Long-Term Outcome of Spinal Cord Stimulation in Failed Back Surgery Syndrome: 20 Years of Experience With 224 Consecutive Patients

Long-Term Outcome of Spinal Cord Stimulation in Failed Back Surgery Syndrome: 20 Years of... Abstract BACKGROUND Failed back surgery syndrome (FBSS) is a challenging condition that lacks a curative treatment. In selected patients, spinal cord stimulation (SCS) has provided a satisfactory outcome. OBJECTIVE To evaluate the long-term outcome of SCS in FBSS, as measured by (1) the explantation rate, (2) complications, and (3) patient satisfaction with the global perceived effect (GPE). METHODS We studied 224 consecutive FBSS patients who underwent an SCS trial with surgically implanted leads at our hospital between January 1996 and December 2014. The patients’ satisfaction with the GPE of treatment was measured through a postal questionnaire at the end of follow-up. RESULTS Based on a 1-wk trial, permanent SCS was implanted in 175 (78%) patients. Out of these patients, 153 (87%) reported satisfactory outcomes after 2 mo. During the mean follow-up of 6 yr, 34 (19%) of SCS devices were permanently explanted due to inadequate pain relief, and 11 (6%) were explanted for other reasons. Electrode revision due to inadequate pain relief was done for 22 patients. In total, 26 complications were reported due to: 7 deep infections, 11 hardware malfunctions, 1 subcutaneous hematoma, 4 instances of discomfort due to the pulse generator, and 3 electrode migrations. One hundred thirty patients (74%) continued with SCS until the end of follow-up. Of them, 61 (47%) returned the questionnaire, and 42 (69%) reported substantially improved or better GPE. CONCLUSION SCS can provide a good outcome in the treatment of FBSS. Patient selection could be further improved by developing novel predictive biomarkers. Spinal cord stimulation, Failed back surgery syndrome, Retrospective observational study, Surgery, Long-term outcome ABBREVIATIONS ABBREVIATIONS FBSS failed back surgery syndrome GPE global perceived effect IPG internal pulse generator LBP Low back pain SCS spinal cord stimulation Pain is a global problem. Each year 10% of the population is diagnosed with chronic pain, and an estimated 20% of adults suffer from pain worldwide.1,2 In Finland, 19% to 48% of the population is estimated to suffer from chronic pain.3 Chronic pain is associated with physical and psychological comorbidities, such as depression and anxiety.4 In a recent survey of 2000 patients with chronic pain, 36% reported that pain had a negative effect on their families and friends, and 27% felt socially isolated and lonely.5 Low back pain (LBP) is common in western countries where 46% of women and 47% of men have experienced LBP in the last 12 mo.6 In most European countries, LBP accounts for the largest proportion of lost workdays of all musculoskeletal conditions.6 LBP is accountable for 12.5% of sick days in the UK and 13.5% in Sweden.6 Furthermore, the number of spine surgeries has steadily increased in the past decades.7,8 Failed back surgery syndrome (FBSS) describes persistent or recurrent pain in the lumbar area with or without a sciatic component after 1 or more lumbar surgeries.9 The incidence of FBSS after lumbar spinal surgery is between 20% and 40%, and it has not declined despite novel mini-invasive surgical techniques.10,11 Spinal cord stimulation (SCS) is a well-established modality for the treatment of intractable neuropathic pain.12-15 In previous studies, adequate pain relief during the SCS trial period has predicted satisfactory long-term outcomes,16,17 and pain reduction can improve over time.18 However, the patient cohorts were heterogeneous, FBSS was pooled with other etiologies, and many patients were lost before the follow-up visit. We present a retrospective analysis of SCS in FBSS in a single institution for almost a 20-yr period with a median follow-up time of 5 yr. Our objective is to evaluate the long-term outcome of SCS in FBSS as measured by the (1) explantation rate due to inefficient pain relief, (2) complications, and (3) patient satisfaction with the global perceived effect (GPE) at the end of the follow-up. METHODS Patients We retrospectively evaluated the medical charts of all 224 FBSS patients with SCS implantation at Kuopio University Hospital (KUH) Neurosurgery between January 1, 1996 and December 31, 2014. During the study period, KUH neurosurgery solely provided full-time acute and elective neurosurgical services for the 850 000 people catchment population in Eastern and Central Finland. A pain physician, neurosurgeon, or orthopedic surgeon provided a diagnosis of FBSS and the initial treatment (oral analgesics and physical therapy). Patients had at least 1 previous lumbar decompressive procedure due to disc herniation or spinal stenosis but suffered from radicular lower limb pain alone or combined with lumbar pain. Before SCS implantation, any surgically treatable pathology was ruled out by a neurosurgeon. Two patients with lumbar pain only were treated with epidural SCS, but they were excluded in this study. Untreated depression was considered as a contraindication for SCS. Clinical Evaluation All medical records were reviewed for details regarding SCS treatment, complications, and revisions. The baseline characteristics included age, gender, and previous lumbar procedures, including instrumented fusions, and duration and localization of pain. Follow-up data were gathered for all visits, including the type and location of the electrode, complications, revisions, and total follow-up time in years. All patients were followed up from medical records until December 31, 2015. Digital imaging data were available for all 188 patients with SCS implanted 2003 or later. The GPE of the treatment was measured in a postal questionnaire delivered to all 130 patients with SCS at the end of follow-up December 31, 2015. The GPE was measured using a 7-point Likert-scale: 1 = completely recovered, 2 = substantial improvement, 3 = little improvement, 4 = no change, 5 = little decline, 6 = substantial decline, and 7 = totally failed. This scale has been shown to be a valid measure for GPE.12,19 SCS Implantation The SCS electrode was implanted into the epidural space microsurgically under direct visual control with the operating microscope using a paddle-lead electrode (Resume 3586, Symmix 3982, Specify 2 × 4 3998, or Specify 5-6-5 39565, Medtronic, Dublin, Ireland) under general anesthesia. The techniques for implantation have been described previously.20 Before surgery, a methylene blue mark was placed in an X-ray control to identify the level of entry into the spinal canal. The electrode was then pushed upward into the epidural space, yielding an actual implantation level that was 1 level higher than the entry level. Thoracic implantation level was determined by pain localization and previous operations. No intraoperative testing was used. The mean duration of the trial was 7 d (range 0-21). After the trial period, patients who reported paresthesia covering most of the limb pain area with adequate pain relief received an internal pulse generator (IPG, model 7425, model 37703, model 7427V, model 37702, or model 97702, Medtronic). All of the patients that received an IPG visited an outpatient clinic 2 to 3 mo (mean 60 d) after surgery, and a final questionnaire was sent in 2015. Patients that experienced problems with their SCS therapy were admitted to hospital outpatient clinic whenever needed (total 287 visits). Statistical Analysis The statistical analyses were performed using SPSS version 24.0 (IBM Corporation, Armonk, New York). The demographic and SCS-related data were analyzed by calculating the means and standard deviations for the normally distributed variables or medians, and ranges were calculated for the other variables. A cross-table analysis was used for the categorical outcome. A logistic regression analysis was used for the uni- and multivariate analysis of variables associated with (1) successful trial stimulation and (2) GPE of treatment at the end of the follow-up visit. A Cox regression analysis was used to analyze the uni- and multivariate variables associated with SCS explantation that resulted from inadequate pain relief or other causes. Ethical Issues Study protocol and informed consent were approved by the Institutional Review Board of Kuopio University Hospital, and all subjects responding to the questionnaire gave informed consent. RESULTS FBSS History The median age of the 224 patients during the trial period was 48 yr (range 22-83), and 52% were male (Table 1). The median duration of pain was 6 yr (range 0-33), and the median number of previous operations was 2 (range 1-9). The initial underlying pathology was disc herniation (50%), disc herniation with stenosis (23%), stenosis (lateral or central 20%), or other (6%, including cysts and spondylolysis). Most of the patients had single-level surgeries at L4-L5 (35%), while 32% had multilevel surgeries. Radicular pain alone was described by 41% of patients. Seventy-three (33%) patients received instrumented fusion, of which 3 (4%) were later removed. TABLE 1. Patient Demographics and Multivariate Analysis of Variables Associated With Successful Trial Stimulation, SCS Explantation, and Pain Relief at the End of the Follow-up Period             Permanent SCS implanted n = 175      Trial only n = 49  SCS explanted n = 45  SCS in use at the end of follow up n = 130 (61a)      All  %  OR (95% Cl)b  P  All  %  HR (95% Cl)c  P  Alld  %  OR (95% Cl)e  P  Gender                                   Female    20  41  1    25  56  1    63 (34)  49  1     Male    29  59  0.64 (0.34-1.2)  .84  20  44  1.4 (0.74-2.5)  .32  67 (27)  51  1.4 (0.35-5.9)  .68  Age (mean ± SD)    47.6 ± 11.3    0.98 (0.95-1.0)  .25  48.7 ± 12.4    1.0 (0.97-1.0)  .91  49 ± 10.4    0.96 (0.88-1.0)  .96  Location of pain                                   Extremity    21  43  1    19  42  1    51 (29)  39  1     Extremity and back    28  57  1.1 (0.53-2.1)  .86  26  58  0.86(0.46-1.6)  .65  79(32)  61  0.18(0.02-1.5)  .11  Duration of pain in years (mean ± SD)    8.6 ± 7.7    1.0 (1.0-1.1)  .08  6.8 ± 6.6    0.98 (0.93-1.0)  .48  7.3 ± 5.8    1.2 (0.99-1.4)  .07  Level of operation                                   L4-L5 and above    21  43  1    15  33  1    53 (25)  41  1     L5-S1    11  22  0.64 (0.26-1.6)  .34  14  31  0.93 (0.42-2.1)  .86  40 (22)  31  0.80 (0.12-5.3)  .82   Multiple level    17  35  0.97 (0.43-2.2)  .95  16  36  0.83 (0.37-1.8)  .63  37 (14)  28  6.9 (0.89-54)  .07  Reason for operation                                   Disc herniation    26  53  1    24  53  1    64 (34)  49  1     Stenosis    11  22  0.79 (0.34-1.9)  .60  10  22  1.2 (0.51-2.6)  .73  35 (15)  27  0.12 (0.01-1.4)  .09   Both    12  25  0.85 (0.32-2.3)  .76  11  24  1.2 (0.47-3.3)  .67  31 (12)  24  0.43 (0.04-4.8)  .50  Number of previous operations (mean ± SD)    2.3 ± 1.3    1.0 (0.79-1.3)  .87  2.6 ± 1.9    1.2 (0.93-1.5)  .20  2.2 ± 1.3    0.38 (0.16-0.89)  .03f  Spinal fusion                                   No    35  71  1    31  69  1    85 (39)  65  1     Yes    14  29  1.4 (0.65-3.2)  .37  14  31  1.1 (0.55-2.4)  .72  45 (22)  35  9.1 (1.1-74)  .04f  Electrode location                                   T9-T10    32  65  1    30  67  1    81 (36)  62  1     Other    17  35  1.2 (0.57-2.4)  .66  15  33  1.1 (0.59-2.2)  .70  49 (25)  38  0.73 (0.14-3.8)  .71  Type of electrodeg                                   Symmix/Resume 1 × 4    42  86  1    40  89  1    98 (43)  75  1     Specify 5-6-5/2 × 4    7  14  1.7 (0.64-4.5)  .29  5  11  0.86 (0.30-2.5)  .78  32 (18)  25  3.8 (0.45-32)  .22  Deceased    5  10      1  2      4  3                  Permanent SCS implanted n = 175      Trial only n = 49  SCS explanted n = 45  SCS in use at the end of follow up n = 130 (61a)      All  %  OR (95% Cl)b  P  All  %  HR (95% Cl)c  P  Alld  %  OR (95% Cl)e  P  Gender                                   Female    20  41  1    25  56  1    63 (34)  49  1     Male    29  59  0.64 (0.34-1.2)  .84  20  44  1.4 (0.74-2.5)  .32  67 (27)  51  1.4 (0.35-5.9)  .68  Age (mean ± SD)    47.6 ± 11.3    0.98 (0.95-1.0)  .25  48.7 ± 12.4    1.0 (0.97-1.0)  .91  49 ± 10.4    0.96 (0.88-1.0)  .96  Location of pain                                   Extremity    21  43  1    19  42  1    51 (29)  39  1     Extremity and back    28  57  1.1 (0.53-2.1)  .86  26  58  0.86(0.46-1.6)  .65  79(32)  61  0.18(0.02-1.5)  .11  Duration of pain in years (mean ± SD)    8.6 ± 7.7    1.0 (1.0-1.1)  .08  6.8 ± 6.6    0.98 (0.93-1.0)  .48  7.3 ± 5.8    1.2 (0.99-1.4)  .07  Level of operation                                   L4-L5 and above    21  43  1    15  33  1    53 (25)  41  1     L5-S1    11  22  0.64 (0.26-1.6)  .34  14  31  0.93 (0.42-2.1)  .86  40 (22)  31  0.80 (0.12-5.3)  .82   Multiple level    17  35  0.97 (0.43-2.2)  .95  16  36  0.83 (0.37-1.8)  .63  37 (14)  28  6.9 (0.89-54)  .07  Reason for operation                                   Disc herniation    26  53  1    24  53  1    64 (34)  49  1     Stenosis    11  22  0.79 (0.34-1.9)  .60  10  22  1.2 (0.51-2.6)  .73  35 (15)  27  0.12 (0.01-1.4)  .09   Both    12  25  0.85 (0.32-2.3)  .76  11  24  1.2 (0.47-3.3)  .67  31 (12)  24  0.43 (0.04-4.8)  .50  Number of previous operations (mean ± SD)    2.3 ± 1.3    1.0 (0.79-1.3)  .87  2.6 ± 1.9    1.2 (0.93-1.5)  .20  2.2 ± 1.3    0.38 (0.16-0.89)  .03f  Spinal fusion                                   No    35  71  1    31  69  1    85 (39)  65  1     Yes    14  29  1.4 (0.65-3.2)  .37  14  31  1.1 (0.55-2.4)  .72  45 (22)  35  9.1 (1.1-74)  .04f  Electrode location                                   T9-T10    32  65  1    30  67  1    81 (36)  62  1     Other    17  35  1.2 (0.57-2.4)  .66  15  33  1.1 (0.59-2.2)  .70  49 (25)  38  0.73 (0.14-3.8)  .71  Type of electrodeg                                   Symmix/Resume 1 × 4    42  86  1    40  89  1    98 (43)  75  1     Specify 5-6-5/2 × 4    7  14  1.7 (0.64-4.5)  .29  5  11  0.86 (0.30-2.5)  .78  32 (18)  25  3.8 (0.45-32)  .22  Deceased    5  10      1  2      4  3      SCS = spinal cord stimulation; aquestionnaire answered; bodds ratio for successful trial, i.e., pulse generator implantation after trial; c hazard ratio for SCS explantation; din parentheses: questionnaire answered; odds ratio; efor complete recovery or substantial improvement (Global Perceived Effect, GPE 1-2) at the end of follow up; fP < .05; gall electrodes manufactured by Medtronic. View Large TABLE 1. Patient Demographics and Multivariate Analysis of Variables Associated With Successful Trial Stimulation, SCS Explantation, and Pain Relief at the End of the Follow-up Period             Permanent SCS implanted n = 175      Trial only n = 49  SCS explanted n = 45  SCS in use at the end of follow up n = 130 (61a)      All  %  OR (95% Cl)b  P  All  %  HR (95% Cl)c  P  Alld  %  OR (95% Cl)e  P  Gender                                   Female    20  41  1    25  56  1    63 (34)  49  1     Male    29  59  0.64 (0.34-1.2)  .84  20  44  1.4 (0.74-2.5)  .32  67 (27)  51  1.4 (0.35-5.9)  .68  Age (mean ± SD)    47.6 ± 11.3    0.98 (0.95-1.0)  .25  48.7 ± 12.4    1.0 (0.97-1.0)  .91  49 ± 10.4    0.96 (0.88-1.0)  .96  Location of pain                                   Extremity    21  43  1    19  42  1    51 (29)  39  1     Extremity and back    28  57  1.1 (0.53-2.1)  .86  26  58  0.86(0.46-1.6)  .65  79(32)  61  0.18(0.02-1.5)  .11  Duration of pain in years (mean ± SD)    8.6 ± 7.7    1.0 (1.0-1.1)  .08  6.8 ± 6.6    0.98 (0.93-1.0)  .48  7.3 ± 5.8    1.2 (0.99-1.4)  .07  Level of operation                                   L4-L5 and above    21  43  1    15  33  1    53 (25)  41  1     L5-S1    11  22  0.64 (0.26-1.6)  .34  14  31  0.93 (0.42-2.1)  .86  40 (22)  31  0.80 (0.12-5.3)  .82   Multiple level    17  35  0.97 (0.43-2.2)  .95  16  36  0.83 (0.37-1.8)  .63  37 (14)  28  6.9 (0.89-54)  .07  Reason for operation                                   Disc herniation    26  53  1    24  53  1    64 (34)  49  1     Stenosis    11  22  0.79 (0.34-1.9)  .60  10  22  1.2 (0.51-2.6)  .73  35 (15)  27  0.12 (0.01-1.4)  .09   Both    12  25  0.85 (0.32-2.3)  .76  11  24  1.2 (0.47-3.3)  .67  31 (12)  24  0.43 (0.04-4.8)  .50  Number of previous operations (mean ± SD)    2.3 ± 1.3    1.0 (0.79-1.3)  .87  2.6 ± 1.9    1.2 (0.93-1.5)  .20  2.2 ± 1.3    0.38 (0.16-0.89)  .03f  Spinal fusion                                   No    35  71  1    31  69  1    85 (39)  65  1     Yes    14  29  1.4 (0.65-3.2)  .37  14  31  1.1 (0.55-2.4)  .72  45 (22)  35  9.1 (1.1-74)  .04f  Electrode location                                   T9-T10    32  65  1    30  67  1    81 (36)  62  1     Other    17  35  1.2 (0.57-2.4)  .66  15  33  1.1 (0.59-2.2)  .70  49 (25)  38  0.73 (0.14-3.8)  .71  Type of electrodeg                                   Symmix/Resume 1 × 4    42  86  1    40  89  1    98 (43)  75  1     Specify 5-6-5/2 × 4    7  14  1.7 (0.64-4.5)  .29  5  11  0.86 (0.30-2.5)  .78  32 (18)  25  3.8 (0.45-32)  .22  Deceased    5  10      1  2      4  3                  Permanent SCS implanted n = 175      Trial only n = 49  SCS explanted n = 45  SCS in use at the end of follow up n = 130 (61a)      All  %  OR (95% Cl)b  P  All  %  HR (95% Cl)c  P  Alld  %  OR (95% Cl)e  P  Gender                                   Female    20  41  1    25  56  1    63 (34)  49  1     Male    29  59  0.64 (0.34-1.2)  .84  20  44  1.4 (0.74-2.5)  .32  67 (27)  51  1.4 (0.35-5.9)  .68  Age (mean ± SD)    47.6 ± 11.3    0.98 (0.95-1.0)  .25  48.7 ± 12.4    1.0 (0.97-1.0)  .91  49 ± 10.4    0.96 (0.88-1.0)  .96  Location of pain                                   Extremity    21  43  1    19  42  1    51 (29)  39  1     Extremity and back    28  57  1.1 (0.53-2.1)  .86  26  58  0.86(0.46-1.6)  .65  79(32)  61  0.18(0.02-1.5)  .11  Duration of pain in years (mean ± SD)    8.6 ± 7.7    1.0 (1.0-1.1)  .08  6.8 ± 6.6    0.98 (0.93-1.0)  .48  7.3 ± 5.8    1.2 (0.99-1.4)  .07  Level of operation                                   L4-L5 and above    21  43  1    15  33  1    53 (25)  41  1     L5-S1    11  22  0.64 (0.26-1.6)  .34  14  31  0.93 (0.42-2.1)  .86  40 (22)  31  0.80 (0.12-5.3)  .82   Multiple level    17  35  0.97 (0.43-2.2)  .95  16  36  0.83 (0.37-1.8)  .63  37 (14)  28  6.9 (0.89-54)  .07  Reason for operation                                   Disc herniation    26  53  1    24  53  1    64 (34)  49  1     Stenosis    11  22  0.79 (0.34-1.9)  .60  10  22  1.2 (0.51-2.6)  .73  35 (15)  27  0.12 (0.01-1.4)  .09   Both    12  25  0.85 (0.32-2.3)  .76  11  24  1.2 (0.47-3.3)  .67  31 (12)  24  0.43 (0.04-4.8)  .50  Number of previous operations (mean ± SD)    2.3 ± 1.3    1.0 (0.79-1.3)  .87  2.6 ± 1.9    1.2 (0.93-1.5)  .20  2.2 ± 1.3    0.38 (0.16-0.89)  .03f  Spinal fusion                                   No    35  71  1    31  69  1    85 (39)  65  1     Yes    14  29  1.4 (0.65-3.2)  .37  14  31  1.1 (0.55-2.4)  .72  45 (22)  35  9.1 (1.1-74)  .04f  Electrode location                                   T9-T10    32  65  1    30  67  1    81 (36)  62  1     Other    17  35  1.2 (0.57-2.4)  .66  15  33  1.1 (0.59-2.2)  .70  49 (25)  38  0.73 (0.14-3.8)  .71  Type of electrodeg                                   Symmix/Resume 1 × 4    42  86  1    40  89  1    98 (43)  75  1     Specify 5-6-5/2 × 4    7  14  1.7 (0.64-4.5)  .29  5  11  0.86 (0.30-2.5)  .78  32 (18)  25  3.8 (0.45-32)  .22  Deceased    5  10      1  2      4  3      SCS = spinal cord stimulation; aquestionnaire answered; bodds ratio for successful trial, i.e., pulse generator implantation after trial; c hazard ratio for SCS explantation; din parentheses: questionnaire answered; odds ratio; efor complete recovery or substantial improvement (Global Perceived Effect, GPE 1-2) at the end of follow up; fP < .05; gall electrodes manufactured by Medtronic. View Large Trial Stimulation Out of the 224 patients, 175 (78%) received an IPG after the trial period. The remaining 49 patients did not experience adequate pain relief and had their electrode removed (Figure 1). The electrode location was T9-10 in 143 (64%) patients. The type of electrode was Symmix in 177 (79%) patients, Specify 5-6-5 in 33 (15%), Specify 2 × 4 in 11 (5%), and Resume in three (1%) (all electrodes Medtronic). The median duration of the trial was 7 d (range 0-21). During the trial, the electrode was repositioned in 6 patients due to inadequate pain relief, of whom all except 1 received a permanent SCS device with a good outcome. Preoperative MRI covering the implantation area was available for 77 patients, revealing 6 (8%) thoracic disc protrusions, 2 lateral stenosis, 1 syringohydromyelia, and 1 posterior element hypertrophy. In all cases, cerebrospinal fluid was visible anterior and posterior to the spinal cord. FIGURE 1. View largeDownload slide Flow chart of 224 consecutive FBSS patients undergone SCS with surgically implanted paddle lead from 1996 to 2014 at Hospital. FIGURE 1. View largeDownload slide Flow chart of 224 consecutive FBSS patients undergone SCS with surgically implanted paddle lead from 1996 to 2014 at Hospital. In the multivariate logistic regression analysis, age, gender, cause of operation, duration of pain, pain distribution, number of previous operations, level of operation, instrumented fusion, type of electrode, and level of electrode did not predict a successful trial. Postoperative Outcome At the first postoperative follow-up visit (mean 60 d, range 3-137 d), 153 (91%) patients reported good or adequate pain relief, 8 (5%) patients reported pain relief but inadequate pain coverage, 7 (4%) patients reported no pain relief, and 1 patient (0.6%) suffered worse pain after IPG implantation. Data were missing for 6 patients. Explantation Rate At the mean follow-up of 6 yr (range 0-18, total 1395 follow-up years), 45 (26%) SCS devices were explanted for the following reasons: 34 (76%) inefficient pain relief, 3 (6%) IPG depletion, 3 (6%) no further need for SCS, 1 (2%) surgical site infection, 1 (2%) electrode migration, 1 (2%) IPG region discomfort, 1 (2%) need for MRI, and 1 (2%) unsuccessful implantation. The median time for explantation due to inadequate pain relief was 3 yr (range 0-14), and 4 yr (range 0-8) due to other reasons (Figure 2). FIGURE 2. View largeDownload slide Kaplan–-Meier survival curve for all 175 patients with implanted SCS device after trial period. The end point of follow up was SCS explantation due to (1) loss of satisfactory pain relief or (2) other reasons (IPG depletion, no further need for SCS, surgical site infection, electrode migration, IPG region discomfort, need for MRI and unsuccessful implantation). The curve illustrates gradual loss of treatment efficacy in some patients at long-term follow-up. FIGURE 2. View largeDownload slide Kaplan–-Meier survival curve for all 175 patients with implanted SCS device after trial period. The end point of follow up was SCS explantation due to (1) loss of satisfactory pain relief or (2) other reasons (IPG depletion, no further need for SCS, surgical site infection, electrode migration, IPG region discomfort, need for MRI and unsuccessful implantation). The curve illustrates gradual loss of treatment efficacy in some patients at long-term follow-up. In the Cox regression analysis, age, gender, cause of operation, duration of pain, pain distribution, number of previous operations, level of operation, instrumented fusion, type of electrode, and level of electrode did not predict the outcome, as measured by the explantation rate for SCS. GPE at the End of the Follow-up Of the 130 patients with permanent SCS devices at the end of the follow-up, 61 (47%) answered the questionnaire. The mean follow-up time for these patients was 5 yr (range 0-16). Of them, 4 (6%) reported complete recovery, 40 (63%) substantial improvement, 15 (23%) slightly better situation, and 4 (6%) same or worse situation (Table 2). TABLE 2. Global Perceived Effect (GPE) of Spinal Cord Stimulation at the End of the Follow-up Period   All (%)  %  Female  %  Male  %  Completely recovered  4  7  2  6  2  7  Substantial improvement  38  62  23  68  15  56  Little improvement  15  25  7  21  8  30  No change  2  3  0  0  2  7  Little decline  0  0  0  0  0  0  Substantial decline  1  2  1  3  0  0  Total failure  1  2  1  3  0  0    All (%)  %  Female  %  Male  %  Completely recovered  4  7  2  6  2  7  Substantial improvement  38  62  23  68  15  56  Little improvement  15  25  7  21  8  30  No change  2  3  0  0  2  7  Little decline  0  0  0  0  0  0  Substantial decline  1  2  1  3  0  0  Total failure  1  2  1  3  0  0  View Large TABLE 2. Global Perceived Effect (GPE) of Spinal Cord Stimulation at the End of the Follow-up Period   All (%)  %  Female  %  Male  %  Completely recovered  4  7  2  6  2  7  Substantial improvement  38  62  23  68  15  56  Little improvement  15  25  7  21  8  30  No change  2  3  0  0  2  7  Little decline  0  0  0  0  0  0  Substantial decline  1  2  1  3  0  0  Total failure  1  2  1  3  0  0    All (%)  %  Female  %  Male  %  Completely recovered  4  7  2  6  2  7  Substantial improvement  38  62  23  68  15  56  Little improvement  15  25  7  21  8  30  No change  2  3  0  0  2  7  Little decline  0  0  0  0  0  0  Substantial decline  1  2  1  3  0  0  Total failure  1  2  1  3  0  0  View Large In the multivariate logistic regression analysis, instrumented fusion (odds ratio [OR] 9.1; confidence interval [CI] 95% 1.1-74; P = .04), and a smaller number of previous spinal operations (OR 0.4; CI 95% 0.2-0.9; P = .03), predicted a good outcome (GPE 1 or 2). However, age, gender, cause of operation, duration of pain, pain distribution, level of operation, type of electrode, and level of electrode did not. Complications and Revisions Seventy revisions were done in 64 (37%) of the 175 patients, of which 26 were due to complications in 25 (14%) patients (Table 3). The overall infection rate, including the trial, was 3.1%. All of the deep infections were positive for bacterial culture (Staphylococcus aureus in six patients and Acinetobacter baumannii in 1 patient; Table 3). There were no neurological injuries requiring surgical intervention. All of the infections appeared after an operation (range 7-29 d). TABLE 3. Complications Resulting for the SCS Device Removal or Revision (Includes Trial Complications) Complication  Removal  Revision  Details of revisions  Deep infection  1  6  All revisions were short-time explantations. Infection occurred in 2 patients during the trial period, in 2 patients after primary IPG implantation, and in 2 patients after electrode revision. All patients got a new device later without a trial.  Hardware malfunction  0  11  Extension leads were replaced in 4 patients. The electrode was replaced in 3 patients. The IPG was replaced once in 1 patient and in 1 patient twice. The whole SCS device was removed and later reimplanted in 1 patient.  Subcutaneous hematoma  0  1  Hematoma was evacuated.  Discomfort over pulse generator  1  3  IPG was relocated in all 3 patients.  Electrode migration  1  2  Electrode was relocated in both patients.  Complication  Removal  Revision  Details of revisions  Deep infection  1  6  All revisions were short-time explantations. Infection occurred in 2 patients during the trial period, in 2 patients after primary IPG implantation, and in 2 patients after electrode revision. All patients got a new device later without a trial.  Hardware malfunction  0  11  Extension leads were replaced in 4 patients. The electrode was replaced in 3 patients. The IPG was replaced once in 1 patient and in 1 patient twice. The whole SCS device was removed and later reimplanted in 1 patient.  Subcutaneous hematoma  0  1  Hematoma was evacuated.  Discomfort over pulse generator  1  3  IPG was relocated in all 3 patients.  Electrode migration  1  2  Electrode was relocated in both patients.  View Large TABLE 3. Complications Resulting for the SCS Device Removal or Revision (Includes Trial Complications) Complication  Removal  Revision  Details of revisions  Deep infection  1  6  All revisions were short-time explantations. Infection occurred in 2 patients during the trial period, in 2 patients after primary IPG implantation, and in 2 patients after electrode revision. All patients got a new device later without a trial.  Hardware malfunction  0  11  Extension leads were replaced in 4 patients. The electrode was replaced in 3 patients. The IPG was replaced once in 1 patient and in 1 patient twice. The whole SCS device was removed and later reimplanted in 1 patient.  Subcutaneous hematoma  0  1  Hematoma was evacuated.  Discomfort over pulse generator  1  3  IPG was relocated in all 3 patients.  Electrode migration  1  2  Electrode was relocated in both patients.  Complication  Removal  Revision  Details of revisions  Deep infection  1  6  All revisions were short-time explantations. Infection occurred in 2 patients during the trial period, in 2 patients after primary IPG implantation, and in 2 patients after electrode revision. All patients got a new device later without a trial.  Hardware malfunction  0  11  Extension leads were replaced in 4 patients. The electrode was replaced in 3 patients. The IPG was replaced once in 1 patient and in 1 patient twice. The whole SCS device was removed and later reimplanted in 1 patient.  Subcutaneous hematoma  0  1  Hematoma was evacuated.  Discomfort over pulse generator  1  3  IPG was relocated in all 3 patients.  Electrode migration  1  2  Electrode was relocated in both patients.  View Large An additional 22 revisions were done due to IPG battery depletion (20 patients). The median battery duration was 5.5 yr (range 1-10). In 1 case, after IPG depletion, the whole SCS device was replaced with a new type of electrode without a trial. Due to inadequate pain relief, 22 revisions were done to 19 (11%) patients, of which 15 were electrode repositionings. SCS devices were later explanted in 7 of these patients (Table 4). TABLE 4. Revisions Due to Inadequate Pain Relief Type of revision  SCS in use at the end of follow-up  SCS explanted during follow-up  All  Electrode repositioned  10  5  15  Electrode replaced  2  0  2  Explantation and immediate new trial  3  0  3  Explantation and immediate new SCS device  0  2  2  All  15  7  22  Type of revision  SCS in use at the end of follow-up  SCS explanted during follow-up  All  Electrode repositioned  10  5  15  Electrode replaced  2  0  2  Explantation and immediate new trial  3  0  3  Explantation and immediate new SCS device  0  2  2  All  15  7  22  View Large TABLE 4. Revisions Due to Inadequate Pain Relief Type of revision  SCS in use at the end of follow-up  SCS explanted during follow-up  All  Electrode repositioned  10  5  15  Electrode replaced  2  0  2  Explantation and immediate new trial  3  0  3  Explantation and immediate new SCS device  0  2  2  All  15  7  22  Type of revision  SCS in use at the end of follow-up  SCS explanted during follow-up  All  Electrode repositioned  10  5  15  Electrode replaced  2  0  2  Explantation and immediate new trial  3  0  3  Explantation and immediate new SCS device  0  2  2  All  15  7  22  View Large DISCUSSION This retrospective study analyzed 224 consecutive patients who had spinal cord stimulators implanted to treat FBSS from 1996 to 2014. The analysis was based on medical records, postal questionnaires, and national registry data. Furthermore, this study involved an extremely long follow-up period. We measured both the short- and long-term outcomes in these patients using the trial success rate, explantation rate due to inadequate pain relief, complication rate, and patient satisfaction as the GPE at the end of follow-up period. Trial Period Success The success rate after 1-wk during the trial period approached 80%, which is comparable to previous studies.21 This indicates that a 2- to 3-wk trial period, as reported in many centers, is unnecessary to differentiate patients that are likely to benefit from SCS. Due to infection risk and patient discomfort, the trial length should be kept to a minimum. New treatment modalities, such as burst and high frequency, may require longer trials due to the nature of the treatment. In the early years, a permanent device was not implanted if the stimulation did not provide a “tail effect,” ie, the response stopped when the device was turned off. Currently, we use numerical rating scale to measure pain relief after trial period, but the decision on permanent IPG implantation is based on global patient satisfaction instead of formal percentage of pain relief. No factors that could predict the trial success could be identified based on patient history, electrode type, or location. Long-Term Success Three out of 4 patients who received a permanent SCS device after the trial period continued to use it throughout the follow-up time, which reached 18 yr in some patients. This long-term success rate is higher than the 40% to 60% reported previously.22 In line with previous reports, there were no strong predictors for successful treatment outcome.23-25 Almost half of the patients replied to a questionnaire delivered by post, and 2 out of 3 reported substantial improvements or total recovery with SCS. This indicates that in carefully selected patients, long-lasting and satisfactory pain relief can be obtained. Fewer spinal operations and instrumented fusions predicted better satisfaction. The lower number of previous spinal surgeries as an indicator of positive outcomes supports general findings about spinal surgery outcomes. The positive correlation with instrumented fusion is logical since SCS is not supposed to improve instability related LBP. It is emphasized that fusion surgery with appropriate indication (instability)26 and SCS with appropriate indication (chronic neuropathic pain) may complement each other. In contrast to previous studies, prolonged neuropathic pain did not worsen the treatment outcome, whether it was measured by explantation rate or patient satisfaction.22 This indicates that SCS is a valid treatment even after long lasting pain, although we advocate that it should be trialed earlier, before starting strong opioids. A potential bias is caused by the fact that more than half of the patients did not respond to the questionnaire and may have less-than-optimal responses to the treatment. However, their SCS devices were in place until the end of the follow-up period, which might be an indication of at least some benefit. Complications and Revisions Two out of 3 patients with permanent SCS after the trial did not need additional surgery during the follow-up period. The complication rate was 14%, which is markedly less than the 30% to 40% reported previously.27-29 Complications were mainly minor and did not lead to serious neurological sequelae. One out of 8 patients had mild narrowing of the spinal canal at the level of implantation. Since ventral pathology such as osteophytes and disc herniations cannot reliably be excluded by visual inspection during operation, we recommend preoperative lumbar and thoracic MRI for all patients as suggested by Levy et al.27 The infection rate (3%) was in line with previous studies, reporting 3% to 6% infection rates.28,30,31,32 All infections appeared less than 1 month after an operation, indicating that long-term subclinical infections are rare. Only 1 patient had a permanent explantation due to an infection. In all other cases, the device could be reimplanted after sufficiently long and targeted antibiotic therapy. Benefits of Surgical Electrodes All of the patients in the current study were treated with a surgical SCS lead, using a preoperative methylene blue mark to spot the correct level for the electrode. Surgical paddle-lead electrodes were solely used for FBSS because of neurosurgeons’ preference at the time. The electrode migration rate (1%) was much lower than the 13% to 22% reported in other studies.33,34 The low migration rate of the electrodes and the lack of CSF leakage problems reflect the benefits of surgical electrodes. All explantations were complete and safe, and no serious adverse events, including compression of the medulla, were found in the data. The careful design of the electrode site has been found to be an important factor in the success of SCS treatment.35 In our series, the level of the electrode did not affect the short- or long-term outcome. However, if the patient experiences inadequate pain relief, revision with lead replacement may be advisable because this led to a good result in most cases (68%) in our series. New, wider surgical electrodes, that have more contacts, also enable directional stimulation and longer battery duration due to less loss of efficiency. In our hospital, shifting from 4 contact to more advanced 8 and 16 contact surgical paddle lead electrodes has been influenced by neurosurgeons’ preferences, costs of the SCS devices, and the legislation regarding competitive tendering in Finland. Limitations of this Study This is a retrospective study with obvious limitations. The patients come from a geographically wide area of 850 000 people in Eastern and Central Finland. Kuopio University Hospital serves as the sole neurosurgical unit in the area. During the study, neurosurgeons performing implantations have changed, as well as criteria for permanent SCS implantation. Implantable devices have also changed, and most patients have received an electrode that is not be used presently. Reliable information about patient history and clinical characteristics could be derived from hospital records, but sufficient information about pain relief is lacking and no structured questionnaires for psychological evaluation or quality of life have been used to study this population. Strengths of this Study This study's strength is its homogenous study cohort with only FBSS patients, in contrast to many studies that mix different pain etiologies. The follow-up time is longer than in most studies and we have been able to trace complications and explantations for almost 20 yr. National registries provide reliable data on the survival and causes of deaths of patients. Follow-up data are complete, since all postoperative controls were arranged in our own hospital, and all revisions and complications were recorded until the end of the follow-up. Consequently, there were no drop outs. Suggestions for Further Research This study is hospital based, including all consecutive patients with surgical lead implanted for FBSS at Kuopio University Hospital, and provides a positive picture of the quality and effectiveness of treating patients with SCS. The holistic situation of patients would be an important research topic, as well as the effect of psychological factors on the outcome, and the effects of SCS on neuropathic and opioid drug usage. We could not find predicting factors for the short- or long-term success of the SCS. Multidisciplinary patient selection is important so that different therapies can communicate together and the choice of treatment is not dependent on the treatment unit. Novel biomarkers, including psychological profiling, should be developed to improve patient selection. Ten patients deceased during the follow-up and 4 of them were suicides. In all of these patients, the equipment was either removed or a plan for removal had been made. Because treatment is often the last resort in this difficult patient group, it should be ensured that patients have adequate psychiatric support during this phase. CONCLUSION SCS with surgical paddle lead is a safe and effective form of treatment for FBSS. This study involved an extremely long follow-up period with accurate follow-up data. Patient selection should be further improved by developing novel predictive biomarkers. Disclosures Funding was from a Government Research Fund. Dr Nissen has received travel funding from the Medtronic, Boston Scientific and Abbott St Jude Medical. Ms Ikäheimo, Dr Huttunen, and Dr von und zu Fraunberg have received travel funding from the Medtronic and Abbott St Jude Medical. Dr Leinonen has no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Harstall C, Ospina M. How prevalent is chronic pain? Pain: Clinical Updates . 2003; 11( 2): 1- 4. Google Scholar CrossRef Search ADS   2. Goldberg D, McGee S. Pain as a global public health priority. BMC Public Health . 2011; 11( 1): 770. Google Scholar CrossRef Search ADS PubMed  3. Turunen J, Mäntyselkä P, Kumpusalo E, Ahonen R. How do people ease their pain? A population-based study. J Pain . 2004; 5( 9): 498- 504. Google Scholar CrossRef Search ADS PubMed  4. Breivik H, Collett B, Ventafridda V. Survey of chronic pain in Europe: prevalence, impact on daily life, and treatment. Eur J Pain . 2006; 10( 4): 287- 287. Google Scholar CrossRef Search ADS PubMed  5. InSites Consulting. Pain Proposal Patient Survey . July–September 2010. https://www.dgss.org/fileadmin/pdf/Pain_Proposal_European_Consensus_Report.pdf. Accessed [01.05.2018]. 6. Bevan S, Quadrello T, McGee R, Mahdon M, Vavrovsky A, Barham L. Fit for Work? Musculoskeletal Disorders in the European Workforce . The Work Foundation; 2009. http://www.bollettinoadapt.it/old/files/document/3704FOUNDATION_19_10.pdf. Accessed [01.05.2018]. 7. Deyo RA, Gray DT, Kreuter W et al.   United States trends in lumbar fusion surgery for degenrative conditions. Spine . 2005; 30( 12): 1441- 1445. Google Scholar CrossRef Search ADS PubMed  8. Gray DT, Deyo RA, Kreuter W et al.   Population-based trends in volumes and rates of ambulatory lumbar spine surgery. Spine . 2006; 31( 17): 1957- 1963 Google Scholar CrossRef Search ADS PubMed  9. North RB, Campbell JN, James CS et al.   Failed back surgery syndrome: 5-year follow-up in 102 patients undergoing repeated operation. Neurosurgery . 1991; 28( 5): 685- 691. Google Scholar PubMed  10. Wilkinson HA. The Failed Back Syndrome: Etiology and Therapy . Philadelphia, PA: Harper & Row; 1991. 11. Liedgens H, Obradovic M. A burden of illness study for neuropathic pain in Europe. Econ Outcomes Res . 2016; 8: 113- 126. 12. Boswell MV, Trescot AM, Datta S. Interventional techniques: evidence-based practice guidelines in the management of chronic spinal pain. Pain physician . 2007; 10( 1): 7- 111. Google Scholar PubMed  13. Kumar K, Hunter G, Demeria D. Spinal cord stimulation in treatment of chronic benign pain: challenges in treatment planning and present status, a 22-Year experience. Neurosurgery . 2006; 58( 3): 481- 496. Google Scholar CrossRef Search ADS PubMed  14. North RB, Kidd DH, Farrokh F, Piantadosi SA. Spinal cord stimulation versus repeated lumbosacral spine surgery for chronic pain: a randomized, controlled trial. Neurosurgery . 2005; 56( 1): 98- 107. Google Scholar CrossRef Search ADS PubMed  15. Mailis-Gagnon A, Furlan AD, Sandoval JA. Spinal cord stimulation for chronic pain. A systematic literature synthesis. Cochrane Database Syst Rev . 2004; (3): CD003783. 16. Frank ED, Menefee LA, Jalali S et al.   The utility of a 7-day percutaneuous spinal cord stimulator trial measured by a pain diary: a long term retrospective analysis. Neuromodulation . 2005; 8 (3): 162- 170. Google Scholar CrossRef Search ADS PubMed  17. May MS, Banks C, Thomson SJ. A retrospective, long-term, third-party follow-up of patients considered for spinal cord stimulation. Neuromodulation . 2002; 5( 3): 137- 144. Google Scholar CrossRef Search ADS PubMed  18. Oakley JC, Kramer ES, Stamatos J, Foster AM. Successful long-term outcomes of spinal cord stimulation despite limited pain relief during temporary trialing. Neuromodulation . 2008; 11( 1): 66- 73. Google Scholar CrossRef Search ADS PubMed  19. Kamper SJ, Ostelo RW, Knol DL. Global perceived effect scales provided reliable assessments of health transition in people with musculoskeletal disorders, but ratings are strongly influenced by current status. J Clin Epidemiol . 2010; 60( 7): 760- 766. Google Scholar CrossRef Search ADS   20. Kumar K, Wyant GM, Ekong CEU. Epidural spinal cord stimulation for treatment of chronic pain—some predictors of success. A 15-year experience. Surg Neurol . 1998; 50( 2): 110- 121. Google Scholar CrossRef Search ADS PubMed  21. Kumar K, Nath RK, Toth C. Spinal cord stimulation is effective in the management of reflex sympathetic dystrophy. Neurosurgery . 1997; 40 (3): 503- 508. Google Scholar PubMed  22. Kumar K, Toth C, Nath RK, Laing P. Epidural spinal cord stimulation for treatment of chronic pain—some predictors of success. A 15-year experience. Surg Neurol . 1998; 50( 2): 110- 121. Google Scholar CrossRef Search ADS PubMed  23. Taylor R, Desai M, Rigoard P et al.   Predictors of pain relief following spinal cord stimulation in chronic back and leg pain and failed back surgery syndrome: a systematic review and meta-regression analysis. Pain Pract . 2014; 14( 6): 489- 505. Google Scholar CrossRef Search ADS PubMed  24. Fiume D, Sherkat S, Callovini GM, Parziale G, Gazzeri G. Treatment of the failed back surgery syndrome due to lumbo-sacral epidural fibrosis. Acta Neurochir Suppl . 1995; 64: 116- 118. Google Scholar CrossRef Search ADS PubMed  25. Son B, Kim D, Lee S. Factors associated with the success of trial spinal cord stimulation in patients with chronic pain from failed back surgery syndrome. J Korean Neurosurg Soc . 2013; 54( 6): 501- 506. Google Scholar CrossRef Search ADS PubMed  26. Gibson JA, Waddell G. Surgery for degenerative lumbar spondylosis. Cochrane Database Syst Rev . 2005; 19( 4): CD001352. 27. Levy R, Henderson J, Slavin K, Simpson BA, Barolat G, Shipley J, North R: Incidence and avoidance of neurologic complications with paddle type spinal cord stimulation leads. Neuromodulation  2011; 14( 5): 412- 422. Google Scholar CrossRef Search ADS PubMed  28. Lee AW, Pilitsis JG. Spinal cord stimulation: indications and outcomes. Neurosurg Focus . 2006; 21( 6): 1- 6. Google Scholar CrossRef Search ADS   29. Turner JA, Loeser JD, Deyo RA, Sanders SB. Spinal cord stimulation for patients with failed back surgery syndrome or complex regional pain syndrome: a systematic review of effectiveness and complications. Pain . 2004; 108( 1-2): 137- 147. Google Scholar CrossRef Search ADS PubMed  30. Rosenow J, Stanton-Hicks M, Rezal A. Failure modes of spinal cord stimulation hardware. J Neurosurg Spine . 2006; 5( 3): 183- 190. Google Scholar CrossRef Search ADS PubMed  31. Mekhail NA, Mathews M, Nageeb F, Guirguis M, Mekhail MN, Cheng J. Retrospective review of 707 cases of spinal cord stimulation: indications and complications. Pain Pract . 2011; 11( 2): 148- 153. Google Scholar CrossRef Search ADS PubMed  32. Kumar K, Hunter G, Demeria D. Spinal cord stimulation in treatment of chronic benign pain: challenges in treatment planning and present status, a 22-Year experience. Neurosurgery . 2006; 58( 3): 481- 496. Google Scholar CrossRef Search ADS PubMed  33. Mekhail NA, Mathews M, Nageeb F. Retrospective review of 707 cases of spinal cord stimulation: indications and complications. Pain Pract . 2011; 11( 2): 148- 153. Google Scholar CrossRef Search ADS PubMed  34. Kumar K, Buchser E, Linderoth B, Meglio M. Avoiding complications from spinal cord stimulation: practical recommendations from an international panel of experts. Neuromodulation . 2007; 10( 1): 24- 33. Google Scholar CrossRef Search ADS PubMed  35. North R, Ewend M, Lawton M. Spinal cord stimulation for chronic, intractable pain: superiority of “multi-channel” devices. Pain . 1991; 44( 2): 119- 130. Google Scholar CrossRef Search ADS PubMed  COMMENTS Over the last 5 decades, spinal cord stimulation (SCS) has become a routine intervention in management of chronic pain due to variety of clinical conditions, including the persistent or recurrent pain in the back and legs that is observed in patients after previous lumbar spine surgeries (referred here and in many other publications as the failed back surgery syndrome [FBSS] – the term we are now trying to replace with something more meaningful and objective). The authors of this study share their long-term series of SCS in FBSS patients, once again confirming overall positive effect of the procedure, with ∼60% of patients that were screened for SCS (130 out of 224) continuing using it at the latest follow-up. This finding is in line with many previous publications and may be a sort of baseline for all new stimulation targets and paradigms. One has to keep in mind that the authors’ findings may not necessarily be applied to the real-world situation in your hospital/region/country. First of all, the exclusive use of paddle type electrodes does not reflect worldwide situation where very many SCS systems are now implanted with percutaneous electrode leads. The discussion about pros and cons of each electrode lead type is beyond the scope of this comment; however, the types of complications may be quite different if one uses paddle type leads only when there are clinical reasons not to use percutaneous ones. Secondly, the authors have been using devices from a single manufacturer – and on my latest count, there are now at least 6 device manufacturers who produce commercially available SCS systems. Each of these systems has its own advantages and unique features, and by using an individually tailored device selection it is possible, at least theoretically, to increase long-term success rates and the effectiveness of the modality. Lastly, there is a major concern about reliability of the presented data. Due to the blinded nature of the review process, I am not sure from which European country it is coming. And although I generally accept the authors’ assumption that all patients’ problems and explants would have been accounted for due to their hospital being the sole neurosurgical facility in the region, I would caution the authors and the readers that the only reliable information about long-term outcome may be derived from 61 patient responses to the questionnaire. There is a very real possibility that among those who did not respond there are many SCS failures who are not interested to have their failed systems removed because it does not bother them and/or because of the real or perceived risk of yet another surgery. As the matter of fact, I would venture to say that there are many patients who are not using their devices anymore as there were only 22 device replacements in 20 patients due to battery depletion whereas one would expect to have at least 3 times more device depletions over this long-term follow-up period. The study also does not take into account the population mobility as these days people can easily move out of their geographic area and have their devices explanted or complications addressed in other institutions. Despite all these limitations, I applaud the authors for their interest in collecting data from a very long institutional experience and for their remarkably low complication rates. Hopefully, there will at some point be a different study that compares new reality of rechargeable devices, paresthesia-free stimulation paradigms, closed-loop stimulation approach, etc, with the previous conventional “one-size-fits-all” approach. Moreover, I sincerely hope that in the future articles the diagnosis of FBSS will be replaced by a more focused and precise definition of clinical condition. Konstantin Slavin Chicago, Illinois Copyright © 2018 by the Congress of Neurological Surgeons This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Neurosurgery Oxford University Press

Long-Term Outcome of Spinal Cord Stimulation in Failed Back Surgery Syndrome: 20 Years of Experience With 224 Consecutive Patients

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Congress of Neurological Surgeons
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Copyright © 2018 by the Congress of Neurological Surgeons
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0148-396X
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1524-4040
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10.1093/neuros/nyy194
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Abstract

Abstract BACKGROUND Failed back surgery syndrome (FBSS) is a challenging condition that lacks a curative treatment. In selected patients, spinal cord stimulation (SCS) has provided a satisfactory outcome. OBJECTIVE To evaluate the long-term outcome of SCS in FBSS, as measured by (1) the explantation rate, (2) complications, and (3) patient satisfaction with the global perceived effect (GPE). METHODS We studied 224 consecutive FBSS patients who underwent an SCS trial with surgically implanted leads at our hospital between January 1996 and December 2014. The patients’ satisfaction with the GPE of treatment was measured through a postal questionnaire at the end of follow-up. RESULTS Based on a 1-wk trial, permanent SCS was implanted in 175 (78%) patients. Out of these patients, 153 (87%) reported satisfactory outcomes after 2 mo. During the mean follow-up of 6 yr, 34 (19%) of SCS devices were permanently explanted due to inadequate pain relief, and 11 (6%) were explanted for other reasons. Electrode revision due to inadequate pain relief was done for 22 patients. In total, 26 complications were reported due to: 7 deep infections, 11 hardware malfunctions, 1 subcutaneous hematoma, 4 instances of discomfort due to the pulse generator, and 3 electrode migrations. One hundred thirty patients (74%) continued with SCS until the end of follow-up. Of them, 61 (47%) returned the questionnaire, and 42 (69%) reported substantially improved or better GPE. CONCLUSION SCS can provide a good outcome in the treatment of FBSS. Patient selection could be further improved by developing novel predictive biomarkers. Spinal cord stimulation, Failed back surgery syndrome, Retrospective observational study, Surgery, Long-term outcome ABBREVIATIONS ABBREVIATIONS FBSS failed back surgery syndrome GPE global perceived effect IPG internal pulse generator LBP Low back pain SCS spinal cord stimulation Pain is a global problem. Each year 10% of the population is diagnosed with chronic pain, and an estimated 20% of adults suffer from pain worldwide.1,2 In Finland, 19% to 48% of the population is estimated to suffer from chronic pain.3 Chronic pain is associated with physical and psychological comorbidities, such as depression and anxiety.4 In a recent survey of 2000 patients with chronic pain, 36% reported that pain had a negative effect on their families and friends, and 27% felt socially isolated and lonely.5 Low back pain (LBP) is common in western countries where 46% of women and 47% of men have experienced LBP in the last 12 mo.6 In most European countries, LBP accounts for the largest proportion of lost workdays of all musculoskeletal conditions.6 LBP is accountable for 12.5% of sick days in the UK and 13.5% in Sweden.6 Furthermore, the number of spine surgeries has steadily increased in the past decades.7,8 Failed back surgery syndrome (FBSS) describes persistent or recurrent pain in the lumbar area with or without a sciatic component after 1 or more lumbar surgeries.9 The incidence of FBSS after lumbar spinal surgery is between 20% and 40%, and it has not declined despite novel mini-invasive surgical techniques.10,11 Spinal cord stimulation (SCS) is a well-established modality for the treatment of intractable neuropathic pain.12-15 In previous studies, adequate pain relief during the SCS trial period has predicted satisfactory long-term outcomes,16,17 and pain reduction can improve over time.18 However, the patient cohorts were heterogeneous, FBSS was pooled with other etiologies, and many patients were lost before the follow-up visit. We present a retrospective analysis of SCS in FBSS in a single institution for almost a 20-yr period with a median follow-up time of 5 yr. Our objective is to evaluate the long-term outcome of SCS in FBSS as measured by the (1) explantation rate due to inefficient pain relief, (2) complications, and (3) patient satisfaction with the global perceived effect (GPE) at the end of the follow-up. METHODS Patients We retrospectively evaluated the medical charts of all 224 FBSS patients with SCS implantation at Kuopio University Hospital (KUH) Neurosurgery between January 1, 1996 and December 31, 2014. During the study period, KUH neurosurgery solely provided full-time acute and elective neurosurgical services for the 850 000 people catchment population in Eastern and Central Finland. A pain physician, neurosurgeon, or orthopedic surgeon provided a diagnosis of FBSS and the initial treatment (oral analgesics and physical therapy). Patients had at least 1 previous lumbar decompressive procedure due to disc herniation or spinal stenosis but suffered from radicular lower limb pain alone or combined with lumbar pain. Before SCS implantation, any surgically treatable pathology was ruled out by a neurosurgeon. Two patients with lumbar pain only were treated with epidural SCS, but they were excluded in this study. Untreated depression was considered as a contraindication for SCS. Clinical Evaluation All medical records were reviewed for details regarding SCS treatment, complications, and revisions. The baseline characteristics included age, gender, and previous lumbar procedures, including instrumented fusions, and duration and localization of pain. Follow-up data were gathered for all visits, including the type and location of the electrode, complications, revisions, and total follow-up time in years. All patients were followed up from medical records until December 31, 2015. Digital imaging data were available for all 188 patients with SCS implanted 2003 or later. The GPE of the treatment was measured in a postal questionnaire delivered to all 130 patients with SCS at the end of follow-up December 31, 2015. The GPE was measured using a 7-point Likert-scale: 1 = completely recovered, 2 = substantial improvement, 3 = little improvement, 4 = no change, 5 = little decline, 6 = substantial decline, and 7 = totally failed. This scale has been shown to be a valid measure for GPE.12,19 SCS Implantation The SCS electrode was implanted into the epidural space microsurgically under direct visual control with the operating microscope using a paddle-lead electrode (Resume 3586, Symmix 3982, Specify 2 × 4 3998, or Specify 5-6-5 39565, Medtronic, Dublin, Ireland) under general anesthesia. The techniques for implantation have been described previously.20 Before surgery, a methylene blue mark was placed in an X-ray control to identify the level of entry into the spinal canal. The electrode was then pushed upward into the epidural space, yielding an actual implantation level that was 1 level higher than the entry level. Thoracic implantation level was determined by pain localization and previous operations. No intraoperative testing was used. The mean duration of the trial was 7 d (range 0-21). After the trial period, patients who reported paresthesia covering most of the limb pain area with adequate pain relief received an internal pulse generator (IPG, model 7425, model 37703, model 7427V, model 37702, or model 97702, Medtronic). All of the patients that received an IPG visited an outpatient clinic 2 to 3 mo (mean 60 d) after surgery, and a final questionnaire was sent in 2015. Patients that experienced problems with their SCS therapy were admitted to hospital outpatient clinic whenever needed (total 287 visits). Statistical Analysis The statistical analyses were performed using SPSS version 24.0 (IBM Corporation, Armonk, New York). The demographic and SCS-related data were analyzed by calculating the means and standard deviations for the normally distributed variables or medians, and ranges were calculated for the other variables. A cross-table analysis was used for the categorical outcome. A logistic regression analysis was used for the uni- and multivariate analysis of variables associated with (1) successful trial stimulation and (2) GPE of treatment at the end of the follow-up visit. A Cox regression analysis was used to analyze the uni- and multivariate variables associated with SCS explantation that resulted from inadequate pain relief or other causes. Ethical Issues Study protocol and informed consent were approved by the Institutional Review Board of Kuopio University Hospital, and all subjects responding to the questionnaire gave informed consent. RESULTS FBSS History The median age of the 224 patients during the trial period was 48 yr (range 22-83), and 52% were male (Table 1). The median duration of pain was 6 yr (range 0-33), and the median number of previous operations was 2 (range 1-9). The initial underlying pathology was disc herniation (50%), disc herniation with stenosis (23%), stenosis (lateral or central 20%), or other (6%, including cysts and spondylolysis). Most of the patients had single-level surgeries at L4-L5 (35%), while 32% had multilevel surgeries. Radicular pain alone was described by 41% of patients. Seventy-three (33%) patients received instrumented fusion, of which 3 (4%) were later removed. TABLE 1. Patient Demographics and Multivariate Analysis of Variables Associated With Successful Trial Stimulation, SCS Explantation, and Pain Relief at the End of the Follow-up Period             Permanent SCS implanted n = 175      Trial only n = 49  SCS explanted n = 45  SCS in use at the end of follow up n = 130 (61a)      All  %  OR (95% Cl)b  P  All  %  HR (95% Cl)c  P  Alld  %  OR (95% Cl)e  P  Gender                                   Female    20  41  1    25  56  1    63 (34)  49  1     Male    29  59  0.64 (0.34-1.2)  .84  20  44  1.4 (0.74-2.5)  .32  67 (27)  51  1.4 (0.35-5.9)  .68  Age (mean ± SD)    47.6 ± 11.3    0.98 (0.95-1.0)  .25  48.7 ± 12.4    1.0 (0.97-1.0)  .91  49 ± 10.4    0.96 (0.88-1.0)  .96  Location of pain                                   Extremity    21  43  1    19  42  1    51 (29)  39  1     Extremity and back    28  57  1.1 (0.53-2.1)  .86  26  58  0.86(0.46-1.6)  .65  79(32)  61  0.18(0.02-1.5)  .11  Duration of pain in years (mean ± SD)    8.6 ± 7.7    1.0 (1.0-1.1)  .08  6.8 ± 6.6    0.98 (0.93-1.0)  .48  7.3 ± 5.8    1.2 (0.99-1.4)  .07  Level of operation                                   L4-L5 and above    21  43  1    15  33  1    53 (25)  41  1     L5-S1    11  22  0.64 (0.26-1.6)  .34  14  31  0.93 (0.42-2.1)  .86  40 (22)  31  0.80 (0.12-5.3)  .82   Multiple level    17  35  0.97 (0.43-2.2)  .95  16  36  0.83 (0.37-1.8)  .63  37 (14)  28  6.9 (0.89-54)  .07  Reason for operation                                   Disc herniation    26  53  1    24  53  1    64 (34)  49  1     Stenosis    11  22  0.79 (0.34-1.9)  .60  10  22  1.2 (0.51-2.6)  .73  35 (15)  27  0.12 (0.01-1.4)  .09   Both    12  25  0.85 (0.32-2.3)  .76  11  24  1.2 (0.47-3.3)  .67  31 (12)  24  0.43 (0.04-4.8)  .50  Number of previous operations (mean ± SD)    2.3 ± 1.3    1.0 (0.79-1.3)  .87  2.6 ± 1.9    1.2 (0.93-1.5)  .20  2.2 ± 1.3    0.38 (0.16-0.89)  .03f  Spinal fusion                                   No    35  71  1    31  69  1    85 (39)  65  1     Yes    14  29  1.4 (0.65-3.2)  .37  14  31  1.1 (0.55-2.4)  .72  45 (22)  35  9.1 (1.1-74)  .04f  Electrode location                                   T9-T10    32  65  1    30  67  1    81 (36)  62  1     Other    17  35  1.2 (0.57-2.4)  .66  15  33  1.1 (0.59-2.2)  .70  49 (25)  38  0.73 (0.14-3.8)  .71  Type of electrodeg                                   Symmix/Resume 1 × 4    42  86  1    40  89  1    98 (43)  75  1     Specify 5-6-5/2 × 4    7  14  1.7 (0.64-4.5)  .29  5  11  0.86 (0.30-2.5)  .78  32 (18)  25  3.8 (0.45-32)  .22  Deceased    5  10      1  2      4  3                  Permanent SCS implanted n = 175      Trial only n = 49  SCS explanted n = 45  SCS in use at the end of follow up n = 130 (61a)      All  %  OR (95% Cl)b  P  All  %  HR (95% Cl)c  P  Alld  %  OR (95% Cl)e  P  Gender                                   Female    20  41  1    25  56  1    63 (34)  49  1     Male    29  59  0.64 (0.34-1.2)  .84  20  44  1.4 (0.74-2.5)  .32  67 (27)  51  1.4 (0.35-5.9)  .68  Age (mean ± SD)    47.6 ± 11.3    0.98 (0.95-1.0)  .25  48.7 ± 12.4    1.0 (0.97-1.0)  .91  49 ± 10.4    0.96 (0.88-1.0)  .96  Location of pain                                   Extremity    21  43  1    19  42  1    51 (29)  39  1     Extremity and back    28  57  1.1 (0.53-2.1)  .86  26  58  0.86(0.46-1.6)  .65  79(32)  61  0.18(0.02-1.5)  .11  Duration of pain in years (mean ± SD)    8.6 ± 7.7    1.0 (1.0-1.1)  .08  6.8 ± 6.6    0.98 (0.93-1.0)  .48  7.3 ± 5.8    1.2 (0.99-1.4)  .07  Level of operation                                   L4-L5 and above    21  43  1    15  33  1    53 (25)  41  1     L5-S1    11  22  0.64 (0.26-1.6)  .34  14  31  0.93 (0.42-2.1)  .86  40 (22)  31  0.80 (0.12-5.3)  .82   Multiple level    17  35  0.97 (0.43-2.2)  .95  16  36  0.83 (0.37-1.8)  .63  37 (14)  28  6.9 (0.89-54)  .07  Reason for operation                                   Disc herniation    26  53  1    24  53  1    64 (34)  49  1     Stenosis    11  22  0.79 (0.34-1.9)  .60  10  22  1.2 (0.51-2.6)  .73  35 (15)  27  0.12 (0.01-1.4)  .09   Both    12  25  0.85 (0.32-2.3)  .76  11  24  1.2 (0.47-3.3)  .67  31 (12)  24  0.43 (0.04-4.8)  .50  Number of previous operations (mean ± SD)    2.3 ± 1.3    1.0 (0.79-1.3)  .87  2.6 ± 1.9    1.2 (0.93-1.5)  .20  2.2 ± 1.3    0.38 (0.16-0.89)  .03f  Spinal fusion                                   No    35  71  1    31  69  1    85 (39)  65  1     Yes    14  29  1.4 (0.65-3.2)  .37  14  31  1.1 (0.55-2.4)  .72  45 (22)  35  9.1 (1.1-74)  .04f  Electrode location                                   T9-T10    32  65  1    30  67  1    81 (36)  62  1     Other    17  35  1.2 (0.57-2.4)  .66  15  33  1.1 (0.59-2.2)  .70  49 (25)  38  0.73 (0.14-3.8)  .71  Type of electrodeg                                   Symmix/Resume 1 × 4    42  86  1    40  89  1    98 (43)  75  1     Specify 5-6-5/2 × 4    7  14  1.7 (0.64-4.5)  .29  5  11  0.86 (0.30-2.5)  .78  32 (18)  25  3.8 (0.45-32)  .22  Deceased    5  10      1  2      4  3      SCS = spinal cord stimulation; aquestionnaire answered; bodds ratio for successful trial, i.e., pulse generator implantation after trial; c hazard ratio for SCS explantation; din parentheses: questionnaire answered; odds ratio; efor complete recovery or substantial improvement (Global Perceived Effect, GPE 1-2) at the end of follow up; fP < .05; gall electrodes manufactured by Medtronic. View Large TABLE 1. Patient Demographics and Multivariate Analysis of Variables Associated With Successful Trial Stimulation, SCS Explantation, and Pain Relief at the End of the Follow-up Period             Permanent SCS implanted n = 175      Trial only n = 49  SCS explanted n = 45  SCS in use at the end of follow up n = 130 (61a)      All  %  OR (95% Cl)b  P  All  %  HR (95% Cl)c  P  Alld  %  OR (95% Cl)e  P  Gender                                   Female    20  41  1    25  56  1    63 (34)  49  1     Male    29  59  0.64 (0.34-1.2)  .84  20  44  1.4 (0.74-2.5)  .32  67 (27)  51  1.4 (0.35-5.9)  .68  Age (mean ± SD)    47.6 ± 11.3    0.98 (0.95-1.0)  .25  48.7 ± 12.4    1.0 (0.97-1.0)  .91  49 ± 10.4    0.96 (0.88-1.0)  .96  Location of pain                                   Extremity    21  43  1    19  42  1    51 (29)  39  1     Extremity and back    28  57  1.1 (0.53-2.1)  .86  26  58  0.86(0.46-1.6)  .65  79(32)  61  0.18(0.02-1.5)  .11  Duration of pain in years (mean ± SD)    8.6 ± 7.7    1.0 (1.0-1.1)  .08  6.8 ± 6.6    0.98 (0.93-1.0)  .48  7.3 ± 5.8    1.2 (0.99-1.4)  .07  Level of operation                                   L4-L5 and above    21  43  1    15  33  1    53 (25)  41  1     L5-S1    11  22  0.64 (0.26-1.6)  .34  14  31  0.93 (0.42-2.1)  .86  40 (22)  31  0.80 (0.12-5.3)  .82   Multiple level    17  35  0.97 (0.43-2.2)  .95  16  36  0.83 (0.37-1.8)  .63  37 (14)  28  6.9 (0.89-54)  .07  Reason for operation                                   Disc herniation    26  53  1    24  53  1    64 (34)  49  1     Stenosis    11  22  0.79 (0.34-1.9)  .60  10  22  1.2 (0.51-2.6)  .73  35 (15)  27  0.12 (0.01-1.4)  .09   Both    12  25  0.85 (0.32-2.3)  .76  11  24  1.2 (0.47-3.3)  .67  31 (12)  24  0.43 (0.04-4.8)  .50  Number of previous operations (mean ± SD)    2.3 ± 1.3    1.0 (0.79-1.3)  .87  2.6 ± 1.9    1.2 (0.93-1.5)  .20  2.2 ± 1.3    0.38 (0.16-0.89)  .03f  Spinal fusion                                   No    35  71  1    31  69  1    85 (39)  65  1     Yes    14  29  1.4 (0.65-3.2)  .37  14  31  1.1 (0.55-2.4)  .72  45 (22)  35  9.1 (1.1-74)  .04f  Electrode location                                   T9-T10    32  65  1    30  67  1    81 (36)  62  1     Other    17  35  1.2 (0.57-2.4)  .66  15  33  1.1 (0.59-2.2)  .70  49 (25)  38  0.73 (0.14-3.8)  .71  Type of electrodeg                                   Symmix/Resume 1 × 4    42  86  1    40  89  1    98 (43)  75  1     Specify 5-6-5/2 × 4    7  14  1.7 (0.64-4.5)  .29  5  11  0.86 (0.30-2.5)  .78  32 (18)  25  3.8 (0.45-32)  .22  Deceased    5  10      1  2      4  3                  Permanent SCS implanted n = 175      Trial only n = 49  SCS explanted n = 45  SCS in use at the end of follow up n = 130 (61a)      All  %  OR (95% Cl)b  P  All  %  HR (95% Cl)c  P  Alld  %  OR (95% Cl)e  P  Gender                                   Female    20  41  1    25  56  1    63 (34)  49  1     Male    29  59  0.64 (0.34-1.2)  .84  20  44  1.4 (0.74-2.5)  .32  67 (27)  51  1.4 (0.35-5.9)  .68  Age (mean ± SD)    47.6 ± 11.3    0.98 (0.95-1.0)  .25  48.7 ± 12.4    1.0 (0.97-1.0)  .91  49 ± 10.4    0.96 (0.88-1.0)  .96  Location of pain                                   Extremity    21  43  1    19  42  1    51 (29)  39  1     Extremity and back    28  57  1.1 (0.53-2.1)  .86  26  58  0.86(0.46-1.6)  .65  79(32)  61  0.18(0.02-1.5)  .11  Duration of pain in years (mean ± SD)    8.6 ± 7.7    1.0 (1.0-1.1)  .08  6.8 ± 6.6    0.98 (0.93-1.0)  .48  7.3 ± 5.8    1.2 (0.99-1.4)  .07  Level of operation                                   L4-L5 and above    21  43  1    15  33  1    53 (25)  41  1     L5-S1    11  22  0.64 (0.26-1.6)  .34  14  31  0.93 (0.42-2.1)  .86  40 (22)  31  0.80 (0.12-5.3)  .82   Multiple level    17  35  0.97 (0.43-2.2)  .95  16  36  0.83 (0.37-1.8)  .63  37 (14)  28  6.9 (0.89-54)  .07  Reason for operation                                   Disc herniation    26  53  1    24  53  1    64 (34)  49  1     Stenosis    11  22  0.79 (0.34-1.9)  .60  10  22  1.2 (0.51-2.6)  .73  35 (15)  27  0.12 (0.01-1.4)  .09   Both    12  25  0.85 (0.32-2.3)  .76  11  24  1.2 (0.47-3.3)  .67  31 (12)  24  0.43 (0.04-4.8)  .50  Number of previous operations (mean ± SD)    2.3 ± 1.3    1.0 (0.79-1.3)  .87  2.6 ± 1.9    1.2 (0.93-1.5)  .20  2.2 ± 1.3    0.38 (0.16-0.89)  .03f  Spinal fusion                                   No    35  71  1    31  69  1    85 (39)  65  1     Yes    14  29  1.4 (0.65-3.2)  .37  14  31  1.1 (0.55-2.4)  .72  45 (22)  35  9.1 (1.1-74)  .04f  Electrode location                                   T9-T10    32  65  1    30  67  1    81 (36)  62  1     Other    17  35  1.2 (0.57-2.4)  .66  15  33  1.1 (0.59-2.2)  .70  49 (25)  38  0.73 (0.14-3.8)  .71  Type of electrodeg                                   Symmix/Resume 1 × 4    42  86  1    40  89  1    98 (43)  75  1     Specify 5-6-5/2 × 4    7  14  1.7 (0.64-4.5)  .29  5  11  0.86 (0.30-2.5)  .78  32 (18)  25  3.8 (0.45-32)  .22  Deceased    5  10      1  2      4  3      SCS = spinal cord stimulation; aquestionnaire answered; bodds ratio for successful trial, i.e., pulse generator implantation after trial; c hazard ratio for SCS explantation; din parentheses: questionnaire answered; odds ratio; efor complete recovery or substantial improvement (Global Perceived Effect, GPE 1-2) at the end of follow up; fP < .05; gall electrodes manufactured by Medtronic. View Large Trial Stimulation Out of the 224 patients, 175 (78%) received an IPG after the trial period. The remaining 49 patients did not experience adequate pain relief and had their electrode removed (Figure 1). The electrode location was T9-10 in 143 (64%) patients. The type of electrode was Symmix in 177 (79%) patients, Specify 5-6-5 in 33 (15%), Specify 2 × 4 in 11 (5%), and Resume in three (1%) (all electrodes Medtronic). The median duration of the trial was 7 d (range 0-21). During the trial, the electrode was repositioned in 6 patients due to inadequate pain relief, of whom all except 1 received a permanent SCS device with a good outcome. Preoperative MRI covering the implantation area was available for 77 patients, revealing 6 (8%) thoracic disc protrusions, 2 lateral stenosis, 1 syringohydromyelia, and 1 posterior element hypertrophy. In all cases, cerebrospinal fluid was visible anterior and posterior to the spinal cord. FIGURE 1. View largeDownload slide Flow chart of 224 consecutive FBSS patients undergone SCS with surgically implanted paddle lead from 1996 to 2014 at Hospital. FIGURE 1. View largeDownload slide Flow chart of 224 consecutive FBSS patients undergone SCS with surgically implanted paddle lead from 1996 to 2014 at Hospital. In the multivariate logistic regression analysis, age, gender, cause of operation, duration of pain, pain distribution, number of previous operations, level of operation, instrumented fusion, type of electrode, and level of electrode did not predict a successful trial. Postoperative Outcome At the first postoperative follow-up visit (mean 60 d, range 3-137 d), 153 (91%) patients reported good or adequate pain relief, 8 (5%) patients reported pain relief but inadequate pain coverage, 7 (4%) patients reported no pain relief, and 1 patient (0.6%) suffered worse pain after IPG implantation. Data were missing for 6 patients. Explantation Rate At the mean follow-up of 6 yr (range 0-18, total 1395 follow-up years), 45 (26%) SCS devices were explanted for the following reasons: 34 (76%) inefficient pain relief, 3 (6%) IPG depletion, 3 (6%) no further need for SCS, 1 (2%) surgical site infection, 1 (2%) electrode migration, 1 (2%) IPG region discomfort, 1 (2%) need for MRI, and 1 (2%) unsuccessful implantation. The median time for explantation due to inadequate pain relief was 3 yr (range 0-14), and 4 yr (range 0-8) due to other reasons (Figure 2). FIGURE 2. View largeDownload slide Kaplan–-Meier survival curve for all 175 patients with implanted SCS device after trial period. The end point of follow up was SCS explantation due to (1) loss of satisfactory pain relief or (2) other reasons (IPG depletion, no further need for SCS, surgical site infection, electrode migration, IPG region discomfort, need for MRI and unsuccessful implantation). The curve illustrates gradual loss of treatment efficacy in some patients at long-term follow-up. FIGURE 2. View largeDownload slide Kaplan–-Meier survival curve for all 175 patients with implanted SCS device after trial period. The end point of follow up was SCS explantation due to (1) loss of satisfactory pain relief or (2) other reasons (IPG depletion, no further need for SCS, surgical site infection, electrode migration, IPG region discomfort, need for MRI and unsuccessful implantation). The curve illustrates gradual loss of treatment efficacy in some patients at long-term follow-up. In the Cox regression analysis, age, gender, cause of operation, duration of pain, pain distribution, number of previous operations, level of operation, instrumented fusion, type of electrode, and level of electrode did not predict the outcome, as measured by the explantation rate for SCS. GPE at the End of the Follow-up Of the 130 patients with permanent SCS devices at the end of the follow-up, 61 (47%) answered the questionnaire. The mean follow-up time for these patients was 5 yr (range 0-16). Of them, 4 (6%) reported complete recovery, 40 (63%) substantial improvement, 15 (23%) slightly better situation, and 4 (6%) same or worse situation (Table 2). TABLE 2. Global Perceived Effect (GPE) of Spinal Cord Stimulation at the End of the Follow-up Period   All (%)  %  Female  %  Male  %  Completely recovered  4  7  2  6  2  7  Substantial improvement  38  62  23  68  15  56  Little improvement  15  25  7  21  8  30  No change  2  3  0  0  2  7  Little decline  0  0  0  0  0  0  Substantial decline  1  2  1  3  0  0  Total failure  1  2  1  3  0  0    All (%)  %  Female  %  Male  %  Completely recovered  4  7  2  6  2  7  Substantial improvement  38  62  23  68  15  56  Little improvement  15  25  7  21  8  30  No change  2  3  0  0  2  7  Little decline  0  0  0  0  0  0  Substantial decline  1  2  1  3  0  0  Total failure  1  2  1  3  0  0  View Large TABLE 2. Global Perceived Effect (GPE) of Spinal Cord Stimulation at the End of the Follow-up Period   All (%)  %  Female  %  Male  %  Completely recovered  4  7  2  6  2  7  Substantial improvement  38  62  23  68  15  56  Little improvement  15  25  7  21  8  30  No change  2  3  0  0  2  7  Little decline  0  0  0  0  0  0  Substantial decline  1  2  1  3  0  0  Total failure  1  2  1  3  0  0    All (%)  %  Female  %  Male  %  Completely recovered  4  7  2  6  2  7  Substantial improvement  38  62  23  68  15  56  Little improvement  15  25  7  21  8  30  No change  2  3  0  0  2  7  Little decline  0  0  0  0  0  0  Substantial decline  1  2  1  3  0  0  Total failure  1  2  1  3  0  0  View Large In the multivariate logistic regression analysis, instrumented fusion (odds ratio [OR] 9.1; confidence interval [CI] 95% 1.1-74; P = .04), and a smaller number of previous spinal operations (OR 0.4; CI 95% 0.2-0.9; P = .03), predicted a good outcome (GPE 1 or 2). However, age, gender, cause of operation, duration of pain, pain distribution, level of operation, type of electrode, and level of electrode did not. Complications and Revisions Seventy revisions were done in 64 (37%) of the 175 patients, of which 26 were due to complications in 25 (14%) patients (Table 3). The overall infection rate, including the trial, was 3.1%. All of the deep infections were positive for bacterial culture (Staphylococcus aureus in six patients and Acinetobacter baumannii in 1 patient; Table 3). There were no neurological injuries requiring surgical intervention. All of the infections appeared after an operation (range 7-29 d). TABLE 3. Complications Resulting for the SCS Device Removal or Revision (Includes Trial Complications) Complication  Removal  Revision  Details of revisions  Deep infection  1  6  All revisions were short-time explantations. Infection occurred in 2 patients during the trial period, in 2 patients after primary IPG implantation, and in 2 patients after electrode revision. All patients got a new device later without a trial.  Hardware malfunction  0  11  Extension leads were replaced in 4 patients. The electrode was replaced in 3 patients. The IPG was replaced once in 1 patient and in 1 patient twice. The whole SCS device was removed and later reimplanted in 1 patient.  Subcutaneous hematoma  0  1  Hematoma was evacuated.  Discomfort over pulse generator  1  3  IPG was relocated in all 3 patients.  Electrode migration  1  2  Electrode was relocated in both patients.  Complication  Removal  Revision  Details of revisions  Deep infection  1  6  All revisions were short-time explantations. Infection occurred in 2 patients during the trial period, in 2 patients after primary IPG implantation, and in 2 patients after electrode revision. All patients got a new device later without a trial.  Hardware malfunction  0  11  Extension leads were replaced in 4 patients. The electrode was replaced in 3 patients. The IPG was replaced once in 1 patient and in 1 patient twice. The whole SCS device was removed and later reimplanted in 1 patient.  Subcutaneous hematoma  0  1  Hematoma was evacuated.  Discomfort over pulse generator  1  3  IPG was relocated in all 3 patients.  Electrode migration  1  2  Electrode was relocated in both patients.  View Large TABLE 3. Complications Resulting for the SCS Device Removal or Revision (Includes Trial Complications) Complication  Removal  Revision  Details of revisions  Deep infection  1  6  All revisions were short-time explantations. Infection occurred in 2 patients during the trial period, in 2 patients after primary IPG implantation, and in 2 patients after electrode revision. All patients got a new device later without a trial.  Hardware malfunction  0  11  Extension leads were replaced in 4 patients. The electrode was replaced in 3 patients. The IPG was replaced once in 1 patient and in 1 patient twice. The whole SCS device was removed and later reimplanted in 1 patient.  Subcutaneous hematoma  0  1  Hematoma was evacuated.  Discomfort over pulse generator  1  3  IPG was relocated in all 3 patients.  Electrode migration  1  2  Electrode was relocated in both patients.  Complication  Removal  Revision  Details of revisions  Deep infection  1  6  All revisions were short-time explantations. Infection occurred in 2 patients during the trial period, in 2 patients after primary IPG implantation, and in 2 patients after electrode revision. All patients got a new device later without a trial.  Hardware malfunction  0  11  Extension leads were replaced in 4 patients. The electrode was replaced in 3 patients. The IPG was replaced once in 1 patient and in 1 patient twice. The whole SCS device was removed and later reimplanted in 1 patient.  Subcutaneous hematoma  0  1  Hematoma was evacuated.  Discomfort over pulse generator  1  3  IPG was relocated in all 3 patients.  Electrode migration  1  2  Electrode was relocated in both patients.  View Large An additional 22 revisions were done due to IPG battery depletion (20 patients). The median battery duration was 5.5 yr (range 1-10). In 1 case, after IPG depletion, the whole SCS device was replaced with a new type of electrode without a trial. Due to inadequate pain relief, 22 revisions were done to 19 (11%) patients, of which 15 were electrode repositionings. SCS devices were later explanted in 7 of these patients (Table 4). TABLE 4. Revisions Due to Inadequate Pain Relief Type of revision  SCS in use at the end of follow-up  SCS explanted during follow-up  All  Electrode repositioned  10  5  15  Electrode replaced  2  0  2  Explantation and immediate new trial  3  0  3  Explantation and immediate new SCS device  0  2  2  All  15  7  22  Type of revision  SCS in use at the end of follow-up  SCS explanted during follow-up  All  Electrode repositioned  10  5  15  Electrode replaced  2  0  2  Explantation and immediate new trial  3  0  3  Explantation and immediate new SCS device  0  2  2  All  15  7  22  View Large TABLE 4. Revisions Due to Inadequate Pain Relief Type of revision  SCS in use at the end of follow-up  SCS explanted during follow-up  All  Electrode repositioned  10  5  15  Electrode replaced  2  0  2  Explantation and immediate new trial  3  0  3  Explantation and immediate new SCS device  0  2  2  All  15  7  22  Type of revision  SCS in use at the end of follow-up  SCS explanted during follow-up  All  Electrode repositioned  10  5  15  Electrode replaced  2  0  2  Explantation and immediate new trial  3  0  3  Explantation and immediate new SCS device  0  2  2  All  15  7  22  View Large DISCUSSION This retrospective study analyzed 224 consecutive patients who had spinal cord stimulators implanted to treat FBSS from 1996 to 2014. The analysis was based on medical records, postal questionnaires, and national registry data. Furthermore, this study involved an extremely long follow-up period. We measured both the short- and long-term outcomes in these patients using the trial success rate, explantation rate due to inadequate pain relief, complication rate, and patient satisfaction as the GPE at the end of follow-up period. Trial Period Success The success rate after 1-wk during the trial period approached 80%, which is comparable to previous studies.21 This indicates that a 2- to 3-wk trial period, as reported in many centers, is unnecessary to differentiate patients that are likely to benefit from SCS. Due to infection risk and patient discomfort, the trial length should be kept to a minimum. New treatment modalities, such as burst and high frequency, may require longer trials due to the nature of the treatment. In the early years, a permanent device was not implanted if the stimulation did not provide a “tail effect,” ie, the response stopped when the device was turned off. Currently, we use numerical rating scale to measure pain relief after trial period, but the decision on permanent IPG implantation is based on global patient satisfaction instead of formal percentage of pain relief. No factors that could predict the trial success could be identified based on patient history, electrode type, or location. Long-Term Success Three out of 4 patients who received a permanent SCS device after the trial period continued to use it throughout the follow-up time, which reached 18 yr in some patients. This long-term success rate is higher than the 40% to 60% reported previously.22 In line with previous reports, there were no strong predictors for successful treatment outcome.23-25 Almost half of the patients replied to a questionnaire delivered by post, and 2 out of 3 reported substantial improvements or total recovery with SCS. This indicates that in carefully selected patients, long-lasting and satisfactory pain relief can be obtained. Fewer spinal operations and instrumented fusions predicted better satisfaction. The lower number of previous spinal surgeries as an indicator of positive outcomes supports general findings about spinal surgery outcomes. The positive correlation with instrumented fusion is logical since SCS is not supposed to improve instability related LBP. It is emphasized that fusion surgery with appropriate indication (instability)26 and SCS with appropriate indication (chronic neuropathic pain) may complement each other. In contrast to previous studies, prolonged neuropathic pain did not worsen the treatment outcome, whether it was measured by explantation rate or patient satisfaction.22 This indicates that SCS is a valid treatment even after long lasting pain, although we advocate that it should be trialed earlier, before starting strong opioids. A potential bias is caused by the fact that more than half of the patients did not respond to the questionnaire and may have less-than-optimal responses to the treatment. However, their SCS devices were in place until the end of the follow-up period, which might be an indication of at least some benefit. Complications and Revisions Two out of 3 patients with permanent SCS after the trial did not need additional surgery during the follow-up period. The complication rate was 14%, which is markedly less than the 30% to 40% reported previously.27-29 Complications were mainly minor and did not lead to serious neurological sequelae. One out of 8 patients had mild narrowing of the spinal canal at the level of implantation. Since ventral pathology such as osteophytes and disc herniations cannot reliably be excluded by visual inspection during operation, we recommend preoperative lumbar and thoracic MRI for all patients as suggested by Levy et al.27 The infection rate (3%) was in line with previous studies, reporting 3% to 6% infection rates.28,30,31,32 All infections appeared less than 1 month after an operation, indicating that long-term subclinical infections are rare. Only 1 patient had a permanent explantation due to an infection. In all other cases, the device could be reimplanted after sufficiently long and targeted antibiotic therapy. Benefits of Surgical Electrodes All of the patients in the current study were treated with a surgical SCS lead, using a preoperative methylene blue mark to spot the correct level for the electrode. Surgical paddle-lead electrodes were solely used for FBSS because of neurosurgeons’ preference at the time. The electrode migration rate (1%) was much lower than the 13% to 22% reported in other studies.33,34 The low migration rate of the electrodes and the lack of CSF leakage problems reflect the benefits of surgical electrodes. All explantations were complete and safe, and no serious adverse events, including compression of the medulla, were found in the data. The careful design of the electrode site has been found to be an important factor in the success of SCS treatment.35 In our series, the level of the electrode did not affect the short- or long-term outcome. However, if the patient experiences inadequate pain relief, revision with lead replacement may be advisable because this led to a good result in most cases (68%) in our series. New, wider surgical electrodes, that have more contacts, also enable directional stimulation and longer battery duration due to less loss of efficiency. In our hospital, shifting from 4 contact to more advanced 8 and 16 contact surgical paddle lead electrodes has been influenced by neurosurgeons’ preferences, costs of the SCS devices, and the legislation regarding competitive tendering in Finland. Limitations of this Study This is a retrospective study with obvious limitations. The patients come from a geographically wide area of 850 000 people in Eastern and Central Finland. Kuopio University Hospital serves as the sole neurosurgical unit in the area. During the study, neurosurgeons performing implantations have changed, as well as criteria for permanent SCS implantation. Implantable devices have also changed, and most patients have received an electrode that is not be used presently. Reliable information about patient history and clinical characteristics could be derived from hospital records, but sufficient information about pain relief is lacking and no structured questionnaires for psychological evaluation or quality of life have been used to study this population. Strengths of this Study This study's strength is its homogenous study cohort with only FBSS patients, in contrast to many studies that mix different pain etiologies. The follow-up time is longer than in most studies and we have been able to trace complications and explantations for almost 20 yr. National registries provide reliable data on the survival and causes of deaths of patients. Follow-up data are complete, since all postoperative controls were arranged in our own hospital, and all revisions and complications were recorded until the end of the follow-up. Consequently, there were no drop outs. Suggestions for Further Research This study is hospital based, including all consecutive patients with surgical lead implanted for FBSS at Kuopio University Hospital, and provides a positive picture of the quality and effectiveness of treating patients with SCS. The holistic situation of patients would be an important research topic, as well as the effect of psychological factors on the outcome, and the effects of SCS on neuropathic and opioid drug usage. We could not find predicting factors for the short- or long-term success of the SCS. Multidisciplinary patient selection is important so that different therapies can communicate together and the choice of treatment is not dependent on the treatment unit. Novel biomarkers, including psychological profiling, should be developed to improve patient selection. Ten patients deceased during the follow-up and 4 of them were suicides. In all of these patients, the equipment was either removed or a plan for removal had been made. Because treatment is often the last resort in this difficult patient group, it should be ensured that patients have adequate psychiatric support during this phase. CONCLUSION SCS with surgical paddle lead is a safe and effective form of treatment for FBSS. This study involved an extremely long follow-up period with accurate follow-up data. Patient selection should be further improved by developing novel predictive biomarkers. Disclosures Funding was from a Government Research Fund. Dr Nissen has received travel funding from the Medtronic, Boston Scientific and Abbott St Jude Medical. Ms Ikäheimo, Dr Huttunen, and Dr von und zu Fraunberg have received travel funding from the Medtronic and Abbott St Jude Medical. Dr Leinonen has no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article. REFERENCES 1. Harstall C, Ospina M. How prevalent is chronic pain? Pain: Clinical Updates . 2003; 11( 2): 1- 4. Google Scholar CrossRef Search ADS   2. Goldberg D, McGee S. Pain as a global public health priority. BMC Public Health . 2011; 11( 1): 770. Google Scholar CrossRef Search ADS PubMed  3. Turunen J, Mäntyselkä P, Kumpusalo E, Ahonen R. How do people ease their pain? A population-based study. J Pain . 2004; 5( 9): 498- 504. Google Scholar CrossRef Search ADS PubMed  4. Breivik H, Collett B, Ventafridda V. Survey of chronic pain in Europe: prevalence, impact on daily life, and treatment. Eur J Pain . 2006; 10( 4): 287- 287. Google Scholar CrossRef Search ADS PubMed  5. InSites Consulting. Pain Proposal Patient Survey . July–September 2010. https://www.dgss.org/fileadmin/pdf/Pain_Proposal_European_Consensus_Report.pdf. Accessed [01.05.2018]. 6. Bevan S, Quadrello T, McGee R, Mahdon M, Vavrovsky A, Barham L. Fit for Work? Musculoskeletal Disorders in the European Workforce . The Work Foundation; 2009. http://www.bollettinoadapt.it/old/files/document/3704FOUNDATION_19_10.pdf. Accessed [01.05.2018]. 7. Deyo RA, Gray DT, Kreuter W et al.   United States trends in lumbar fusion surgery for degenrative conditions. Spine . 2005; 30( 12): 1441- 1445. Google Scholar CrossRef Search ADS PubMed  8. Gray DT, Deyo RA, Kreuter W et al.   Population-based trends in volumes and rates of ambulatory lumbar spine surgery. Spine . 2006; 31( 17): 1957- 1963 Google Scholar CrossRef Search ADS PubMed  9. North RB, Campbell JN, James CS et al.   Failed back surgery syndrome: 5-year follow-up in 102 patients undergoing repeated operation. Neurosurgery . 1991; 28( 5): 685- 691. Google Scholar PubMed  10. Wilkinson HA. The Failed Back Syndrome: Etiology and Therapy . Philadelphia, PA: Harper & Row; 1991. 11. Liedgens H, Obradovic M. A burden of illness study for neuropathic pain in Europe. Econ Outcomes Res . 2016; 8: 113- 126. 12. Boswell MV, Trescot AM, Datta S. Interventional techniques: evidence-based practice guidelines in the management of chronic spinal pain. Pain physician . 2007; 10( 1): 7- 111. Google Scholar PubMed  13. Kumar K, Hunter G, Demeria D. Spinal cord stimulation in treatment of chronic benign pain: challenges in treatment planning and present status, a 22-Year experience. Neurosurgery . 2006; 58( 3): 481- 496. Google Scholar CrossRef Search ADS PubMed  14. North RB, Kidd DH, Farrokh F, Piantadosi SA. Spinal cord stimulation versus repeated lumbosacral spine surgery for chronic pain: a randomized, controlled trial. Neurosurgery . 2005; 56( 1): 98- 107. Google Scholar CrossRef Search ADS PubMed  15. Mailis-Gagnon A, Furlan AD, Sandoval JA. Spinal cord stimulation for chronic pain. A systematic literature synthesis. Cochrane Database Syst Rev . 2004; (3): CD003783. 16. Frank ED, Menefee LA, Jalali S et al.   The utility of a 7-day percutaneuous spinal cord stimulator trial measured by a pain diary: a long term retrospective analysis. Neuromodulation . 2005; 8 (3): 162- 170. Google Scholar CrossRef Search ADS PubMed  17. May MS, Banks C, Thomson SJ. A retrospective, long-term, third-party follow-up of patients considered for spinal cord stimulation. Neuromodulation . 2002; 5( 3): 137- 144. Google Scholar CrossRef Search ADS PubMed  18. Oakley JC, Kramer ES, Stamatos J, Foster AM. Successful long-term outcomes of spinal cord stimulation despite limited pain relief during temporary trialing. Neuromodulation . 2008; 11( 1): 66- 73. Google Scholar CrossRef Search ADS PubMed  19. Kamper SJ, Ostelo RW, Knol DL. Global perceived effect scales provided reliable assessments of health transition in people with musculoskeletal disorders, but ratings are strongly influenced by current status. J Clin Epidemiol . 2010; 60( 7): 760- 766. Google Scholar CrossRef Search ADS   20. Kumar K, Wyant GM, Ekong CEU. Epidural spinal cord stimulation for treatment of chronic pain—some predictors of success. A 15-year experience. Surg Neurol . 1998; 50( 2): 110- 121. Google Scholar CrossRef Search ADS PubMed  21. Kumar K, Nath RK, Toth C. Spinal cord stimulation is effective in the management of reflex sympathetic dystrophy. Neurosurgery . 1997; 40 (3): 503- 508. Google Scholar PubMed  22. Kumar K, Toth C, Nath RK, Laing P. Epidural spinal cord stimulation for treatment of chronic pain—some predictors of success. A 15-year experience. Surg Neurol . 1998; 50( 2): 110- 121. Google Scholar CrossRef Search ADS PubMed  23. Taylor R, Desai M, Rigoard P et al.   Predictors of pain relief following spinal cord stimulation in chronic back and leg pain and failed back surgery syndrome: a systematic review and meta-regression analysis. Pain Pract . 2014; 14( 6): 489- 505. Google Scholar CrossRef Search ADS PubMed  24. Fiume D, Sherkat S, Callovini GM, Parziale G, Gazzeri G. Treatment of the failed back surgery syndrome due to lumbo-sacral epidural fibrosis. Acta Neurochir Suppl . 1995; 64: 116- 118. Google Scholar CrossRef Search ADS PubMed  25. Son B, Kim D, Lee S. Factors associated with the success of trial spinal cord stimulation in patients with chronic pain from failed back surgery syndrome. J Korean Neurosurg Soc . 2013; 54( 6): 501- 506. Google Scholar CrossRef Search ADS PubMed  26. Gibson JA, Waddell G. Surgery for degenerative lumbar spondylosis. Cochrane Database Syst Rev . 2005; 19( 4): CD001352. 27. Levy R, Henderson J, Slavin K, Simpson BA, Barolat G, Shipley J, North R: Incidence and avoidance of neurologic complications with paddle type spinal cord stimulation leads. Neuromodulation  2011; 14( 5): 412- 422. Google Scholar CrossRef Search ADS PubMed  28. Lee AW, Pilitsis JG. Spinal cord stimulation: indications and outcomes. Neurosurg Focus . 2006; 21( 6): 1- 6. Google Scholar CrossRef Search ADS   29. Turner JA, Loeser JD, Deyo RA, Sanders SB. Spinal cord stimulation for patients with failed back surgery syndrome or complex regional pain syndrome: a systematic review of effectiveness and complications. Pain . 2004; 108( 1-2): 137- 147. Google Scholar CrossRef Search ADS PubMed  30. Rosenow J, Stanton-Hicks M, Rezal A. Failure modes of spinal cord stimulation hardware. J Neurosurg Spine . 2006; 5( 3): 183- 190. Google Scholar CrossRef Search ADS PubMed  31. Mekhail NA, Mathews M, Nageeb F, Guirguis M, Mekhail MN, Cheng J. Retrospective review of 707 cases of spinal cord stimulation: indications and complications. Pain Pract . 2011; 11( 2): 148- 153. Google Scholar CrossRef Search ADS PubMed  32. Kumar K, Hunter G, Demeria D. Spinal cord stimulation in treatment of chronic benign pain: challenges in treatment planning and present status, a 22-Year experience. Neurosurgery . 2006; 58( 3): 481- 496. Google Scholar CrossRef Search ADS PubMed  33. Mekhail NA, Mathews M, Nageeb F. Retrospective review of 707 cases of spinal cord stimulation: indications and complications. Pain Pract . 2011; 11( 2): 148- 153. Google Scholar CrossRef Search ADS PubMed  34. Kumar K, Buchser E, Linderoth B, Meglio M. Avoiding complications from spinal cord stimulation: practical recommendations from an international panel of experts. Neuromodulation . 2007; 10( 1): 24- 33. Google Scholar CrossRef Search ADS PubMed  35. North R, Ewend M, Lawton M. Spinal cord stimulation for chronic, intractable pain: superiority of “multi-channel” devices. Pain . 1991; 44( 2): 119- 130. Google Scholar CrossRef Search ADS PubMed  COMMENTS Over the last 5 decades, spinal cord stimulation (SCS) has become a routine intervention in management of chronic pain due to variety of clinical conditions, including the persistent or recurrent pain in the back and legs that is observed in patients after previous lumbar spine surgeries (referred here and in many other publications as the failed back surgery syndrome [FBSS] – the term we are now trying to replace with something more meaningful and objective). The authors of this study share their long-term series of SCS in FBSS patients, once again confirming overall positive effect of the procedure, with ∼60% of patients that were screened for SCS (130 out of 224) continuing using it at the latest follow-up. This finding is in line with many previous publications and may be a sort of baseline for all new stimulation targets and paradigms. One has to keep in mind that the authors’ findings may not necessarily be applied to the real-world situation in your hospital/region/country. First of all, the exclusive use of paddle type electrodes does not reflect worldwide situation where very many SCS systems are now implanted with percutaneous electrode leads. The discussion about pros and cons of each electrode lead type is beyond the scope of this comment; however, the types of complications may be quite different if one uses paddle type leads only when there are clinical reasons not to use percutaneous ones. Secondly, the authors have been using devices from a single manufacturer – and on my latest count, there are now at least 6 device manufacturers who produce commercially available SCS systems. Each of these systems has its own advantages and unique features, and by using an individually tailored device selection it is possible, at least theoretically, to increase long-term success rates and the effectiveness of the modality. Lastly, there is a major concern about reliability of the presented data. Due to the blinded nature of the review process, I am not sure from which European country it is coming. And although I generally accept the authors’ assumption that all patients’ problems and explants would have been accounted for due to their hospital being the sole neurosurgical facility in the region, I would caution the authors and the readers that the only reliable information about long-term outcome may be derived from 61 patient responses to the questionnaire. There is a very real possibility that among those who did not respond there are many SCS failures who are not interested to have their failed systems removed because it does not bother them and/or because of the real or perceived risk of yet another surgery. As the matter of fact, I would venture to say that there are many patients who are not using their devices anymore as there were only 22 device replacements in 20 patients due to battery depletion whereas one would expect to have at least 3 times more device depletions over this long-term follow-up period. The study also does not take into account the population mobility as these days people can easily move out of their geographic area and have their devices explanted or complications addressed in other institutions. Despite all these limitations, I applaud the authors for their interest in collecting data from a very long institutional experience and for their remarkably low complication rates. Hopefully, there will at some point be a different study that compares new reality of rechargeable devices, paresthesia-free stimulation paradigms, closed-loop stimulation approach, etc, with the previous conventional “one-size-fits-all” approach. Moreover, I sincerely hope that in the future articles the diagnosis of FBSS will be replaced by a more focused and precise definition of clinical condition. Konstantin Slavin Chicago, Illinois Copyright © 2018 by the Congress of Neurological Surgeons This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices)

Journal

NeurosurgeryOxford University Press

Published: May 21, 2018

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