Final answer:
When the sternum is seen next to the vertebral column on a medical image, it indicates that the patient has been over-rotated.
Step-by-step explanation:
If the sternum is demonstrated next to the vertebral column, then the patient was over-rotated. In medical imaging, particularly during chest radiographs, the sternum and vertebral column should appear in alignment if the patient is properly positioned. If the sternum is visible next to the spine, it suggests that the patient has been rotated too much towards the image receptor, causing an over-rotation artifact.
Concerning the other options, under-rotation would result in the sternum being obscured or overlapped by the thoracic spine, correctly positioned indicates no significant misalignment of these structures, and tilted refers to an inclination that would affect the symmetry of the thoracic structures, but not specifically the sternum's position relative to the spinal column in the same way that rotation does.