Dean Lerner's reply:
There are different kinds of pain, and we must discriminate between the good and the bad. Good pain might be experienced as an intense stretching of fibers. When the posture is released, the student feels relief and a positive sensation, such as increased circulation and freedom or spaciousness. A bad pain may be felt as a sharp, biting sensation or strain created by some imbalance, misalignment, compression, or pinching of a nerve. This may result in irritation of a joint or fibers. The pain you are describing falls into the second category and therefore should be avoided.
Complaints of inner knee pain in Trikonasana are not uncommon. Unless there is a pre-existing injury, the pain comes from misalignment and improper extension, and from the knee moving laterally from the outside inward, straining the inner knee. To alleviate and prevent this problem, see that the root of the big toe, the center of the heel, and especially the center outer edge of the front foot all press firmly down, and from the outer knee draw straight up into the hip socket. See that the inner ankle bone is well lifted and does not collapse inward. These actions will correctly align the front leg and knee and remove the strain. If this is ineffective, try turning the front foot considerably out to help increase the external rotation of the top leg, and then, again, draw the leg up into the socket.
In Upavistha Konasana, move the top corners of the knees deep in and upward in order to avoid knee pain. See that the toes, the center of the kneecaps, and the center of the top thighs are facing straight up toward the ceiling, not rolling out as they do among many beginners. Firmly draw the quadriceps (the top, front thigh muscles) in toward the thighbones and up toward the hips, and simultaneously ground the femurs and extend the legs through the ballpoints of the feet. Try these actions—both the correct and the incorrect ones—on yourself before you have your students try them.
Certified Advanced Iyengar instructor Dean Lerner is co-director of the Center for Well-being in Lemont, Pennsylvania and teaches workshop across the United States. He is a longtime student of B.K.S. Iyengar and served a four-year term as president of the Iyengar National Association of the United States. Known for his ability to teach yoga with clarity and precision, as well as warmth and humor, Dean has conducted teacher training classes at Feathered Pipe Ranch in Montana and other locations.