Which sign is used to evaluate PCL pathology by assessing the tibia sag in knee flexion?

Which sign is used to evaluate PCL pathology by assessing the tibia sag in knee flexion?

• A. Thessaly sign
• B. Joint line tenderness
• C. Posterior sag sign
• D. McMurray test

Answer: (C)

The sign tests the PCL’s ability to prevent posterior movement of the tibia. When the knee is flexed to about 90 degrees, gravity should keep the tibia in line with the femur. If the PCL is torn, the tibia sags backward relative to the femur, producing a posterior sag sign. This makes it a targeted indicator of PCL injury rather than a test for meniscal issues or joint tenderness, which are suggested by signs like the Thessaly test, joint line tenderness, or the McMurray test.

The sign tests the PCL’s ability to prevent posterior movement of the tibia. When the knee is flexed to about 90 degrees, gravity should keep the tibia in line with the femur. If the PCL is torn, the tibia sags backward relative to the femur, producing a posterior sag sign. This makes it a targeted indicator of PCL injury rather than a test for meniscal issues or joint tenderness, which are suggested by signs like the Thessaly test, joint line tenderness, or the McMurray test.