I finally got through the paperwork to visit the physio department of my local hospital. It's a small town, the hospital isn't on a par with big town facilities, so I was surprised to find them using a technology unknown to me - Electro-Magnetic Pulse Therapy. I'd expected a few gentle manipulations and a hot compress, with some advice on follow-up exercises at home. I got the hot and heavy compress treatment, twenty minutes front and back, and then twenty minutes with the machine, which looks like a large shower head attached to a mysterious white box on castors. They pass this "shower head" over you back without any pressure, like ironing a sheet or something, and you feel these very pleasurable pulses, at varying speeds and force, working on your muscles and nerves in an entirely different way to massage (which has never suited me). I could feel the tingle go down my arm and twitch my fingers. Result - although it felt good, it didn't seem to have much effect until several hours later, when the pain left me. I have booked a course of this treatment, twice a week for five weeks, and it may be that I don't need it this long. 500 baht a session, but for the effect it's had so far it's an absolute bargain - you'd pay that for some masseuse going through the motions while she thinks about what she's going to have for lunch.
So there you go - came here asking for advice and ended up giving it!
https://neurolaunch.com/emp-therapy/