The Posterior Sag Test, also known as Godfrey’s Test, is another clinical examination procedure used to assess the integrity of the posterior cruciate ligament (PCL) in the knee.
The PCL is crucial for stabilizing the knee by preventing the tibia (shinbone) from moving backwards under the femur (thighbone). This test specifically looks for a sign called the “posterior sag,” indicating that the tibia has sagged or dropped backwards due to a compromised PCL.
How the test is performed:
- Patient Positioning: The patient lies flat on their back (in the supine position). The knee in question is flexed (bent) to 90 degrees, and the hip is also flexed to 90 degrees. This can be achieved by the examiner lifting the patient’s leg by the heel, so the sole of the foot faces upwards, perpendicular to the examination table.
- Examination: The examiner observes the position of the tibia relative to the femur from the side. In a healthy knee, the tibia should be aligned with or slightly anterior (forward) to the femur’s position due to the support provided by the intact PCL.
- Identifying Posterior Sag: The key indicator in this test is the presence of a “sag” or backward drop of the tibia relative to the femur. If the PCL is injured or insufficient, gravity will cause the tibia to sag posteriorly (backwards) because the ligament is not adequately supporting it against the pull of gravity.
- Interpreting the Results: A visible posterior sag indicates a potential PCL injury. The absence of a sag suggests that the PCL may be intact.
This test is valued for its simplicity and the minimal discomfort it causes the patient. However, like the posterior drawer test, the posterior sag test should be part of a comprehensive knee assessment. The results are considered alongside other tests, patient history, and symptoms to accurately diagnose the condition of the PCL. Since accurately interpreting these signs requires expertise, these tests should be performed by a trained healthcare provider.
