Judy, thanks for your very thorough reply it was very helpful.
With his breed I was concerned about intervertebral disc disease in his neck affecting his left front leg but that seems less likely given that he is not painful, nor does he have any pain or flexibility problems with his neck. I would have expected the Metacam to help with that as well and it has not seemed to.
Is the affected joint his "wrist" joint? See the picture of the dog below. On one front leg he is normal but the other wrist is what we call hyperextended, meaning that the wrist ligaments are too loose and allow the dog to walk "flatfooted". (I know that Fritz's wrist may not be that bad but I wanted an extreme picture so you can see what I am talking about).
Carpal hyperextension is more common in big dogs but it is seen in overweight, older small dogs. It can happen suddenly after a jump down from a high place or it can be slowly progressive. If both front legs were affected and the joints were swollen then I would be concerned about immune mediated (or body attacking itself) as a cause but that seems less likely with him and his history.
Treatment in mild cases is based upon supporting the joint with splints or braces for a matter of months to allow the ligaments to tighten and the joint to regain normal function. Anti-inflammatories are used to reduce swelling so the ligaments can heal but won't be enough alone. The joint may feel stiff after laying down for a period of time and he may be developing some secondary arthritis as the joint has been inflamed due to the strain of an abnormal position and function for several months.
In some cases we need surgical intervention to stabilize the joint.
Have any radiographs been taken of his affected joint? If not I recommend that be done.
I would discuss splinting his leg or getting a brace to use for several months to see if we cannot get his ligaments to heal.
Here are some links to look at some of the available braces:
Long term for joint injuries I do recommend using a combination of a glucosamine/chondroitin product (examples are Dasuquin or Cosequin) and an
omega 3 fatty acid (like 3V Caps or Derm Caps). These work synergistically and
improve cartilage health and joint fluid quality and quantity as well as reducing inflammation. They can take several weeks to see full improvement but some dogs do very well with them alone. They are available over the counter.
Another option is a product called Duralactin. This is an anti-inflammatory product derived from milk proteins and it also has omega 3 fatty acids incorporated into it which can be very helpful. See this link for further information: http://www.duralactin.com/products_canine.htm
Best of luck with your fellow, please let me know if you have any further questions.