Day 16 - Everybody has bad knees

As I limped home from physical therapy today, a guy stopped me on the street, saying, "How's your knee feeling?"

I was a little surprised since I didn't know the guy. But as I told him about my knee he explained he was going in for knee surgery himself and was a little apprehensive about it.

It's not uncommon to meet people who have torn their ACLs. Last week, a guy stopped me on the elevator to ask who had done the surgery on my knee because he was considering the operation himself. Last Saturday at a party --when I was still wearing my conversation-starting brace-- I met a girl who had torn her ACL in both knees. I know a family where the dad has torn his ACL and so has his son and daughter. Several other people I know have also told me their tales of knee woe.

It's not surprising that there are so many people with torn ACLs. According to the American Academy of Orthopedic Surgeons, 200,000 ACL ruptures and 100,000 reconstruction surgeries occur each year in the United States. Over time, that adds up to a lot of people.

And women are more at risk than men for reasons that are uncertain. Various hypotheses have been put forward, such as differences in pelvis angle and muscular strength, but no one is really sure what the culprit is.

Clearly, the human race is making their knees do things they just weren't designed to do. This 1938 paper in the Journal of Bone and Joint Surgery on the evolution of the knee might help explain why the joint is so often injured. We evolved from animals that either walked on 4 legs or brachiated. So we had to make do with materials that weren't up to the task of all the jobs we make our knees do. As the 1938 paper notes: "Man is the only animal to assume the completely erect posture, and the knee joint is completely extended while bearing the weight of the body."

But luckily for all of the minions who tear their ACLs each year, we have surgeons who have devised ways to patch us back together again.