Originally Posted by Littlepaw

Maybe the MRI will give you some more info. Muscle spasm can be motor signal that isn't getting through properly. Swelling or contraction in a certain position could make that tendency worse. The main nerves of the wrist are under maximum tension and most likely to get pressed on by swelling or mechanical issue when the wrist is flexed upwards. Definitely something to tell your doctor about...That it is worse in certain positions is important.