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° and 90° 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° at 30° of knee flexion and 11.88 ± 4.03° at 90° of knee flexion. In the sequential dial test performed with the tibia reduced, the mean side-to-side difference was 15.94 ± 4.17° (p < 0.05) at 30° of knee flexion and 16.88 ± 4.42° (p = 0.001) at 90° of knee flexion. The mean tibial external rotation was 5.31 ± 2.86° and 6.87 ± 3.59° higher in the reduced position than in the posterior subluxation at both 30° and 90° 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.