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Classification system applied for the evaluation of the length of the first rib.
| Grade | Morphologic Appearance |
|---|---|
| Normal | 75% of the height of the cranial aspect of the body of T1 |
| 1—large rudimentary | 74–51% of the height of the cranial aspect of the body of T1 |
| 2—medium rudimentary | 50–30% of the height of the cranial aspect of the body of T1 |
| 3—small rudimentary | <30% of the height of the cranial aspect of the body of T1 |
| 4 | absent |
