I have the same opinion as "draconusRex", there are three common positions for a prostate exam in a doctor's office or an hospital, it depends on the doctor of course.
if the doctor is more concerned by the modesty and embarrassment of the patient, he will ask for the second position, that means lying on left side. As an adult man, i am often asking to take this position now.
But if the doctor is more concerned by the best method to reach the prostate, he will ask for the three position that means on all fours if he has enough time and if there is a table in the exam room, or for the second position if he is in a hurry with no table in the exam room.
I remember of a sports physical in high school which was performed in that way because we were a lot to be examined in a gym and there was no table available, so we were instructed to bend over and to grab our ankles but it was only a visual inspection of our anus, not a real prostate exam.
On the opposite, for a draft physical, I was instructed to squat on all fours on a table in front of a military doctor, and when he had finished and removed his fingers from my asshole, he gave me a smack on our cheeks while instructing me to stand up as he did for the other draftees examined before or after me.
After being inducted in the army for military service, I had an other thorough physical and the prostate exam was performed in a large group and we were instructed to bend over and grab our anklesall at the same time in a line.
I was also sometimes on all fours in a civil doctor's office when I was a young man for an annual routine exam or for a first job physical, it seems to me that it is the best position and the more comfortable for a doctor but they consider often that it is the more embarrassing for the patient.
I was never told to lay back on the exam table and to spread my legs.I think that this position is more for ladies examination.