Final answer:
A lateral projection is an acceptable substitute for an AP projection of the thumb when the patient cannot assume the required position.
Step-by-step explanation:
If an elderly patient is unable to assume the required position for the AP (anteroposterior) projection of the thumb, a lateral projection would be an acceptable substitute. The lateral projection allows the healthcare provider to view the thumb from the side, which can provide similar diagnostic information as the AP projection, especially if the thumb is injured or if the patient has limited mobility.
The PA (posteroanterior) projection, axial projection, and oblique projection are other types of radiographic views, but in the context of a thumb where AP is not possible, the lateral position is typically the next best alternative.