You will get pain in your back and your legs because they have to compensate for the lack of mobility in your joint the gout has attacked. Your muscles are getting pulled because they are doing the job your joint should have been doing.
For instance when I get gout on one side of my foot, the calf muscle will get very very sore after a couple days because of the way I have been walking.
Trying to make the joint comfortable also puts strain on your back because your probably not sitting in normal positions and walking differently then the body is used to.
I had that happen to me when I got it in my knee. Id also get you potassium checked, low levels can lead to very painful muscle cramps, spasms, and take the muscle longer to heal if its pulled.