MRI zeroes in on medial meniscal tears

Studies from Korea and the U.S. show that MR imaging of the knee is a reliable and accurate test for the detection of specific subtypes of medial meniscal tears. Good understanding of MR-depicted anatomic features helps identify false-positive injuries of the menisci and avoid unnecessary surgeries.

Radial tears are a common type of medial meniscal root injury that can be fixed in most cases with minimally invasive surgery. These lesions can be easily overlooked, however. Without a correct diagnosis, tears of the medial meniscal root may lead to osteoarthritis of the knee and further disabling symptoms.

Imagers speculate that MRI could bolster the diagnosis and management of medial meniscal tears, but no studies compare MR's accuracy with arthroscopy - the diagnostic standard - in this setting, according to lead investigator Dr. So Yeon Lee, a radiologist at the Catholic University of Korea's Kangnam St. Mary's Hospital.

Lee and colleagues retrospectively reviewed the records of 192 patients who underwent arthroscopy and MRI of the knee from July 2003 through March 2006. Two independent radiologists looked for evidence of radial tear of the medial meniscus, interpreted results, and scored findings. The investigators found that MRI of the knee was reliable and accurate for the diagnosis of radial tears of the medial meniscal root and that T2-weighted imaging provided the most useful sequence for diagnosis.

Arthroscopy confirmed 29 patients with radial tears of the medial meniscal root. MRI's sensitivity, specificity, and accuracy for detection were 88%, 94%, and 94%, respectively. Detection of medial meniscal root tears on T2-weighted coronal images was not significantly different between the two readers, but their interpretations provided significantly different sensitivities and specificities with other MR imaging sequences.

In another study, University of Wisconsin researchers agreed that MRI of the knee offers a high accuracy for diagnosing medial meniscal tears. They warned, however, that false-positive diagnoses remain a frequent problem despite research into the causes of these errors. A good correlation between clinical and MRI findings could lead to a proper diagnosis and avoid unnecessary invasive treatment, according to the investigators.

Principal investigator radiologist Dr. Arthur A. De Smet and colleagues sought to determine the clinical variables or locations associated with false-positive diagnoses of medial meniscal tears. They reviewed records of 559 patients who underwent knee MR scanning and arthroscopy.

The investigators found false-positive MR diagnoses of medial meniscal tears are more common for longitudinal tears than for other tear types, particularly after acute trauma and when there is an associated anterior cruciate ligament tear. They also found these false-positive diagnoses to be more common with MR abnormalities at either the superior surface or the meniscocapsular junction.

"Our study confirmed our clinical impression that false-positive MR diagnoses of a medial meniscal tear are most common with longitudinal tears and that these tears can spontaneously heal," the researchers said.

Both studies were published in the July issue of the American Journal of Roentgenology.

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