Why The Human Knee Is A Design Disaster – Cheddar Explores

by birtanpublished on August 25, 2020

ACL tears are some of the most common injuries and sports from elite athletes like Tom Brady Lindsey Vonn Tiger Woods and Megan Rapinoe to everyday teenagers playing high school sports and young professionals in rec leagues it also seems like everyone has a parent aunt

Uncle grandparent or someone close to them who's dealt with knee pain that's no surprise considering about 4.7 million Americans have had knee replacement surgery which is more than the entire population of the Seattle

Metro area clearly this knee of ours has some design flaws and the crazy thing is we're actually seeing more knee problems now than ever before so what's going on here Nathan Lentz a biology professor at John

Jay College in New York wrote a whole book about evolutionary shortcomings in the human body he says the root of our knee problems goes back about three to four million years we evolved from walking on four

Limbs to walking on two limbs really quickly in the evolutionary blink of an eye and anything you do quickly you don't do well of all things climate change like me pushed this rapid transformation four to five million

Years ago the rainforests shrunk in Africa that's when our ancestors sort of came down from the trees found themselves in the grasslands and having to adapt to that walking around on two legs offered a ton of advantages to our

Ancestors we can walk with much greater efficiency than the other Apes can there's a number of other advantages of course it freed our hands which was the big one we had big brains and now we had hands that were free to develop tools

And other things carry things around and this transition to upright walking happened in less than half a million years which is a tiny period of time considering an evolution of walking on four limbs had stretched back hundreds

Of millions of years to early mammal vertebrates and even their tetrapod ancestors now in many ways evolution did an amazing job honing the mechanics of the human knee considering how fast it emerged the need itself from a

Mechanical standpoint is what we call a four bar linkage throughout the range of motion the ligaments both on the outside of the knee and the inside of the knee work together to evenly distribute load and they

Function with the articular cartilage and the spacer cartilage or the meniscus that's dr. Erin kritch from the Mayo Clinic he specializes in orthopedic surgery and sports medicine the knee takes many biomechanical forces take

Something like walking up the stairs or down the stairs for example we put about six to eight times our body weight through our knee joint so the knee is very intelligently designed obviously to be a stable structure that can help

Cushion all the forces that we see with normal life but also with athletic activities like jumping sprinting cutting pivoting and it's quite amazing that the knee gives us a lot of longevity and allows us to do a lifetime

Of activity so where did the evolutionary design fall short or at least not do its best first of all there is just more force being put on our two knee joints but with ligaments that still closely

Resemble the ligaments of our ape-like ancestors evolution didn't really strengthen them and so you have very thin ligaments that are doing an enormous amount of labor and what happens is anytime you change your

Weight particularly if you're moving quickly and you change directions if your leg straightens during that change in momentum you're in trouble because this little tiny ligament is having to bear hundreds and hundreds of pounds of

Force and it just simply can't do it but it's not just the extra weight that is problematic there is also additional issues associated with the way the lower part of the human body is shaped versus our ape-like ancestors and relatives

With the adaptation or upright walking one thing that needed to happen to become smooth walkers on two feet is your legs maybe come straight down from your pelvis and be as close together as possible so that you can have what we

Call as a striding gait where our center of gravity does not bounce back and forth very much with each step and if you've ever seen a chimpanzee walk around on two legs they can do it but they swing their legs out in these wide

Steps and their center of gravity bounces back and forth from the left to the right with each step on the one hand going bipedal demanded a more narrow pelvis but on the other hand the pelvis had to remain wide enough for our heads

To get through the birth canal as our brains later began to grow and one of our most advantageous traits became our intelligence that fit got even tighter evolution never fully resolved this issue this is one of the reasons that

Giving birth is comparatively so risky for humans versus many other primates and one of the reasons why so many women today undergo cesarean sections so one of the ways that we evolved a more narrow center of gravity without

Narrowing the pelvis too much was pulling the knees in that angled our thigh bone increasing something we refer to today as the cue angle or valgus angle angling that thigh bone lets us move efficiently and gracefully and at

Higher speeds relative to our ancestors lumbering around on all fours but that movement also puts extra pressure on our knees our knees hold together pretty well most of the time as other parts of our bones muscles and ligaments have

Evolved to support them but the knee also has a glitch of sorts when we put it through certain stresses and sports or even modern daily life sometimes the whole contraption just can't deal with those stresses and that's when we get

Some of these really nasty ACL tears when we look at injuries and our young athletes it's really when they're coming down from like a jumping position dr. Krick has meticulously studied the forces that produce ACL injuries in a

Controlled lab setting we not only look at the knee but we also look at their entire body mechanics we know that athletes that get into risk for injuries like an ACL tear for example tend to have for mechanics either in their hip

Or their core that leads to abnormal stresses in their knee our ape-like relatives on the other hand the snapped ACL would be almost unheard of in any other ape so a lot of the regular injuries that we have including and

Especially sports injuries are related to the unique features in our joints there's another factor too and that's just age those big heads of ours have allowed us to develop modern medicine public health infrastructures and

Dynamic industrialized economies that have drastically increased our lifespans over just the past handful of centuries we have pushed our life expectancy from about 30 years old in pre-modern societies around the world to about 79

Years old in the United States today and all of those additional years are putting extra wear and tear on our knees 10 to 15 million doctor visits a year are for knee problems as we age they become more prevalent so if you look at

Adults over the age of 60 for example you know 15 percent will have symptomatic arthritis injuries and wear and tear that come about later in life are largely an evolutions blind spot in the sense that you've already probably

Passed on whatever genes are going to modern technology has also given us more food to eat while allowing us to live much more sedentary lives we have a obesity epidemic and those elevated body weight forces translate down to the knee

So we are seeing a direct link that patients who have an increased BMI definitely have an increased risk of injury and even for seasoned athletes a long day can increase the risk of injury when a particular individuals at risk is

Really during times of fatigue athlete will be in a tournament for a while play a lot of hours have a lot of contact hours and that's ease the play for a bit overall but there's also a lot people can do to prevent these injuries to take

Advantage of our body's strongest design components while protecting ourselves against its weaknesses dr. Krish is working on creating prevention programs that do just that we really try to look for athletes that are at high risk for

Example female soccer players we know are some of the highest risk athletes for knee injuries prevention programs that look at conditioning and targeting the way they move the way they land from their jumps definitely are successful

Cutting-edge technology is also helping doctors refine treatment techniques for injuries we're becoming a lot better in diagnosing problems for example MRIs have become really incredible the level of detail that we're able to see in the

Knee and we really diagnose sometimes early or sometimes if it is a significant injury there's a lot more data that we have on terms of how they should be treated so those big brains of ours are already coming through once

Again to help us deal with some of the design drawbacks in our knee and who knows maybe within a few more generations we will figure out how to overcome those design flaws all together it might sound crazy today

But wouldn't the average person in 1500s think the idea that most people could live to 79 sounds pretty crazy so hey why not dream a little and in the meantime make sure to take care of those knees hey everyone thanks for watching

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