Which of the following would NOT immobilize a fractured arm?

The choice of a stereotactic device stands out as the correct answer because it is primarily used in specific medical procedures that require precise localization, such as during brain surgery or radiation therapy. These devices are designed to hold instruments or imaging systems in fixed positions and do not serve to immobilize limbs such as a fractured arm.

In contrast, a cast, bandage, and splint are all commonly utilized to immobilize a fractured arm. A cast encases the limb completely and keeps it stable, allowing for proper healing. A bandage can provide support and compression but isn’t as rigid as a cast. However, it can still help in minimizing movement to a degree. A splint, often used initially in the treatment of fractures, is designed to stabilize the broken bone and can be adjustable or removable.

Therefore, while the other options are associated directly with the immobilization of a fractured arm, the stereotactic device is unrelated to this function, making it the correct selection for this question.