Iliac crest presence and obstruction of TP approach per side and zone.
| Disc Level | Right Side | Left Side | ||||||
| Zone #1 | Zone #2 | Zone #3 | Zone #4 | Zone #1 | Zone #2 | Zone #3 | Zone #4 | |
| Percentage of Time Iliac Crest Is Present in TP Approach | ||||||||
| L1 to L2 | 0% | 0% | 0% | 0% | 0% | 0% | 0% | 0% |
| L2 to L3 | 0% | 0% | 0% | 0% | 0% | 0% | 0% | 0% |
| L3 to L4 | 0% | 0% | 0% | 0% | 0% | 0% | 0% | 0% |
| L4 to L5 | 32% | 40% | 50% | 50% | 29% | 45% | 54% | 55% |
| L5 to S1 | 88% | 89% | 89% | 89% | 87% | 88% | 89% | 89% |
| Percentage of Obstruction Caused by Iliac Crest When Present in TP Approach | ||||||||
| L1 to L2 | NA | NA | NA | NA | NA | NA | NA | NA |
| L2 to L3 | NA | NA | NA | NA | NA | NA | NA | NA |
| L3 to L4 | NA | NA | NA | NA | NA | NA | NA | NA |
| L4 to L5 | 82.0% | 87.1% | 90.0% | 99.8% | 81.9% | 76.1% | 93.2% | 97.1% |
| L5 to S1 | 98.9% | 99.0% | 100% | 100% | 98.1% | 99.2% | 99.1% | 100% |
Abbreviation: NA, not applicable.