Demographics and clinical data (N = 366).
| Risk Factor | Surgical Site Infection Cohort | Control Group | P Value |
| Age, y, mean (SD) | 48.2 (19.0) | 50.1 (19.7) | 0.722 |
| Female sex, n (%) | 21 (81) | 21 (81) | 1.00 |
| Body mass index, mean (SD) | 33.4 (9.1) | 28.9 (6.9) | 0.049 |
| No. of levels, mean (SD) | 4.1 (4.4) | 3.5 (4.3) | 0.632 |
| Length of anesthesia, min, mean (SD) | 334 (119) | 354 (124) | 0.552 |
| Estimated blood loss, mL, mean (SD) | 571 (459) | 400 (265) | 0.106 |
| Serum glucose on day 3, mmol/L, mean (SD) | 8.58 (3.5) | 7.49 (1.9) | 0.168 |
| Drain use, n (%) | 13 (50) | 14 (54) | 0.781 |
| Days from initial procedure to reoperation, mean (SD) | 21.7 (14.6) | N/A | N/A |
| Skin to SP on x-ray, mm, mean (SD) | 47.9 (14.9) | 37.7 (17.1) | 0.017 |
| Skin to SP on sagittal MRI, mm, mean (SD) | 43.5 (14.9) | 35.0 (17.1) | 0.062 |
| Skin to SP on axial MRI, mm, mean (SD) | 39.3 (14.2) | 34.3 (16.1) | 0.248 |
| Skin to lamina on MRI, mm, mean (SD) | 61.2 (16.7) | 55.4 (16.5) | 0.213 |
Abbreviations: MRI, magnetic resonance imaging; SP, spinous process.