Background: The posterior cruciate ligament (PCL) is the primary restraint to posterior tibia translation, which is difficult to determine by physical examination because manual assessment is imprecise, subjective, and not reproducible. The stress radiographic device (SRD) was developed to objectively measure these displacements.

Objective: To assess the accuracy of SRD and determine correlations between the results of SRD and magnetic resonance imaging (MRI) in PCL tear and healthy PCL.

Materials and Methods: Forty-nine knees with MRI-confirmed diagnosis of PCL-tear or healthy PCL were examined. The SRD was applied with a 90-newton posterior force in the 90 degrees knee flexion position. The present study determined the distance of the most posterior part of the medial femoral condyle and the tibia plateau that was projected perpendicular to the medial tibia articular line from lateral radiography (posterior femoral-tibia distance, PFTD).

Results: The present study examined 49 knees, 25 healthy PCLs and 24 complete-tear PCLs diagnosed by MRI. The mean PFTD measured by the stress radiograph was 15.78±4.65 mm (range 6.68 to 25.02 mm) in PCL tears and 2.42±2.32 mm (0 to 7.07 mm) in healthy PCLs, and these figures were significantly different. There was a strong correlation between the results obtained from the SRD and those found using MRI in diagnosing PCL tear. Using the SRD with a 9 mm cut-off point of PFTD for diagnosis of complete rupture of PCL, the accuracy was 97.96%, sensitivity 95.83%, specificity 100%, PPV 100%, and NPV 96.15%.

Conclusion: The SRD is a useful tool for diagnosis of PCL tear with high levels of accuracy (97.96%), sensitivity (95.83%), and specificity (100.00%). The SRD is highly reliable and reproducible, and the results obtained using SRD and MRI have a strong correlation in diagnosis of PCL tear. The SRD is cheap and easy to use with simple radiography. Therefore, it is an appropriate tool for use in screening for diagnosis of PCL-tear knees.

Keywords: Posterior cruciate ligament tears, Posterior tibia translation, Stress radiographic device