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James Kiernan
The Knee
The knee is a single joint where the femur/thighbone, articulates with the tibia/shinbone. Also the fibula, while not part of the knee joint itself, is also with noting because muscles that move and hold the knee firm attach here, as well as an important ligament.
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The knee joint is a condyloid joint because of the two condyles, which are rounded mounds at the bottom of the femur. This is a similar shape at the elbow as well. And although the knee is referred to as a condyloid joint, it acts almost exclusively as a hinge joint, meaning it primarily moves in flexion and extension. Smaller movements of rotation can happen for positions like lotus. But for the most part, the knee shouldn't rotate
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At the front of our knee resides our Patella, commonly called the knee cap. While it is not a part of the knee joint, it is important because it protects the knee while the knee is in extension.
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Looking at the muscles that change knee position, well start with knee flexion. The muscles that create this action are the hamstring and the calf. The hamstrings all attach to the bottom of the pelvis and connect down at the shin bone below the knee. So when the hamstrings contract, they bring the back of the shin bone toward the back of the thigh, resulting in bending the knee. This is also done with the gastrocnemius, commonly called the calf muscle. It also connects from the back of the shin to the back of femur.
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The opposite of this is straightening or extension of the knee. This is done primarily with the Quadriceps muscles. These are the strongest muscle group in the body. The 4 separate components all attach at the pelvis and then come together at the base of the knee and form the Patellar Ligament. The Patellar Ligament (knee cap) runs down and attaches at the front of the shin. When engaged it brings the front of the shin closer to the front of the pelvis, which straightens the knee.
There are other connective tissue in our knee, which provide stability and support. These are the tissues that are fairly susceptible to injury. The Patellar Ligament was already mentioned as connection for the Quadriceps to the lower leg. Additionally, we have other ligaments shown in the figure to the right. Our Menisci provide support and shock absorption between the upper thigh and lower leg. There are two per knee. On top of providing cushion like a horse saddle, they track movement, and give our femur a place to settle when standing.
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Other ligaments shown on the first diagram are the Posterior Cruciate Ligament, and the Anterior Cruciate Ligament. These prevent the upper leg from moving forward and backward relative to our shin. And so it may be easy to understand how sports can quickly injure these connective tissue, there is also chronic issue that if given enough time, can cause problems in our knee. Hyperextension of the knee is where the knee extends past a straight leg position in the opposite direction of knee bending. I'll discuss this more in a bit, where you can diagnose if you're able to hyperextend, and if so, how to engage your legs to keep your knee safe.
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On our second picture to the right, the Medial Collateral Ligament and Lateral Collateral Ligament prevent movement from side to side in the knee. This picture is displaying the back side of the left knee. Injuries can happen when a sudden movement displaces the upper body laterally relative to the lower leg and feet. Flat feet can also contribute to a wearing down of the ligaments. As mentioned in the feet section, what happens below can affect what is above. A condition known as "knock knee" occurs when the knees angle in and touch each other when standing tall.
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Knee Hyperextension: Don't fix with "micro-bend"
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The risk of injury from hyperextension of the knee is greater when the body's weight is supported b a single leg. In postures where the weight is on a single leg, typically the supporting legs hip is in flexion. Working with hyperextension of the knee and correcting it is accessible if we know how to engage with our leg.
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But before I touch on how to correct this issue, its important to understand why simply bending the knee a little is not ideal in these standing postures. The first reason this is important is when a leg is supposed to be straight, it is important that the leg is working to create stability. And when we "micro bend" the knee, we start to turn off muscles in our leg that should be very active, and in doing so we begin to loose necessary stability for a solid foundation in our posture. Also, think about the muscles that straighten the knee, our Quadriceps. These muscles also flex the hip, and as mentioned before, many of our standing postures like Pyramid Pose, Revolved Triangle, Warrior 3, the standing leg is in hip flexion. So if we relax the standing knee, we're also loosing musculature control of the hip flexion, which is not ideal.
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So rather than micro bend, lets learn how to use our musculature to keep our knees safe.
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Lets start by identifying if you are able to hyperextend. Either sitting down or laying down on the floor with the legs straight, try to straighten your legs as best as you can. If you notice that your heels lift, you have the ability to hyperextend. But fear not, we can correct this.
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Now bring your heels back down to the floor, and begin to press your heels very firmly into the ground. Press them into the ground so much that the knees begin to begin to bend and lift off the ground. Notice any sensation you may be feeling on the back side of your legs. Now, while keeping that very strong engagement of heels pressing into the ground, begin to press your thighs down simultaneously. Do not relax the action that presses the heels down, try not to even allow the heels to get any lighter. What you are doing here is engaging the hamstrings which bend the knee, while also engaging the Quadriceps which straighten the knee. And this simultaneous effort can be brought into standing postures to keep your knee in a safe and engaged position.
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