Health Tip: Hear a Pop in Your Knee?

(HealthDay News) -- The knee's anterior cruciate ligament (ACL) can be stretched or torn during activities that strain the knee.

A torn ACL may require extensive therapy or surgery to repair it.

Here are primary symptoms of a torn ACL, courtesy of the U.S. National Library of Medicine:

• A loud popping noise as the knee it hit or twisted.
• Immediate, severe pain in the knee.
• Significant swelling of the knee in fewer than six hours after the injury.
• Difficulty walking or standing, and general weakness of the knee.