I recently changed to the "Paul Gilbert style" of picking where the thumb joint is at 90 degrees. I've been doing a lot of alternate picking practice, and today when I pick my first note there's this sharp pain in the that joint. It doesn't feel like muscle pain. I'm going to have to stop playing. F#ck.
Ibanez RG1570
Fender Mexican Fat Strat

Engl Thunder 50 Reverb combo
Engl Classic Combo 350C
Line 6 Flextone III
Roland Microcube

Line 6 Podxt Live
Marshall Guv'nor
Dude... It's not even near 90 degrees. It's just angled.
He who joyfully marches to music in rank and file has already earned my contempt.
He has been given a large brain by mistake, since for him the spinal cord would fully suffice.

Remember: A prudent question is one half of wisdom.