So if your feet are fucked up, the rest of your body is going to be fucked up. If your calves are tight, they will cause issues up the chain and it will/can eventually lead to pain in the back. If your thigh muscles are too tight, same thing happens.
For those of us who sit often, we tend to get what is called an anterior pelvic tilt -- or in plain english a pelvis that is rotated or tilted slightly forward. This ends up causing your lower back to pick up the slack and curve more than it is supposed to, and on and on up the chain.
The single best thing I have found for releasing a tight psoas (to remove the tension and allow your pelvis to orient itself correctly) is to use a ~20lb slam ball and basically lie directly on top of it with it lodged right in the trinagle area that is below your belly button and to the side of your groin. Shove it in there, take a deep breath, lean into it and you will really feel it loosen the tension on your posas. This is makes a profound difference in my hip flexibility and usually does a killer job eliminating lower back pain.
For a good video demo of the psoas release I do often: https://www.youtube.com/watch?v=_F-0rtFbOgI @ 1:15 is the pose that I use.