Overview of Osteoarthritis of the Knee

Peter L. Salgo, MD: Thank you for joining us for this MD Magazine^® Peer Exchange^®, which explores the treatment of osteoarthritis of the knee. Osteoarthritis is the most common form of degenerative joint disease, and is a leading cause of disability in people over 50 years of age. It is a debilitating form of arthritis that most commonly affects the knees and the hips. The typical symptoms of osteoarthritis of the knee include gradual onset of knee pain, stiffness, and swelling. Treatment often starts with conservative measures, and progresses to injectable medications. In this Peer Exchange^®, my colleagues and I will explore the diagnosis, patient management, and treatment of osteoarthritis of the knee, including the clinical rationale for treatment decision making.

I’m Dr. Peter Salgo. I’m a professor of medicine and anesthesiology at Columbia University College of Physicians and Surgeons, and I’m the associate director of Surgical Intensive Care at New York-Presbyterian Hospital. Joining me for this panel discussion is: Dr. Richard Iorio, orthopedic surgeon, chief of Adult Reconstruction, and William and Susan Jaffe professor of orthopedic surgery at the New York Langone Medical Center; Dr. Paul Lachiewicz, an orthopedic surgeon at Chapel Hill Orthopedics and Sports Medicine, and consulting professor of orthopedic surgery at Duke University School of Medicine; and Dr. Andrew Spitzer, orthopedic surgeon and director of the Joint Replacement Program at Cedars-Sinai orthopedic Center. I want to thank all of you guys for joining me today. We’re talking about osteoarthritis. So, why don’t we define it? What is osteoarthritis?

Andrew Spitzer, MD: Osteoarthritis is a degenerative process, as you mentioned in your introduction, that ultimately is caused by a host of combined intrinsic and extrinsic factors that destroy the cartilage on the ends of the bones. Over time, the bones begin to grind against bones. That smooth cartilage—that normally lines the ends of the bones and enables smooth movement and stability—is destroyed and deteriorates. Ultimately, as the bone begins to grind against bone, creating inflammatory mediators, we see generalized inflammation within the joint and swelling that results in pain. That pain subsequently creates the disability that is the hallmark of osteoarthritis of the knee.

Peter L. Salgo, MD: It’s interesting that you started off with a mechanical insult, and then you went toward mediators and inflammatory mediators where, it seems to me, the other common form of arthritis, which is rheumatoid arthritis, starts off with inflammatory mediator and goes toward pain.

Paul Lachiewicz, MD: Well, I think there’s a lot that we don’t know about in arthritis. I was always taught that it was a disease of the cartilage cell. For some reason, the cartilage cell becomes sick. That’s what I tell the patients. I say, “Your cartilage is sick. It’s not making the matrix or the spongy substance that is like the shock absorber for your knee.” We don’t quite understand why that happens.

Peter L. Salgo, MD: It’s interesting that you say that. I was always taught that it was this hammering on the cartilage. Eventually, the cartilage gets destroyed. But, the body should be able to make new cartilage. Day in and day out, we’re destroying something, right? So, his point is, as I take it, that something’s wrong with the regenerative process after a while?

Richard Iorio, MD: Cartilage is a very metabolically slow-to-act tissue. It doesn’t heal itself well, at all. We haven’t really solved that problem yet, but I think we have to remember that degenerative arthritis is the end of the process. There are multiple insults that can cause this process. Those can involve inflammatory responses to the arthritic process, mechanical issues with alignment or deformity, and wear and tear, which can result either from trauma or perhaps from some metabolic environment that also inhibits the cartilage from functioning correctly.

Peter L. Salgo, MD: So, it’s not just simply hammering away at your cartilage until it’s gone?

Richard Iorio, MD: That will do it, if severe enough. But, there are other factors that can contribute to this issue.

Andrew Spitzer, MD: The combined issue of both the intrinsic factors, that sick cartilage and the cells that are not making the matrix, and the extrinsic factors—the pounding away, the meniscal tear, the overuse over a lifetime or, perhaps, some other injury that creates an irregularity in the joint surface—combine to sort of the final common pathway of osteoarthritis, which is the degenerative process.

Peter L. Salgo, MD: What I think I heard from all 3 of you, maybe I’m reading into this, so please tell me, is that if you do enough pounding on cartilage, you seem to expose antigens? You expose something and that induces an inflammatory response to something that shouldn’t be exposed to?

Paul Lachiewicz, MD: I’m not sure that’s exactly correct. There are people who can run until they’re in their 80s or 90s, and never get arthritis. So, I think there’s a lot that we don’t understand. There’s probably some genetic predisposition. But, one of the things I wanted to pick up on—that you said before—is, why doesn’t the cartilage repair itself? It actually does try to repair itself, but it does so in an abnormal way that the body will regrow cartilage at the edges of the joint. Those eventually become bone spurs or osteophytes. And so, it’s an abnormal repair process that sometimes leads to symptoms.

Peter L. Salgo, MD: I’ve got it. So, in terms of evolution, if you’re running away from a Saber-toothed tiger, it doesn’t really matter. You’re only 30 years old, and you may not get to age 40, anyway.

Paul Lachiewicz, MD: That’s right.

Peter L. Salgo, MD: You’re not playing football at the age of 38.

Transcript edited for clarity.