Posterior Tibial Translation Measurements on Magnetic Resonance Imaging Improve Diagnostic Sensitivity for Chronic Posterior Cruciate Ligament Injuries and Graft Tears.

BACKGROUND: Magnetic resonance imaging (MRI) of the knee is a highly sensitive and specific method for diagnosing acute posterior cruciate ligament (PCL) tears, with a reported accuracy of 96% to 100%. In chronic and revision settings, these injuries may be missed on MRI because of the apparent continuity of nonfunctional PCL fibers. Posterior tibial translation (PTT) of the medial compartment has been identified as a potential secondary finding of PCL tear on routine MRI. Purpose/Hypothesis: The purpose of this study was to evaluate the sensitivity of PTT on MRI associated with PCL injuries and compare it with the sensitivity of a radiologist's MRI interpretation with preoperative posterior knee stress radiographs as the gold standard. Our hypothesis was that the MRI measurement of PTT of the medial compartment would improve diagnostic sensitivity as compared with the diagnosis made by the interpreting radiologist's evaluation of the continuity of the PCL fibers for chronic and postrecostruction graft injuries. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 2. METHODS: Cases of patients who underwent a primary or revision PCL reconstruction, without anterior cruciate ligament injury, by a single surgeon between 2010 and 2016 were retrospectively analyzed. Measurements of medial and lateral compartment PTT were performed with the MRI of PCL-injured cases and controls without clinical or MRI evidence of ligamentous injury. The sensitivity of this technique was compared with the preoperative MRI diagnosis determined by review of the musculoskeletal radiologist's report and confirmed by the gold standard of posterior knee stress radiographs. The sensitivity of medial compartment PTT was determined by receiver operator characteristic (ROC) analysis and compared with the MRI sensitivity for chronic PCL and PCL graft tears. RESULTS: One hundred patients (80 males and 20 females) with a mean age of 31.1 years (range, 15-66 years) met the inclusion criteria: 57 acute primary tears, 32 chronic primary, and 11 PCL graft tears. MRI sensitivity was 100% for acute primary PCL tears, 62.5% for chronic primary PCL tears, and 18.1% for PCL graft tears. There were significant differences in medial compartment PTT on MRI for acute versus chronic injuries ( P = .025) and acute versus graft injuries ( P = .007). ROC curve analysis indicated that the most accurate cutoff point for the detection of chronic PCL tears was 2.0 mm of medial compartment PTT on MRI, with a sensitivity and specificity of 0.80 and 0.89, respectively. For PCL graft injuries, the ROC curve indicated that the most accurate medial compartment PTT cutoff for the detection of PCL graft failure was 3.6 mm (sensitivity, 0.92; specificity, 0.72). CONCLUSION: MRI evaluation of the PCL fibers had poor sensitivity for chronic PCL tears and PCL reconstruction graft tears. The sensitivity for diagnosing chronic PCL tears and PCL reconstruction graft failures was improved by measuring posteromedial tibial translation.