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.