Read Maty Ezraty's response:
Making a good diagnosis is crucial to figuring out a remedy or a remedial approach. When students experience pain in the knees, you need to know which part of the knee is hurting: the front, the inside, the outside, or the back. Each of the different areas indicates a different problem.
Also keep in mind that all injuries are different, so it is necessary to have an open mind and be willing to experiment. Remedial work often requires some trial and error, as well as feedback from the student.
Here are some helpful questions to ask:
Where exactly is the pain? Does the student feel the pain while in the pose, or while coming in and out of it? How long have they had this pain? Does the pain last after class? Is the pain sharp or dull? Did the pain happen as a result of yoga or something else?
Pain in the back of the knees is generally related to forward bending. I would not expect your students to be complaining of that in this pose.
The most common complaint in this pose is pain in the front of the knee. In bent-leg poses, it is important to stack the knees directly over the heels and to have the weight in the heels rather then in the ball of the foot.
Take time to teach the setup for each pose you teach. The problem often lies in the foundation, or root, of the pose. The foundation must be correct in order to build a solid, healthy pose.
In setting up for Setu Bandha Sarvangasana, most students place their heels too close to their sitting bone. This will only work for students with open groins and an open backbend. For most students, this setup will cause the knees to go past the ankles, putting pressure on the front of the knees. Also, in this pose, the knees often go forward relative to the heels, causing pressure at the front of the knee. This frequently happens if the students are trying to hold their heels with their hands before being flexible enough to do so correctly.
Start most students with the heels two or three inches forward relative to their sitting bone, so that once they are up, the knees are over the ankles. In poses where the leg is bent, the weight needs to be in the heels to protect the knees. The action of moving the shin toward the calf and the calf down into the heel is a good one to help relieve pain in the front of the knee.
If the pain is on the inside or the outside of the knees, it can be due either to incorrect placement of the feet, incorrect tracking of the knees, or overworking the knees. Again, start by looking at the foundation of the pose. Start with the feet at least two inches forward of the sitting bone, and make sure the feet are hip-width apart and parallel. If the feet are too close together or too far apart, too much pressure can fall on the knees. It is always good to check and make sure that your student knows how to evenly ground all four corners of their feet.
Incorrect tracking of the knees can also put pressure on them. The knees should point over the second toe. If the student is tracking the knees in or out too much, this can cause pressure on the inside or outside of the knee.
The inside of the knee is the final most common area of pain in this pose. It can occur when a student is using the knees to rotate the thighs, rather then using the upper thigh. Therefore, do not teach students to rotate the knees in, but rather to keep the knees hip-width apart and parallel. The proper rotation of the legs in backbending occurs in the upper thigh, not the knees.
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. For more information, visit http://www.chuckandmaty.com.