What Causes Knee Pain While Climbing Stairs?

I am a dance teacher. I dance 8-10 hours per day. I kneeled into the floor with my left knee and heard a crunch sound. The center, top, (above my knee cap) of my left knee has hurt ever since. (3 weeks. ) It is especially painful to walk up stairs, and landing jumps. Squatting, (plea) hurts a little, but not like climbing stairs or landing a jump. I don t feel it at all with Basic walking, turning.