There were 237 patients total, of whom 143 patients were implanted with an LF-SCS and 94 who were implanted with an HF-SCS (Table 1). Patients implanted with HF-SCS tended to be older (61.02±14.48 vs 54.07±15.05, p<0.001) and Non-Hispanic (84% vs 77.6%, p=0.03). The most common primary indication for implant was FBSS in both groups (44.8% LF-SCS vs. 39.4% HF-SCS), followed by lumbar radiculopathy (21% LF-SCS vs. 21.3% HF-SCS), CRPS (16.1% LF-SCS vs. 7.4% HF-SCS) and lumbar spondylosis (1.4% LF-SCS vs 14.9% HF-SCS).
Table 1
Patient Characteristics by Type of Stimulator
| HF-SCS | LF-SCS | p-value |
n | 94 | 143 | |
Sex = Male (%) | 54 ( 57.4) | 70 ( 49.0) | 0.251 |
Age (mean (SD)) | 61.02 (14.48) | 54.07 (15.05) | <0.001 |
Ethnicity (%) | | | 0.027 |
African American | 0 ( 0.0) | 2 ( 1.4) | |
Caucasian | 3 ( 3.2) | 17 ( 11.9) | |
Hispanic | 9 ( 9.6) | 5 ( 3.5) | |
Non-Hispanic | 79 ( 84.0) | 111 ( 77.6) | |
Unknown (Patient cannot or refuses to declare ethnicity) | 3 ( 3.2) | 8 ( 5.6) | |
Marriage Status (%) | | | 0.838 |
Married | 60 ( 63.8) | 89 ( 62.2) | |
Other/Unknown | 1 ( 1.1) | 2 ( 1.4) | |
Separated/Divorced | 13 ( 13.8) | 19 ( 13.3) | |
Single | 16 ( 17.0) | 30 ( 21.0) | |
Widowed | 4 ( 4.3) | 3 ( 2.1) | |
Payor Name (%) | | | <0.001 |
Medicare | 30 ( 31.9) | 23 ( 16.1) | |
None/Unknown | 49 ( 52.1) | 84 ( 58.7) | |
Other Government | 8 ( 8.5) | 3 ( 2.1) | |
Private Insurance | 7 ( 7.4) | 28 ( 19.6) | |
Workman's Compensation | 0 ( 0.0) | 5 ( 3.5) | |
Primary Diagnosis for Implant (%) | | | <0.001 |
Complex Regional Pain Syndrome | 7 ( 7.4) | 23 ( 16.1) | |
Cranial Neuropathy | 2 ( 2.1) | 5 ( 3.5) | |
Failed Back Surgery Syndrome | 37 ( 39.4) | 64 ( 44.8) | |
Lumbar Radiculopathy | 20 ( 21.3) | 30 ( 21.0) | |
Lumbar Spondylosis | 14 ( 14.9) | 2 ( 1.4) | |
Neuropathic Pain | 7 ( 7.4) | 17 ( 11.9) | |
Other Chronic Pain | 7 ( 7.4) | 2 ( 1.4) | |
Revision or Explant (%) | 25 ( 17.5) | 15 ( 16.0) | 0.897 |
Patient status (%) | | | 0.016 |
Alive | 78 ( 83.0) | 120 ( 83.9) | |
Deceased | 0 ( 0.0) | 9 ( 6.3) | |
Unknown | 16 ( 17.0) | 14 ( 9.8) | |
HF-SCS and LF-SCS patients had significantly lower VAS compared to baseline at 3 months (HF-SCS 4.25±2.3, p<0.001; LF-SCS 4.87±2.48, p<0.001) and 6 months (HF-SCS 4.91±2.42, p<0.001; LF-SCS 5.71±2.17, p=0.005) after implantation; however this effect did not survive to 12 months and there were no differences across the two groups (3 months p=0.18, 6 months p=0.13, Figure 2a, Table 2). Both HF-SCS and LF-SCS had better PPR post-implantation (HF-SCS 55.41±27.54), p=0.006; LF-SCS 48.17±29.84, p<0.001) and at 3 months (HF-SCS 61.18±25.35, p<0.001; LF-SCS 47.93±28.12, p=0.004); however this effect was sustained to 6 (HF-SCS 58.38±26.54, p=0.003; LF-SCS 33.70±25.94, p=0.09) and 12 months (HF-SCS 57.17±28.44, p<0.001; LF-SCS 42.50±26.75, p=0.052) only for the HF-SCS group. In addition, HF-SCS patients had significantly improved PPR compared to LF-SCS patients at 3 and 6 months (p=0.008, p<0.001 respectively, Figure 2b). There were no differences in opioid use in HF-SCS or LF-SCS patients compared to baseline; however patients with LF-SCS required significantly more opioids compared to HF-SCS at every time point (baseline 105.44±118.49 LF-SCS vs. 41.45±60.27 HF-SCS, p<0.001; post-implantation 107.91±142.99 LF-SCS vs. 35.15±51.72 HF-SCS, p<0.001; 3 months 110.23±197.08 LF-SCS vs 47.63±97.28 HF-SCS, p=0.027; 6 months 112.98±142.97 LF-SCS vs. 19.67±24.96 HF-SCS, p<0.001 and 12 months 106.03±146.08 LF-SCS vs. 33.92±48.66 HF-SCS, p=0.014). Nine patients died during this study, all of whom were in the LF-SCS group. There were no differences in sex (49% LF-SCS vs. 57.4% HF-SCS, p=0.25), marriage status (p=0.84), and revisions or explants (16% LF-SCS vs. 17.5% HF-SCS, p=0.89) between the two groups.
Table 2
Visual analog scale scores, perceived pain reduction and opioid use by type of stimulator. P-values are based on paired t-test between baseline and each individual time point based on stimulator type. *p-value compares HF-SCS to LF-SCS at a given time point
| HF-SCS | p-value | LF-SCS | p-value | *p-value across |
VAS Scores (mean (SD)) | | | | | |
Baseline | 6.61 (1.85) | | 6.31 (2.09) | | 0.26 |
Post-Implantation | 6.01 (2.22) | 0.09 | 5.73 (2.34) | 0.061 | 0.47 |
3 Months Post Implant | 4.25 (2.3) | <0.001 | 4.87 (2.48) | <0.001 | 0.18 |
6 Months Post Implant | 4.91 (2.42) | <0.001 | 5.71 (2.17) | 0.005 | 0.127 |
12 Months Post Implant | 5.52 (2.39) | 0.16 | 5.69 (1.87) | 0.15 | 0.81 |
Perceived Pain Reduction (mean (SD)) | | | | | |
Baseline | 31.74 (26.31) | | 31.21 (29.91) | | 0.99 |
Post-Implantation | 55.41 (27.54) | 0.006 | 48.17 (29.84) | <0.001 | 0.09 |
3 Months Post Implant | 61.18 (25.35) | <0.001 | 47.93 (28.12) | 0.004 | 0.008 |
6 Months Post Implant | 58.38 (26.54) | 0.003 | 33.70 (25.94) | 0.09 | <0.001 |
12 Months Post Implant | 57.17 (28.44) | 0.01 | 42.50 (26.75) | 0.052 | 0.067 |
Morphine mili-Equivalents (mean (SD)) | | | | | |
Baseline | 41.45 (60.27) | | 105.44 (118.49) | | <0.001 |
Post-Implantation | 35.15 (51.72) | 0.99 | 107.91 (142.99) | 0.8 | <0.001 |
3 Months Post Implant | 47.63 (97.28) | 0.21 | 110.23 (197.08) | 0.35 | 0.027 |
6 Months Post Implant | 19.67 (24.96) | 0.12 | 112.98 (142.97) | 0.79 | <0.001 |
12 Months Post Implant | 33.92 (48.66) | 0.15 | 106.03 (146.08) | 0.36 | 0.014 |
Sex Subset Analysis
There were 73 females implanted with LF-SCS and 40 with HF-SCS (Table 3). The females implanted with HF-SCS tended to be older (53.70±14.98 LF-SCS vs 65.03±12.60 HF-SCS, p<0.001). LF-SCS females had improved VAS scores post-trial (5.78±2.44, p=0.04) compared to baseline, and both HF-SCS and LF-SCS patients had improved VAS at 3 (HF-SCS 4.38±2.32, p<0.001; LF-SCS 5.16±2.56, p=0.001) and 6 (HF-SCS 5.35±2.03, p=0.023; LF-SCS 6.03±1.92, p=0.032) months, which did not survive to 12 months (HF-SCS 5.89±2.29, p=0.37; LF-SCS 5.82±1.91, p=0.35), and there were no differences in VAS between HF-SCS and LF-SCS females (Figure 3a).
Table 3
Patient Characteristics by Type of Stimulator and Sex
| Female | | Male | |
| HF-SCS | LF-SCS | p-val | HF-SCS | LF-SCS | p-val |
n | 40 | 73 | | 54 | 70 | |
Age (mean (SD)) | 65.03 (12.60) | 53.70 (14.98) | <0.001 | 58.06 (15.17) | 54.46 (15.21) | 0.193 |
Ethnicity (%) | | | 0.62 | | | 0.031 |
African American | 0 (0.0) | 1 ( 1.4) | | 0 ( 0.0) | 1 ( 1.4) | |
Caucasian | 2 (5.0) | 5 (6.8) | | 1 ( 1.9) | 12 ( 17.1) | |
Hispanic | 1 ( 2.5) | 1 ( 1.4) | | 8 ( 14.8) | 4 ( 5.7) | |
Non-Hispanic | 37 (92.5) | 63 (86.3) | | 42 (77.8) | 48 ( 68.6) | |
Unknown (Patient cannot or refuses to declare ethnicity) | 0 (0.0) | 3 (4.1) | | 3 (5.6) | 5 ( 7.1) | |
Marriage Status (%) | | | 0.73 | | | 0.79 |
Married | 24 ( 60.0) | 42 (57.5) | | 36 ( 66.7) | 47 ( 67.1) | |
Other/Unknown | 0 ( 0.0) | 0 ( 0.0) | | 1 ( 1.9) | 2 ( 2.9) | |
Separated/Divorced | 8 ( 20.0) | 14 ( 19.2) | | 5 ( 9.3) | 5 ( 7.1) | |
Single | 5 ( 12.5) | 14 ( 19.2) | | 11 ( 20.4) | 16 ( 22.9) | |
Widowed | 3 ( 7.5) | 3 ( 4.1) | | 1 ( 1.9) | 0 ( 0.0) | |
Insurance Type (%) | | | 0.07 | | | 0.018 |
Medicare | 15 ( 37.5) | 12 ( 16.4) | | 15 ( 27.8) | 11 ( 15.7) | |
None/Unknown | 19 ( 47.5) | 39 ( 53.4) | | 30 ( 55.6) | 45 ( 64.3) | |
Other Government | 1 ( 2.5) | 1 ( 1.4) | | 7 ( 13.0) | 2 ( 2.9) | |
Private Insurance | 5 ( 12.5) | 18 ( 24.7) | | 2 ( 3.7) | 10 ( 14.3) | |
Workman's Compensation | 0 ( 0.0) | 3 ( 4.1) | | 0 ( 0.0) | 2 ( 2.9) | |
Primary Diagnosis for Implant (%) | | | 0.25 | | | 0.006 |
Complex Regional Pain Syndrome | 4 ( 10.0) | 13 ( 17.8) | | 3 ( 5.6) | 10 ( 14.3) | |
Cranial Neuropathy | 1 ( 2.5) | 2 ( 2.7) | | 1 ( 1.9) | 3 ( 4.3) | |
Failed Back Surgery Syndrome | 18 ( 45.0) | 32 ( 43.8) | | 19 ( 35.2) | 32 ( 45.7) | |
Lumbar Radiculopathy | 8 ( 20.0) | 15 ( 20.5) | | 12 ( 22.2) | 15 ( 21.4) | |
Lumbar Spondylosis | 5 ( 12.5) | 1 ( 1.4) | | 9 ( 16.7) | 1 ( 1.4) | |
Neuropathic Pain | 3 ( 7.5) | 9 ( 12.3) | | 4 ( 7.4) | 8 ( 11.4) | |
Other Chronic Pain | 1 ( 2.5) | 1 ( 1.4) | | 6 ( 11.1) | 1 ( 1.4) | |
Revision or Explant (%) | 6 ( 15.0) | 17 ( 23.3) | 0.42 | 9 ( 16.7) | 8 ( 11.4) | 0.564 |
Patient Status (%) | | | 0.036 | | | 0.198 |
Alive | 33 ( 82.5) | 64 ( 87.7) | | 45 ( 83.3) | 56 ( 80.0) | |
Deceased | 0 ( 0.0) | 5 ( 6.8) | | 0 ( 0.0) | 4 ( 5.7) | |
Unknown | 7 ( 17.5) | 4 ( 5.5) | | 9 ( 16.7) | 10 (14.3) | |
Females with HF-SCS had greater PPR compared to baseline at 3 months (HF-SCS 60.71±24.91, p=0.016; LF-SCS 48.45±26.63, p=0.053), and 6 months (HF-SCS 63.19±28.02, p=0.022; LF-SCS 33.54±28.11, p=0.11), without improvement at 12 months (HF-SCS 59.64±28.79, p=0.053; LF-SCS 44.72±29.28, p=0.18; Table 4, Figure 3c). In addition, HF-SCS females had significantly better PPR scores at 6 months compared to LF-SCS females (p=0.004). While there were no differences in HF-SCS and LF-SCS females comparing each time point to baseline, LF-SCS females required significantly more opioids compared to HF-SCS at baseline (HF-SCS 28.52±29.13; LF-SCS 95.99±93.76, p=0.003), post-trial (HF-SCS 25.77±25.3; LF-SCS 103.84±147.40, p=0.001), 3 months (HF-SCS 28.93±34.52; LF-SCS 89.06±99.04, p=0.006), and 6 months (HF-SCS 22.05±30.7; LF-SCS 129.1±166.53, p=0.011), with a trend for higher opioid use for LF-SCS patients at 12 months (HF-SCS 25.69±28.55; LF-SCS 118.63±140.99, p=0.064; Figure 3e). There were no differences in ethnicity (p=0.62), marriage status (p=0.73), insurance type (p=0.07), primary implant diagnosis (p=0.25) or revision/explant (p=0.42) between the female HF-SCS and LF-SCS patients.
Table 4
Visual analog scale scores, perceived pain reduction and opioid use by type of stimulator. P-values are based on paired t-test between baseline and each individual time point based on stimulator type. *p-value compares HF-SCS to LF-SCS for the specific sex at a given time point
| Female | Male |
| HF-SCS | p-val | LF-SCS | p-val | p-val* | HF-SCS | p-val | LF-SCS | p-val | p-val* |
VAS Scores (mean (SD)) | | | | | | | | | | |
Baseline | 6.77 (2.03) | | 6.62 (2.13) | | 0.67 | 6.49 (1.73) | | 5.93 (2.01) | | 0.13 |
Post-Trial | 6.00 (2.46) | 0.13 | 5.78 (2.44) | 0.04 | 0.68 | 6.01 (2.05) | 0.139 | 5.68 (2.24) | 0.74 | 0.52 |
3 Months Post Implant | 4.38 (2.32) | <0.001 | 5.16 (2.56) | 0.001 | 0.26 | 4.14 (2.32) | <0.001 | 4.46 (2.34) | <0.001 | 0.66 |
6 Months Post Implant | 5.35 (2.03) | 0.023 | 6.03 (1.92) | 0.032 | 0.32 | 4.38 (2.78) | 0.018 | 5.32 (2.42) | 0.074 | 0.25 |
12 Months Post Implant | 5.89 (2.29) | 0.37 | 5.82 (1.91) | 0.35 | 0.74 | 5.35 (2.6) | 0.22 | 5.50 (1.83) | 0.27 | 0.99 |
Perceived Pain Reduction | | | | | | | | | | |
Baseline | 29.82 (30.23) | | 28.65(30.54) | | 0.96 | 34 (23.32) | | 34.09 (29.38) | | 0.96 |
Post-Trial | 57.03 (32.26) | 0.053 | 45.11 (31.54) | 0.014 | 0.12 | 54.19 (23.50) | 0.049 | 51.10 (28.13) | 0.023 | 0.45 |
3 Months Post Implant | 60.71 (24.91) | 0.016 | 48.45 (26.63) | 0.053 | 0.12 | 61.47 (25.98) | 0.009 | 47.29 (30.26) | 0.033 | 0.034 |
6 Months Post Implant | 63.19 (28.02) | 0.022 | 3.54 (28.11) | 0.11 | 0.004 | 53.46 (24.61) | 0.09 | 33.86 (24.00) | 0.60 | 0.027 |
12 Months Post Implant | 59.64 (28.79) | 0.053 | 44.72 (29.28) | 0.18 | 0.22 | 53.33 (29.16) | 0.19 | 40.00 (24.29) | 0.18 | 0.23 |
Morphine mili-Equivalents | | | | | | | | | | |
Baseline | 28.52 (29.13) | | 95.99 (93.76) | | 0.003 | 49.89 (73.36) | | 115.77 (140.92) | | 0.053 |
Post-Trial | 25.77 (25.3) | 0.78 | 103.84 (147.40) | 0.45 | 0.001 | 42.59 (65.11) | 0.25 | 112.16 (139.25) | 0.86 | 0.006 |
3 Months Post Implant | 28.93 (34.52) | 0.11 | 89.06 (99.04) | 0.48 | 0.006 | 58.54 (119.22) | 0.37 | 134.37 (267.58) | 0.87 | 0.19 |
6 Months Post Implant | 22.05 (30.7) | 0.45 | 129.1 (166.53) | 0.12 | 0.011 | 17.50 (19.45) | 0.21 | 96.52 (113.5) | 0.017 | 0.01 |
12 Months Post Implant | 25.69 (28.55) | 0.83 | 118.63 (140.99) | 0.071 | 0.064 | 39.62 (59.27) | 0.23 | 92.82 (151.8) | 0.10 | 0.13 |
Seventy males were implanted with LF-SCS and 54 with HF-SCS. There were more Hispanic patients in the HF-SCS group (14.8% vs 5.7%, p=0.03). LF-SCS patients had more private insurance compared to HF-SCS (14.3% vs 3.7%), while HF-SCS had more Medicare (27.8% vs. 15.7%) or other governmental insurance (13% vs. 2.9%, p=0.018). LF-SCS patients had more FBSS (45.7% vs 35.2%) and CRPS (14.3% vs 5.6%), while lumbar spondylosis was more common in HF-SCS (16.7% vs 1.4%, p=0.006).
HF-SCS and LF-SCS males had improved VAS scores at 3 months (HF-SCS 4.14±2.32, p<0.001; LF-SCS 4.46±2.34, p<0.001) compared to baseline, which persisted to 6 months only for HF-SCS (HF-SCS 4.38±2.78, p=0.018; LF-SCS 5.32±2.42, p=0.074), and did not survive to 12 months (HF-SCS 5.35±2.6, p=0.022; LF-SCS 5.50±1.83, p=0.27), with no differences across groups (Figure 3b). PPR was improved among HF-SCS and LF-SCS males post-trial (HF-SCS 54.19±23.50, p=0.049; LF-SCS 51.10±28.13, p=0.023) and at 3 months (HF-SCS 61.47±25.98, p=0.009; LF-SCS 47.29±30.26, p=0.033) compared to baseline (Figure 3d). Furthermore, HF-SCS males had significantly better PPR at 3 (p=0.034) and 6 months (HF-SCS 53.46±24.61, p=0.09; LF-SCS 33.86±24.00, p=0.60) compared to LF-SCS males which did not survive to 12 months (HF-SCS 53.33±29.16, p=0.19; LF-SCS 40.00±24.29, p=0.18; p=0.23 across).
LF-SCS males had significant reduction it opioid use at 6 months (LF-SCS 96.52±113.5, p=0.017) compared to baseline, but this was not present at other time points, or among HF-SCS (6 months HF-SCS 17.50±19.45 p=0.21) patients. In addition, LF-SCS males required significantly more opioids compared to HF-SCS post-trial (HF-SCS 42.59±65.11; LF-SCS 112.16±139.25, p=0.006), and at 6 months (p=0.01) but not at 3 (HF-SCS 58.54±119.22; LF-SCS 134.37±267.58, p=0.19) and 12 months (HF-SCS 39.62±59.27; LF-SCS 92.82±151.8, p=0.13, Figure 3e). There were no differences in age (p=0.19), marriage status (0.79), revision/explant (p=0.56) between the male HF-SCS and LF-SCS patients.
Linear Mixed Model
In the linear mixed model including age, sex, stimulator type, and time, VAS decreased with age (-0.015, 95% CI -0.0003-(- 0.03), p=0.047), at each time point, with the strongest effects seen at 3 months, (post implantation -0.14, 95%CI -0.21-(-1.16), 3 months -1.1, 95%CI -1.09-(-2.12); 6 months -1.0, 95%CI -0.33-(-1.41), 12 months -0.26, 95%CI -0.24-(-1.43), p<0.001), and a trend towards increasing for female sex (0.44, 95%CI -0.003-0.88, p=0.053), with a trend towards significant interaction between stimulator type and time (p=0.068).
In the same model for PPR, 3 months (4.23, 95%CI 0.71-7.78) and 6 months (6.17, 95%CI 2.37-9.99) were associated with higher PPR (p<0.001), while HF-SCS was associated with lower PPR (-4.95, 95%CI -8.36- (-1.5), p=0.005), and there was a significant interaction between stimulator type and time (p=0.027).
Finally, in the same model for opioid use, HF-SCS was associated with lower opioid use (-70.02, 95%CI -23.75- (-116.294), p=0<0.001), without significant effect of age, sex, time or the interaction between time and stimulator type.