It is sometimes hard to tell the difference between back pain that is caused by a bone or muscle problem and back pain (flank pain) that is caused by a kidney or bladder infection or a kidney stone.
Back pain that is caused by a bone or muscle problem:
Flank pain that is caused by a kidney infection or a kidney stone:
Flank pain with fever and urinary symptoms may mean a kidney infection (pyelonephritis) is present.
WebMD Medical Reference from Healthwise