Final answer:
For a lateral sternum radiograph, if left and right anterior ribs are not superimposed with the right thorax appearing rotated anteriorly, it indicates the patient was over-rotated. Correct positioning would show the ribs superimposed.
Step-by-step explanation:
The question pertains to radiographic positioning for imaging the thoracic cage, which includes the sternum and 12 pairs of ribs with their costal cartilages. When performing a lateral sternum radiograph, if the left and right anterior ribs are not superimposed and the right thorax appears rotated anteriorly, this indicates that the patient was over-rotated. In proper positioning, the ribs should be superimposed to ensure an accurate image is produced. An over-rotation results in the thorax being turned too far towards the X-ray source, causing one side of the ribs to appear more anterior (nearer to the X-ray source) than the other.
For a correctly positioned lateral sternum X-ray, the patient's shoulders and hips should be aligned perpendicular to the X-ray table, and there should be no tilting or rotation of the thorax. If the anterior ribs are not overlapping as they should, it is clear that there has been an over-rotation during positioning.