Originally Posted by 10isfreak
Your grip has surprisingly little to do with your shot. All a more extreme grip does is closing your racket face a little more, which does make it easier to get top spin at contact (because a racket that leans forward makes contact off center on the ball). However, you can use a plethora of swings to hit with the exact same grip.
If you want an advice on how to manage this pain, think about rotation. Open up your stance if it's not already an open stance forehand or, at least , a semi-open stance forehand. Once you get that open stance, understand that bending your knee before swinging has the purpose of enabling you to use a leg extension (literally a push from your racket side leg) to make your hip rotation faster. With the great degree of rotation that these more contemporary stance allows, you can still get a decent shot without bending much at the knees.
This advice is spot-on. It's not the grip. Opening up the stance will have a greater effect than changing the grip. Here's a good video that illustrates this-
I'm On Your Side Tennis w/ Dan Brown Modern Forehand Lesson