When patients suffer from chronic pain after multiple back surgeries, this is denominated as the 'failed back surgery syndrome'. A possible treatment for these patients is spinal cord stimulation. This is an invasive treatment where no other treatment options (medication, minimal invasive treaments) can offer progress to the patients' health status. In spinal cord stimulation, an electrode will be placed at the spinal cord under local anaesthesia whereas via a battery a painless electrical stimulation will arise. Clinical research have demonstrated that a new way of spinal cord stimulation can improve back and leg pain significantly. This will lead to a better quality of life for the patients and a decreased use of medications. In Ziekenhuis Oost-Limburg, different manners of spinal cord stimulation will be compared to each other.

The patients in our pain centre are implanted with Medtronic material. This material cannot deliver the 10kHz frequency but can deliver up to 5000 Hz (hereinafter referred to as high density stimulation). This also delivers high energy to the spinal cord without palpable paresthesia, with a beneficial effect on the pain.

We wish to include patients who, in accordance with Belgian regulations, have undergone a normal evaluation period with an external battery and who have subsequently had a definitive system implanted. The implant procedure, evaluation period and the material used are identical to patients outside the study context.

We wish to compare different stimulation modes within a patient population in which an epidural electrode for failed back surgery syndrome (FBSS) has been implanted, in order to evaluate the effectiveness. We will evaluate the modality "high-density", conventional stimulation and sham stimulation in the same patient. This can be easily adjusted by reprogramming the implanted battery. For this study we want to use a relatively new study design, namely: single case design (N-of-1 trial). In this, many variables will be evaluated with a limited number of study subjects in order to determine an effect. We want to investigate to what extent the patient experiences the different stimulation modes and to what extent he can compare or prefer these stimulation modes. The stimulation that the patient prefers as most pleasant can be continued afterwards. If the patient does not experience pain reduction during a certain stimulation mode, he can always fall back on his own pain medication.

Inclusion Criteria:

• Patients with an implanted neurostimulation system met een FBSS met geïmplanteerd

Exclusion Criteria:

• no knowledge of the Dutch language
• Addicted to drugs