It's a very attractive surgical support thingy made of white stiff fabric with velcro, you wear it around your hips and tighten the straps and it is supposed to help. I wore it for about 25 seconds so it is effectively brand new. I hate throwing things away and thought this might be a good place to offer it - it might work better for someone else than it did for me. PM me your address if you'd like me to pop it in the post.
SPD is a nightmare and anyone who has it has my eternal sympathy.