Posterior Sag Sign (or Gravity Drawer Test) is used to assess the integrity of the posterior cruciate ligament of knee (PCL tears).
It’s also called Godfrey Sign.
How do you do Posterior Sag Sign?
The patient lies in the supine position with the knees flexed to approximately 90 degrees and the legs supported under the lower calf/ heel by the clinician’s arm.
The clinician assesses the contour of the tibial tuberosities.
What does a positive Posterior Sag Sign mean?
Positive sign when the affected tibia sags posteriorly compared to the unaffected knee.
If there is a rupture (partial) of the PCL, the tibial tuberosity on the involved side will be less visible than that on the noninvolved side.
This discrepancy is caused by an abnormal posterior translation, resulting from a rupture of the PCL.
Sensitivity & Specificity
This test may have some value as a screening test when negative due to its high sensitivity:
Sensitivity: 79 %
Specificity: 100 %
In cases of doubt, the patient can be asked to contract the hamstrings slightly by pushing the heels into the clinician’s arm. This maneuver usually results in an increase in the posterior translation of the tibia and is often performed as a quick test of the integrity of the PCL.
Posterior sag sign can be shown by passive elevation of the leg in a fully extended position of knee, with the examiner applying the elevating force at the ankle. The test is interpreted as positive sag sign, if the tibia falls back on the femur in case of PCL insufficiency
Gravity Sign and Genu Recurvatum Test
The patient lies supine with the hip and knee of the affected leg flexed 90°. With one hand, the examiner grasps the patient’s lower leg while stabilizing the knee proximal to the patella with the other hand. The examiner then abruptly pulls away the stabilizing hand from the knee.
If the posterior cruciate ligament is torn, the tibia will recede posteriorly (posterior droop).
In the genu recurvatum test, the extended leg is lifted. A torn posterior cruciate ligament will result in a posterior drop of the tibia.
Quadriceps Contraction Test
Quadriceps Contraction Test is a similar test used to assess the posterior cruciate ligament injury.
The patient is supine. The injured leg is flexed 90° at the knee and placed in external rotation. The patient is asked to tense the quadriceps and lift the leg on the examining table.
In the presence of posterolateral instability, the external rotation of the foot causes posterior subluxation of the lateral tibia relative to the lateral femoral condyle. The examiner observes this as a posterior drop of the lateral tibial plateau. The active quadriceps contraction and increasing knee extension cause the lateral tibial plateau to move anteriorly out of posterior subluxation and into reduction with a sort of reverse pivot shift. The joint reduces at about 30 to 20° of flexion. This test is also called an active reduction test and can usually be demonstrated only in the presence of chronic ligament injuries.
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. Am J Sports Med. 1994 Jul-Aug;22(4):550-7. doi: 10.1177/036354659402200419. PMID: 7943523.