The initial symptoms of arthritis and tendonitis can feel very similar, so here’s an easy home-diagnosis way to tell the difference: try taking glucosamine for two weeks. If it helps, you likely have osteoarthritis. If not, it’s more likely a tendon problem.
What’s the reasoning here? Glucosamine (often packaged with MSM and/or chondroitin) has been shown in quite a few scientific studies to help with cartilage formation. Cartilage is what your joints are made of, and what arthritis attacks, so upping the rate of production in turn helps your joints. End result: you’ll probably feel better…if you have arthritis.
On the other hand, glucosamine will not help with collagen formation, and tendons are made of collagen. So it stands to reason that if you feel like you have “joint pain”, take glucosamine, and don’t experience any relief, one very likely culprit could be your tendons. (Tendon insertion points are often very close to joints and it can be difficult to tell exactly where the pain is coming from.)
Taking NSAIDs, using ice and so on can provide temporary relief for either condition, but since both arthritis and tendonitis are both the result of inflammation, using these treatments won’t help you distinguish between the two. And knowing which one you have is of course very important if you intend to treat the condition yourself.
If you do decide that you have a tendon problem, however, and you’ve had your pain for more than a couple of weeks, I caution you against assuming that the issue is tendonitis. More likely it’s tendonosis, which is an actual degeneration of the tendon. (This is especially true if you take NSAIDs and they don’t help.) If you think that this might be your problem, have a look at my tendon test. It’ll only take a minute, is completely free, will tell you whether you have tendonitis or tendonosis, and give you some options about what to do about it.