Anterior Horn Meniscal Tears — Fact or Fiction
Anterior Horn Meniscal Tears—Fact or Fiction
Abstract & Commentary
Synopsis: In a consecutive series of nearly 1000 knee MRIs, there was a 74% false-positive rate for the diagnosis of anterior horn meniscal tears. Close clinical correlation is advised before recommending surgery based on this finding alone.
Source: Shepard MF, et al. The clinical significance of anterior horn meniscal tears diagnosed on magnetic resonance images. Am J Sports Med. 2002;30(2):189-192.
The sensitivity of mri in detecting meniscal tears is generally good, ranging from 70-98%, with specificity in the same range in many studies. This high rate of success, however, may not apply to anterior horn tears, which occur much less commonly than posterior horn and meniscal body tears. Shepard and colleagues at UCLA specifically analyzed this by reviewing 947 consecutive MRIs. Fellowship-trained musculoskeletal radiologists read 99% of the MRIs. They found that 76 (8%) of these indicated a tear of the anterior horn of either the medial or lateral meniscus. Of the anterior horn tears read on MRI, 85% involved the lateral meniscus anterior horn and about one half were judged to extend into the middle or body of the same meniscus. Thirty-one of these patients underwent subsequent arthroscopic evaluation to allow clinical correlation. Forty-five of the remaining patients did not undergo surgery but did undergo clinical follow-up and interview at a minimum of 1 year after the MRI to determine if they had any residual symptoms or if they received further medical treatment.
Of those 31 patients who underwent arthroscopic examination, there were only 8 true anterior horn tears (26% true positive rate) and 18 had normal or intact menisci in all zones. Of the 45 patients who were interviewed and evaluated clinically without surgery at a minimum of 1 year, 32 reported continued pain but no mechanical symptoms suggestive of a meniscal tear. Of these 45 patients, there was an average of 3.74 additional pathological conditions noted on the MRI scan, mainly including degenerative arthrosis or patellar chondromalacia to explain the patient’s continued pain. Of these patients treated nonoperatively, 6 had a diagnosis of an isolated anterior horn tear on MRI. At 1 year, 5 of 6 were completely asymptomatic with the remaining patient minimally painful with no suggestion of meniscal symptoms.
Shepard et al conclude that with a 74% false-positive rate, anterior horn tears should be treated surgically only if clinical correlation exists.
Comment by David R. Diduch, MS, MD
The anterior horn of the menisci, especially the lateral meniscus, is an area commonly confused on MRI. Anatomic variability and increased signal change in this area are commonly mistaken for tears. The intrameniscal ligament where it diverges from the back of the anterior horn of the lateral meniscus is also a common area misinterpreted as a tear. Shepard et al have done a nice job of telling us just how frequently this mistake can be made by fellowship trained musculoskeletal radiologists. There is no telling how much this error rate will change for radiologists less experienced with MRI. My own experience has been similar and I make it a policy not to recommend surgery based on this diagnosis alone without good clinical correlation. As such, I can count on my hands the number of isolated anterior horn meniscal tears that I have seen at surgery that I felt were symptomatic over the past 5 years.
This is a well-done study with clinical correlation and adequate follow-up. Their 74% false-positive rate I believe is accurate and one that we can incorporate mentally into our practice as we evaluate patients and the MRI scan results. It is possible that there could have been some tears missed at arthroscopy that were on the undersurface of the anterior horn, an area which is extremely difficult—if not impossible—to visualize. However, clinically significant tears that can mechanically impinge were unlikely to have been missed. Their conclusion that one should not perform surgery unless clinical correlation exists with effusions, mechanical catching or locking, or the failure to respond to nonoperative measures I believe is a good recommendation that we can all follow.
Dr. Diduch, Associate Professor, Department of Orthopaedic Surgery, University of Virginia School of Medicine, Charlottesville, VA, is Editor of Sports Medicine Reports.
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