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Understanding Osteoarthritis & Knee Pain

Medically Reviewed on May 15, 2013 by George Krucik, MD, MBA
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Understanding Knee Pain

How common is knee pain? About one in every five American adults complains of some pain or stiffness in their knees. As you move the slider from left to right, you’ll dive deep into the knee, discovering one of the most common sources of knee pain: osteoarthritis (OA).

OA of the knee is the number one leading cause of disability in the U.S, affecting about nine million Americans every year. In this Bodies In Motion, you’ll explore why arthritic knees hurt so badly and learn more about the key pieces of the knee-pain puzzle.  

A Severely Arthritic Knee

OA occurs when the cartilage covering the ends of your bones wears away over time. In this image, you can see the ragged remains of cartilage on an extremely arthritic knee joint. As you move the slider, the knee joint will move.

When it does, exposed bone peeking through the torn cartilage on either side of the joint rubs against more exposed bone. This bone-on-bone contact causes extreme pain. Where joint movement was formerly smooth and easy, it is now rough and difficult. Every step you take, your bones rub together, causing pain. 

A Healthy Knee Joint

In a healthy knee, cartilage completely covers any areas in which your shinbone comes into contact with your thighbone.

The cartilage protects the tibia and also absorbs shock to your joint that may result from any physical activity that puts pressure on the knee: running, playing sports, biking, even walking. As you move the slider, you can see how, when the cartilage is healthy and full, there is a generally frictionless, painless movement of the knee joint, with no bone-on-bone contact.

A Moderately Damaged Knee

OA doesn’t happen all at once. It’s a disease of attrition—the slow deterioration of the cartilage. This image shows a knee joint that is typical of someone in his or her 40s or 50s—or someone who lives a life rough on his or her knees such as an athlete or physical laborer.

In these cases, the cartilage has most likely begun to thin out and there may be some wear-and-tear. There is, however, probably still enough cartilage to fully cover the bone and prevent any painful bone-on-bone contact. While you can't undo cartilage damage, there are things you can do to prevent it from getting worse.

Understanding Cartilage: Normal Use

In this image, you can see a cross section of the articular cartilage that sits atop your shinbone, and acts as cushioning between the shinbone and thighbone when you flex your knee. As you walk, it compresses and decompresses.

Your cartilage is mostly water, so every time your cartilage is compressed, water within the outer layers of cartilage seeps out and into your joint space. Then, when it is decompressed, that water is reabsorbed from the joint space back into the cartilage.

How Overuse Affects Cartilage

Imagine a kitchen sponge: Squeeze a wet sponge into a bucket, and the water all seeps out; squeeze it again, and it can reabsorb that water. This is more or less how your cartilage works. However, over time, the outer, more absorbent layers of cartilage wear away, removing its ability to cushion and protect the joint.

Cartilage wears out over time, but if your knee is abused and overused, your cartilage can start to wear out earlier than it normally would. This image shows how excess use can quickly wear out the outer layer of cartilage, leading to OA.

Weight Gain & Cartilage Damage

Whenever you bend your knee or otherwise put pressure on the knee joint, the articular cartilage is partially depressed in order to take pressure off of the bone itself.

But if you carry extra weight, the cartilage is going to be compressed more than it should be. Every time you step, the full force of your upper body presses down on your knee joint, compressing the cartilage and wearing it out. As shown in this image, being overweight or obese can lead quickly to cartilage deterioration and OA.

More Osteoarthritis Resources

While OA of the knee is non-reversible, that doesn't mean there isn't anything you can do. By eating right, exercising properly, and getting the treatment that is right for you, you will be able to ease your knee pain and stay as mobile as you've always been.

Understanding Knee Pain

How common is knee pain? About one in every five American adults complains of some pain or stiffness in their knees. As you move the slider from left to right, you’ll dive deep into the knee, discovering one of the most common sources of knee pain: osteoarthritis (OA).

OA of the knee is the number one leading cause of disability in the U.S, affecting about nine million Americans every year. In this Bodies In Motion, you’ll explore why arthritic knees hurt so badly and learn more about the key pieces of the knee-pain puzzle.  

A Severely Arthritic Knee

OA occurs when the cartilage covering the ends of your bones wears away over time. In this image, you can see the ragged remains of cartilage on an extremely arthritic knee joint. As you move the slider, the knee joint will move.

When it does, exposed bone peeking through the torn cartilage on either side of the joint rubs against more exposed bone. This bone-on-bone contact causes extreme pain. Where joint movement was formerly smooth and easy, it is now rough and difficult. Every step you take, your bones rub together, causing pain. 

A Healthy Knee Joint

In a healthy knee, cartilage completely covers any areas in which your shinbone comes into contact with your thighbone.

The cartilage protects the tibia and also absorbs shock to your joint that may result from any physical activity that puts pressure on the knee: running, playing sports, biking, even walking. As you move the slider, you can see how, when the cartilage is healthy and full, there is a generally frictionless, painless movement of the knee joint, with no bone-on-bone contact.

A Moderately Damaged Knee

OA doesn’t happen all at once. It’s a disease of attrition—the slow deterioration of the cartilage. This image shows a knee joint that is typical of someone in his or her 40s or 50s—or someone who lives a life rough on his or her knees such as an athlete or physical laborer.

In these cases, the cartilage has most likely begun to thin out and there may be some wear-and-tear. There is, however, probably still enough cartilage to fully cover the bone and prevent any painful bone-on-bone contact. While you can't undo cartilage damage, there are things you can do to prevent it from getting worse.

Understanding Cartilage: Normal Use

In this image, you can see a cross section of the articular cartilage that sits atop your shinbone, and acts as cushioning between the shinbone and thighbone when you flex your knee. As you walk, it compresses and decompresses.

Your cartilage is mostly water, so every time your cartilage is compressed, water within the outer layers of cartilage seeps out and into your joint space. Then, when it is decompressed, that water is reabsorbed from the joint space back into the cartilage.

How Overuse Affects Cartilage

Imagine a kitchen sponge: Squeeze a wet sponge into a bucket, and the water all seeps out; squeeze it again, and it can reabsorb that water. This is more or less how your cartilage works. However, over time, the outer, more absorbent layers of cartilage wear away, removing its ability to cushion and protect the joint.

Cartilage wears out over time, but if your knee is abused and overused, your cartilage can start to wear out earlier than it normally would. This image shows how excess use can quickly wear out the outer layer of cartilage, leading to OA.

Weight Gain & Cartilage Damage

Whenever you bend your knee or otherwise put pressure on the knee joint, the articular cartilage is partially depressed in order to take pressure off of the bone itself.

But if you carry extra weight, the cartilage is going to be compressed more than it should be. Every time you step, the full force of your upper body presses down on your knee joint, compressing the cartilage and wearing it out. As shown in this image, being overweight or obese can lead quickly to cartilage deterioration and OA.

More Osteoarthritis Resources

While OA of the knee is non-reversible, that doesn't mean there isn't anything you can do. By eating right, exercising properly, and getting the treatment that is right for you, you will be able to ease your knee pain and stay as mobile as you've always been.

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