Suggest Treatment For Sharp Pain In Knee While Walking

I am trying to figure out what is wrong with my knee. Symptoms: Sharp pain when walking down stairs or down hill; the best way to describe it woud be trying to slow motion walk down stairs I get a sharp pain in the front of the knee, like the patella. The only tramatic event I can think of was a impact into hard pack snow while snow boarding that happened 6 years ago, but I didn't notice any problem imediately. It was up to a year or more later before I started noticeing the symptom.