Posterior Sag Sign
Original Editor - Matt Huey
Top Contributors - Uchechukwu Chukwuemeka, Matt Huey and Jess Bell
Introduction
The posterior sag sign, also known as the Godfrey’s test is a special test for a rupture of the posterior cruciate ligament (PCL) which commonly occurs with a "dashboard injury" where there is a posterior force applied to the tibia when the knee is in a flexed position. It examines the posterior tibiofemoral joint stability. Also is could be regarded as a passive form of the Muller's test as it requires only visual observation without any movement after placing the foot at the starting position for the test.
The earliest description of this test was reported in a case study by Dr. A. W. Mayo Robson, which involved a miner who was involved in an accident that tore both cruciate ligaments.[1] He writes, " When the muscles were braced up, the bones were in good position, but as soon as the muscles relaxed, the tibia fell backwards until stopped by the ligamentum patellae. On manipulation, the head of the tibia could be brought forward in front of the femur."
Technique
This test is relatively simple to perform and is a passive observation for excessive posterior displacement of the tibia relative to the contralateral side:
- Patient lies in the supine position
- The hip is placed in 45 degrees of flexion, along with the knee in 90 degrees of flexion, with the foot on the table
- Observe the position of the tibia
The video below gives a further visual depiction of this test
[2] If the PCL is ruptured, the tibia will sit more posteriorly. The tibia is normally approximately 1 centimetre anterior to the femoral condyle. This is due to the origin of the PCL on the anterolateral aspect of the medial femoral condyle within the notch and attaches to the posterior aspect of the tibial plateau.
Evidence
There is relatively little evidence on this test. Malanga et al observed that the posterior drawer test is quite sensitive and specific, although it is further improved by the existence of a posterior sag sign.[3] Another study by Rubinstein et al.[4] performed a series of tests for ACL and PCL tears with varying grades (Grade I, II, III). For PCL tears, using posterior drawer test, the overall sensitivity was 70%, and the specificity was 99% for low-grade tears. The sensitivity increased to 97%, and the specificity remained 100% for higher-grade tears. But for the posterior sag sign, their sensitivity was 79%, and the specificity was 100%.
References
- ↑ Robson, A. M. (1903). VI. Ruptured crucial ligaments and their repair by operation. Annals of surgery, 37(5), 716.
- ↑ Educom Continuing Education. Posterior Sag Sign. Available from: http://www.youtube.com/watch?v=nkXyNvMjxHQ[last accessed 8/6/2025]
- ↑ Malanga GA, Andrus S, Nadler SF, McLean J. Physical examination of the knee: a review of the original test description and scientific validity of common orthopedic tests. Arch Phys Med Rehabil. 2003;84:592-603.
- ↑ Rubinstein, R. A., Shelbourne, K. D., McCarroll, J. R., VanMeter, C. D., & Rettig, A. C. (1994). The Accuracy of the Clinical Examination in the Setting of Posterior Cruciate Ligament Injuries. The American Journal of Sports Medicine, 22(4), 550–557.