ok so I am reviving this thread. I have an issue/concern and this is the most relevant topic.
So on my forehand I actually don't have any fingers out of place and extra tight or anything. Sometimes my pointing finger is pointed up the handle especially while volleying but if i am putting any amount of topspin at all its just a normal grip. like
no problems there. my backhand on the other hand, recently i have been trying to put more and more power and driving it fully a lot more. I realize i hold a more eastern grip for my backhand which means i hit more flat and through the ball than topspin but i am working on the topspin too. So I am hitting harder. And on my backhand, my thumb's actually point up towards the head. like this.
(looking at the picture gives me some kinda confidence that i am not doing a "wrong" thing).
After three days of good hitting and one more day of hitting against the wall (which is in some ways more intense on the arms and fingers) my joint between thumb and rest of palm is hurting. Its hurting exactly like it would hurt if I banged against your thumb with more pressure at its base, pusing it away from your palm.. and do this over and over. So its more like a soreness and general hurting, not a "pull it this way and it hurts" sorta thing.
I considered why I had this pain today. I haven't done anything out of the ordinary lately. I thought maybe I am using the space bar so much that my thumb is stretched out 
.. I really didn't think of anything and today in class I realized this. that grip overthere, if you hit harder and harder, the head of the racquet and the whole racquet in genearl is pushed back by the ball isn't it? And whats the major thing that's keeping my racquet from going back at impact? my thumb. my outstretched thumb. And the harder the ball hits my racquet, the more shock i am putting on my thumb.
is that right description of whats happening? if that's so, is this the finger that I am supposed to be holding on tightest or am I not holding it tight enough. Or is it just a strenghtening thing going on or am I doing something wrong. Perhaps the racquet moving back on impact should be stopped by my wrists and forearms/shoulder and there really shouldn't be as much pressure on my thumb? Obviously the thumb also helps guide the ball... am I using it too much to guide the racquet through the impact and perhaps I should watch other things to control that and not my thumb?
I also recently mentioned in my journal how I have more of a push/drive through than a swing through and up on my backhand. Well I am working on it as i said but that also sounds to me like I am basically absorbing all the impact on my extended thumb and driving through the ball right where it came from. I can see how driving up on the ball won't have nearly the same impact on my thumb as what I might be doing has.
Any advice? also in the picture above of the backhand, the forefinger is a little seperated as well. I don't do this. I can see how this might absorb some shock as well but the rest of my fingers are pretty much together. Dmast said above that this isn't done on the backhand usually, especially one hander but this picture shows it like that (I am not saying this random picture is in any way an authority over dmast, I would take dmast's word over garbage i find on the net anyday)
oh sorry for making this a personal rant but hey.. its about time we discussed some real world tennis here in the tennis discussion forum instead of how many hardcourts professionals play on or what bag Roger's carrying lately or the lack of curves on the WTA tour 
What the heck is that lump in your grip?
I agree with DMast, playing wall ball can definitely cause some physical problems just from the sheer number of shots you hit in such a short period of time. Try hitting 100 consequtive volleys off the wall and see what your hand/wrist feels like!!! The wall can be great for improving many aspects of your game, just be careful not to over do it.
To your body listen grasshopper.
