Hyperextension of the knee is when the knee joint is forced to extend beyond its normal range of motion. In these instances, a large amount of stress is put upon one or more of the four major ligaments of the knee joint.

A hyperextended knee is a common injury among athletes across a wide variety of sports. The severity of the condition can vary. In most cases, hyperextension of the knee will have obvious symptoms, including swelling, reduced range of motion, sharp localized pain, and instability on the affected leg.