The human body is like a complex machine that is able to adapt to all sorts of environments. No matter whether you want to run an ultra-marathon or climb the highest mountain on earth, the body will find a way to adapt. The only problem with this wondrous machine is that there is no manual. There’s no one book that gives all the answers about what to do if things aren’t the way they should be. Concerning knee pain this means that finding and fixing the problem can sometimes be tricky and to understand pain, you need at least a basic understanding of anatomy.
Personally, I always found it to be very motivational if what I was spending time on trying to understand had a real purpose later in life. Instead of just having to learn it for some arbitrary exam. With that in mind I will limit this post to those aspects of anatomy that are relevant for our quest to fix knee pain.
Passive structures: Bones, ligaments and cartilage
The knee joint is comprised of three bones and six articulating surfaces. Those three bones are the femur, the tibia and the patella. As you can see on the picture to the right, the femur is the big bone you have in your thigh. The knee joint connects it to the tibia and the patella.
At this point it is important to note that angle at which the femur meets the tibia is different in males and females, because women have a wider hip. In women the angle at which the femur meets the tibia (Q-Angle) is higher, which makes women more likely to suffer from certain types of knee injuries such as ACL-tears or patellofemoral syndrome. Barely two paragraphs into the anatomy and we already had the first fundamental revelation: women are different (I always had a hunch).
The knee is a special type of hinge joint that not only allows flexion and extension, but also a certain degree of rotation. However, if we compare the range of motion (ROM) we have at the knee to the ROM we have at the ankle or the hip, one thing becomes clear: the knee is a very stable joint, whereas ankle and hip are a lot more mobile.
Taking a closer look at the knee we can make out passive stabilizing structures: the ligaments and the cartilage. On the right you will find a schematic drawing of the right knee. Look at the individual ligaments: where are they attached? What kinds of movement can they prevent?
The Lateral Collateral Ligament (LCL)
What does lateral mean anyways? Lateral always designates the outer side of the body, whereas medial indicates that something is more towards the middle of the body. We can tell that the schematic drawing is of the right knee, because the LCL and the fibula are on the right.
The LCL connects the fibula and the femur, thereby stabilizing the knee laterally. It prevents the knee from bending to the outside. There are other important ligaments in the knee: the ACL, the PCL and the MCL. Let’s take a brief look at these as well.
The medial collateral ligament
The MCL connects the femur to the tibia, which is why it is also called tibial collateral ligament. It resists forced that would push the knees inward (to the middle of the body) and therefor it’s the counterpart to the LCL. Because of the increased need for stability on that side the MCL is a lot thicker in comparison to the LCL.
The anterior cruciate ligament
The ACL connects the medial front part of the tibia (anteromedial) to the lateral back part of the femur (posterolateral). Put more simply it runs from the back of the femur to the front of the tibia. The anterior cruciate ligament prevents the tibia from travelling forward.
The posterior cruciate ligament
The PCL runs from the lateral front part of your femur to the medial back part of your tibia. In other words it connects the front of the femur to the back of the tibia and thereby provides posterior stability to the knee (prevents the tibia from moving backward).
These stabilizing structures can be damaged by acute trauma, as it happened to Kendrick Perkins in the 2010 NBA finals:
Coming down awkwardly between Bryant and Bynum, Perkins suffered a torn MCL and a torn PCL.
Cartilage in the knee
There are two types of cartilage in the knee: hyaline cartilage that covers the surface along which the joints articulate and fibrous cartilage (the menisci). Hyaline cartilage contains a lot of water and is very elastic under pressure. Fibrous cartilage has a different alignment of collagen fibers, which makes it more force-resistant. The menisci in the human knee are made of fibrous cartilage. They are two crescent-shaped rings that have several functions. For one they provide additional stability to the joint, while also providing a certain degree of shock absorption. The menisci also spread synovial fluid (more about that stuff later) and provide proprioceptive feedback to the central nervous system.
The interesting point about cartilage is that nutrients are delivered to it through diffusion from its surface. This is where the synovial fluid comes in, as it is one supplier of nutrients. However, for this to work the whole joint needs to move through its complete range of motion. Future posts will deal with joint mobility and how it helps to maintain joint health.
By looking at how the body is built we can see how force travels through the limbs and understand the causes of knee pain better. This knowledge also provides additional motivation to move and exercise the right way, because even if we don’t understand every detail of the body, we can at least tell that there’s a way our body was designed to be used.