Which ligament is most likely injured in a patient who hyperextended the knee and heard a pop?

The anterior cruciate ligament (ACL) is the structure most often injured during a hyperextension injury of the knee, especially when a patient reports hearing a popping sound at the time of injury. The ACL is vital for stabilizing the knee joint, particularly during activities that involve sudden stops, changes of direction, and jumping.

When the knee is forced into hyperextension, the ACL is put under significant tension, leading to tears. The accompanying sensation of a "pop" is commonly reported when such injuries occur, signaling a potential rupture of the ligament. Hyperextension movements often compromise the integrity of the ACL more than other ligaments, which typically would be affected by different mechanisms of injury, such as twisting or lateral impacts.

Injuries to the medial collateral ligament and lateral collateral ligament primarily occur from valgus or varus stress, respectively, while the posterior cruciate ligament injuries often result from direct trauma to the front of a bent knee or excessive force applied to the knee while in a flexed position. Thus, the presentation of hyperextension and a popping sound strongly indicates an ACL injury.