My forearm stump allowed only very limited pronation and supination until three months ago.

As it appears, there are some 'technical promises' around that include a promise for better pronation and supination as part of their promised betterments:

• Osseointegration
• High-fidelity sockets

I found that just for good pronation or supination, neither seems to be necessary. In fact, all that had happened was that I shrank and as a consequence, my previous sockets had become both rather wide and loose.

So I applied for two new sockets with a tight and perfect fit. We played with the temporary PET sockets until we got all little curves right. Now, pronation / supination works as well as it ever can work - using conventional socket technology. I also use a bit of shoulder motion to add to my pronation and supination to get it almost to a full 180%.

The principle behind optimal pronation and supination lies in getting full pressure on specific areas of the socket (but not on others). My stump (image left) has two very strong parts (bones, image middle). Regional pressure of my socket (yellow, image right) is then placed between the two bones both front and back. In other words, the socket compresses the regions that are colored yellow. That allows me to act on the bones  to turn the socket for pronation and supination.

That however is old school prosthetic good practice. No high tech, risks, extra costs or materials required for that.