I am sorry to hear Dino has been diagnosed with arthritis, especially so young. Thor has it in his shoulders. I would talk to your vet about something other then an NSAID (Non-Steroidal Anti-Infammatory Drug) such as Rimadyl and Derramaxx, especially if it going to be for long term use. It can play havoc on the liver and kidneys.
For the inflammation of joints, I give Thor fish oil and vitamin e. Fish oil is a natural anti-inflammatory. It does take a lot of vitamin e to break down the fish oil in the body, hence the vitamin e supplement. The standard dosage of fish oil for dogs is 20 mg/lb, but you need to double this for anti-inflammatory benefits. Vitamin standard is 100 iu's for a dog 50 lbs and over, but you will want to double that as well.
For days that he is in pain I give tramadol. On cold damp days put a jacket on him to keep his back warm and dry. I even have an old thermal shirt that that Thor wears on on cold winter days. Since Dino can't get up on the furniture, make sure he has a bed that is not too soft and not too firm. You'll want to keep him off a floor that is too cold.
As long as Thor stays on his fish oil we use a lot less tramadol. He was taken off the fish oil when he got pancreatitis, and he was getting tramadol 2-3 times a day. He had eye surgery last year and needed an NSAID, so I was told to keep the swelling down in his eye and not cause any complictions leading to losing his sight, and after debating with the eye doctor, he was put on Deramaxx, which is suppose to have less side effects than Rimadyl. It almost killed my boy. Some dogs tolerate them well. I am not trying to scare you. I just want you to be informed. If you notice any change such as lethargy, decreased appetite, or changes in urnation and drinking habits, please get your dog to the vet ASAP, and have them check his bloodwork.