

• Back pain component of more than 20% or VAS > 40mm on 100mm scale
• Bilateral limb pain
• Subjects with a previous SCS implantation
• Changes in pain medication in the 2 months preceding the trial period
• Expected inability of subjects to correctly operate the neurostimulation system
• Presence of any other clinically significant or disabling chronic pain condition (eg. hip arthrosis, rheumatoid arthritis, fibromyalgia, etc.)
• History of coagulation disorders, lupus erythematosus, diabetes mellitus
• Symptoms or proof of any malignant disease
• Current use of medicines affecting coagulation which cannot be temporarily stopped
• Evidence of an active disruptive psychiatric disorder or other known condition significant enough to impact the perception of pain, compliance to intervention and/or ability to evaluate treatment outcome as determined by the investigator
• Life expectancy of less than 1 year
• Existing or planned pregnancy in the trial period