IMAGING
For decades, MR imaging has been used as a primary determinant for meniscal injuries. MR imaging uses magnetic frequency to read radio waves given off by protons in the body; through these waves, the MRI is able to identify different tissues in the body and produce a semi-accurate picture of these tissues. The fact that MR imaging is more sensitive to some tissues than others, however, can prevent it from producing a completely accurate picture of an injured area. This can cause injured tissues to remain undetected, or other “abnormalities” on the MRI to be misread as actual injuries. These errors include shadows, truncation artifacts, and even foreign tissues, such as scar tissue, that can have the appearance of an injury on an MRI film. As a result, relying on MR imaging alone, especially as it relates to meniscal tears, will very often lead to an improper diagnosis and, subsequently, improper treatment.
One study that brought these issues into the spotlight was performed on college basketball players at Duke University who displayed no clinical symptoms of knee abnormality. Internal irregularities of the knee including cartilage defects, joint effusions, bone marrow edema, and even discoid menisci were found on the MRIs of 75% of subjects, who never displayed any symptoms of meniscal abnormality.47 When an MRI shows a tear or meniscal degeneration when the person has no symptoms, this is called a false positive. The MRI is falsely positive. Kornick and associates investigated 64 volunteers, between the ages of 10 and 74, and found that over 25% had abnormal signals in their menisci, despite being totally asymptomatic.48 More distressing is the fact that in another study on children, mean age 12.2 years, 66% showed a high signal intensity within the menisci.49 A high signal intensity is one of the criterion to diagnose degenerative menisci. (See Figure 8.) Perhaps the best study to date to document abnormal meniscal MRI findings in asymptomatic individuals was published in the New England Journal of Medicine in 2008.50 In this study, MRI scans on 991 knees were taken and compared to clients responses about pain and disability in those knees. The prevalence of meniscal tear or of meniscal destruction in the knee as detected on MRI ranged from 19% among women 50 to 59 years of age to 56% among men 70 to 90 years of age. The MRIs in these patients ages 50 to 90 showed that over 60% had meniscal tears documented on MRI and that 61% of subjects who had meniscal tears did not have any pain, aching, or stiffness in their knees.
Not only do MRI findings often fail to correlate with the associated symptoms of meniscal injury, they are also frequently found to be inaccurate in correctly predicting meniscal pathology found on arthroscopy.51-54 This was the case in a study in which clinical examination correctly identified 97% of medial meniscal tears and 85% of lateral meniscal tears found on arthroscopy, as opposed to MRI predictions, which were 10% less accurate in each category.55 Gelb et al. found that, when compared to arthroscopic findings, clinical examination was 100% accurate in the diagnosis of ACL injuries, 91% accurate for meniscal tears, and 100% accurate for articular cartilage damage. MR imaging, on the other hand, was 95% sensitive for ACL injuries, 82% sensitive for meniscal tears, and only 33% accurate in predicting articular cartilage injuries.56 Other published studies by Liodakis and his colleagues found similar results when studying the preoperative MRI scans of 2,000 arthroscopic meniscectomy patients. Their patients’ MRI findings only correlated with the intraoperative arthroscopic findings a mean of 52% of the time.57 One study published in the Journal of Arthroscopic Surgery reported that 35% of their patients would have undergone unnecessary surgery if the examiner had relied on just MRI findings of meniscal tear alone, leading the researchers to conclude that MRIs are “an expensive, unnecessary procedure.”58 (See Figure 9.)
Just as MRIs can lead to false-positive readings, they may also produce false-negative findings by failing to detect an actual meniscal injury. This was the case in one study of 254 human knees, where the researchers found that 13% of their patients presented with normal MRIs, despite exhibiting symptoms of meniscal injury confirmable on arthroscopy.59 In studying the correlation between arthroscopy, clinical examination, and MR imaging, Stanitski found that 71% of his patients were given inaccurate MRI readings, with 24% showing falsepositive evidence of meniscal tears, while actual ACL, meniscal, and cartilage injuries went undetected in half of the patients.60
| Figure 8. False-positive MRIs of the knee in teenagers. Because significant abnormalities show up in the menisci on MRI in teenagers, when no true injury exists, relying on this modality to make a diagnosis is a scary proposition, especially if surgery is contemplated. Used with permission of Beulah Land Press © 2001 Oak Park, IL. Prolo Your Sports Injuries Away!, fig. 16-10. |
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| Figure 9. MRI of the right knee without contrast. Noted are changes in the medial meniscus. See how even the radiologist cannot determine whether this represents a recurrent meniscal tear or is just post surgical changes. |
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