The dial test is a clinical examination test that is performed to diagnose posterolateral instability due to posterolateral corner injury, with or without posterior cruciate ligament (PCL) injury.
There are three main structures of the posterolateral corner. They are the lateral collateral ligament (LCL), the popliteofibular ligament, and the popliteus tendon.
Isolated injuries of the posterolateral corner are rare, and often cause instability and varus thrust. By performing the dial test, you can detect if there is any isolated injury of the posterolateral corner of the knee. When the posterolateral corner injury is a combined injury, the combined injury with the posterior cruciate ligament injury is more common than the combined injury with the anterior cruciate ligament injury. Failure to identify the posterolateral corner injury combined with injury to the ACL will lead to failure of ACL reconstruction. Therefore, it is important to properly diagnose this injury! Injury to the posterolateral corner should be suspected when there is a positive reverse pivot shift test and a negative posterior drawer test. This means that the posterolateral corner is injured and the posterior cruciate ligament is NOT injured.
Imaging
There may be an avulsion fracture of the fibula called an arcuate fracture, which can be detected on x-ray images.
Longstanding radiographs are important to evaluate the alignment of the extremity. The patient may have a bony varus, but also ligamentous varus in addition to the bony varus. The ligamentous varus can come from injury to the lateral collateral ligament, and an occult injury can come from the posterolateral corner.
MRI is a great study to diagnose the posterolateral corner injury and also to check for a combined injury, especially the PCL.
Performing the Dial Test
The dial test can be performed with the patient in the supine or the prone position. Some physicians prefer to perform the test in the prone position. The thigh needs to be supported during the dial test so that is does not move, especially while performing in the supine position. Both knees are put into 30 degrees of flexion and 90 degrees of flexion positions. The tibia is then passively externally rotated on the femur, which is done by applying external rotation force to both feet. The amount of external rotation to both lower extremities is measured at the ankles.
Testing the injured extremity at 30 degrees of flexion is done to diagnose injury to the posterolateral corner. The dial test done at 90 degrees of flexion at the knee will test the posterior cruciate ligament for injury. The external rotation is then assessed to compare the right and the left side. A difference in sides of 10 degrees or more of external rotation indicates that the test is positive and that there is a significant injury.10 degrees of external rotation asymmetry at 30 degrees and 90 degrees of flexion of the knee is consistent with posterolateral corner AND posterior cruciate ligament combined injury. However, and increase of external rotation at 30 degrees, but not at 90 degrees, of flexion indicates an injury to the posterolateral corner only.
A proximal tibial osteotomy should be done for the bony varus of the knee before reconstruction of the posterolateral corner, otherwise the reconstruction will fail. Additionally, a long leg standing x-ray should always be obtained before performing surgery to check if the varus is primary or secondary.
