Rib 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 Ribs Are Present in TP Approach | ||||||||
| L1 to L2 | 67% | 62% | 64% | 68% | 76% | 81% | 78% | 84% |
| L2 to L3 | 59% | 53% | 56% | 58% | 27% | 23% | 21% | 24% |
| L3 to L4 | 0% | 0% | 0% | 0% | 0% | 0% | 0% | 0% |
| L4 to L5 | 0% | 0% | 0% | 0% | 0% | 0% | 0% | 0% |
| L5 to S1 | 0% | 0% | 0% | 0% | 0% | 0% | 0% | 0% |
| Percentage of Obstruction Caused by Ribs When Present in TP Approach | ||||||||
| L1 to L2 | 82.6% | 68.3% | 69.4% | 83.4% | 82.5% | 81.9% | 74.8% | 93.9% |
| L2 to L3 | 75.8% | 63.3% | 67.7% | 76.5% | 100% | 54% | 41% | 93% |
| L3 to L4 | NA | NA | NA | NA | NA | NA | NA | NA |
| L4 to L5 | NA | NA | NA | NA | NA | NA | NA | NA |
| L5 to S1 | NA | NA | NA | NA | NA | NA | NA | NA |
Abbreviation: NA, not applicable.