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1 Department of Radiology, Orthopedic University Hospital Balgrist, Forchstr.
340, CH-8008 Zurich, Switzerland.
2 Department of Orthopedic Surgery, Orthopedic University Hospital Balgrist,
CH-8008 Zurich, Switzerland.
3 Institute of Biostatistics, University of Zurich, Sumatrastr. 30, CH-8006
Zurich, Switzerland.
Received November 7, 2002;
accepted after revision March 14, 2003.
Address correspondence to M. Zanetti
(marco.zanetti{at}balgrist.ch).
Abstract
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SUBJECTS AND METHODS. One hundred patients (mean age, 42.7 years; range, 18-73 years) referred for suspected meniscal tears were prospectively examined with MRI of both knees when the contralateral knee was asymptomatic. The prevalence of various types of meniscal tears and other MR abnormalities was determined.
RESULTS. Meniscal tears were found in 57 symptomatic knees and in 36 contralateral asymptomatic knees. In those 57 patients with a meniscal tear on the symptomatic side, the prevalence of asymptomatic tears in the contralateral side was 63% (36/57). Horizontal or oblique meniscal tears were found medially in 32 and laterally in 11 symptomatic knees, and medially in 29 and laterally in eight asymptomatic knees. Radial, vertical, complex, or displaced tears were found medially in 18 and laterally in five symptomatic knees, and medially in five and laterally in none of the asymptomatic knees. Collateral ligament abnormalities were found in 53 symptomatic knees and in six asymptomatic knees. Pericapsular soft-tissue abnormalities were found in 64 symptomatic and in 12 asymptomatic knees. Edema-like bone marrow abnormalities were found in 36 symptomatic and in three asymptomatic knees.
CONCLUSION. Horizontal or oblique meniscal tears are frequently encountered in both asymptomatic and symptomatic knees and may not always be related to symptoms. However, radial, vertical, complex, or displaced meniscal tears and abnormalities of the collateral ligaments, pericapsular soft tissues, and bone marrow are found almost exclusively on the symptomatic side and appear to be clinically more meaningful.
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The purpose of the study was to evaluate the prevalence of MR abnormalities of the knee on the symptomatic and on the contralateral asymptomatic sides in patients with suspected meniscal tears.
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For inclusion in the study, patients had to be at least 18 years old and had to have unilateral symptoms with no complaints in the contralateral knee either on the day of the examination or before; have never visited a physician for complaints in the contralateral knee; have never missed work because of complaints in the contralateral knee; have never interrupted sports activity because of complaints in the contralateral knee; and have had no prior surgery in either knee. A standardized questionnaire was used to check these items. Patient recruitment was consecutive. From the original 142 patients, 40 were excluded because the MR examination of the contralateral knee could not be performed immediately because of scheduling constraints. Two patients refused to participate in the study. The study was approved by the hospital's institutional review board, and written informed consent was obtained from each patient.
MRI
MRI was performed on a 1.0-T scanner (Expert, Siemens Medical Systems,
Erlangen, Germany) in 64 patients and on a 1.5-T scanner (Symphony, Siemens
Medical Solutions) in 36 patients, depending on the availability of the
scanners. A dedicated circularly polarized, send-receive extremity coil was
used in both MR scanners. The MR sequences were identical on both sides of
each patient. The following MR sequences were acquired with the 1.0 T-scanner:
sagittal intermediate-weighted (TR/TE, 3800/16) and T2-weighted (3800/98)
turbo spin-echo sequences (section thickness, 3 mm; field of view, 156 x
250 mm; matrix, 170 x 512); coronal T1-weighted (608/20) spin-echo
sequences (section thickness, 4 mm; field of view, 140 x 160 mm; matrix,
224 x 512); and coronal T2-weighted (4500/96) turbo spin-echo sequences
with fat suppression (section thickness, 4 mm; field of view, 135 x 180
mm; and matrix, 210 x 512). The acquisition times for each sequence
varied between 2 min 18 sec and 4 min 35 sec.
The MRI protocol on the 1.5-T scanner included the following sequences: sagittal intermediate-weighted (3610/14) and T2-weighted (3610/9) turbo spin-echo sequences (section thickness, 3 mm; field of view, 143 x 180 mm; matrix, 204 x 512); coronal T1-weighted (450/14) spin-echo sequences (section thickness, 3 mm; field of view, 138 x 170 mm; and matrix, 208 x 512); and coronal short tau inversion recovery (STIR) sequences (5550/35; inversion time, 160 msec; slice thickness, 3 mm; field of view, 135 x 170 mm; matrix, 203 x 512). The acquisition times for the sequences varied between 2 min 57 sec and 4 min 38 sec.
Data Analysis and Statistics
MRIs were evaluated independently by two experienced musculoskeletal
radiologists who were unaware of the side on which the symptoms occurred. In
cases of disagreement, a consensus was reached. The observers had 5 and 10
years' experience in musculoskeletal radiology.
Menisci, collateral ligaments, pericapsular soft tissues, bone marrow, and cartilage were analyzed. Abnormalities of these structures were considered to be potentially responsible for pain in patients with clinically suspected meniscal tears. The medial and lateral sides were analyzed separately. A meniscal tear was diagnosed when a signal abnormality unequivocally reached the articular surface of the meniscus in at least two adjacent images. Meniscal tears were classified into four groups adapted from previously published classification systems [1, 3, 14]: horizontal or oblique partial-thickness tears, radial tears, vertical or complex full-thickness tears, and tears with displaced meniscal fragments.
The collateral ligaments were classified as normal, thickened, or torn [15]. The pericapsular soft tissue was classified as normal or abnormal (high signal on T2-weighted or STIR images as found in the presence of soft-tissue edema, bleeding, or granulation tissue) [16, 17]. The bone marrow was assessed according to the following classification: normal; edema-like zones (zones with ill-defined high signal on T2-weighted fat-suppressed or STIR images compared with normal fatty bone marrow, low signal on the T1-weighted images); edema-like zones plus well-defined zones (low signal intensity on T1- and T2-weighted sequences) indicating possible necrosis; and edema-like zones plus linear structures indicating possible fractures [18]. Cartilage lesions were characterized in accordance with a commonly used arthroscopic classification for cartilage lesions [19] and adapted for MRI [20]: 0 = normal, 1 = signal changes, 2= a defect of less than half the cartilage thickness, 3 = a defect of more than half the cartilage thickness but bone not exposed, 4 = bone exposed, 5 = bone exposed plus bone erosion.
The different types of meniscal abnormalities were related to traumatic versus nontraumatic onset of symptoms. Mean age was related to the presence or absence of meniscal tears on one or both sides. The McNemar test was used to determine whether the imaging findings in the symptomatic and contralateral asymptomatic knees were significantly different [21]. A p value of less than 0.05 was considered to be statistically significant. StatView software (version 4.0, SAS Institute, Cary, NC) was used for statistical analysis.
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Symptomatic partial-thickness tears were associated with a history of trauma in 16 cases and were not associated with trauma in 27 cases. Symptomatic full-thickness tears were evenly distributed between the patients with and those without trauma (n = 7 each). All symptomatic displaced tears (n = 5) were associated with trauma. (Table 3). The mean age of patients with bilateral meniscal tears was 49 years (± 16 years [SD]), of patients with unilateral meniscal tears was 43 years (± 16 years), and of patients without meniscal tears was 37 years (± 3 years). The mean age of patients with unilateral or bilateral meniscal tears was not significantly different (p = 0.21, unpaired Student's t test).
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Collateral ligament abnormalities were found in 53 symptomatic and in six asymptomatic knees (p < 0.001) (Table 4). Ligament tears were never found in asymptomatic knees. Pericapsular edema was found in 64 symptomatic and in 12 asymptomatic knees (p < 0.001). Edema-like bone marrow abnormalities were found in 36 symptomatic and in three asymptomatic knees (p < 0.001) (Table 5). Additional bone marrow abnormalities consistent with necrosis and fracture were found exclusively on the symptomatic side (n = 11). Cartilage lesions were found in 32 symptomatic and in 25 asymptomatic contralateral knees (p = 0.23) (Table 6). The prevalence of the most advanced cartilage lesions (grades 3-5) (Fig. 5) differed substantially on the medial side between the symptomatic (n = 16) and asymptomatic (n = 5) sides but not on the lateral side (symptomatic side, n = 5; asymptomatic side, n = 7).
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In the orthopedic literature, so-called leave-alone lesions of the menisci have been described [23, 24]. DeHaven [24] considered partial-thickness tears to be stable tears that should be left alone. More debate exists about vertical full-thickness tears, which may also be stable, short (< 5 mm) tears. The conclusion of Weiss et al. [23] about such vertical full-thickness was equivocal: "The tear (stable vertical tears) should be left alone unless it is the only abnormality that is found and it is causing symptoms that warrant treatment." This statement reveals a common dilemma for orthopedic surgeons: when symptoms are present, abnormalities found during arthroscopy or MRI are often considered to be responsible for the patient's complaints. This approach to treatment decisions may become more problematic with the increasing availability of noninvasive imaging techniques. Potentially self-limited or minor complaints are more commonly assessed with imaging. In such situations, many meniscal tears, especially horizontal or oblique partial-thickness tears, need not be associated with symptoms. Surgery may be inadequate and may even cause complications [25].
Studies have shown that surgery of the knee is less frequently performed after MRI than initially planned before MRI [2, 8, 26]. The change to a nonoperative treatment plan was explained by the high prevalence of medial collateral ligament abnormalities found during MRI that may mimic a meniscal lesion clinically. Medial collateral ligament abnormalities are rarely treated surgically. Our study confirms that clinical signs of meniscal tear may be mimicked by collateral ligament abnormalities even if the physical examination is performed by a qualified referring physician. The 88% (88/100) of referring clinicians in our study were specialists in orthopedic surgery, general surgery (with special interest in musculoskeletal disorders), or rheumatology.
Pericapsular soft-tissue abnormality was the most common finding in our symptomatic knees (62/100). Apparently these pericapsular soft-tissue abnormalities may mimic the clinical symptoms of a meniscal tear. Pericapsular edema in the knee has been suggested as an indirect sign for a meniscal tear [16]. However, such an association between posterolateral pericapsular edema and a lateral meniscal tear could not be confirmed in a subsequent study [27]. De Smet et al. [16] believe that this edema is probably caused by hemorrhage resulting from capsular tearing or stretching. Stretching of the pericapsular structures causing signal abnormalities has also been described in association with osteoarthritis. This relationship is most pronounced on the medial side [17].
In our study, edema-like bone marrow abnormalities were identified in 35 symptomatic and in only three asymptomatic knees. These findings are also called "bone bruise" when they are associated with a distinct trauma. Histologic examinations of so-called bone marrow edema zones have rarely been reported in the literature. However, the few reports revealed unspecified histologic findings, including bone marrow necrosis, bone marrow fibrosis, trabecular bone abnormalities, and fragments of cartilage, but only a small portion of the reports revealed bone marrow edema [28-30]. Therefore, the term "edema-like" has been used in this investigation for such abnormalities. Histologically, bone marrow necrosis and trabecular necrosis are consistently found in the presence of such signal abnormalities [30]. Such necrotic areas are not only found in avascular necrosis of bone but may also accompany an insufficiency fracture [31]. On the basis of our results, these edema-like bone marrow abnormalities are associated with symptoms, which is not unanticipated because of experiences in osteoarthritis of the knee in which a strong association between pain and edema-like bone marrow lesions has been shown [32]. A strong association between edema-like changes and pain has been also seen in early-stage osteonecrosis of the femoral head [33].
In conclusion, horizontal or oblique meniscal tears are frequently encountered in both asymptomatic and symptomatic knees and may not always be related to symptoms. On the contrary, radial, vertical, complex, or displaced meniscal tears, as well as abnormalities of the collateral ligaments, pericapsular soft tissues, and bone marrow, are found almost exclusively on the symptomatic side and appear to be clinically more meaningful. These findings should be specifically emphasized in radiology reports.
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