Our knees are not poorly designed, nor are they overly prone to injury. Why do we say this? Because of silly articles like this one from the Wall Street Journal. And one of us is an Orthopedic Surgeon—that should count for something.
We will be calling out junk articles from the media and other gurus on our quest to scale simple, accurate, and actionable information to as large of an audience as possible. The last thing we should be doing is throwing up roadblocks in front of people trying to improve their lifestyles.
Our knees are a marvel of engineering. Personally, I think the shoulder is even better... but that's for another piece.
Our knees have four main ligaments holding the tibia to the femur. The ligaments are tough, resilient tissues with very little give to them. They hold the bones together firmly yet are perfectly placed and "designed" to allow our knee an incredible range of motion and 6 degrees of rotational freedom.
Cartilage cushions the bony surfaces. Cartilage is a thick, slick, shiny substance made of cells (chondrocytes) that secrete a matrix. It is the matrix that gives cartilage its biomechanical properties. Cartilage can withstand an enormous amount of stress. More importantly, within reason, repetitive loading of cartilage is beneficial to its overall health.
Picture this. When you are running, you are placing 5-8x your bodyweight of force across your knee with every step. Now, imagine that you are running a marathon. An MRI before and after the marathon will show some swelling in the cartilage. But 24-28 hours later, the cartilage appears normal. It is a very resilient tissue. Cartilage is also capable of healing... to a point.
There are a series of signaling molecules in the body that comprise the Wnt pathway. In a joint such as the knee, the Wnt pathway is felt to have a significant role in the maintenance of cartilage health. This is the likely reason why sports such as running do not cause osteoarthritis in healthy individuals.
In the second half of this article, for paid subscribers only, we go into more detail on the latest treatments for osteoarthritis, why knee replacement candidates aren't generally thin and healthy, and why some knee injuries happen anyway.