Asana Requires a lot from the knees. When we practice poses, we stretch the supporting structures in front of, behind, and on the sides of the joint: We bend and twist them for Padmasana (Lotus Pose), kneel on them in Virasana (Hero Pose), and compress them deeply in Balasana (Child’s Pose).
Unlike the hip joint, which is designed for stability and multi-directional movement, knee joint surfaces are much shallower and (therefore) less stable—plus the muscles aren’t as large or as powerful. Knees take on weight and pressure as we walk and do yoga. This, when coupled with imperfect knee alignment, can contribute to cartilage deterioration and stress on the ligaments and tendons surrounding the joint.
The knee joint is the union of the femur and the tibia. The fibula, the thin lateral lower leg bone, acts as a strut for stability. Think of the patella (kneecap) like the roof of the knee joint, resting in the tendon of the quadriceps (upper thigh) muscle. It protects the front of the knee joint and allows for kneeling, which is made more comfortable by surrounding fat pad and fluid-filled sacs (bursae).
The patella also functions as a lever that strengthens the quadriceps when the knee straightens, like when you kick a ball.
The cruciate ligaments make an X shape in the center of the knee joint. Together they stabilize the knee and are responsible for forward and backward motion.
By far, the medial knee (the inside) is the most vulnerable part of the joint and is most susceptible to injury. This is, in part, because the medial collateral ligament (the band of tissue that runs along the inner edge of the knee) blends into one of the medial hamstring muscles that stems from the sitting bones. When we stretch this muscle (and therefore its tendinous attachment) in standing poses, forward bends, and even sitting in Upavistha Konasana (Wide-Angle Seated Forward Bend), it can overstretch the medial collateral ligament, leading to strains, sprains, tears, bruising, and swelling.
Deeper in the knee joint, the medial meniscus (cartilage), connects to the knee’s exterior structure. The medial meniscus creates space between the end of the femur and top of the tibia, allowing room for normal movements
of the knee. It adds padding between the bones and, because of its deep, thick, ring-like shape, it also contributes to stability in the joint by creating a deeper articular (joint) surface where the tibia and femur meet.
The medial meniscus connects to the medial collateral ligament at the inner knee. If you overstretch the medial collateral ligament in poses such as Wide-Angle Seated Forward Bend and Lotus Pose, you could damage your medial meniscus.
Anatomy in Action
While you’re standing, walking, and practicing asana, the knee joint is always balancing stability and mobility. The most stable position for the knee joint is extension, with standing extension being more stable than sitting extension. The most mobile position is flexion, with standing flexion being more mobile than sitting flexion.
Your knees are the most vulnerable to misuse and injury in poses where they are bent. When you bend your knee to a 90-degree angle like in Virabhadrasana II (Warrior Pose II), you greatly reduce the congruence between the femur and the tibia—the less congruence in the joint surfaces, the less stable the knee joint.
In these poses, focus on alignment and stability before range of movement. For example, when you align the feet, legs, and pelvis in Utthita Parsvakonasana (Extended Side Angle Pose), you may not go as far down into the pose (your hand may not reach the floor), but by meticulously aligning your bones in the pose without striving to maximize your range of movement, you are much less likely to get hurt. Let the range of movement come slowly over time.
The Knees and Hyperextension
Putting too much stress on ligaments can cause the knee to bend backwards, known as hyperextension. Hyperextended knees are less stable than those with a normal range of motion: When the tibia pushes back past the vertical line, it causes excess strain on other tissues in and around the knee.
If you have hyperextended knees, avoid squatting for long periods of time in yoga asana practice, as this stretches the ACL. However, the ACL is most stressed at 30 degrees and 90 degrees of flexion when bearing weight. This means that standing poses where your knee is flexed at a 90-degree angle, such as Extended Side Angle Pose, hold increased potential for stress and injury to the ACL; be sure to watch your alignment in these poses.
Not sure if your knees are hyperextended? Try this: Sit on the floor in Dandasana (Staff Pose) with your spine long and legs together, stretched straight out in front of you. Roll your thigh bones to a neutral position so your kneecaps face the ceiling. Strongly contract your quadriceps muscles. Notice the urge to stretch out through your heels. Resist this; keep your feet completely and totally relaxed, practically floppy. If your feet are relaxed, not pulled up toward you, yet your heels lift off the floor, you have hyperextended knees.