Evaluating posterior cruciate ligament injury by using two-dimensional ultrasonography and sonoelastography

Purpose: This study aimed to elucidate the diagnostic criteria for posterior cruciate ligament (PCL) injury using ultrasonography. Methods: Thirty-three patients with clinically suspected PCL injuries and 30 normal control subjects were recruited. Both groups were assessed using sonographic examination with reliability testing. Patients also underwent posterior stress radiography and magnetic resonance imaging (MRI). PCL thickness on two-dimensional ultrasonography (2D US), pixel intensity on sonoelastography, displacement on posterior stress view, and severity grading using MRI were analysed. Receiver operating characteristic (ROC) curves were plotted using MRI as the gold standard. Correlation coefficients among variables were calculated. Results: Good to excellent reliabilities were noted for 2D US and red pixel intensity on sonoelastography. In injured knees, PCL thicknesses were significantly greater, and red pixel intensities were significantly lower, compared to non-injured knees of patients and healthy controls. This indicates increased swelling and softness in injured PCLs. The area under the PCL thickness ROC curve was 0.917 (p < 0.001), and the best diagnostic criterion was a thickness ≥6.5 mm (90.6 % sensitivity and 86.7 % specificity). Thickness correlated with red pixel intensity, International Knee Documentation Committee examination grade, and MRI severity grading. In addition, effusions were detected on 2D US in all knees with “tears” of other structures on MRI. Conclusions: 2D US is a useful tool to diagnose PCL injury, and PCL thickness ≥6.5 mm is the recommended diagnostic criterion. Level of evidence: II.