Comparing wrists and hands in the same position is tricky, especially as regards to rotation. I would get a true PA view (more comfortable) and concentrate on getting the best shot accros the DRUJ. It may be that you need to use an image intesifier to get the exact rotation. You might even need a jig to hold the hand. I would try to compare arthritis in the radio-scaphoid joint and then move onto MCPJ, PIPJ and DIPJ joints. Different arthritic process affect these joints in different patterns. Good luck.