I tore cartilage in my knee, should i go see a doctor at a er?

See an orthopedist: If you know you have a torn cartilage or meniscus, presumably by an MRI or other imaging, i'd recommend you schedule a consultation with an orthopedic surgeon to discuss treatment options. An er physician will only be able to give you a brace/splint, some meds and then likely refer you to an orthopedist. If your insurance allows, i'd bypass the er doc.