Radiographic Evaluation of Meniscal Extrusion

Background Magnetic resonance imaging (MRI) is well established as the preferred noninvasive tool for meniscal evaluation. To our knowledge, there has been no study examining the utility of diagnosing meniscal extrusion from radiography alone. We hypothesize that with appropriate window settings, meniscal extrusion may be diagnosed on radiography with high sensitivity and specificity. Materials and methods We included 190 patients with MRI of the knee performed within three months of knee radiography. As defined within the literature, we utilized the MRI criteria of meniscal extrusion as meniscal tissue extending 3 mm or greater beyond the tibial plateau, excluding osteophytes. Two attending radiologists blindly and independently identified the absence or presence, in millimeters, of medial meniscal extrusion on plain film radiography. Kappa test and Pearson correlation coefficient were calculated to assess the extent of inter-reader agreement and correlation. Sensitivity and specificity were calculated for each reader, assuming the concurrent MRI served as the gold standard. Results Ninety-six patients had medial meniscal extrusion and 94 had no medial extrusion by MRI. Kappa test for inter-reader agreement = 0.61. Pearson coefficient for inter-reader measurement correlation = 0.69. Reader A had sensitivity of 0.59 (95% CI 0.49-0.69) and specificity of 0.88 (95% CI 0.79-0.94). Reader B had sensitivity of 0.61 (95% CI 0.51-0.71) and specificity of 0.85 (95% CI 0.76-0.91). Conclusion There is substantial inter-reader agreement and high correlation of meniscal extrusion measurement between readers. Our results suggest that while radiographs have low sensitivity for evaluation of meniscal extrusion, their high specificity may be of clinical utility.