Read Maty Ezraty's response:
Padmasana is a pose that we must respect. When we hurt our knees in this pose or related ones, it is almost always due to tight hips. Pushing too far into the pose, or misplacing the foot, ankle, and heel, can also contribute to an injury. Additionally, students often try to clasp the Half-Lotus leg too soon.
Pain or pressure in the knee or elsewhere is not a desirable yogic result. I am sorry that it was an injury that caused you to reflect on this subject.
It is important that we teach yoga principles to help our students avoid unnecessary suffering. The first yama in the eight limbs of Ashtanga Yoga is ahimsa. It is, unfortunately, often forgotten or misunderstood in our attempts to accomplish poses. The teacher must constantly reinforce this most important yogic principle.
Often in Ashtanga or flow classes, there is a focus on heat and on the next posean emphasis on a sense of accomplishment. This causes students to want to get ahead and try what is not yet appropriate for them. In this case, we must remember asteya, the third yama: We ought not take what is not freely offered.
I cannot stress enough the importance of bringing the yogic principles into the classroom. I have been traveling to teach in the last few years and am appalled by the amount of injuries I see occurring in classes. Students are being led to believe that they should just push through pain. This is ridiculous and not yogic at all.
Let's look at some of the poses that can best help you assess whether a student is ready to start working on Padmasana or the Half-Lotus poses. The standing poses come at the beginning of Ashtanga practice for a good reason: They are heating, and they use grosser muscles. Those most helpful to the Lotus poses are the "externally rotated" standing poses, such as Virabhadrasana II (Warrior II Pose) and Utthita Parsvakonasana (Extended Side Angle Pose). There are also sitting poses, such as Sukhasana (Easy Pose) and Baddha Konasana (Bound Angle Pose), which are helpful indicators. If a student has a hard time rotating the front leg correctly in the standing poses, or if the knees are way off the ground in the sitting poses, this is an indication that they should wait and not attempt the Lotus poses.
The word vinyasa is often misunderstood. Students associate it with a vigorous practice that includes 'jumping.' In Ashtanga, students misunderstand it to mean the actual order of the poses in a given series. The meaning behind vinyasa is really a gradual progression. When we are not open enough in the hips, we will hurt the knees in our attempt at Padmasana.
We can find an appropriate, gradual, or vinyasic way of working toward this pose. One way to work toward the Half-Lotus is to sit up straight and take hold of the foot from underneath. Lifting out of the lower back and holding the leg up without pulling it in toward you is very challenging. This variation can also be done while doing the standing version of the pose.
The work is to rotate the leg correctly from deep inside the hip socket. This is very hard if you have tight hips, hamstrings, and/or a lower back. This is the start of Padmasana work. The externally rotated standing postures like the ones listed above are the best for working on this. They are safer than the sitting postures.
Lastly, how you bring the foot into the position is important. Look to see that the student is not sickling the foot. The foot and ankle need to be neutral, not overstretching the outer or inner ankle. It is important to develop the habit of holding the foot from underneath and not grabbing it from the top, which is aggressive and can put pressure on the knee. The heel should lift up toward the ceiling and press away from the knee. This comes from the hips.
There are many safe hip openers that you can teach your students to add to their practice. I often give my stiffer students extra homework: I have them practice Virabhadrasana II more often, and I have them repeat Utthita Parsvakonasana.
"Thread the Needle" is useful to add to the end of a practice, as is sitting in Sukhasana and folding forward.
Maty Ezraty has been teaching and practicing yoga since 1985, and she founded the Yoga Works schools in Santa Monica, California. Since the sale of the school in 2003, she has lived in Hawaii with her husband, Chuck Miller. Both senior Ashtanga teachers, they lead workshops, teacher trainings, and retreats worldwide.