Arthritis is an inflammation in a joint, while tendonitis is inflammation of a tendon, the gristle-like cable that links muscle and bone. It can get confusing because a tendon is one component of the complex structure of a joint, though it’s not inside the joint itself. Overuse or repetitive stress – like lots of tennis or jogging – can lead to either arthritis, tendonitis or both, depending on where the damage occurs.
Tendons are often, though not always, covered with a coating, or sheath, called the synovium, which contains cells and blood vessels, says Dr. Lee Simon, a rheumatologist at Beth Israel Deaconess Medical Center. Between the sheath and the tendon is a layer of lubricating fluid, which protects the tendon as it moves. If the sheath becomes inflamed, that’s tendonitis, aka “tennis elbow” if it’s your elbow. Sometimes, taking ibuprofen or similar drugs is enough to calm this inflammation.
Arthritis is inflammation inside the joint itself. It comes in roughly 100 different forms. Osteoarthritis, sometimes called “wear and tear” arthritis, affects 21 million Americans. The cartilage on the surface of bones inside a joint gets worn away. As the body tries to heal this damage, chronic, low-grade inflammation sets in, causing pain. Rheumatoid arthritis, which strikes 2.1 millions, is an auto-immune disease in which the immune system mistakenly attacks the synovium inside joints. In some cases, ibuprofen and similar drugs help with this also.
As a practical matter, then, your initial treatment – ibuprofen-type drugs – will probably be the same, whether you have tendonitis or arthritis, notes Dr. David Felson, a rheumatologist at the Boston University School of Medicine. But knowing which you’ve got does become important if you need physical therapy because the exercises and rehabilitation programs are different.