Praise be to Allah.
We put this question to Shaykh Muhammad ibn Saalih al-‘Uthaymeen, may Allaah preserve him, who answered as follows:
If this is done with the knowledge of the patient and serves the interests of all, there is nothing wrong with it. But if it is done without the patent’s consent, then it is not allowed.
Q: What if the sickness is located in the area of the thighs?
A: Then the private parts should be covered. And Allaah knows best.