Predicting the Weather

I think my knee can predict the weather!

A few years ago, I tore my ACL. Not in some dramatic way, such as skiing down a slope in a whoosh of snow or leaping high over defenders to make a dramatic slam before crashing to the basketball court.

No, I was just hiking at the Delicate Arch in Utah and felt a pop as I was stepping down from a higher trail to a lower trail. Not dramatic, but every bit as painful. My orthopedic doctor tells me most of his patients tear their ACLs in pretty routine ways and not necessarily playing sports. That helped, a little.

However, since my surgery, which inserted a new ACL with the help of staples, I swear my knee can tell when the weather is going to change. It’s not a painful feeling, but a dull ache.

I’ve heard stories similar to mine. And when I called the doctor’s office to ask about the feeling, his assistant confirmed that other patients who underwent similar procedures as well as other surgeries much more complicated all shared the same experiences.

The funny thing is nobody knows why.

Titanium is the metal used for almost all implants these days, and medical-grade titanium is expensive. One screw is roughly $500-1000. But the metal is resistant to all bodily fluids and chemicals that would cause corrosion. Also, it has almost no release of metallic ions in the body, which can lead to rejection. In addition, it can be shaped into almost any form that is needed, and is very strong.

But titanium has a very wide operating temperature, meaning it can get cold, which could explain some of the joint’s sensitivity to weather changes.

Another leading theory is that the falling barometric pressure that usually precedes a storm changes the pressure inside joints. The connections between bones, which are held together by tendons and ligaments, aren’t just empty spaces. Sacs of fluid and trapped gases fill the connections in the joints. That’s why people can “pop” their knuckles or knees. So, as the outside pressure drops, the sacs of gas and fluid expand, which presses against surrounding nerves and other tissues. The pain would likely be worse in newly-repaired joints, where nerves are irritated and more sensitive as the healing process begins.

Again, nobody knows for sure why human joints seem to be able to predict the weather. But those are the best theories my research found and my doctor could provide. 

By the way, my knee thinks it will rain tomorrow.

- Frank Graff

Frank Graff is a producer/reporter with UNC-TV, focusing on North Carolina Science Now, a weekly science series that airs Wednesdays, beginning in August 2013, as part of North Carolina Now on UNC-TV. In addition to producing these special segments, Frank will provide additional information related to his stories through this North Carolina Science Now Reporter's Blog!

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