Final answer:
The sternum appearing into the auxiliary on the RAO indicates that the patient is over-rotated. Proper rotation usually requires 15 to 20 degrees anteriorly to view the sternum without superimposition by other structures.
Step-by-step explanation:
If the sternum appears into the auxiliary on the RAO, it indicates that the patient is over-rotated. During an RAO (right anterior oblique) positioning, the sternum should be seen in profile, projecting over the heart shadow when the patient has been rotated correctly. Proper rotation is usually around 15 to 20 degrees anteriorly. If more of the sternum is visible within the thoracic cage, it might suggest that the patient's position is overly rotated beyond what is required for an optimal view, while an under-rotated position would mean less of the sternum is visible. The sternum, which is part of the thoracic cage, is composed of the manubrium, body, and xiphoid process. With the anatomy involved, the aim of imaging techniques such as this is to ensure the sternum is visible without superimposition of other structures for a clear diagnosis or assessment.