You might ask your vet about using an arthritis supplement if the problem is with the elbow joint. Glucosamine chondroitin is one used to help arthritic joints.

Adequan shots may help to jump start the glucosamine use. You can read about Adequan here

http://www.petplace.com/drug-library/polysulfated-glycosaminoglycan-adequan/page1.aspx

Sometimes the joint issue in an elbow can be repaired but you have to figure in healing time and any other health issues that might make surgery an undesirable option.

If your cat is overweight slimming him down could help.

You might find pet steps so he doesn't have to jump up or down off of favorite places will help too.

http://tinyurl.com/bqo6xf shows an example

Hope this helps you!

I see you added some more info after I replied (not your fault its a site glitch).

My cats also love a heated pet bed to help with those sore joints. I use a snuggle disc

Here's an example but shop around as prices often drop this time of year

http://www.completepetmart.biz/384602.html

and I also have a pet bed heater that plugs in to warm another bed.

Yes an x-ray of the joint may tell you a lot about what is wrong in there.

If you feel he could have been exposed to a tick carried disease that might be worth checking for.