Which of the following implants is most likely to cause heating issues during an MR exam?

The external fixation system is most likely to cause heating issues during an MR exam due to its construction and the materials used. External fixation devices typically consist of metal components that are often positioned near the skin's surface, which can lead to significant heating effects during exposure to the magnetic field and radiofrequency energy of an MRI. The specific design of these devices, which includes pins and rods that can conduct heat, makes them particularly susceptible to the heating phenomena associated with MRI procedures.

In contrast, while other implants like hip replacements and lumbar fusions may also contain metal, their overall configurations and the depth at which they are placed in the body typically result in less pronounced heating effects. Cardiac stents, while they contain metal and can pose some risks during MRI, are usually made from materials that may not generate as much heat compared to the components of an external fixation system. Moreover, many modern cardiac stents are designed to be MRI-safe, further reducing the likelihood of heating issues.

Understanding the differences in how various implants respond to MRI technology is crucial for ensuring patient safety during scans, making it important to closely evaluate the risks associated with external fixation systems in particular.