Evaluation of the Reliability of the Dial Test for Posterolateral Rotatory Instability: A Cadaveric Study Using an Isotonic Rotation Machine

Purpose: The purpose of our study was to evaluate the reliability of the dial test by assessing the correlation between the severity of posterolateral corner injuries and the amount of external rotation of the tibia. Methods: Fourteen paired cadaveric legs were fixed into a custom-made isotonic rotation machine with the knee flexed at 30°. For group I (7 right knees), the lateral collateral ligament, popliteofibular ligament, popliteus tendon, and posterior cruciate ligament (PCL) were cut serially. For group II (7 left knees), the PCL, lateral collateral ligament, popliteofibular ligament, and popliteus tendon were cut. The external rotation angles were measured with a 6-Nm rotational torque. Results: For group I, the mean increase in the external rotation angle after cutting of the 3 posterolateral ligament structures was 17.9° ± 6.4°. The additional increase in mean external rotation after cutting of the PCL was 4.7° ± 2.1°. For group II, the mean increase in the external rotation angle after cutting of the PCL was 8° ± 4°. Cutting the 3 posterolateral ligament structures increased the external rotation by 10.7° ± 5.3°. The increase in external rotation was significant in group I after cutting of the 3 posterolateral structures and in group II after cutting of the PCL and 2 posterolateral structures (P = .05, Duncan test). Conclusions: The dial test may be a valuable diagnostic method in cases of injury to 3 posterolateral structures or combined injuries to the PCL and 2 posterolateral structures. However, posterolateral instability with injuries to only 1 or 2 posterolateral structures may not be clinically detected by the dial test. Clinical Relevance: In the case of posterolateral instability with only 1 or 2 structure injuries, comprehensive diagnostic methods including the patient's history, other physical examinations, radiographs, and magnetic resonance imaging should be used to diagnose posterolateral rotatory instability.