Clinical/MRI Findings Related to False-Positive MR Diagnoses of Medial Tear
Clinical/MRI Findings Related to False-Positive MR Diagnoses of Medial Tear
Objective: The objective of our study was to determine if false-positive MR diagnoses of a medial meniscal tear are more common with specific clinical variables, tear type or location, or MRI findings of a longitudinal tear.
Materials and Methods: We reviewed the records of 559 patients who underwent knee MR examinations and arthroscopy. We compared the positive predictive values (PPVs) of an MR diagnosis of a medial meniscal tear for differences in tear location or type, delay between knee injury and MRI, delay between MRI and arthroscopy, and the presence of an anterior cruciate ligament (ACL) tear. We also retrospectively reviewed the MR examinations of 50 longitudinal tears to compare the PPVs of various MRI findings of a longitudinal tear.
Results: There was no association between either the delay between injury and MRI or the delay between MRI and arthroscopy and false-positive diagnoses. The PPV of 64% (32/50) for longitudinal tears was lower than the values of 83% (15/18) to 100% (116/116) for other types of medial meniscal tears. False-positive diagnoses of medial meniscal tears were more common in patients who had a prior episode of acute trauma (p = 0.004) or an ACL tear (p < 0.0001). Review of longitudinal tears revealed a decreased PPV when MRI showed signal contacting only the superior surface (p = 0.016) or when MRI showed signal contacting the surface at the meniscocapsular junction (p = 0.004). Four of the 18 menisci with a false-positive diagnosis of a longitudinal tear had a healed ACL tear noted at arthroscopy.
Conclusion: False-positive MR diagnoses of medial meniscal tears are more common for longitudinal tears than other tear types and are also more common with MR abnormalities at either the superior surface or the meniscocapsular junction. Spontaneous healing of longitudinal tears accounts for some false-positive MR diagnoses.
Although MRI of the knee has a high accuracy for diagnosing meniscal tears, false-positive diagnoses still occur despite research into the causes of these errors. False-positive diagnoses of a tear have been shown to be more common in the medial meniscus than in the lateral meniscus. In a meta-analysis of 29 studies of MR accuracy for diagnosing meniscal tears, the pooled weighted specificity was 88% for diagnosing medial meniscus tears compared with a specificity of 96% for lateral meniscal tears.
In our clinical practice, we noted that some patients with an apparent longitudinal tear of the medial meniscus on MRI did not have a tear confirmed at arthroscopy. Most of these patients with false-positive MR diagnoses of a meniscal tear had other intraarticular injuries or abnormalities that warranted surgical intervention. However, some patients had medial joint-line pain and the decision to operate was partially based on the MR diagnosis of a tear. We undertook this study to determine if there are clinical variables or certain tear types or locations that are associated with false-positive MR diagnoses of medial meniscal tears. We also wished to determine whether there were MRI findings associated with longitudinal tears that would suggest an apparent tear would not be confirmed at arthroscopy.
Objective: The objective of our study was to determine if false-positive MR diagnoses of a medial meniscal tear are more common with specific clinical variables, tear type or location, or MRI findings of a longitudinal tear.
Materials and Methods: We reviewed the records of 559 patients who underwent knee MR examinations and arthroscopy. We compared the positive predictive values (PPVs) of an MR diagnosis of a medial meniscal tear for differences in tear location or type, delay between knee injury and MRI, delay between MRI and arthroscopy, and the presence of an anterior cruciate ligament (ACL) tear. We also retrospectively reviewed the MR examinations of 50 longitudinal tears to compare the PPVs of various MRI findings of a longitudinal tear.
Results: There was no association between either the delay between injury and MRI or the delay between MRI and arthroscopy and false-positive diagnoses. The PPV of 64% (32/50) for longitudinal tears was lower than the values of 83% (15/18) to 100% (116/116) for other types of medial meniscal tears. False-positive diagnoses of medial meniscal tears were more common in patients who had a prior episode of acute trauma (p = 0.004) or an ACL tear (p < 0.0001). Review of longitudinal tears revealed a decreased PPV when MRI showed signal contacting only the superior surface (p = 0.016) or when MRI showed signal contacting the surface at the meniscocapsular junction (p = 0.004). Four of the 18 menisci with a false-positive diagnosis of a longitudinal tear had a healed ACL tear noted at arthroscopy.
Conclusion: False-positive MR diagnoses of medial meniscal tears are more common for longitudinal tears than other tear types and are also more common with MR abnormalities at either the superior surface or the meniscocapsular junction. Spontaneous healing of longitudinal tears accounts for some false-positive MR diagnoses.
Although MRI of the knee has a high accuracy for diagnosing meniscal tears, false-positive diagnoses still occur despite research into the causes of these errors. False-positive diagnoses of a tear have been shown to be more common in the medial meniscus than in the lateral meniscus. In a meta-analysis of 29 studies of MR accuracy for diagnosing meniscal tears, the pooled weighted specificity was 88% for diagnosing medial meniscus tears compared with a specificity of 96% for lateral meniscal tears.
In our clinical practice, we noted that some patients with an apparent longitudinal tear of the medial meniscus on MRI did not have a tear confirmed at arthroscopy. Most of these patients with false-positive MR diagnoses of a meniscal tear had other intraarticular injuries or abnormalities that warranted surgical intervention. However, some patients had medial joint-line pain and the decision to operate was partially based on the MR diagnosis of a tear. We undertook this study to determine if there are clinical variables or certain tear types or locations that are associated with false-positive MR diagnoses of medial meniscal tears. We also wished to determine whether there were MRI findings associated with longitudinal tears that would suggest an apparent tear would not be confirmed at arthroscopy.
