What occurs if the x-ray beam is perpendicular to the cassette but not to the long axis of the radius and ulna?

When the x-ray beam is perpendicular to the image receptor (cassette) but not aligned with the long axis of the radius and ulna, the resulting image distortion is primarily due to the angle at which the beam interacts with the bones. In this case, the radius and ulna will appear foreshortened because the angle of the beam fails to capture the true length of these structures projections in the image.

Foreshortening occurs because parts of the anatomy are not in line with the x-ray beam, causing them to appear smaller or shorter than their actual physical dimensions. When the x-ray beam is aligned perpendicularly to the film but not to the axes of the forearm bones, both the radius and ulna will project a smaller image of themselves, leading to the entire structure appearing foreshortened in the radiographic image.

This concept is foundational in radiography, as correct beam alignment is crucial in minimizing distortion and achieving accurate representations of anatomical structures.