Whether bent or straight, stiff or hypermobile, we ask our knees to move in a variety of ways in asana practice. A regular yoga practice can improve the function of the knee and enhance our ability to walk, run, jump, squat, and sit in our daily life. But how do we know if we are respecting the anatomy of the knee joint and practicing safely? The knee will function best when the femur (thighbone) and tibia (shinbone) align and the patella (kneecap) is centered.
The knee is a synovial* hinge joint. It is designed to flex and extend with minimal twisting or side bending. The primary muscles that flex (bend) the knee are the hamstrings and the gastrocnemius (the large calf muscle). The quadriceps, a group of four muscles on top of the thighbone, extend (straighten) the knee. The knee joint is supported by tendons and ligaments that serve to stabilize the knee, and knee health depends on not straining these stabilizing connective tissues. Stretching and strengthening the muscles that surround and support the knee joint will help keep the upper and lower leg bones in alignment and the kneecap centered.
*Synovial joints are the most common type of joint in the body. They include a slippery fluid that separates and lubricates the cartilage-covered bone surfaces.
Point your knees and toes in the same direction. In general, whenever your knees are bent, your toes and knees should point in the same direction.* For example in utkata konasana (goddess pose), your knees bend outward; therefore your toes should point outward at the same angle. If your toes are pointing toward the top of your mat, as in virabhadrasana I or II (warrior I or II), your front knee should bend toward the top of your mat. This will help you avoid twisting the knee.
*Exception: Students with tibial torsion may have a foot that turns in/out more than the knee.
In straight leg standing poses, such as trikonasana (triangle), many students with chronic knee hyperextension are unaware that they are practicing with a slightly internally rotated front femur, and this turns the knee inward. This misaligns the upper leg relative to the lower leg and allows the knee joint to press backward against the nerves, tendons, and ligaments along the back of the knee. A strong external rotation of the front thighbone helps align the hamstring tendons and will improve the alignment of the upper and lower leg bones to prevent knee hyperextension. Check the direction of your knee as you hold trikonasana. Is it truly pointing straight ahead or is it turning slightly inward?
Avoid hyperextending the knee by pressing the shinbone forward as you draw the thighbone back to create an active microbend in the knee. In standing poses where the front leg is straight, as in trikonasana, this action will help you avoid pressing into the back of your knee and hyperextending the knee joint. Maintain the external thighbone rotation described above, and press your shinbone forward slightly as you engage the quadriceps to draw your femur up and back. This will create a slight bend in the knee and activate the muscles that support the knee joint. Press strongly into the ball mound of the front foot to shift weight forward and away from the back of the knee.
Keep your shin vertical when the hips are in line with or higher than the bent knee. In any standing pose where the front knee is bent and the hip is in line with or higher than the knee, such as warrior poses, keep your knee stacked directly over your ankle and your shinbone vertical. When your hips are higher than your bent knee, it creates an implied gravitational pull through the femur toward the knee. Avoid letting the knee go past the ankle because that increases the force toward the knee joint. Keep your shin vertical so that the weight of the leg descends into the heel.
When the hip is lower than the knee, it is safe for the knee to go forward of the ankle. In standing poses such as anjaneyasana (low lunge), or in squatting poses such as malasana (garland pose), when the hip is lower than the knee, the line of force through the femur descends away from the knee and it is safe for the knee to go forward of the ankle.
When your leg is bent and externally rotated, keep the ankle dorsiflexed and lengthen through the inner heel to prevent twisting in the knee. This action helps prevent the shinbone from rotating by stabilizing the lower leg so that the rotation comes from the upper leg in the hip socket. When the ankle is lax and the foot sickles (rotates inward), your shinbone tends to externally rotate instead of the femur and, in poses such as variations of padmasana (lotus), eka pada rajakapotasana (one leg king pigeon), or the Iyengar version of supta padangusthasana III (supine big toe pose variation), this will overstretch the outer knee and strain the lateral collateral ligament. If your shinbone rotates instead of your thighbone, you aren’t effectively working in the hip, you are twisting the knee. If you are not accustomed to dorsiflexing the ankle in these poses, you may notice that you might not move as far as you did before, but the rotation will remain in the hip rather than the knee, ultimately allowing you to safely move deeper.
Balance your hamstrings and quadriceps. Your hamstrings bend your knee and your quadriceps straighten your knee. Keeping this pair of opposing muscle groups strong, flexible, and balanced will help protect your knee. The vastus medialis (inner quadriceps) tends to be weak on most of us; place extra attention to strengthening it. You can target the inner quadricep by reclining on your back with one leg bent, the foot placed flat on the floor, and one leg straight. Externally rotate the straight leg femur and slowly lift and lower the straight leg. Biomechanist Katy Bowman calls this corrective exercise “patella centering.”
Practice the following asanas regularly: supta virasana (supine hero pose) to stretch the quads; setu bandha sarvangasana (bridge) to strengthen your hamstrings; and supta padangusthasana to stretch the hamstrings.
Massage and stretch your calves regularly. The gastrocnemius is a knee flexor and is chronically tight on many of us, pulling the lower leg out of healthy knee alignment. Loosen the lower leg muscles with massage, a foam roller, or yoga therapy balls, and stretch your calves as often as you stretch your hamstrings.
When you practice asana, if you feel any discomfort in your knee joint, back off immediately. You may need to modify the pose further or decide if the asana is not appropriate for you at this time.
Learning how to keep the knee joint stable and supported in your yoga practice will help improve your alignment, balance the musculature of the legs, improve the health of your knees, and avoid injury. It is a beneficial cycle that will keep you active and moving both on and off the mat, improving the quality of your practice and your life.
A version of this article originally appeared in the 200-hour and 500-hour Prairie Yoga Teacher Training Manuals.