Table 1 Demographic data and preoperative parameters
| Â | In total | Double-level TLIF group | Single-level TLIF group | P value |
|---|---|---|---|---|
Number of patients | 58 | 38 | 20 | Â |
Gender, n (%) | 0.415 | |||
 Male | 21 (36.2%) | 15 (39.5%) | 6 (30.0%) | |
 Female | 37 (63.8%) | 23 (60.5%) | 14 (70.0%) | |
Age at surgery, year | 57.1 ± 6.9 | 54.4 ± 9.4 | 58.2 ± 5.7 | 0.104 |
Smokers, n (%) | 10 (17.2%) | 7 (18.4%) | 3 (15.0%) | 0.327 |
BMI, kg/m2 | 26.1 ± 4.2 | 26.8 ± 5.2 | 24.7 ± 3.6 | 0.112 |
T score of BMD | − 1.3 ± 1.1 | − 1.1 ± 1.4 | − 1.5 ± 0.9 | 0.252 |
The duration of symptoms, month | 18.5 ± 7.6 (6–46) | 19.7 ± 9.3 (10–46) | 18.1 ± 6.6 (6–39) | 0.497 |
Follow-up period, month | 31.8 ± 10.7 (24–73) | 34.2 ± 11.8 (24–73) | 30.5 ± 9.3 (26–65) | 0.229 |
L4–L5 level |  | |||
 Slip percent, % | 21.6 ± 10.4% | 22.3 ± 13.4% | (18.1 ± 15.8)% | 0.290 |
 Modic change, n (%) | 13 (22.4%) | 9 (23.6%) | 4 (20.0%) | 0.742 |
 Disc height, mm | 10.9 ± 2.6 | 10.6 ± 2.3 | 11.7 ± 2.8 | 0.114 |
 Disc Pfirrmann grade | 3.2 ± 1.7 | 3.6 ± 1.6 | 2.8 ± 2.1 | 0.110 |
L5–S1 level |  | |||
 Slip percent | 17.1 ± 12.3% | 20.1 ± 14.6% | 15.4 ± 13.8% | 0.240 |
 Modic change incidence | 16 (27.6%) | 10 (26.3%) | 6 (30.0%) | 0.683 |
 Disc height, mm | 9.3 ± 3.1 | 8.9 ± 2.8 | 10.2 ± 3.7 | 0.138 |
 Disc Pfirrmann grade | 3.1 ± 1.8 | 3.2 ± 1.4 | 2.5 ± 2.3 | 0.155 |