Anatomy of the knee

PHOTO: CHRISTOPHER DOUGHERTY; ILLUSTRATIONS: MICHELE GRAHAM

In 2007, I slipped while descending a steep trail in Shenandoah National Park. I took a hard blow to the outside of my left knee, shredding the lateral meniscus and articular cartilage and dislocating the kneecap. I faced major surgeries to save the knee from a partial joint replacement. My orthopedic surgeon was upfront: Recovery would be long and arduous. More than anything else, my mindset would be the key to my healing. That meant I needed to cultivate a nurturing relationship with my knees.

Fortunately, prior to the accident I’d been a yoga practitioner with a daily meditation habit for 19 years. Before surgery, I dedicated an hour a day to channeling love and gratitude into my knees. By the time I was wheeled into the operating room for the first of two surgeries that ultimately restored the joint’s structure, the knee had become my most beloved body part. I had learned to celebrate its complexity and vulnerability, and to fine-tune movements to treat it well. The knee is the body’s nexus of faith and duty: One of the first things we do when we seek strength or mercy is get down on our knees. We also drop to our knees when we pledge ourselves to a path of devotion. Each knee is the grand arbiter of mechanical forces received from the foot and hip. For better or worse, the knee adjusts itself to balance and transmit the energies of impact, shear (sliding forces), and torsion (twisting forces).

See also Essential Foot and Leg Anatomy Every Yogi Needs to Know

The knee is often described as a hinge joint, but that’s not the whole story. To the eye, it resembles a hinge because its primary movements are flexion (bending, to draw the thigh and calf toward each other) and extension (straightening, to move the thigh and calf away from each other). In reality, the knee is a modified hinge joint. It glides, and rotates. This makes it more versatile but also more vulnerable. Its range of motion becomes clear when you compare it with the elbow. Bend and straighten your elbow several times. The movement feels similar to opening and closing a laptop. Try it again by moving between Plank Pose and Chaturanga Dandasana (Four-Limbed Staff Pose). Now try Virabhadrasana II (Warrior Pose II), placing your front hand on the inner part of your front knee. Bend your front knee (flexion) and feel the thigh bone, or femur, glide forward and rotate—moving the knee up and out. Straighten your knee (extension) and feel the femur glide backward and rotate—moving the knee down and in.

To keep stable, the knee relies on tendons, ligaments, cartilage, and the joint capsule itself, not large muscles. Among standing yoga poses, Tadasana (Mountain Pose) is most stable for the knee because there is maximal contact between the end of the femur and tibial plateau (the top of the tibia, or shin bone). Things go awry, though, if you “lock” your knees. When we hyperextend—and many of us do so without conscious thought—we excessively squeeze the anterior, or frontal, aspect of the menisci (see drawing), pushing the tissues backward, out of their natural placement. Instead, practice standing with your knees in a “relaxed straight”: stand and press back through one of your knees. Then firm your calf muscles toward your shin bone. Notice how all your leg muscles engage. Take your attention to the middle of your knee. It should feel very stable. Practicing this action over time will reeducate your muscles and correct hyperextension. Also, the inner parts of the knee are larger, thicker, and deeper than the outer parts. This anatomical asymmetry makes it normal for the kneecaps to slightly glance toward each other in poses such as Tadasana and Adho Mukha Svanasana (Downward-Facing Dog Pose). Perhaps you’ve heard the cue to point your kneecaps directly forward in straight-leg asana? Don’t do it; it can injure the knee because it overrides the structure and function of the joint.

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The knee is least stable when bent. When we flex our knees, as in Virabhadrasana II, we have less contact between the femur and tibia. When there is less bony contact, connective tissues strain and become more vulnerable. The vastus medialis, the inner muscle of the front thigh, is primarily responsible for keeping the patella, or kneecap, in its femoral sulcus, the groove at the end of the thigh bone. Ideally, we want the kneecap to slide smoothly up and down that groove, so that the patella functions efficiently as a fulcrum when we bend and straighten the knee. But the vastus medialis is much smaller than the vastus lateralis, on the outside of the front thigh. This strength imbalance in the front thigh muscles, or quadriceps, can cause the kneecap to pull out and up, creating pain in everything from walking to bent-leg standing asana. Lunge poses often make it worse. But we can develop balance between the muscles through “quad setting.” Sit in Dandasana (Staff Pose) with a rolled towel under your knees, toes pointed up. Press out through your heels. Then, press down through your knees, leading with the inner knee. Hold for 10-20 seconds, release, and repeat to fatigue.

Remember, the knees, stuck in the middle, absorb energy from the feet and hips. If you take them beyond normal rotation or put too much pressure on them when bent, you increase the risk of harming your ACL. In turn, several poses demand a high degree of caution. Some I’ve stopped practicing altogether.

• Bhekasana (Frog Pose): Places strain on the ACL and medial meniscus because of torsion from trying to draw the soles down and toward the outer hips.
• Virasana (Hero Pose): When practiced with the knees together and feet outside the hips, we push maximal range of motion for most people and add rotational strain multiplied by body weight.
• Padmasana (Lotus Pose): Without sufficient mobility in the hips (and some of us will never have it due to our particular anatomy), our knees twist too much. The primary axis of movement in the body is the hips, a true ball-and-socket joint uniquely suited to rotation.
• Pasasana (Noose Pose): Without sufficient strength in the hamstrings and calves, gravity wins, putting undue pressure on the knees, which strains the ACL. Laxity in the ACL can reduce power and stability in the knee.

Now that I’ve laid out what to avoid, here is what I recommend. Try this homework for two weeks to get to know your knees.

See also Fascial Glide Exercise for Functional Quads and Healthy Knees

Take a Good Look at Your Knees

If healthful for you, take Adho Mukha Svanasana, and look at your knees. Notice that the inner knees naturally move back farther than the outer knees and the kneecaps glance toward each other. Remember: This is normal!

Gain Knowledge about the Knee Muscles

Sit in Dandasana. With relaxed thighs, lightly grasp the inner and outer edges of your patellae and wiggle them side to side. Lightly grasp the upper and lower edges of your patellae and gently slide them up and down. Next, engage your thighs. Notice how the patellae cinch into the ends of the femurs. The moral of this story? Use your muscles, instead of mobility, to move your knees in asana.

Show Those Knees from Gratitude!

Rest your hands on your knees and send them love. They do so much for you amid so many demands. Show ’em gratitude! When a body part hurts or doesn’t do what we think it should, we often believe it has failed us. More likely, we have failed our body part by blaming or ignoring it. Gratitude is the antidote to shifting that relationship.

See also Practice These Yoga Exercises to Keep Your Knees Healthy

Yoga Knee Anatomy 101

Avoid injury by understanding how connective tissues help knees move, bear weight, and respond to strain.

• Meniscus: Pads the space between the femur and tibia. This C-shaped structure also deepens the tibial plateau and helps stabilize the knee, especially the medial meniscus, which firmly attaches to the joint capsule and resists shear and rotation. Each knee has two menisci.
• Anterior cruciate ligament (ACL): Functions like a stiff bungee cord to keep tibia from sliding too far ahead of femur. It’s one of the most commonly injured parts of the knee due to twisting actions that overstretch or tear it. That means many yoga poses put it at risk.
• Medial collateral ligament (MCL): Keeps the knee from buckling inward. Also works with the ACL to stop the tibia from sliding too far forward. The MCL typically gets injured in sports with heavy physical contact and sudden changes in direction, such as football. It is not commonly injured in asana, though avoid “knee drift” toward the midline of the body in bent-leg asana; when the knee is in flexion, center the kneecap toward the space between the second and third toes.

See also Anatomy 101: Why Anatomy Training is Essential for Yoga Teachers

About our expert

Mary Richards, MS, C-IAYT, ERYT, YACEP, has been practicing yoga for almost 30 years and travels around the country teaching anatomy, physiology, and kinesiology. A hard-core movement nerd and former NCAA athlete, Mary has a master’s degree in yoga therapy.

Learn more Study Experiential Anatomy online with Mary and Judith Hanson Lasater. Sign up today at judithhansonlasater.com/yj.

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