I would think at this age if it is arthritis then it would be rheumatoid - auto immune.
Also, I think a better check w/an ortho and a consult with a chiro after that to confirm...unless you could see yourself by comparison on the x-ray.
I would be more inclined to go with the neck injury because of the bleeding nose.
My aunts dog had acute lameness (a sheltie), suddenly wouldn't jump down off the bed and got lethargic...vet said lets check for HD, didn't have...so put on metacam instead of checking the knee (acute!)...dog now has kidney disease...
Another woman I met, Vet tests for HD, no HD (shep/husky)...couldn't walk, put dog on metacam, started spilling black tarry diarrhea...vet suggested PTS...she was giving the dog another couple of weeks while she struggled with the decision
I had met this woman in line at costco (may 2012) and somehow started talking about our dogs...My dog had blown his knee, so I thought that may have been what teh vet missed w/her dog...I recommended to her Fast Joint Care + (by genuine health), home-made bone stock (mostly chicken cartiledge w/splash of vinigar to the stock) and Wobenzyme...2 weeks later her dog was walking a 1/2hr...she called again a couple months after and couldn't be happier with his improvement, wanted to know if he could go swimming, lol
- she called me again just before x-mas - said he was like a puppy again going on hour long walks, running...you get the idea (?)