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.

Genu valgum, or knock-knee, is a condition where the knees touch but the ankles do not. It appears most frequently in young children. Depending on the cause, treatment can include medication, exercise ...