Which ligaments are primarily involved when testing for sagittal plane stability of the knee?

The primary ligaments involved in testing for sagittal plane stability of the knee are indeed the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). These two ligaments play crucial roles in stabilizing the knee joint during movement in the sagittal plane, which involves flexion and extension.

The ACL is responsible for preventing anterior translation of the tibia relative to the femur and also provides stability against hyperextension. Conversely, the PCL functions to prevent posterior translation of the tibia and also helps in stabilizing the knee during flexion. When assessing sagital plane stability, assessing the integrity and function of both the ACL and PCL is essential, as they work together to maintain the knee's alignment and movement in this plane.

While other ligaments, such as the collateral ligaments, contribute to knee stability, their primary role is in stabilizing the knee in the frontal plane during movements like side-to-side motions rather than in flexion and extension. This distinction clarifies why the combination of the ACL and PCL is correct for evaluating sagittal plane stability.