SPINAL CORD STIMULATION FOR FAIL BACK SURGERY SYNDROME : LITERATURE REVIEW AND CLINICAL STUDY

ABSTRACT Objective: Fail back surgery syndrome (FBSS) is a common cause of pain following spine surgery, and is associated with persistent or recurrent pain despite anatomically correct intervention. Spinal cord stimulation (SCS) is regarded as one of the most effective methods of treatment for fail back surgery syndrome. Methods: We studied 34 patients who underwent test stimulation and chronic SCS for FBSS. Results: Six months postoperatively, mean improvement by the visual analog scale (VAS) of average and maximum daily pain, and the painDETECT score, were 54.4%, 50.7% and 57.3%, respectively. This meets the criteria for effectiveness of the method, according to the literature. Most of patients reported significant improvements in life quality and less need for analgesics. Complications were seen in nine patients (26.4%) and included: intraoperative dura injury (one patient, 2.9%), wound infection (one patient, 2.9%), and electrode displacement (seven patients, 20.5%). No cases of postoperative neurological deterioration were seen. Conclusions: SCS is safe and effective for the treatment of neuropathic pain caused by FBSS. Level of Evidence IV; Case series.


INTRODUCTION
Spine surgery is one of the most rapidly developing fields of modern medicine, and more than 1,000,000 spine operations are currently performed each year, worldwide. 1 Thanks to minimally invasive, endoscopic and percutaneous technologies, the number of intraoperative and early postoperative complications has decreased and the overall postoperative results have dramatically improved.
Nevertheless, the incidence of late postoperative complications is still high. 2One of the main such complications is fail back surgery syndrome (FBSS, or post-laminectomy syndrome), a term that is still controversial.According to different authors, FBSS can be defined as "Persistent or recurrent pain in the back/neck or limbs, despite surgery or treatment thought likely to relieve pain", 3 "Chronic radicular pain that has recurred or persists in the same distribution despite anatomically satisfactory previous spinal surgery", 4,5 "Lumbar (cervical) pain of unknown origin either persisting despite surgical intervention or appearing after surgical intervention for spinal (origin) pain originally in the same topographical distribution". 6As a result, we can emphasize that FBSS always has the following characteristics: chronic neuropathic pain, history of spine surgery (or surgeries), absence of clear etiologic factor of pain, and anatomically correct primary spine surgery.
One of the most modern and encouraging methods of treatment for FBSS is spinal cord stimulation (SCS).The epidural space was punctured percutaneously at level L2-L3 under local anesthesia, using a Tuohy needle.The needle position was verified by a common method (loss of resistance) and intraoperative X-Ray.An electrode was then implanted using fluoroscopic control at level Th7-Th12, depending on the site of the pain.(Figure 1) The technical feasibility of electrode implantation strongly depended on epidural scarring.

METHODS
Intraoperative testing was normally performed at a frequency 60 Hz, pulse width 300 msec.The results of the intraoperative testing were regarded as positive if the patient felt paresthesia and a feeling of vibration in the region of pain.It is important that these feelings should be tolerable and comfortable for patient.At higher frequencies, muscle fibrillation can be seen in the corresponding group of muscles.
The test electrode was pulled through the counteropening in the lumbar region and fixed by suture.(Figure 2) Patient can walk immediately after surgery.During the test period (1-10 days) the results of pain relief were estimated using the pain scales and patient's questionnaire.Reprogramming can also be done if needed.(Figure 3) The main parameters of stimulation are level of perception and level of comfort.
If the test was effective, the second stage (generator implantation) was performed.
The site of electrode insertion was revised and the extension removed.The site of generator implantation ('pocket') was prepared, normally in the right gluteal region (if the patient was right-handed).The generator was connected to the electrode and intraoperative testing, as well as Z-Ray control, were performed.The wounds were closed.(Figure 4) Patient can walk immediately after surgery.
The aim of the postoperative period was to program different modes for stimulation (i.e., for sleeping, walking, the sitting position etc).
The level of comfort depended on the body position during the first two-to-three months postoperatively.
Results were estimated six months postoperatively by following parameters: visual analog scale (VAS) of daily average and maximum daily pain; painDETECT score; postoperative complications.

RESULTS
Thirty-four patients met the inclusion criteria, were included in the study and operated via both stages of SCS system implantation.Five patients (12.8% from the primary selection) matched the inclusion criteria but were excluded because of negative test stimulation results.
The mean hospitalization time was 12.9 days.Six months postoperatively clear pain relief was demonstrated by all three studied parameters.(Table 1) Complications were seen in nine patients (26.4%) and included: intraoperative dura injury (one patient, 2.9%), wound infection (one patient, 2.9%), and electrode displacement requiring surgical correction (seven patients, 20.5%).No cases of postoperative neurological deterioration were seen.

DISCUSSION
According to relevant clinical studies, fail back surgery syndrome (FBSS) is a common condition with prevalence ranging from 10% to 40%. 7FBSS develops around 4.7 years after primary surgery. 8BSS significantly decreases quality of life, and leads to multiple revisions (rate of revisions -4%-19%), 9 chronic pain, depression, medical and social impairment, disability and the need for of medical treatment.Patients with FBSS permanently take antidepressants (38%), anticonvulsants (38%), and opioid analgesics (62%), 10 86% of patients have to use more than four methods of conservative management simultaneously. 11As a result, FBSS is a serious medical and social problem.
Multiple studies have shown effectiveness of SCS for FBSS.To date, after SCS was invented by CN Shealy in 1967 more than 200,000 SCS systems have implanted worldwide, with more than 25,000 implanted each year. 12,13FBSS is one of the most evidence-based indications for SCS. 14A prospective, randomized, multicenter, international, controlled study EVIDENCE trial of 132 patients with FBSS showed stable pain relief in leg or legs (more than 50% from baseline) 6-24 months postoperatively. 15The multicenter, randomized PROCESS trial demonstrated pain relief of 50%-70% and a statistically significant reduction of drug intake. 16B North et al. showed that in USA SCS for FBSS is 17-53% less expensive and more effective than reoperation. 17Retrospective studies (410 patients) also showed that 60% of patients had pain relief of more than 50%. 18Available data in the Russian literature confirm these results: SCS was effective in early and late periods with a more than 75% decrease in analgesic drug intake in a group of more than 100 patients operated at the Neurosurgical Institute named after N.N.Burdenko. 19Another study on 45 patients showed that SCS is more effective than conservative pain management for SCS. 20ur results are comparable with those of other authors; pain relief varies from 50% to 60% depending on the measurement scale used.According to common opinion, test stimulation effectiveness of less than 50% should be regarded as a negative result.Nevertheless 4 of our 34 patients had less than 50% pain relief during the test, but claimed that they wanted the whole SCS system to be implanted as even this pain relief is still important for their quality of life.In some of our patients pain relief in the initial months after implantation was higher than in long-term; this can be explained by phenomenon of neural tolerance, and corresponds to the finding of Isagulyan ID, Tomsky AA et al. 21The rate of technical complications in our group was fairly high (20.5%).This can be explained by learning curve that our surgical team underwent: most complications were seen during 1 st year of mastering the SCS technique.It is interesting that in all patients with long fusions for deformity correction, it was feasible to implant the electrode percutaneously and avoid open surgery.

CONCLUSIONS
SCS is an effective method of the treatment for intractable neuropathic pain caused by FBSS.Chronic SCS led to ≥50% pain relief, significantly improved quality of life, reduced the need for analgesic medications, and helped avoid unnecessary revisions.Adherence to strict indications and precise patient selection are crucial for successful SCS.Neurostimulation in most cases is safe for the patient, and technically feasible; complications include electrode migration, which can be easily corrected.New methods of stimulation such as high-frequency stimulation and non-invasive external generators will improve the results of treatment and decrease the rate of complications.Long-term results of SCS for FBSS should be estimated, while enlarging the study group.We presume that patients with FBSS require a multidisciplinary approach, with the participation of neurosurgeons, neurologists, orthopedists, rehabilitation specialists and other staff.
All authors declare no potential conflict of interest related to this article.
Patients with FBSS treated by chronic SCS in the neurosurgical department of the Research Center of Neurology from 2014 to 2017 were prospectively included in our study.All patients signed an Informed Consent Form.The study was approved by the local Ethics Committee of the Research Center of Neurology.The extended preoperative clinical examination included: • neurological examination (by a neurosurgeon and neurologist, independently); • medical history; • visual analog scales (VAS) of pain, painDETECT score, Beck depression inventory; • magnetic resonance imaging (MRI), computed tomography (CT), dynamic X-Ray; • neurophysiological examination (electroneuromyography, transcranial magnetic stimulation); • test X-Ray assisted blockages; • standard preoperative tests and examinations (blood and urine tests, ECG, chest X-Ray); • other methods, if needed (densitometry, ultrasound etc).The Inclusion criteria were as follows: • neuropathic pain, everyday VAS score ≥ 4, painDETECT score ≥ 19; • no indications for direct revision surgery; • no effect of correct conservative pain management for 3-6 months (estimated by a neurosurgeon and neurologist, independently).The Exclusion criteria were as follows: • clear correlation between body position and pain, indications for revision surgery, satisfactory or good effect of conservative pain management; • radicular or conduction pain; • severe depression (Beck depression inventory ≥ 20), attempted suicide, mental disorders troubling patient education and/or decreasing compliance; • severe comorbidities; • negative test stimulation.All patients underwent two-stage implantation of SCS systems produced by two different manufacturers (St.Jude and Medtronic).The First stage included test stimulation to estimate the coverage and clinical effect of the stimulation.

Figure 1 .
Figure 1.Implantation of test electrode for SCS: A -Needle insertion (angle not more than 30 º); B -gauge insertion; C, D -electrode is located dorsally on Th9-Th10 (A/P and lateral view).

Figure 3 .
Figure 3. Test period: A -Test electrode and extension are connected to the patient's programmer; B -physician's programmer.

Figure 4 .
Figure 4. Implantation of permanent system for chronic SCS: A -Generator; B -"Pocket" for generator; C -connection of generator and electrode; Dconnector; e -wound closure.