In a posterior-stabilized knee design, what is substituted to achieve stability?

• A. The posterior cruciate ligament with a femoral post–cam mechanism
• B. The medial collateral ligament with a tibial tether
• C. The lateral meniscus with a ball-and-socket
• D. The patella with a polyethylene dome

Answer: (A)

The main idea is that stability in a posterior-stabilized knee is provided by a mechanical substitute for the posterior cruciate ligament. In this design, the posterior cruciate ligament is removed and a femoral post–cam mechanism takes its place. As the knee flexes, the cam on the back of the femoral component engages a post on the tibial insert, producing controlled femoral rollback and stabilizing the joint in the sagittal plane. This mimics the stabilizing role of the PCL during flexion and helps prevent excessive anterior movement of the femur relative to the tibia, enabling good range of motion without the native PCL. Other structures like the ligaments or patellofemoral joint aren’t the substitute mechanism here; the post–cam system is specifically designed to replace the PCL’s function in this knee design.