Sue the doctor using AI. For essentially as far as we can imagine, a human doctor will still be on paper the one practicing medicine. They are just using AI as a tool to be more productive.

As the AI gets stronger and stronger the human does less and less, as the AI itself has a confidence level that with the right software algorithms can be extremely accurate. So the human doctor let's AI do it all for the cases where the AI is very confident.

Because many AIs will check anything done for you, this accidental amputation is unlikely, and most suits are going to fail because exact records of their AI reasoning and wha rit new are kept. So you can just see in the logs the AI did everything possible and picked the highest success probability treatment.