To me, hurting his thumb is not an excuse.
I say this because I think he hurt his thumb on the same exact play Andre Gurode went down, which was in the 3rd Quarter and he was already playing horrible. If you look at the replay Fox was showing to try and find when Gurode and later Romo got hurt, Romo had a pile of guys on him on that very same play Gurode got hurt.
Right after that play, they showed the Doctor looking at his thumb and there is no doubt that they would have showed the Doctor looking at it if it had happened earlier.
Obviously it didn't help but I think he was determined to force ball, hurt thumb or not.
And yes, this was probably his worst performance. In the Buffalo Game, he settled down and took what the defense was giving him, which was the Fullback in the flats.
This game, he was off the entire night. It didnt help that his receivers dropped some balls, but his accuracy was horrible and he also forced alot of balls. My memory is shakey on some of his throws, but I think he left 1-2 more Ints on the field.