Final answer:
The instrument used to visualize the interior of a joint is called an endoscope. Endoscopes transmit light to illuminate the inside of the joint and allow doctors to perform surgeries and obtain samples.
Step-by-step explanation:
The instrument used to visualize the interior of a joint is called an endoscope. Endoscopes are devices that are used to explore the body through various orifices or minor incisions. They transmit light down one fiber bundle to illuminate internal parts and transmit the reflected light back out through another bundle to be observed. This allows doctors to perform surgery and obtain samples for examination.