Posterior Sag Sign
Purpose: To assess for integrity of the PCL.
Test Position: Supine.
Performing the Test: Have the patient's involved limb in a position of 45 degrees hip flexion and 90 degrees of knee flexion. Look for the tibia to "sag" compared to the position of the femur.
Diagnostic Accuracy: Sensitivity: .79; Specificity: 1.0; +LR: 79; -LR: .21 ("The accuracy of the clinical examination in the setting of posterior cruciate ligament injuries").
Importance of Test: The posterior cruciate ligament is responsible for resisting against excessive posterior translation of the tibia on the femur, due to its attachments on posteriorly on the tibial plateau and anteriorly on the lateral side of the medial femoral condyle ("Neumann 536"). In the position of 45 degrees of hip flexion and 90 degrees of knee flexion, gravity places a force on the tibia that pulls the tibia posteriorly, but is blocked by an intact PCL. In the absence of a PCL, the tibia appears to "sag." The most common mechanism for PCL injury is posterior translation at 90 degrees of knee flexion. While the PCL can be ruptured through hyperextension and hyperflexion as well, it is unlikely that it is the only ligament torn in these injuries. The ACL has been found to be stressed more than the PCL in both hyperflexion and hyperextension (Ellenbecker, 2000).
Note: these tests should only be used by properly trained health care practitioners
Test Position: Supine.
Performing the Test: Have the patient's involved limb in a position of 45 degrees hip flexion and 90 degrees of knee flexion. Look for the tibia to "sag" compared to the position of the femur.
Diagnostic Accuracy: Sensitivity: .79; Specificity: 1.0; +LR: 79; -LR: .21 ("The accuracy of the clinical examination in the setting of posterior cruciate ligament injuries").
Importance of Test: The posterior cruciate ligament is responsible for resisting against excessive posterior translation of the tibia on the femur, due to its attachments on posteriorly on the tibial plateau and anteriorly on the lateral side of the medial femoral condyle ("Neumann 536"). In the position of 45 degrees of hip flexion and 90 degrees of knee flexion, gravity places a force on the tibia that pulls the tibia posteriorly, but is blocked by an intact PCL. In the absence of a PCL, the tibia appears to "sag." The most common mechanism for PCL injury is posterior translation at 90 degrees of knee flexion. While the PCL can be ruptured through hyperextension and hyperflexion as well, it is unlikely that it is the only ligament torn in these injuries. The ACL has been found to be stressed more than the PCL in both hyperflexion and hyperextension (Ellenbecker, 2000).
Note: these tests should only be used by properly trained health care practitioners
References:
Ellenbecker, Todd. Knee Ligament Rehabilitation. Philidelphia, PA: Churchill Livingstone. 20-21. Print
Neumann, Donald. Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation. 2nd edition. St. Louis, MO: Mosby Elsevier, 2010. 336. Print.
Rubinstein RA, Jr., Shelbourne KD, McCarroll JR, VanMeter CD, Rettig AC. "The accuracy of the clinical examination in the setting of posterior cruciate ligament injuries." The American journal of sports medicine. Jul-Aug 1994; 22(4):550-557.
Ellenbecker, Todd. Knee Ligament Rehabilitation. Philidelphia, PA: Churchill Livingstone. 20-21. Print
Neumann, Donald. Kinesiology of the Musculoskeletal System: Foundations for Rehabilitation. 2nd edition. St. Louis, MO: Mosby Elsevier, 2010. 336. Print.
Rubinstein RA, Jr., Shelbourne KD, McCarroll JR, VanMeter CD, Rettig AC. "The accuracy of the clinical examination in the setting of posterior cruciate ligament injuries." The American journal of sports medicine. Jul-Aug 1994; 22(4):550-557.
