Many people’s knees squeak, crack, or crackle, a phenomenon known as crepitus. Most of the time, it’s no big deal at all. But a loud popping sound accompanied by pain and swelling indicates an injury.

Joints often crack due to harmless gas bubbles in fluid or tendons moving over bones. While usually normal, persistent pain, swelling, or stiffness could signal arthritis or injury. Staying active, ...