I also have that problem for years now. A Female Neurologist told me to squeeze my bladder and that works to help me empty my bladder to avoid the horrible UTIs.

When I went to the hospital, after my fall, they had to catherize me, but just once, then they wanted me to go on my own. This was a real problem for the first few days in the hospital.

When I go and I think I'm finished, I squeeze my bladder and more comes out, so I have a constant tendancy to retain.

I hope you can do this and won't have to cathiterize.