My knee hurts so bad i can't even stand on it it is not swollen but it throbs and has a sharp knife pain what could it be ?

Internal drgmt: Obviously it is hard to be sure. But is sounds like a possible meniscal tear which could be catching in the knee. Sometimes there is not much swelling or obvious injury. Suggest orthopedic exam and possible MRI scan.

Knee pain: The causes of such pain vary with your age. Among adults causes of sharp knee pain without swelling include a specific bursitis (pes anserine), which would be located below the knee joint on the inner side. A plica syndrome where the joint capsule folds up and gets pinched by the large bones in the joint. A torn cartilage can cause buckling of the knee with sharp pain. & knee cap inflammation.