The Influence of Tibial Positioning on the Diagnostic Accuracy of Combined Posterior Cruciate Ligament and Posterolateral Rotatory Instability of the Knee

BACKGROUND To determine if tibial positioning affects the external rotation of the tibia in a dial test for posterolateral rotatory instability combined with posterior cruciate ligament (PCL) injuries. METHODS Between April 2007 and October 2007, 16 patients with a PCL tear and posterolateral rotatory instability were diagnosed using a dial test. The thigh-foot angle was measured at both 30 degrees and 90 degrees of knee flexion with an external rotation stress applied to the tibia in 2 different positions (reduction and posterior subluxation). The measurements were performed twice by 2 orthopedic surgeons. RESULTS In posterior subluxation, the mean side-to-side difference in the thigh-foot angle was 11.56 +/- 3.01 degrees at 30 degrees of knee flexion and 11.88 +/- 4.03 degrees at 90 degrees of knee flexion. In the sequential dial test performed with the tibia reduced, the mean side-to-side difference was 15.94 +/- 4.17 degrees (p < 0.05) at 30 degrees of knee flexion and 16.88 +/- 4.42 degrees (p = 0.001) at 90 degrees of knee flexion. The mean tibial external rotation was 5.31 +/- 2.86 degrees and 6.87 +/- 3.59 degrees higher in the reduced position than in the posterior subluxation at both 30 degrees and 90 degrees of knee flexion. CONCLUSIONS In the dial test, reducing the tibia with an anterior force increases the ability of an examiner to detect posterolateral rotary instability of the knee combined with PCL injuries.