Final answer:
Proper patient instructions for an AP projection of the shoulder involve the patient standing or sitting upright facing the x-ray machine, arm at the side with internal rotation, and holding still during exposure.
Step-by-step explanation:
For an AP projection of the shoulder, patient instructions are crucial for obtaining an accurate image. Patients should be positioned upright, either standing or sitting. The patient faces the x-ray machine with their back straight and both feet flat on the floor, squared to the equipment. The arm being imaged should be at the side with the palm facing the body. The shoulder should be rotated internally, ensuring the epicondyles of the humerus are parallel with the image receptor.
For accurate imaging, it's essential that the patient holds still during the exposure. A receptor is placed behind the shoulder, and the central ray is directed perpendicular to the glenohumeral joint. The resulting image should clearly show the joint space and the outline of the humerus.