They say that insoles may help some people with MILD back pain. I'd try anything to have MILD back pain and bought some yesterday to see if they help in anyway so I will let you know how I get on.
As you probably know the position of your feet effects the curvature of your spine. Insoles, especially shaped ones can correct your posture and help to relieve back ache.
You need to see a podiatrist to get the correct shaped insoles for your back problem or you could try with a pair from your pharmacy. I bought mine from a large Boots yesterday, they have loads to choose from and are very reasonable in price.