Risk differences and score test p values for event rate (probable cases per 1 000 000 patients) comparisons
| Event rate comparisons | Risk difference (CI) | P value |
| Cervical/thoracic versus lumbar/sacral | 24.3 (6.7 to 63.8) | <0.001 |
| Transforaminal versus non-transforaminal | -7.0 (−17.3 to 4.0) | 0.16 |
| Cervical/thoracic (transforaminal vs non-transforaminal) | 70.7 (−3.8 to 311.6) | 0.07 |
| Lumbar/sacral (transforaminal vs non-transforaminal) | −8.8 (−19.1 to -1.1) | 0.04 |