The dial test is performed to diagnose posterolateral instability due to posterolateral corner injury with or without a PCL injury.
Isolated injuries of the posterolateral corner are rare and often cause instability and varus thrust. By performing the Dial test, you can detect whether there is an isolated or combined injury of the posterolateral corner of the knee. Usually this injury is combined with a cruciate ligament injury (more with the PCL than the ACL).
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! This means that the posterolateral corner is injured and the posterior cruciate ligament is not injured. MRI is the diagnostic study of choice for this injury.
How do you perform the Dial test?
The dial test is performed with the patient in the supine or prone position with both knees in 30° and 90° of flexion. It is preferable to perform the test in the prone position. Support the thigh in position if you are going to perform the test in the supine position. An external rotational force is then applied to both feet. The amount of external rotation to both lower extremity is measured at both ankles. Testing of the injured extremity in 30° of flexion is done to determine injury to the posterolateral corner. Flexion at the 90° angle will test the posterior cruciate ligament (PCL) for injury. More than 10° of external rotation indicates a significant injury. More than 10° of external rotation asymmetry at 30° and 90° is consistent with PLC and PCL injury.
Proximal medial open wedge tibial osteotomy should be done for primary varus of the knee before reconstruction of the PLC, otherwise reconstruction will fail. Obtain a long leg standing x-ray before surgery to check if the varus is primary or secondary.