Few people make it to middle age (let alone beyond) without some kind of knee problem, so this entry should be relevant to just about everyone. I’ll start with the basics.
ANATOMY
The knee is a hinge joint, in that it bends and straightens. But like everything in human physiology, it’s more complicated than that. The tibia (shin bone) also does a slight amount of twisting. Additionally, there’s a knee cap, which increases the leverage of our quadriceps, making the thigh muscles more powerful than if they were connected to the shin bone without the knee cap.
Three bones make up the knee: the thigh bone (femur) is the top of the hinge, the shin bone (tibia) is the bottom of the hinge, and the knee cap (patella) is the insertion point for all the tendons of the quadricep muscles on the front of the thigh.
The femur doesn’t come into contact with the tibia, because of two cartilage disks that sit between the femur and tibia. These are the medial and lateral meniscus.
They’re fibrous, spongy discs that keep the bones from wearing on one another. At the ends of the bones is a second kind of cartilage called articular cartilage. (By the way there’s a third type of cartilage that has nothing to do with joints. It’s the stiff tissue that gives shape to your ears and your nose. I don’t know why the experts didn’t come up with different Latin-sounding words for these three different kinds of tissue. After all, there’s about a dozen ways to refer to skin tissue. But I digress.) Back to articular cartilage. Bones are very strong because of how they’re constructed, and they’re lightweight, porous, and brittle. But the ends of the bones are smooth, like the surface of an ivory piano key.
The knee joint is surrounded by a capsule, and inside the capsule is fluid, which acts like the oil or grease in a pinion joint.
The smooth piano key surfaces, lubricated by joint fluid, and protected from wear by fibrous discs, can handle a lot of force and torque.
But with an active lifestyle, or with misalignment, so many things can go wrong with the knee.
CHONDROMALACIA
One of the most common knee problems is chondromalacia patella, or patello-femoral pain syndrome. To find out if you have this condition, sit down on a bed or table with your knee fully extended and your heel supported. Now trap your kneecap with the web of your hand between your thumb and forefinger, gliding your knee cap away from you. Now tighten your quadricep muscles and see what happens. In the photo below the examiner is pressing down much too hard on the distal quadriceps. The test doesn’t require that much force.
Did your kneecap slide smoothly under your hand?
If yes, then you don’t have chondromalacia.
Did you screamed in pain while your kneecap crunched like Rice Krispies as it passed under your hand? Or did your quadriceps muscles just quiver because they wouldn’t allow you to force your patella under your hand. Then the test was positive for patello-femoral pain syndrome.
Several of my teen-age college soccer teammates had chondromalacia, so it’s a condition not necessarily connected to old age. But it is connected to chronic wear and tear of the underside of the knee cap, so it’s more common in young athletes who have poor alignment of their knee cap, with athletes who land on their knees or squat a lot (like goalkeepers and catchers), or with people who have been suffering misalignment of their bones for several decades. So age does factor in for many.
If you’ve ever seen an old piano, you’ve seen piano keys with the ivory surfaces chipped off. If two of those damaged keys were rubbed against each other, they will scrape and erode each another.
With chondromalacia, that’s what the bones of your knee are doing when they’ve lost that smooth articular cartilage. The bones wearing on one another cause a lot of joint inflammation and pain. Even though chondromalacia can happen in one’s youth, it is a progressive condition, so by middle age those knees are pretty irritated. If you have chondromalacia, you’re probably in for a lifetime of arthritic knee pain that will eventually be remedied with knee replacement surgery.
KNEE SPRAINS
Ligaments are tough, inelastic bands of tissue that keep bones connected to one another. These are the tissues we shred when we sprain an ankle or dislocate a finger. The knee has four ligaments. One is on the inner side of the knee (medial collateral ligament, or MCL) to keep the knee from buckling inward. A second ligament is on the outside of the knee (lateral collateral ligament, or LCL) that keeps the knee from buckling outward. There are two ligaments inside the knee joint. The posterior cruciate ligament (PCL) keeps the shin bone from sliding backwards, and the anterior cruciate ligament (ACL) keeps the shin bone from sliding forwards. The image below shows the bones and ligaments of the right knee when viewed from the front. In this image the patella (knee cap) has been removed, because it would be blocking the cruciate ligaments.
If we put extraordinary stresses on our ligaments, the tissues will shred or snap, resulting in a sprain. If we sprain the MCL or LCL, we can put the knee into an immobilizer and let those tissues heal over a period of several weeks. While the ligaments are damaged, the knee will be unstable and will buckle, so keeping the knee immobilized is really important for healing.
Unlike the MCL or LCL, the ACL and PCL won’t heal no matter how long we immobilize them. These tissues exist within the knee joint, which doesn’t get much blood flow. Without blood there is little healing, so these ligaments have to be surgically reconstructed.
You won’t hear about PCL tears very often, because damaging the PCL requires significant force to the front of the shin. This happens most often in sports when a football player tackles another player by diving into his knee and catches the tibia just below the knee. Another way to damage the PCL is when someone is in a car accident and their knees strike the dashboard but the rest of the body keeps going. It’s rare.
The ACL tear, on the other hand, is incredibly common. The ACL can be torn by simply planting the foot and changing directions. You may recall that Lindsey Vonn tore her ACL right before the Olympics when she crashed on a practice run. Adding skis to the feet increases torque on the knee joint, and often results in ACL injuries when the lower leg is twisted.
A fast recovery from an ACL reconstruction surgery is 6 months, but return to play is more common at 9 months after reconstruction. The surgeon harvests a tendon from somewhere else in the knee – usually a hamstring tendon or part of the patellar tendon – and sews it to a grafting material to ensure that the graft won’t be rejected. Then a channel is drilled through the femur, and the new ligament is screwed into place. Tissues have to undergo a change in function from tendon to ligament, and if this process is hurried the new ligament will rupture again.
If someone decides to NOT have their ACL reconstructed, they’ll experience years of knee buckling. Guys my dad’s age used to talk about “my trick knee from the ol’ football days”. Those are guys who grew up before ACL reconstruction was an option, so every time they stepped left and turned right their knee would give out. Years of this excessive mobility between the bones usually results in bone deterioration and arthritis.
MENISCUS TEARS
The final conditions I’ll cover with this entry are meniscus tears. The fibrous discs of tissue that prevent the knee bones from wearing on one another have to endure a lot of stress every day. Occasionally, these discs will tear. When torn, the meniscus flap can cause the knee to lock, unable to bend or to straighten, as if a door stop was jammed into the joint.
I’m going to whine about the repetitive use of the term “cartilage” again, because with the meniscus we have many different terms to describe how the meniscus tears. There’s the bucket handle tear, the parrot beak tear, the horizontal tear, and more. If you ask someone with a meniscus tear what happened, they’ll answer “I tore my cartilage.”
One person who won’t say they have torn cartilage is Evander Holyfield, even though he had some of his cartilage torn off when Mike Tyson bit his ear. But that was a different type of cartilage.

Remember that event? When Mike Tyson bit off a piece of Evander Holyfield’s ear, and then spit it onto the mat?! I swear this is true – the two of them teamed up and created a cannabis edibles product called “Mike Bites,” with gummies shaped like an ear with a bite out of it. Seriously. I swear. It’s crazy. If any of you tries one of these, please tell me if you experience an increase in bloodlust.

That feels like a good place to stop this entry. We’ve covered many of the nasty things that can happen to the knee, but certainly not all of them. If you want to know more about the knee, let me know. There are 14 bursae that can rupture, for example. There's arthritis. There's the ever-popular knee replacement surgery, which many of you already know about. Some knee problems require immobilization and rest, but several require surgery. The knee is so critical to everyday function and mobility that injury or arthritis results in significant change in one’s lifestyle. So keep those knees healthy, people. Keep moving!





