I'm starting to think Vik has a broken toe, or at least a badly sprained one. I took her out for a brief walk, and she went through some freshly cut pine sap/sawdust (hubby is removing dead decorative trees). When we got in, I started trying to get the stuff off her foot (all over her paw/pad) and one toe kept causing her to pull her foot back. I played with all the other toes, and even the toes on the other rear foot, no reaction. When I started to look at it, I think it looks more swollen and the toe is not lying inline with the rest of the foot. Being the neurotic scientist, I just took pics and put them online, see here:
http://www.pbase.com/bostonrott/first_d70_pics
You can click on each pic to enlarge it. As you look at the photos, it's the innermost toe, so on the Left foot picture, the left-most toe, and on the right photo, the right-most toe. I realize the Right foot pic is darker, but you can see that the toes all lie in-line, and the left foot definitely doesn't.
She prefers to lie on the affected leg, which I would think would be very painful if this was her knee, especially as she's on an eggcrate dog bed (which therefore puts a minor degree of torque on the knee). But, if it is her inside toe, by lying affected-side down, that puts the inside toe "up" and not being pressed upon by anything.
Keep your fingers crossed for us!!!!