Which sign is a better test for a PCL tear, assessing posterior tibial displacement with both knees flexed 90 degrees?

• A. Posterior Sag Sign
• B. Lachman Test
• C. Anterior Drawer Test
• D. Patellar Grind Test

Answer: (A)

When the posterior cruciate ligament is torn, it loses its restraint against backward movement of the tibia. With the knee flexed to 90 degrees, gravity makes the tibia sag posteriorly if the PCL is deficient, so the tibias drop back relative to the femur. This is observed as the posterior sag sign (Godfrey sign) and is specifically useful for detecting PCL injuries because it directly demonstrates posterior tibial displacement under load at 90 degrees of knee flexion.

Tests that focus on the ACL, like Lachman or Anterior Drawer, look for forward translation of the tibia and are not designed to reveal PCL laxity. The Patellar Grind Test examines patellofemoral joint issues rather than cruciate ligaments. Therefore, the posterior sag sign best demonstrates a PCL tear by showing posterior tibial displacement when both knees are flexed at 90 degrees.