Osteoarthritis: Causes, Mechanism, and Treatment

  • 0:07 An Old Age Mobility Disease
  • 0:37 What Is Osteoarthritis?
  • 1:57 Why Does Osteoarthritis Occur?
  • 5:12 Clinical Signs,…
  • 6:11 Treatment & Prevention…
  • 6:50 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem is a doctor of veterinary medicine and has taught science and medicine at the college level.

This lesson will discuss osteoarthritis. We'll talk about the basic pathophysiology behind what occurs in this condition, the risk factors involved, and the way by which it can be diagnosed and treated.

An Old Age Mobility Disease

Old age isn't a disease, but with old age you are more likely to be diseased. Some of the most common things we all see with individuals as they get older is that they move a bit slower, take a little more time to adjust from one position to another, and overall sound creaky as they move. While many reasons for those signs exist, this lesson is about one very common symptom associated with age. Although, don't fool yourself - even the young can get this condition.

What Is Osteoarthritis?

This condition is called osteoarthritis, or OA for short, and it's out to get you. Osteoarthritis is a disease that involves the degeneration, modification, and remodeling of the joint cartilage, subchondral bone, joint capsule, and synovial fluid.

As a quick overview, a joint is made up of two or more bones articulating with one another. Imagine making a fist with one of your hands and another fist with the other, with each fist representing a bone and the skin overlying the fist as the cartilage. Now take a full water balloon and press into it with both fists on directly opposite sides. The space in between the two fists is called the joint space, which is filled with fluid, called synovial fluid, all of which is surrounded by the water balloon's rubber, or joint capsule.

All of these components of the joint can become affected in osteoarthritis. Over 1/3 of all people aged 65 or over are affected with this condition, and even people in their 20's can be affected as well. All sorts of things can increase the risk of developing osteoarthritis, including obesity, stress from repetitive motions over a long period of time, and trauma from things like sports.

Why Does Osteoarthritis Occur?

While we are still discovering much about osteoarthritis, we do know some of the basics that occur in this process. Remember one thing from the outset: cartilage is a very smooth layer of tissue located over bone that helps to prevent friction and pain upon movement of the joint, thereby allowing you to move freely and quickly. Cartilage has something called proteoglycans, namely the proteoglycans called aggrecan. Proteoglycans are proteins responsible for retaining water within cartilage to maintain its compressive strength. In essence, proteoglycans are what give your cartilage the ability to act as a shock absorber. Cartilage is also made up of something you've surely heard of: collagen, namely type II collagen.

So, let's take a real-life example. If you play sports, you're at risk of developing osteoarthritis. What may happen is that you suffer an injury as you play a game of football. Whenever you are injured, by anything for any reason, pro-inflammatory molecules, one of which is IL-1, are secreted. IL-1 will in turn increase the activity of MMPs, the degradative enzymes responsible for breaking apart cartilage. The cartilage will therefore lose proteoglycans, lose water, crack, and break apart. This breaking apart of cartilage and the resulting bony changes are what we term osteoarthritis.

In a normal healthy person the cartilage is maintained in a healthy state through a series of absolutely normal degradative and reparative mechanisms. Whether due to age or increased stress from obesity or sport injuries, this delicate healthy balance is broken and the cartilage begins to degrade. This occurs, partially, as a result of the fact that MMPs, or matrix metalloproteinases, which are enzymes responsible for the degradation of cartilage are upregulated by a pro-inflammatory molecule called IL-1.

At first, this entire process causes the cartilage to actually swell with more collagen and proteoglycans as a way to compensate for whatever it was that damaged the cartilage, but eventually the reparative mechanisms lose out and the cartilage ends up actually losing a lot of collagen and proteoglycans instead. Losing the proteoglycans then causes the cartilage to dry and crack. Just like your skin will crack if it's dry, so too will the cartilage if it loses the water-holding proteoglycans.

Once the cartilage begins to crack it begins to wear away, exposing the bone underneath it, called subchondral bone. The bone underneath the cartilage will then develop osteophytes, which are small, bony outgrowths along a joint margin that are also called bone spurs. The bone spurs try to stabilize the joint and prevent further damage to the underlying bone. This entire process of the wearing away of cartilage and bone-on-bone friction leads to a vicious and painful cycle we call osteoarthritis.

Clinical Signs, Symptoms, and Diagnostics

Besides pain, osteoarthritis sufferers will also have joint stiffness and crepitus, which is the grinding noise and sensation people experience when joints move against one another. This condition is diagnosed by taking imaging studies such as an X-ray. The X-ray will reveal the bone spurs in later stages of osteoarthritis and will also show decreased joint space. That's because cartilage is not visible in x-rays. Therefore it is black in radiographs.

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