Symptoms and Signs of Torn Anterior Cruciate Ligament
(Torn ACL or ACL Injury)

Medical Author:
Medically Reviewed on 3/11/2019

Doctor's Notes on Torn Anterior Cruciate Ligament
(Torn ACL or ACL Injury)

ACL is an abbreviation for interior cruciate ligament, the most commonly injured knee ligament that helps to stabilize the knee. A torn ACL means the fibers that make up the ligament are broken or torn. Signs and symptoms are straightforward: the patient usually hears a loud popping sound as the ligament tears – pain is almost immediate in the knee and the knee swells within an hour or two. Walking becomes difficult and the knee feels unstable - the patient may have difficulty in extending or straightening the knee.

Causes of a torn ACL usually involve changing direction quickly, making a sudden stop or landing hard from a jump. In contact sports like football, the foot is usually planted and the knee is hyperextended and pivots at the same time causing the ACL to break and tear. Because of their anatomy, females are at higher risk for a torn ACL.


Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.