I've watched carefully both how my instructor uses her pinky, and how others do so, and it seems to universally be comparatively straight at the second joint to make the stretch, with the first bent to press down on the string.
When I use my pinky in a similar way, the second joint buckles(to 180 degrees or more) upon attack. I had it nearly pop out of place once.
As such, I am trying to keep it arched more than normal, but this makes the stretch far far greater than it would usually be. I can make a 6 fret stretch on a guitar, but this is quite a bit more exhausting, as I'm keeping the second joint at about a 45 degree angle to keep it from snapping flat, which moves my thumb, which moves my other fingers, etc etc.
My question is: is this a usual problem, and I am using my pinky wrong, or am I going to be stuck using more arch than most people? Is there any fix that would let me keep my pinky straighter?