Demystifying the knee joint and knee pain
There’s a lot of talk about the knees in yoga. And that’s not actually unique to yoga! Keeping the knees healthy and functional is a big topic among runners, dancers, gymnasts, cyclists, and in a host of other activities. Our knee joints are one necessary piece of our anatomy that make it possible for us to walk, run, and do so much more. If we’re talking about yoga specifically, our own research here at yoganatomy.com has shown that, among those yoga practitioners who have experienced an injury, the knee was the most common location. So, why is there so much talk about the knee joints? And why are they so often associated with pain or dysfunction? Read on to find out.
Anatomy of the knee joint
The knee joint is the critical and vulnerable middle piece of the kinetic chain that connects our foot and ankle to our pelvis. Three bones, multiple muscles, and a number of ligaments, tendons, and other important structures come together to allow the knee joint to function. Let’s dive into the anatomy of the knee joint.
Bones and joints at the knee
The knee joint includes three bones:
- Femur (thigh bone)
- Tibia (larger of the two lower leg bones)
- Patella (the knee cap bone)
The joint we primarily think of as the knee joint is technically called the femorotibial joint. This is the hinge joint which is formed where the femur meets the tibia.
We also have a second joint at the knee where the patella meets the femur, the patellofemoral joint, which is a gliding joint.
Muscles that cross the knee joint
There is a group of powerful muscles that cross the knee joint and create movement there. We have four quadricep muscles: rectus femoris, vastus medialis, vastus intermedius, and vastus lateralis, which are primarily responsible for extension (straightening) of the knee joint. We have three hamstring muscles: biceps femoris, semitendinosus, semimembranosus, as well as gracilis, sartorius, popliteus, and gastrocnemius, which all contribute to flexion of the knee joint.
Other structures at the knee joint
In addition to muscles, there are a number of other important structures that we find at the knee joint which are critical to its healthy function. The menisci found in the knee are especially important structures for aiding the knee with the mobility aspect of its function. Each knee has two menisci, a medial meniscus and lateral meniscus. Both are semi-circular pieces of cartilage which allow the femur to glide where it meets the tibia. The menisci also contribute to increased stability and shock absorption at the knee. One reason that you may have heard of the meniscus is that it is a common place for people to experience injury in various sports and activities. As much as .06% of the US population will end up having surgery to repair a meniscus tear (Baker et al., 1985).
The knees also have a set of ligaments that are especially important for maintaining stability. The anterior cruciate ligament (ACL) is located inside of the knee joint. It attaches to the front of the tibia and then attaches at the other end on the inside of the femur. The posterior cruciate ligament (PCL) is also located on the inside of the knee, but on the posterior side. It runs from the back of the tibia to the inside of the femur where it meets the tibia.
The medial collateral ligament (MCL) is located superficially on the medial, or inside of the knee, and the lateral collateral ligament (LCL) is located superficially on the lateral side, or outside of the knee. All of these ligaments are important for maintaining stability in the knee by preventing excessive translation in any direction. The ACL and PCL prevent too much anterior or posterior shift at the knee joint, while the MCL and LCL prevent too much medial or lateral shift at the knee joint.
Finally we have the patellar ligament, which is formed by the four quadriceps muscles (rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis) coming together at the distal end to form a common tendon just before they attach to the tibia. This strong ligament helps hold the patella in place where it connects to the femur.
We have one more important structure that contributes to the stability of the knee joint. That is the iliotibial band (IT band), which is also sometimes referred to as the iliotibial tract (IT tract). As with any structure, there is some variability from person to person with respect to exactly where this band of ligamentous fascia attaches. The IT band is interwoven with the fibers of the tensor fascia latae muscle at its proximal attachment. It then runs along the lateral side of the thigh and the knee to eventually attach distally to the tibia. In some cases it may also attach to the linea aspera of the femur and some fibers may merge with the patellofemoral ligament. The iliotibial band functions to help stabilize the knee joint, especially the anterior and lateral sides, when we’re weight-bearing.
Movement at the knee joint
As a hinge joint, the knee primarily does the movements of flexion and extension. However, when the knee is flexed between 5 and 90 degrees, its design also allows us to do up to 45-50 degrees of lateral (external) rotation, and about 10 degrees of medial (internal) rotation. Because the knee is a hinge joint with a small amount of rotation, it makes it different in structure from the elbow joint, which is the other place where we find a hinge joint in the body. The knee’s unique structure allows it to strike a balance, when healthy, between stability and mobility. It’s unique structure can also make it vulnerable to dysfunction in various ways.
What is healthy knee function?
Healthy knee function includes both stability and mobility. A healthy knee can adapt to changes in terrain, momentum, and speed of movement. A healthy knee joint is also a reflection of a healthy chain of joints. When the lower limb kinetic chain is functioning well, we can absorb momentum from the foot’s contact with the ground and transfer that force up through the legs into the pelvis and torso. We can also receive forces in the upper body or pelvis and transfer those forces back down through the kinetic chain of the leg into the ground. This requires that the structures above and below that knee joint be healthy and functioning as well.
As we mentioned in the introduction to this article, knees were identified in our research project as the area of the body where yoga practitioners were most likely to experience an injury. So, why are the knees so vulnerable to dysfunction and injury? As we mentioned already, because of the knee’s location in the middle of a chain of joints, what’s happening at the knee joint is a product of what’s happening above and below the knee joint.
Tension or imbalance in the hips, because they are in the chain above the knee joints, will influence how force moves into and through the knee joints. Similarly, the foot and ankle are our first connection to the ground and influence how we receive forces from the interaction with the ground. So, tension, dysfunction, or imbalance in the ankle joints, will affect how ground forces move up through the chain of joints, including through the knee joints. The source of dysfunction that we experience at the knee joint is often located at the joints above or below.
Our experience of knee pain or dysfunction in yoga commonly fits into one of the following groups:
- Inner knee pain
- Outer knee pain
- Pain through the centerline of the knee
- Generalized sensation or pain, on or around the knee
Common knee injuries, conditions, and dysfunctions that I see include:
- Medial meniscus tear
- Patellar tendinitis
- Iliotibial band syndrome
The knee joint in yoga
Before going any further into knee issues as they relate to yoga, it’s important to distinguish different sensations and what they may mean. Sensation on its own is simply information and feedback from your body. Feeling “something” in or around your knee does not automatically mean that something is bad or wrong. It could, but we shouldn’t just assume that.
The most mild sensations are pressure, fatigue, or generalized sensation. Certainly you should pay attention to these as it may mean you’re overworking or overusing muscles around your knee. Generalized sensation or pain could also mean that there are more general problems, such as inflammation of the joint, which can be due to, or lead to, arthritis.
These types of mild or generalized sensations at the knee joint are also commonly the type that are felt during specific yoga postures but go away immediately when backing out of the posture. And, you may not feel those sensations at all at any other time during the day or during other activities. This is a great time to be cautious and go slowly with any posture that seems to be causing pressure or pain at the knee joint. Regardless, it’s a good time to start taking those postures apart and working to understand them more fully in your body. With some exploration, can you find the tissues or areas of the body that may need to be addressed in order to eliminate that pressure or other generalized sensation in the knee joints?
With respect to generalized knee pain or pressure, there are many places that could be the source. It could be muscular tension. One of the most common culprits for generalized knee pain is the quadriceps muscle group, however there are also other muscles or patterns in the body that can contribute. The technique that we use to enter, exit, or hold a posture can also contribute to where we feel the posture, including whether we are sending pressure or pain into our knees. If you are experiencing generalized sensation or pain on or around the knees, exploring how you approach the posture, move into it, or move out of the posture, is a good general approach for any posture that seems to be placing pressure or pain into the knees.
If, however, the sensation you feel is in a very specific spot or happens all at once, particularly with a sound associated with it, you need to stop what you are doing immediately and evaluate. This type of pain will most likely make you stop right away. You still want to explore how you’re going into the posture, coming out of the posture, and decide if the technique you’re applying in the posture is appropriate for you, but this type of sensation is definitely a caution flag from your body to pay attention.
There are certainly specific postures or types of postures that have the potential to stress the knee joints more than others. Let’s take a look at some of these postures and how you might work with them.
Postures that can stress the knee
Lotus and half lotus
When we talk about postures that can stress the knee joint, lotus and half lotus are always at the top of the list. Our research project confirmed this when our survey identified lotus, half lotus, or a posture that includes a half lotus, as the most common place where practitioners injure their knees. Why? A number of factors have to come together to do a half lotus pose in the body. In order to do a healthy half lotus pose, our hips have to be sufficiently open in order to allow most of the external rotation to come from the hip, leaving only a little remaining external rotation to come from the knee joint (which is normal and natural movement).
Activities that westerners commonly do, like prolonged sitting and sports such as running and cycling, tighten the muscles around the hips, and can get in the way of all of those factors coming together. The main muscles that tighten and restrict rotation at the hip joints are the gluteus minimus and medius, as well as the deep six lateral rotators to some degree. It’s not limited to these, but these are the most common culprits.
The other thing that can get in the way is how we set up a half lotus pose, or in other words, the technique that we use to get into the posture. If we just reach out and grab the foot to bring it on top of the opposite thigh, we can actually inadvertently create internal rotation at the knee joint. This is the opposite of what we really want, which is a little external rotation at the knee joint to create maximum comfort in this pose. But, it really starts at the hip. If the muscles around the hip joints are not open and able to create a sufficient amount of external rotation, you will simply load more stress into the knee joint.
When practitioners experience knee pressure or pain in lotus or half-lotus, they can usually distinguish between inner and outer knee pain. Inner knee pain is far more common than outer knee pain in half-lotus and lotus, but both do occur. Remember, the knee is in the middle of the chain of joints. Restrictions or tension at either end can impact both the amount of force generated at the knee joint as well as where that force is felt at the knee joint.
Inner knee pain often comes from what was described above. That is, we are not creating enough external rotation at the hip joint, which then tends to create too much internal rotation at the knee. If outer knee pain is showing up in a pose that includes a half-lotus or lotus, the first thing I check is whether the IT band is particularly tight.
I can’t say that I know exactly what the relationship is between IT band tension and outer knee pain, but these two often show up together in half-lotus and lotus. Those with tight IT bands are often avid runners or cyclists. Both of these sports create and benefit from a tighter IT band. You can also keep an eye out for whether a person tends to internally rotate their feet/legs in standing, and/or in postures such as downward facing dog to determine whether a tight IT band might be contributing to their knee pain in half-lotus or lotus.
In either case, it is important to remember that the knee is most vulnerable when it is both flexed completely and rotated as we do in lotus. You have to assess whether or not your hips have enough range of motion to do this properly. If only a small amount of space is needed at the knee joint to prevent compression of the meniscus or other structures that seem to be causing pressure or pain at the knee joint, you may be able to alleviate it by folding the knee around a small towel. If that’s not enough to remove the pressure or pain, you may need to wait for your hips to open more. In that case, focus on preparation postures to open your hips for lotus. You don’t want to force this posture.
Poses where we squat or fully close the knee joint
Another common place where knee injuries can come up, or where yoga practitioners report feeling pressure or pain in their knees, is in postures where we are squatting or fully closing the knee joint. Examples of these kinds of postures could include: virasana, triang mukhaikapada paschimottanasana, krounchasana, pasasana, and utkatasana.
Closing the knee fully by itself should not be a problem. However, as I mentioned in the last section, when we add rotational forces to it, we increase the stress in the knee joint. The other factor that adds stress to the joint is when we are bearing weight on it while it is closed, as we do in virasana and the other postures listed above where we are sitting on the floor.
There are a couple of reasons that we might feel pain in these postures. One of those factors is that the meniscus has to move within the knee joint. That’s normal as it adapts to the surface of the femur above it. When you close the knee fully, the meniscus has to move maximally to accommodate this end of range of motion. It’s possible for the meniscus to get “caught up” when we undo some of these postures including squatting positions such as pasasana. I’m not saying that is common, but it does happen.
In addition to that, there is sometimes a stiffness that occurs after closing the knee in positions like I described above. Some of this may have to do with the lengthening of the connective tissues at the front of the knee and the shortening of the connective tissues at the back of the knee. If you’ve spent a decent amount of time in any of these postures, your connective tissue may have literally cooled off somewhat and therefore tightened up a bit. As a result, it can take a moment for your knee to feel comfortable straightening out again. Please be very mindful if this happens to you. As I have traveled and taught over the years, I’ve observed a relationship between this tendency toward stiffness when exiting the pose and a higher likelihood of a knee injury.
Poses where we are weight-bearing with a bent knee
Another place where practitioners sometimes report pressure or pain in their knees is in postures where we are weight-bearing and one of our knees is bent. Examples of this situation include postures like warrior one, warrior two and extended side angle pose.
First and foremost, in these poses, your quadriceps are highly engaged to prevent your knee from bending more than it is. (Although, these are not the only muscles working, just the ones working the hardest from the beginning.) This is why many people feel their quadriceps getting tired in postures like these. If there is an imbalance between the strength of the lateral quadriceps and the medial quadriceps, or if your quadriceps are simply on the tight side, that tension could be felt as a pull on your patella, generalized knee pain, or even inner or outer knee pain. If your knee has other underlying issues, such as arthritis, postures such as these can exacerbate those underlying issues and you can feel more pressure or pain in the knee.
Alignment of your knee may also be a factor. The knee is certainly more vulnerable if we let it fall in or fall out significantly. If we maintain a straight forward and backward direction with the knee, then it’s in a far more stable position. This is where we need to pay attention to the relationship between the openness in our hips and how much that allows or doesn’t allow us to place our knees in a stable position. If our hips are on the tight side, then we may need to change the pose in some way to accommodate that for the health of our knees. We may need to step the feet a little wider or closer, not sink into the pose as deeply, or simply pay attention and reorient our knee if we see it falling inward in these types of postures.
Leg behind head postures
Leg behind head postures may not come up in all styles of yoga asana practice, but they do come up in the Ashtanga practice, so I’ll touch on why they can sometimes stress the knees. First, leg behind head asks the body to move into a position that is nearly at the end of range of motion for most people. Second, like lotus, several things have to come together to create this pose. The hips need to be very open in order to externally rotate sufficiently AND the hamstrings need to be very open to allow us to forward bend with the torso, not just to the leg, but past the leg, if we are going to then put that leg behind our head.
One thing to keep in mind is that when you have tension in your hip and you are going into a posture such as this, your leg naturally wants to return to its original position. That is, if you were to put your leg behind your head and you had just moderately tight hips and you dropped your head so that your leg could come forward, it wouldn’t stay in the externally rotated position. No, it would rotate from that externally rotated position to a more neutral position.
This implies that when doing leg behind head, there is some amount of a rotational force running through your leg. The part of your leg that is tucked behind your head is usually the bottom half of the foreleg toward your ankle. This means that your head and neck are putting a backward moving force (in this position that is an external rotation) against the foreleg while the hips are trying to return to that more neutral position (in this case, that would be internal rotation from an already externally rotated position). What this sets up is potential pressure at the inside of the knee joint. The tighter the hips, the more your leg wants to get back to its neutral position. This is what can cause a pinching sensation on the inside of your knee.
What I have also commonly seen in leg behind head poses, as it relates to the knee joint, is a pain building on the outside (lateral side) of the knee joint. If you feel pain on the outside of your knee when doing a posture like this, it’s an indication that your hips need to open more before you go deeper. Similarly to outer knee pain in lotus, my first place to look for the cause here is the IT band and excess tension. My best guess at what the sensation is that students are feeling on the outside of their knee, in this situation, is irritation at the distal end of an overly-lengthened IT band. If you over stretch this structure repeatedly, then over time the distal attachment on the outside of the knee can get inflamed and irritated.
How do we practice yoga and support healthy knees?
So, how do we keep the knees happy in our yoga practice? The short answer to that question for many people and many situations is: OPEN the hips! Most of us spend many hours a day doing activities or in a static posture (i.e. sitting) that keeps the muscles around the hip joints short and tight. The hip joints are most often what is limiting our range of motion in postures that seem to be stressing our knees, not the knee joints themselves.
Many of the yoga postures that we do are postures that “assume” that we already have open hips. Those postures are not always the best postures to create that opening around the hip joints however. Depending on our situation, age, past injuries, sports we play, etc., we may need to spend time doing additional postures or modifications of postures which work to open the muscles around the hip joints before we move on to postures that include movements like half lotus or leg behind head, which require a significant amount of openness in the hips.
If this is you, really take the time and explore hip-opening postures and preparation for postures, like the fire logs position, before you move on to poses that require a deeper range of motion. Your knees will thank you for it. If you want to learn more about opening the hips, particularly in preparation for the lotus position, check out my online workshop for working with lotus.