Criteria for Diagnosing Osteoarthritis of the Knee

Richard Iorio, MD: Let me say 1 more thing?

Peter L. Salgo, MD: Yes, sure.

Richard Iorio, MD: In regard to diagnosis, which is what we’re speaking about, 1 important thing for our internal medicine colleagues to understand is the exclusion of other diagnoses that are important. What are the confusing or confounding diagnoses around osteoarthritis? So, we need to rule out rheumatoid arthritis and the inflammatory arthritides. That can be done with lab tests, right?

Peter L. Salgo, MD: Which lab tests?

Richard Iorio, MD: A simple sed (sedimentation) rate will help diagnose these.

Peter L. Salgo, MD: They still do those?

Richard Iorio, MD: They still do those. Rheumatoid factor. There are a number of other markers for inflammatory arthritides.

Peter L. Salgo, MD: I want to get back to that. They’re still doing sed rates?

Richard Iorio, MD: They are, and we’ll talk about it in a second. Gout, I think, is another thing that needs to be ruled out, if they have recurrent effusions. And, sepsis needs to be ruled out.

Peter L. Salgo, MD: So, an infected joint?

Richard Iorio, MD: Yes. That’s an emergency. That can’t wait 6 weeks.

Paul Lachiewicz, MD: So, it’s important to put this in context. It’s quite unusual for multijoint rheumatoid arthritis to just present as 1 knee. It can do that, but usually these are women in their 30s or late 20s, or occasionally older, with multijoint condition. Their hands are bothering them…their feet…their knees. For the internist, I think they should be aware that if there’s pain at rest or at night, early on, it could be something else. Usually, osteoarthritis pain is with activities or with weight bearing, or they have difficulty doing an activity. Always worry about hidden neoplasms or something if patients have terrible pain or numbness in a limb. It shouldn’t be confused with osteoarthritis.

Richard Iorio, MD: Osteoarthritis will get better with rest, right?

Peter L. Salgo, MD: I was going to start with that. I was always taught that if they wake up with swelling and pain, it’s probably more likely to be rheumatoid arthritis. If it gets worse with activity during the day, it’s more likely osteoarthritis.

Richard Iorio, MD: Both will have stiffness in the morning. The other mimicker is Lyme disease. We need to be aware of that in the Northeast.

Peter L. Salgo, MD: I wish I had a nickel for every time Lyme disease popped up. It’s common. It’s everywhere, and it’s arthritic. The original phrase that we used to use was “Lyme/arthritis,” right?

Paul Lachiewicz, MD: Correct.

Peter L. Salgo, MD: It was originally misdiagnosed as rheumatoid. So, Lyme is in the differential, everywhere. Even the serologic tests for Lyme are inconsistent. I guess that is the best phrase for it.

Andrew Spitzer, MD: I think the other thing that I would stress along these lines is that doing the basics, the history and the physical examination, will help us enormously—particularly when you find that patient who complains about knee pain but has a completely normal exam, and their X-rays look normal, and they’re not swollen. And you, as an internist, can be of tremendous help to us. I must have 5 or 7 patients a year that come in on statins. The statins are causing musculoskeletal pain. Those kinds of things, which we perhaps may not be as familiar with, are tremendously helpful. Then, once they do come to the specialist, we can sort of focus on the knee and understand what’s going on that’s causing that kind of pain.

Peter L. Salgo, MD: Now, I don’t want to leave this discussion on some of the criteria that leads to the diagnosis without coming back to radiology—plain films, weight bearing, avoid the MRI. What do you look for on a plain film? You mentioned it. Why don’t we just run down it again?

Paul Lachiewicz, MD: You essentially look for the black space on a plain radiograph, which represents the cartilage. It should be roughly 4 mm to 5 mm on each side. If there’s a decrease in that, that’s the earliest sign of osteoarthritis. This is followed by spurring or osteophyte formation at the edges of the joint. One of the things that we didn’t bring up, that the internist should also think about is, if they can, get a chance to see the patient walk. Because oftentimes, hip arthritis will present as knee pain. It’s not that common, but I think we all would agree that we’ve seen patients who’ve had knee arthroscopic surgery, or even partial knee replacements, where the actual problem was the hip. There’s a type of hip arthritis that can present as knee pain.

Peter L. Salgo, MD: Is that because they’re favoring what used to be the good side, because the other side hurts?

Paul Lachiewicz, MD: No, I think it’s referred pain for the most part.

Peter L. Salgo, MD: Really?

Paul Lachiewicz, MD: Yes.

Richard Iorio, MD: Hip pain will start in the groin. It will refer down to the anterior part of the thigh, to the top of the knee.

Peter L. Salgo, MD: Really?

Richard Iorio, MD: And that would be posterior hip pain.

Peter L. Salgo, MD: So, it’s not just an antalgic gait? It is really referred pain?

Richard Iorio, MD: Correct.

Peter L. Salgo, MD: I did not know that. You learn something new every day.

Paul Lachiewicz, MD: See, you learned something, Peter.

Peter L. Salgo, MD: That’s great.