I'm SOOOO relieved to report that the issue was a split toenail that was bothering him.  I don't know how I missed that =)  The vet trimmed it and said he would probably lose the nail, but he is already starting to use his leg again.

This scare has opened my eyes to the importance of being vigilant about the health of his remaining good legs.  Up until now I've taken it for granted.  Bostons can live up to 20 years, and Loki is still a pup by those standards.  I don't want to lose him because I neglected to give him the best care I could.

Thanks so much, I feel soo much better!

That said, I was going to try Musher's Secret paw wax to help with his slipping problem.  Is there anything else I should be doing or looking out for to help protect his remaining legs?

Some background on Loki:  I got him in 2006.  A couple of years later I took him to a friend's house.  Even though I walked the fence line and could find no holes or gaps he managed to slip out after I took my eyes off of him for less than a minute.  The next think I heard was him panting outside the gate where I found him a bloody mess.  I was crushed.

I rushed him to the vet where an xray showed his right hind femur was broken into 5 small pieces.  They tried to repair the damage, but I knew when I first saw the xray that the chances were slim that his leg would heal.

Sure enough, the titanium rod in his leg broke.  Twice.  Amputation was the only option at that point as there was little bone left to repair. 

I was so heartbroken, but his recovery was instantaneous and I was so grateful to still have my buddy with me.

I'd post some pics of him, but I have no idea how.  Here is a video of him a year or so after his amputation.

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Cheers!

Eric