I read that the #1 people go to the doctor under 40 is back pain. Also, incredibly, back pain is the #1 cause of people being on the welfare benefit called Disability in the United States.
Iontophoresis can cause drugs to migrate 1-3cm into skin by using electricity. I do not know if that is far
enough or not to reach the nerves of the back. I do not even know if the nerves of the back that bring people to the doctor mean nonspinal-cord nerves, like perhaps the smaller bunch of nerves at the back that do vertebrae sensing, or if it has to do with the spinal cord.
Put electrically polymer conductive dots on the head of a wand vibrator (wand vibrator: you may have seen one in an erotic video) there is a circuit running between your hand holding the vibrator's conductive handle and the opposite (+) polarity head.
Smear medicated cream on the vibrator head or the back.
When the massager head is in contact with the cream the medicine in the cream iontophoretically migrates into the skin of the back. It reaches 1-3 cm deep, the process takes about 20 minutes at one brochure [link]
The iontophoretic back massager can be improved by incorporating the "plaid conductor" here at the halfbakery. Basically there are lots of little conductive stripes or dots on the wand head, and a CPU figures out which ones out of a 100 to activate together to get the best iontophoretic migration of active medicine.
Another version uses a very simple glove with 100 discretely addressible conductive polymer sections (or painted on areas); the CPU makes sure the (-) electricity goes to the fairly snug wrist, far from the fingertips, and the + is always on the fingertips. Rapid hand motions dynamically reallocate where the glove has (-) and (+) contacts with the body. Using the glove you just rub iontophoretic pain relief cream onto the back, a joint, or even onto the face as a drug-delivery beauty treatment.
The CPU can tell when a full dose of drug has been delivered and lets you know when to stop. There are a couple competing schemes (microfluctuations in conductivity; color change of invisible IR or UV dye that wand/glove sees; pH change of skin surface)
So it might work, some drug, migrated an entire 1-3cm into back tissue near vertebrae and muscles might relieve back pain.