More On The Anatomy Of The Knee
In Part 1 of this article we left off looking at the deepest, most intrinsic structures that make the knee function as it does. In this part of the article we’ll continue to look at another deep structure, the meniscus, and also talk about some of the soft-tissues (muscles and ligaments) that affect this joint and how that all fits into our yoga practice.
The menisci (plural) are two semi-circular pieces of additional cartilage attached to the very top, almost flat area of the tibia. There is one on either side, hence the terms medial meniscus (inside) and lateral meniscus (outside) of the knee. They also have what are known as “horns” and for each meniscus there is both an anterior (front) and posterior (back) horn. The horn is the rounded end that is facing the middle of the tibia.
These two additional pieces of cartilage have a few different purposes in the knee. First, because of their shape they create a deeper cup for the knobby ends of the femur to meet the relatively flat plateau of the tibia, creating additional stability. Because they are also flexible they also play a role in absorption of shock and force coming through the knee joint. Finally the meniscus also helps with the functional movements that happen at the knee joint (like flexion and extension).
Instead of being completely fixed in place, the menisci actually move and distort in shape based on the movements being performed by the knee joint. Every time the knee flexes the meniscus must slide back on top of the tibia to help keep those knobby ends on the tibia. In extension, the opposite happens. Rotations of the knee also force the menisci to move and shift according to the direction of rotation.
The most common meniscus to tear is the medial meniscus. Although in size it is slightly larger than the lateral meniscus it has less mobility than its lateral counterpart. This inherent tightness seems to be part of why it is the most common one to be torn. There are of course other factors that could lead to tearing, such as quick squats or returning to standing from a squat which don’t allow the meniscus to move quick enough within the knee so that they get pinched between the bones and therefore torn. Even quick twisting motions within the knee that can injure the ligaments can also tear the menisci.
I’ve worked with a few people post meniscus tear surgery. All of them feel a relief in pain when I add to the natural lateral rotation in their knee joint. I don’t do this while they’re standing, but instead in poses that compress the meniscus such as full flexion of the knee that we find in, janu sirsasana A, badha konasana, as well as any form of ardha badha padmasana. In essence what I described way back in the “Sitting for Meditation” article was to find a way to increase and take advantage of the natural lateral rotation of the lower leg.
While sitting with the student I simply hold their knee (usually raise it off the floor slightly and slide a foot or shin under for support, of course a block or bolster could be used as well) and quite simply try to open the inside of their knee taking the pressure off of the medial meniscus. (picture)
So, let’s talk soft tissues (muscles). One of the largest groups of muscles in the body are the thigh muscles known as the quadriceps (feel free to blow the dust off that old anatomy book and follow along with their pictures), which literally means four heads. They are vastus lateralis, vastus medialis, vastus intermedius, and rectus femoris. The first three only cross the knee joint and therefore are simply dedicated to doing one action and only one action, that is, to extend (straighten) the knee. This simple action is essential of course for walking and running.
The fourth of these four muscles crosses two joints, the knee (for extension) and the hip joint above to flex it (ie, lifting the leg forward from a standing position). These four muscles converge around and attach to the patella first (knee-cap) and then continue through a ligament to get to the top of the tibia. The patella assists the function of the knee by helping to keep the tibia in a more or less straight line as it flexes and extends.
These muscles are also the last line of defense in dealing with loss of stability of the knee from a tearing of the ligaments we discussed last time. Often times minor tears of the ACL are left alone (depending on factors of age and activity level) and the quadriceps primarily become responsible for taking up the slack quite literally of the torn ACL.
The hamstrings in the back of the thigh create the balance for the quadriceps. There are three muscles that make up the hamstring group, biceps femoris, semitendinosus and semimembranosus. I wouldn’t worry too much about the names but more importantly what they do. All three of these muscles cross both the knee and the hip joint and do the opposite actions of the quadriceps. The hamstrings flex the knee and extend the hip joint (ie, take your leg backward from a standing position). The other action they do is the very rotation of the flexed knee that we’ve been talking so much about. Semimembranosus even has an attachment to the medial meniscus and helps it move backward as the knee flexes.
There is no complete conversation about this group without including the hip joint above (a future article) so we’ll keep the conversation around the knee, knowing that it isn’t quite complete. Another function of the hamstrings at the knee is to be the last line of defense in a hyperextended knee. The first line of defense is of course the PCL and the hamstrings merely play a back up to it. They almost act like a sling and cradle the back of the knee. To keep it simple, the balance between the length and strength of both the quadriceps and hamstrings is lost in a hyperextended knee with the quadriceps winning the battle (there is of course a genetic component to hyperextended knees and may play more of a role than the simple tension of tissues).
Considerations for the Practice
Because the knee is between the ankle and the hip joint, it negotiates for, or regulates the leg and its movements. As we talked about in previous articles, the knee is the center of the kinetic chain and can be used to negotiate balance in poses that require it. By bending the knee in a standing pose when heading out of balance, the center of gravity in the body lowers and the muscles of the leg become active helping one right themselves before falling over.
In transitions between standing poses, the knee can bend to prevent strain in the lower back or the sides of the back as well as requiring the large muscle of the leg to do the work of maintaining body weight that would otherwise be handled by other muscles, namely those in the back and sides.
Keep in mind the legs are all about foundation and connection to earth energy. Even in your seated poses, active and strong legs lend themselves to giving the asanas a foundation from which the upper half of the body can grow and move out of. The most troublesome area and pose for most westerners however is padmasana.
Any variation of this pose, one sided or two sided almost always brings up issues around the knee. If you look back to the “Sitting for Meditation” article, you’ll find a description for making your way into lotus that I work with in yoga students with tight hips or knees that are already questionable.
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Knee pain and injuries are common in the general population as well as in the practice of yoga. Here we take a wide perspective and look at the basic function of the knee joint, what structures are located around the knee, where problems tend to arise during yoga practice, and finally, what you can do about knee pain. Read our most in-depth knee post which will help you more fully understand what is going on in the knee, as well as lead you to other great articles that we’ve previously written.