Recently the American Academy of Neurosurgeons reviewed medical studies on TENS, which is a small device you wear to mask the pain. It is a mild form of neurostimulation. The AAN found that TENS is not really effective for back pain, and they recommend against it for this purpose.
TENS is a conservative treatment. Spinal cord stimulation is an invasive pain management therapy that does pretty much the same thing but with a lot more intensity. You might think of spinal cord stimulation as the industrial strength version of TENS. The main differences are that spinal cord stimulators have to be surgically implanted, and the impulses they deliver are much more powerful and flexible than those of TENS. Of course SCS is not for everyone. If you think it might be for you, check with your doctor or pain management specialist.
Although currently there are few studies on how spinal cord stimulation addresses chronic back pain, it is a promising therapy. There will likely be more studies done in the future.
Richard M. Dubinsky MD, MPH, FAAN and Janis Miyasaki MD, MEd, FAAN. Assessment: Efficacy of transcutaneous electric nerve stimulation in the treatment of pain in neurologic disorders (an evidence-based review). Report of the Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology. Neurology 2009, doi:10.1212/WNL.0b013e3181c918fc.