Just an update on this if anyone's interested. I had X-rays and looked at them with my doc. The metacarpals aren't fused together at the base but there is are two bone spurs close against each other, one portruding from the metacarpal and one from the carpal bone, and that is what limits ROM. Here
is an illustration. I also have De Quervain's syndrome in the right hand (tendonitis in the wrist below the thumb with some osteoperosis in the head of the ulna there). Doc perscribed physical therapy and ultrasound for the bone.
news is that it doesn't bother me very much anymore. I can't let the wrist go much beyong 90 degrees so doing planches with the hands pointing forward is out of the question, but I don't feel like my hand is going to be torn apart every time I put some weight on it anymore. My shoulders used to be so tight that the wrists were forced to compensate for them in handstands. They're so much better now that it's not an issue anymore. It took a couple months layoff from Capoeira/gymnastics and Feldenkrais 4-5 times a week to fix this long standing problem but it was worth it!