Which sign is commonly positive in PCL injuries on exam?

Which sign is commonly positive in PCL injuries on exam?

• A. Posterior sag sign
• B. Pad test
• C. Medial clear space sign
• D. Posterior drawer sign

Answer: (A)

The sign most commonly positive with a PCL injury is the posterior sag sign. When the knee is flexed to about 90 degrees and the patient is relaxed, gravity pulls the tibia backward if the PCL is torn, causing the tibia to sag posteriorly relative to the femur. This gravity-driven translation is a direct result of the loss of the PCL’s posterior restraint and is often readily observed or felt, making it a reliable bedside indicator. The posterior drawer sign also tests for posterior tibial translation, but it relies on applying a posterior force and can be influenced by hamstring guarding or patient effort, so it isn’t as consistently positive in isolated PCL tears as the sag sign. The pad test assesses joint effusion rather than ligament integrity, and the medial clear space sign is a radiographic finding related to other knee structures, not a typical exam sign of PCL injury.

The sign most commonly positive with a PCL injury is the posterior sag sign. When the knee is flexed to about 90 degrees and the patient is relaxed, gravity pulls the tibia backward if the PCL is torn, causing the tibia to sag posteriorly relative to the femur. This gravity-driven translation is a direct result of the loss of the PCL’s posterior restraint and is often readily observed or felt, making it a reliable bedside indicator.

The posterior drawer sign also tests for posterior tibial translation, but it relies on applying a posterior force and can be influenced by hamstring guarding or patient effort, so it isn’t as consistently positive in isolated PCL tears as the sag sign. The pad test assesses joint effusion rather than ligament integrity, and the medial clear space sign is a radiographic finding related to other knee structures, not a typical exam sign of PCL injury.