Osteoarthritis (OA): Pathogenesis

by Carlo Raj, MD

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    00:01 Pathogenesis. It's quite complex: biochemical, biomechanical, cytokine-mediated, to a certain extent, right? Because you do have WBCs, but it's < 2000 in the synovial fluid.

    00:15 Now, commonly, the problem is obesity.

    00:19 So you take a look at the patient who's obese.

    00:21 Apart from Diabetes Type 2 and so on and so forth, that the patient has developed, metabolic syndrome as you know, the patient now is at risk of definitely developing osteoarthritis.

    00:30 A lot of weight that the patient might… has to then put on the knees and such.

    00:35 That incidence, unfortunately, osteoarthritis increases with age. You can't help it, right? But there are certain things that we can do to maybe protect ourselves.

    00:43 Depends on our, well, genetics.

    00:47 Signs and symptoms. Well, important here.

    00:50 As I told you, as you move through osteoarthritis in your head, you're going to be comparing this with rheumatoid arthritis.

    00:58 In rheumatoid arthritis… and that's the first time that I'm giving you a true comparison now.

    01:03 In rheumatoid arthritis, as you know, it's a autoimmune issue, isn't it? Autoimmune most likely going to affect a female, no doubt.

    01:11 Autoimmune diseases.

    01:14 Here, we have a lot of information.

    01:16 In rheumatoid arthritis, for example, the WBC count in the synovial fluid can exceed 2,000 cells per microliter.

    01:24 They are generally in the range of 5,000 to 50,000.

    01:28 Remember, what should be normal for synovial fluid? It's less than 200 cells per microliter.

    01:34 Next, the patient says...

    01:37 Who's your patient, a lady, young, maybe 35 or so? And she tells you, "Doc, I wake up in the morning and I'm having a hard time moving." "How long does it take before you get better?" "Hmm, maybe about an hour, hour and a half." That's a long time.

    01:51 That's rheumatoid arthritis.

    01:53 "And then upon moving, do your joints feel better or do they feel worse?" "Doc, actually, to tell you the truth, I mean, it just… When I start moving, it starts…they start feeling a lot better. So I like to move." Osteoarthritis doesn't do that.

    02:07 Osteoarthritis, OA, worsens with use. Is that clear? It's wear and tear. And the more wear, the more tear.

    02:15 Clinically, remind me the joints again? Reach out your hand, and you're going to give me your DIP.

    02:22 When the DIP has undergone inflammatory or osteoarthritis, then it's called Heberden nodes.

    02:29 HEB.

    02:32 The one that will be proximal, go in alphabetical order. H will be distal, B will be your PIP. Those are called Bouchard, okay, at your PIP.

    02:42 And then which finger did I have you put up? Not the middle finger, the thumb, yeah.

    02:48 The thumb. That's called your carpometacarpal phalangeal joint.

    02:51 That will be affected commonly in osteoarthritis.

    02:55 Frequently, as I told you also, apart from that, the knees, the spine, the areas in which you'd expect dependency.

    03:01 Now, there's a little bit of an exception.

    03:06 Think about the metacarpophalangeal joint.

    03:08 What are those? At times, don't you feel like you just want to punch me with your knuckles? Those knuckles are your metacarpophalangeal joints.

    03:17 Notice, that is not affected here. Commonly, it's not.

    03:22 The wrist is not commonly affected in osteoarthritis.

    03:25 But what if you did have a patient who is an occupation, a welder, what have you, and deals with the hands as an occupation for decades.

    03:37 Wear and tear.

    03:38 And so, therefore, in that particular instance, in that occupation, whatever it may have been, has come to be known as your Missouri metacarpophalangeal joint.

    03:49 Otherwise, osteoarthritis normally will not affect those joints. Keep that in mind.

    03:55 And crepitus of affected, so a little bit of, let's say, noise.

    04:00 In osteoarthritis, you'll notice here that the DIP is affected. What is that called again, please? Heberden.

    04:07 What is it called if the PIP is affected? Good. The Bouchard.

    04:11 Are your metacarpophalangeal joint commonly affected? Yes or no? No. Good.

    04:18 Wrist commonly affected? No.

    04:22 Could it be affected? Yes.

    04:24 What's your patient doing? Occupation? Dealing with hands and wear and tear over a long period of time.

    04:33 And then what about the thumb? Yes.

    04:36 At what joint? Carpometacarpal joint, CMC.

    04:41 Welcome to osteoarthritis.

    04:45 On your examination, on X-ray, what are you going to find? Well, immediately, you'll notice the picture on the left of an X-ray of the knee.

    04:56 And you'll notice that the joint space has indeed narrowed.

    05:00 That's what happens with all that wear and tear taking place.

    05:03 In addition, you might find areas that are a little bit… You see that? A little bit more opaqueness taking place? That area of being more bright white? The bright white area that you're seeing there, the bone is undergoing changes.

    05:16 It's sclerotic changes.

    05:18 And with that sclerosis, you might even find what's known as osteophytes, or bone spurs.

    05:24 For example, you ride a horse with those boots, got the spurs sticking out of your boots.

    05:30 Well, these are the spurs that are sticking out of a knee…of a bone called osteophytes.

    05:34 That's your fun in osteoarthritis.

    05:37 And what about the cartilage that's undergoing ulceration? And what do we call cartilage? Chondral, so subchondral sclerosis, subchondral type of cyst.

    05:47 The joint capsule might become inflamed.

    05:50 But be careful, though. Remember, the synovial fluid.

    05:52 Is it…would you call it truly inflammatory or non-inflammatory? Good. Non inflammatory. Why? Because if you did check the synovial fluid in osteoarthritis, WBC count, < 2000.

    06:06 So, by definition, not truly inflammatory. Is that understood? Now, once you have the cartilage which is being ulcerated, now it looks as though the bone is smooth.

    06:18 A smooth bone is then called eburnation.

    06:21 That's what we're seeing here on X-ray.

    06:26 On labs, the sedimentation rate will be normal.

    06:30 That's important.

    06:32 Rheumatoid factor has nothing to do with rheumatoid arthritis, so it's not immune, remember? So, it's therefore, non-immune.

    06:40 The X-ray, I showed you, subchondral sclerosis.

    06:43 What does sclerosis mean? Thickening.

    06:46 And with that thickening, what may then happen? Give formation to osteophytes, which are known as your bone spurs.

    06:53 These osteophytes, if they're in the PIP, you would call them Bouchard.

    06:58 If they're affecting the DIP you call them what? Heberden. Good.

    07:02 What about management? NSAIDs, definitely a COX inhibitor.

    07:06 Commonly, as I told you, obesity.

    07:09 So, conservatively, tell your patient to exercise, physical therapy and such.

    07:15 Worst-case scenario, maybe the knee is so far gone that surgery is recommended.

    07:20 And there's really no role here for PO steroids.

    07:24 Intraarticular, you could then inject, maybe, glucocorticoids, though. Keep that in mind.

    07:29 Or perhaps, hyaluronic acid. Remember? The synovial lining, it's producing synovial fluid that's made up of hyaluronic type of fluid, isn't it?

    About the Lecture

    The lecture Osteoarthritis (OA): Pathogenesis by Carlo Raj, MD is from the course Introduction and Non-Autoimmune Arthritis. It contains the following chapters:

    • The Pathogenesis of Osteoarthritis
    • Examination and Treatment of Osteoarthritis

    Included Quiz Questions

    1. Subchondral sclerosis is a late finding.
    2. Erythrocyte sedimentation rate is often elevated.
    3. The rheumatoid factor is often positive with osteoarthritis.
    4. Prolonged morning stiffness is often present.
    5. Joint space narrowing is not seen on X-ray.
    1. Diabetes
    2. Obesity
    3. Increasing age
    4. Joint overuse
    5. Joint injury or past trauma

    Author of lecture Osteoarthritis (OA): Pathogenesis

     Carlo Raj, MD

    Carlo Raj, MD

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