The knee joint relies heavily on the anterior cruciate ligament (ACL) to maintain stability. Positioned at the center of the knee joint, the ACL is a robust ligament that runs from the femur to the tibia. However, if the ACL sustains a tear, it cannot regenerate on its own and often causes a sensation of instability in the knee.
An injury to the ACL usually arises from sports activities that require abrupt movements or excessive knee extension. The following scenarios can lead to an ACL injury:
Typically, an ACL injury results in a clear "pop" sound and a feeling of knee instability. Swelling in the knee due to bleeding within the torn ligament may occur within hours of the injury. The knee may feel weak and susceptible to giving way, especially when changing direction.
A comprehensive physical examination of the knee, as well as diagnostic tests like X-rays (to rule out fractures), MRI scans, and arthroscopy, can aid in diagnosing an ACL injury. Furthermore, doctors often conduct the Lachman's test to determine if the ACL is intact. In a knee with a torn ACL, the Lachman's test may reveal increased forward movement of the tibia and a soft or mushy endpoint, in contrast to a healthy knee.
Another method to assess ACL tears is the pivot shift test. During this test, if the ACL is torn, the tibia may shift forward when the knee is completely straight, but then move back into place as the knee bends beyond 30° in relation to the femur.
