I have been reading the forums, but haven't located anything on this yet. I'm sure its here somewhere though. Question: Can I file a claim for traumatic arthritis in my left knee and both elbows secondary to my service connected right knee injury that has traumatic arthritis?

Sure - you can file a claim for anything.

You will need medical evidence from a doctor stating your
additional conditions are secondary to your SC'd conditions
to prevail.
jmho,
carlie

Wow, that was quick! Thanks Carlie!

You might want to get a medical opinion that they are related, this will help your claim out a lot

The elbows will require some explanation and medical rational to show how they are related to your knee.

Ok. Thanks everybody! Just trying to determine which avenue to take.

The skeletal system consists of many bones and joints...therefore when you have an injury to one area ie knee, it will affect more than just the knee. The opposite leg will be affected, as well as hips, ankles, back too as your body tries to compensate and erect itself(x's) so therefore over the years esp one will notice the further c/o pain, possibly edema(swelling), joint pain with noisey joints ie possible r/t arthritis, etc.
It doesn't just pertain to that one area.
As others have stated you need to have the in-service injury, diagnosis per physian, and hopefully records of pain or treatment over the years...pain is very important with injury's. If you come running to your appointment and are smiling they will be suspecious, but if you limp, walk slowly, wear a brace, use a cane and speak of all the modalities you have tried unsuccessfully ie pain meds, heat, ice, braces, etc and still have the problem and you look sad(or grimace in pain) they are more likely to believe you.
DO NOT MAKE UP ANY complaints if you don't have the symptoms, don't say you do. Be honest.
Most importantly with back injuries if you are able to sit upright throught out your appointment and never have positional changes it may look suspecious of how disabling your back injury really is.
The majority of injuries do become worse over the years and many factors can be attributed ie weight, mobility, diet, B&B habits, prolonged use, further injuries to site...also if you have continued to seek out treatment from the original injury, these factor in the continunity of the claimed area for disability. You got the problem, claim it!