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1 All authors: Department of Radiology, Duke University Medical Center, Box 3808, Durham, NC 27710.
Received January 21, 2002;
accepted after revision June 25, 2002.
Presented at the annual meeting of the American Roentgen Ray Society,
Seattle, April—May 2001.
Abstract
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MATERIALS AND METHODS. A database search of our institution's records from January 1998 to July 2000 yielded 2140 MR examinations of the knee, all of which had been performed with a standard knee protocol on a 1.5-T magnet. Of these 2140 examinations, 156 included patients younger than 18 years. Fifty-nine of these patients underwent surgery, and the orthopedic surgeons' operative reports were used as the gold standard with which the MR imaging results were compared. Thirty-four boys and 25 girls who ranged in age from 11 to 17 years (mean age, 15 years) were examined. The clinical notes for the remaining 97 patients were evaluated for information about management and clinical improvement.
RESULTS. The sensitivity and specificity values for MR imaging of the menisci and cruciate ligaments in adolescents were as follows: medial meniscus, 92% sensitivity and 87% specificity; lateral meniscus, 93% sensitivity and 95% specificity; anterior cruciate ligament, 100% sensitivity and 100% specificity; and posterior cruciate ligament, 0% sensitivity and 100% specificity.
CONCLUSION. Our data suggest that MR imaging of the knee in adolescents is sensitive, specific, and accurate.
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One of five musculoskeletal radiologists from our institution had prospectively evaluated each MR imaging examination. For each patient, the radiologist's interpretations of the menisci and cruciate ligaments were compared with the arthroscopic surgical findings; surgery was performed by various orthopedic surgeons. MR imaging data were then categorized as true-positive, true-negative, false-positive, and false-negative. From these data, sensitivity and specificity for the detection of meniscal and cruciate ligament tears in our study group of adolescents were computed and compared with the same values in adults for the same radiologists (obtained from another study) over approximately the same time period.
All the MR imaging examinations were performed on a 1.5-T magnet (Signa; General Electric Medical Systems, Milwaukee, WI), and identical protocols were used for each of the examinations. Our standard knee protocol includes axial, sagittal, and coronal fast spin-echo T2-weighted imaging (TR/TE effective, 3500/65) with fat suppression and sagittal proton density imaging (TR/TE, 2000/20) with fat suppression. The remaining parameters include a matrix of 256 x 192, 2 excitations, a field of view of 16 x 16 cm, and a slice thickness of 4 mm/0.4 mm.
Meniscus tears were identified if linear high signal abutting the articular surface or abnormal morphology was seen. The anterior cruciate ligament was identified as torn if the fibers were disrupted and were no longer parallel to the intercondylar notch.
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In the group of adolescents with arthroscopic correlation, arthroscopy showed 11 medial meniscus tears, 14 lateral meniscus tears, 25 anterior cruciate ligament tears, and one posterior cruciate ligament tear. Comparison of the arthroscopic and MR imaging findings yielded the following results. MR evaluation of the medial meniscus revealed 11 true-positives, 41 true-negatives, six false-positives, and one false-negative; these values resulted in a 92% sensitivity and 87% specificity. For the lateral meniscus, the MR interpretations consisted of 14 true-positives, 42 true-negatives, two false-positives, and one false-negative, which resulted in a 93% sensitivity and 95% specificity. MR findings for the anterior cruciate ligament yielded 26 true-positives and 33 true-negatives with zero false-positives and zero false-negatives, which resulted in a 100% sensitivity and specificity. For the posterior cruciate ligament, neither true-positives nor false-positives were recorded for the MR imaging findings; there were 58 true-negatives and one false-negative. These values yielded a 0% sensitivity and 100% specificity.
The sensitivities and specificities of MR imaging for the detection of tears in the adolescent group were essentially the same as those for the adult group, which included a series of 203 patients (Table 1).
Of the 97 patients who did not undergo arthroscopy, "normal" was assigned as the diagnosis in 39 patients. Forty-six patients had no additional follow-up. Other diagnoses encountered were 10 bone contusions, seven patellar dislocations (contusion pattern not counted in previous group), four anterior cruciate ligament tears, two hematomas, two cases of Osgood-Schlatter disease, two cases of jumper's knee, two osteochondral lesions, one posterior cruciate ligament injury, one case of abnormal signal in the Hoffa fat pad, one Wrisberg variant of discoid lateral meniscus, one medial collateral ligament sprain, and one bucket-handle meniscus tear. Of the four patients with anterior cruciate ligament tears, two refused surgery and two were lost to follow-up. One patient had an anterior cruciate ligament tear and a bucket-handle meniscus tear. Twenty-five patients had a final impression in the dictated report as "signal in either the meniscus or soft tissues not felt to be significant." Therefore, the total number of cases that were not diagnosed with pathology was 64.
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A number of differences between our study and that conducted by Stanitski [4] exist. First, the latter study included results from only 28 patients, whereas our study included results from 59 patients. However, although the number of patients in our study is more than double that in the other study, the total number is still small. Therefore, a small sample is a potential shortcoming of our study. Possible explanations for the small number of MR imaging studies in adolescents include the reluctance of orthopedic surgeons to use MR imaging in these patients because of the report by Stanitski and the possibility that adolescents are less likely to have internal derangement of the knee than adults.
Another difference between our study and that of Stanitski [4] is that Stanitski used grade 2 meniscal signal abnormality as evidence for meniscus tear in an unspecified number of patients. It is well known that grade 2 intrameniscal signal is evidence of intrasubstance degeneration rather than a tear, because grade 2 intrameniscal signal does not disrupt the articular surface. These cases were erroneously diagnosed as tears in that study, therefore reducing the accuracy of MR imaging for revealing meniscal abnormalities. In addition, Stanitski did not provide the imaging parameters used to evaluate the meniscus. If sequences with a long TE were chosen to evaluate the meniscus, tears could have been overlooked. Proper protocols will aid the radiologist (and surgeon) in accurately assessing the integrity of the meniscus.
In the Stanitski study [4], the accuracy of the radiologists' interpretations of the MR images of adults is not known. A potential shortcoming in our study is that only musculoskeletal radiologists interpreted MR images rather than general radiologists. However, the radiology literature reports 95-100% accuracy for anterior cruciate ligament tears, 90-95% for medial meniscus tears, and 85-90% accuracy for lateral meniscus tears [1,2,3, 6, 7], and there is no reason to believe that these numbers should not hold true for general radiologists. Stanitski asserted that sensitivity and specificity of MR imaging for detecting internal derangements of the knee were inferior in adolescents compared with adults. After evaluating our data, we found that the sensitivity and specificity values for MR imaging of adolescents and adults were essentially the same (Table 1).
Although our primary intention was to determine the accuracy of MR imaging of the knee compared with arthroscopy in adolescents, we also assessed the outcomes for the 97 patients who did not undergo arthroscopy. Forty-six patients did not undergo a follow-up examination. A lack of follow-up could indicate that either the symptoms resolved so clinical follow-up was not needed or the patient was seen elsewhere for additional follow-up. Of the remaining patients who did undergo follow-up, the visit consisted of one-time physical therapy or orthopedic follow-up without any additional follow-up or intervention. Four anterior cruciate ligament tears were identified, but the patients did not undergo surgery at our institution: two did not want surgery and the other two were lost to follow-up. The patient with the bucket-handle meniscus tear was among these four patients. No additional "surgical lesions" were identified. None of the patella dislocations had associated cartilage loss (our surgeons' indication for operating). The osteochondral lesions were stable by MR appearance. Surgery was not considered for these two patients.
In conclusion, we believe that MR imaging of the knee is just as useful as a clinical adjunct in adolescents as in adults. Therefore, MR imaging of the knee in adolescents can assist in preventing unnecessary surgery such as diagnostic arthroscopy. In circumstances in which surgery is deemed necessary, MR imaging can aid in surgical planning, which benefits the orthopedic surgeon as well as the patient because the information provided by MR imaging leads to decreased procedure and tourniquet time.
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