Hmm. Looking at the close up, and bearing in mind the distortion also showing between the ring finger and pinky, I do believe you've got a bit of 'beyond limits' twisting or lateral bending going on. The other clue in this view is the lighting; remember that for light to appear brighter on some parts of the mesh implies that the angle of the polygons being lit is different from surrounding areas. I know this sounds like a statement of the bleedin' obvious, but here you have a part of the hand that should be in the shade (between the fingers) actually showing as brightly lit. I therefore suspect that what you are showing us is an optical illusion .. what appears as contiguous mesh between two fingers actually isn't. Render a sideways view and it'll show the fingers at odd angles to each other. Either that or I'll eat my words. Which is cool cos I'm a bit peckish!