When i bend my knee it hurts in front?

Likely knee cap wear: The most common and likely cause of pain in front of the knee is an irritated or early wear of the knee cap cartilage or the surface cartilage of the thigh bone that it rubs. Other causes could include a meniscus tear, plica, patellar tendonitis etc. Some fluid build up in the knee causes cracking. Try therapy, antiinflammatories, ice and sometimes a knee sleeve. See orthopedist.