Why Good Knees Go Bad (An Illustration)

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 Illustration by Bryan Christie

On the left is a healthy knee. On the right, one with moderate to advanced osteoarthritis — the breakdown of bone and cartilage. If you experience chronic stiffness or pain, maybe from an old sports injury or just long-term wear, there’s a good chance your knee looks more like the one at right. The good news: “You can do a lot to mitigate damage and prevent future problems by building the muscles supporting your knee via exercise,” says the orthopedic surgeon Nicholas DiNubile.

Exactly How Good Knees Go Bad

  • Articular cartilage lies between the thigh and shinbones. When healthy, it provides a smooth, lubricated surface for the knee to flex and extend. 
  • The ACL is one of the knee’s most important stabilizers. While the ligament won’t break down like the meniscus, it is fragile and prone to tearing — particularly if the joint and surrounding muscles are weak
  • The meniscus, which is another type of cartilage, sits atop the tibia and acts like a shock absorber, a cushion, between the shin and thigh bones. 
  • Cartilage degeneration can lead to painful bone-on-bone arthritis.
  • A torn or thinning meniscus causes pain, stiffness, and swelling, making it harder to straighten the knee fully.