Was there any signficance to that other than that, as stated, he cut it during the fire? Seems like there should be more to it, but I can't figure it out.
What a lovely way to burn...
Apparently not. His injury had no impact on any of his actions later, didn't hinder him, didn't foreshadow anything and didn't have any symbolism of its own. Unlike the morphine, for example.
share(SPOILERS)
showed that Bauer was able to take an injury for his friend, while Cartwright prefered to look at a picture and cry instead of saving his partner, it was a matter of morality. You can say in response that Bauer was inmoral because he wanted to kill someone in order to save Cartwhrigt but he was really looking for the greatest result: if the two of them were able to survive the rest od the pods would also be saved, since they were the keepers of the order, so a single dead would be nothing compared with the survival of the human race... but he was not evil... so he prefered to die instead of killing the human hope at the end.