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AJR 2001; 177:1189-1192
© American Roentgen Ray Society

Original Report

MR Imaging of Meniscal Contusion in the Knee

R. Lee Cothran, Jr.1, Nancy M. Major1, Clyde A. Helms1 and Laurence D. Higgins2

1 Department of Radiology, Duke University Medical Center, P. O. Box 3808, Durham, NC 27710.
2 Division of Orthopaedic Surgery, Duke University Medical Center, P. O. Box 3371, Durham, NC 27710.

Received March 29, 2001; accepted after revision May 21, 2001.

 
Address correspondence to R. L. Cothran.


Abstract
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 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
OBJECTIVE. We describe focal abnormal signal of the meniscus in the knees of six patients who had a history of acute trauma to the knee. This signal abuts the articular surface of the meniscus on MR imaging but does not meet criteria for a meniscal tear or degeneration.

CONCLUSION. Acute trauma to the knee may cause an abnormal signal in the meniscus that does not meet the previously described criteria for a meniscal tear or an intrasubstance degeneration. This abnormal signal could be misinterpreted as a tear because of its contact with the articular surface; this signal is seen most often in our series in the setting of an anterior cruciate ligament tear with adjacent bone contusions. We suggest that this signal may be due to a contusion of the meniscus and that the signal may resolve over time in some patients.


Introduction
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 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
The value of MR imaging after knee trauma has been well established with high sensitivity and specificity for tears of the menisci [1,2]. In our institution, preoperative evaluation of the menisci is now routinely performed. In the past, three categories of abnormal meniscal signal on MR imaging have been described [3], with further elaboration of grade 2 signal into subcategories by subsequent authors [4]. However, several cases with abnormal signal in the menisci do not fall neatly into these categories. Many of these cases do not represent meniscal tears and are of an unclear cause and significance [5]. The primary difference between the abnormal signal and the signal classically seen with a meniscal tear is the lack of a definite linear component to the abnormal signal. We have primarily seen abnormal meniscus signal in the setting of acute trauma and postulate that it may be due to a transient injury to the meniscus, which we refer to as a meniscal contusion.

Recognition of meniscal contusions has diagnostic and clinical implications because they do not represent frank tears of the meniscus on arthroscopy. Thus, meniscal contusions may be a source of false-positive interpretations for meniscal tear in the preoperative evaluation of the posttraumatic knee and may provide a potential explanation for the pattern of signal abnormality in the meniscus. This report describes the appearance and clinical significance of meniscal contusions, to our knowledge a previously unrecognized entity.


Materials and Methods
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 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
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During the course of our routine quality assurance conferences, several cases of abnormal signal abutting the articular surface on arthroscopy were found not to represent meniscal tears. These signal abnormalities were more amorphous in character than a meniscal tear but did not fit criteria for meniscus degeneration as a result of contact with the articular surface (Fig. 1A). Because of hyperemia in the affected meniscus on arthroscopy in one of these cases, a contusion mechanism was postulated. The words "contusion" and "potential meniscus contusion" were then placed in our musculoskeletal MR imaging database when cases with this type of signal were observed, so that subsequent follow-up could be performed. We used the term "contusion" to retrieve the cases from the database and to determine the association of abnormal meniscus signal of with other internal derangements of the knee. A database search included a word search for "contusion," "meniscus contusion," "meniscal contusion," and "amorphous."



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  		Fig. 1A. —30-year-old man with injury 2 weeks before imaging. Sagittal spin-echo proton density—weighted MR image (TR/TE, 2000/20) with fat suppression reveals amorphous signal in posterior horn of medial meniscus (arrow), with subjacent high signal in tibial plateau.

 

Of the 2518 MR imaging examinations of the knee found in the database between July 1996 and July 1999, 21 included a description of amorphous signal in a portion of the meniscus that met our criteria for a meniscal contusion: amorphous signal in the meniscus abutting an articular surface but without a linear component to suggest a meniscal tear. The MR imaging examinations described in these reports were then reviewed by three radiologists. Of the 21 patients with an amorphous signal on imaging, 12 went on to surgery. The arthroscopy reports were also reviewed.

Six of the 12 patients had findings on MR imaging that suggested either a tear of the meniscus adjacent to the suspected contusion (three patients, two degenerative tears and one small transverse tear or decompressed meniscal cyst), or on radiographic review the patients did not meet our criteria for contusion (three patients, two with an amorphous signal not abutting the articular surface and one with a linear component to the abnormal signal). Although some of these patients may have had a component of contusion in their menisci, the six patients were excluded from the data set used to characterize a contusion because of these additional findings. The three patients with suspected adjacent tears on MR imaging did have adjacent meniscal tears on arthroscopy. One of the patients who had a signal in the meniscus that was not abutting an articular surface at the time of imaging was found to have a degenerative tear on arthroscopy. The patient with a linear component to the signal was found on arthroscopy to have a horizontal cleavage tear of the meniscus in question. None of the remaining six patients had a meniscal tear on arthroscopy. These six patients without meniscal tear on arthroscopy composed our study population.

Arthroscopy was performed at an average of 4 weeks 3 days after initial imaging (range, 1 day—10 weeks 2 days). Three women and three men with an average age of 29.9 years (range, 22-39 years) were involved in our study. Patients were imaged using our institution's standard knee imaging protocol consisting of sagittal spin-echo proton density—weighted images with fat suppression (TR range/TE, 1800-2000/20; matrix, 256 x 192; field of view, 16 cm; slice thickness, 4 mm with a 0.4-mm gap) and sagittal, axial, and coronal fast spin-echo T2-weighted images with fat suppression (TR range/TE range, 4000-4500/69-75; matrix, 256 x 192; field of view, 16 cm; slice thickness, 4 mm with a 0.4-mm gap). Imaging was performed on a Signa 1.5-T scanner (General Electric Medical Systems, Milwaukee, WI). Meniscal signal was evaluated primarily on sagittal spin-echo proton density—weighted images with fat suppression. After an extensive review at our institution, we found that a second meniscal-sensitive sequence did not considerably improve our detection of meniscal abnormalities. Therefore, the follow-up images consisted only of sagittal proton density—weighted fat-suppressed images with the same parameters as the initial examinations to evaluate the menisci.

Because of the unclear significance of the meniscal signal and the concomitant anterior cruciate ligament (ACL) tears in most of our patients, there was some clinical concern that this injury might progress to a tear. Therefore, four of these six patients (one woman, three men) returned for follow-up imaging of the menisci in the sagittal plane to reevaluate the region of the meniscus that was interpreted as abnormal on the original MR imaging examination. The mean interval between the initial imaging and follow-up imaging for these four patients was 47 weeks 1 day (range, 20 weeks 2 days—69 weeks 1 day).


Results
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 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
All six patients included in this study presented with a history of acute trauma to the knee. Each of the patients had a bone contusion adjacent to the area of amorphous high signal intensity in the meniscus (Fig. 1A). Five of the six patients had meniscal signal abnormality in the posterior horn of the medial meniscus (Figs. 1A and 2A) One patient had an abnormal meniscal signal in the anterior horn of the lateral meniscus. In addition, five of the six patients with meniscal appearance had ACL tears. In none of these six patients was a tear found on arthroscopy in the region of the meniscus in question. The orthopedic surgeon described an abnormal injection and vascularity on arthroscopy in the periphery of the meniscus in one of the six patients (Fig. 3A,3B). It is unknown whether this appearance was present in the remainder of the patients because the gross appearance of the menisci in the absence of a tear is not always described in the operative reports. No other meniscal textural or structural abnormalities were mentioned in the operative reports. The orthopedic surgeons at our institution routinely probe the undersurface of the menisci during arthroscopy, in addition to assessing the visible surfaces. No undersurface tears were identified in these six patients.



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  		Fig. 2A. —23-year-old man with reported knee dislocation. Spin-echo proton density—weighted MR image (TR/TE, 2000/20) with fat suppression reveals meniscal contusion (black arrow) and subtle adjacent bone contusion (white arrow).

 


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  		Fig. 3A. —39-year-old woman who injured her knee skiing several days before imaging. Patient had tibial plateau fracture and avulsed anterior cruciate ligament. Sagittal spin-echo proton density—weighted MR image (TR/TE, 2000/20) with fat suppression reveals abnormal signal in posterior horn of medial meniscus with adjacent bone contusion.

 


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  		Fig. 3B. —39-year-old woman who injured her knee skiing several days before imaging. Patient had tibial plateau fracture and avulsed anterior cruciate ligament. Arthroscopic photograph of meniscus reveals abnormal injection and vascularity at periphery of injured meniscus (arrows). No meniscal tear or meniscocapsular separation was identified on arthroscopy (F = femur; m = body of meniscus).

 

On follow-up imaging, the abnormal signal seen at the initial examination had completely resolved in two patients (Figs. 1B and 2B), with no change in one patient and a slight decrease in the abnormal signal in the second patient.



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  		Fig. 1B. —30-year-old man with injury 2 weeks before imaging. Follow-up MR image (2000/20) after 67 weeks reveals interval resolution of meniscal signal with considerable decrease in underlying bone signal.

 


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  		Fig. 2B. —23-year-old man with reported knee dislocation. Follow-up MR image (1800/20) obtained 20 weeks after initial imaging reveals resolution of abnormal meniscal signal.

 


Discussion
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 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
As mentioned previously, an abnormal high signal intensity in the menisci of the knee was placed into three broad categories by Lotysch et al. [3], with subsequent elaboration of the second category into three subtypes by Dillon et al. [4]. By Lotysch's original system, a grade 1 signal is a rounded or amorphous signal in the meniscus that does not disrupt an articular surface. A grade 2 signal is a linear signal that does not disrupt an articular surface. Grades 1 and 2 signals have been shown to be due to intrasubstance degeneration of the meniscus [6]. A grade 3 signal is a signal that disrupts an articular surface and indicates a meniscal tear. A grade 2 signal was then broken down into 2A, 2B, and 2C categories representing a linear signal not in contact with an articular surface, an abnormal signal in contact with an articular surface on a single image, and an extensive wedgeshaped signal abnormality not in contact with an articular surface, respectively [3, 4].

Despite this extensive classification system, there are appearances of abnormal signal in the meniscus that do not fit easily into a single category [5]. This is the case with the signal we have described in our selected group of patients. The signal is a globular or amorphous area of abnormally high signal intensity that contacts an articular surface but is less discrete than the signal abnormality typically seen with a meniscal tear and less well-defined than the signal seen with intrasubstance degeneration. This signal abnormality does not represent a tear of the meniscus on arthroscopy.

The signal associated with intrasubstance degeneration has been found to represent an increase in mucoid intercellular ground substance in studies correlating MR imaging and histologic data [6]. The same study suggested that the signal and pathologic changes in the meniscus corresponding to intrasubstance degeneration are progressive changes that may eventually result in tears of the meniscus in the affected regions. The fact that the abnormal signal observed in our patients resolved completely in some and improved or did not change in others suggests that this abnormality is not along the spectrum of intrasubstance degeneration, because signal from degeneration would not be expected to improve over time, much less completely resolve. The abnormal signal that we describe appears to be from some type of transient injury to the meniscus, with unknown long-term effects.

The mechanism for the type of meniscal injury we describe is suggested by the pattern of associated findings in our patient population. All the patients in our group had adjacent bone contusions in the region of the abnormal meniscal signal, and most of the patients also had a complete ACL tear. We observed several similarities between the location of this injury and the "contrecoup" injury described by Kaplan et al. [7], in which an impaction injury exists on the posteromedial aspect of the tibial plateau and meniscus during reduction after an ACL tear. We postulate that the meniscus may undergo a compressive injury during this reduction because of the same forces that result in the bone contusion of the posteromedial tibial plateau. In those patients whose injury was not in the posterior horn of the medial meniscus, we suggest that there was likely some type of compressive force exerted on the meniscus by the adjacent bone, resulting in both the adjacent bone contusion and the abnormal meniscal signal. No menisco-capsular separation or peripheral medial meniscal tear was identified in our group of patients on arthroscopy. Therefore, the injury we describe may be along a spectrum with the injuries described by Kaplan et al. and may result from a similar mechanism.

It is unclear what causes the abnormal signal in the meniscus in a meniscal contusion. The periphery of the meniscus is known to have a vascular zone, with the exception of the posterior lateral aspect of the lateral meniscus [8]. Therefore, one could postulate that an injury in which blood products from a compressive injury to the vascular zone of the meniscus or meniscocapsular junction might track along the fibers of the meniscus and result in an increased signal on MR imaging. The arthroscopic findings of an injected hypervascular appearance in the periphery of the meniscus seen in the patient in Figure 3A,3B would lend credence to this hypothesis.

Animal experiments have shown that injuries to the meniscus with communication with the vascular zone can heal via formation of a fibrin clot followed by vascular proliferation into the zone of injury and the subsequent formation of a fibrovascular scar [9]. However, these experiments were performed with actual transection of the meniscus rather than a compressive injury. Despite this difference, an alternative explanation for the abnormal signal seen in a contusion might involve a similar response to injury in the avascular zone of the meniscus, resulting in the influx of a fibrin clot with or without neovascularity to the area of the compressive injury. However, this has not yet been histologically proven in human studies.

Potential limitations of this study involve the small number of patients included in the study group. One explanation for the small numbers may be that some patients were over-looked because our search for cases occurred after the beginning of our quality assurance conferences. We have since found meniscal contusion to be a relatively uncommon entity and no longer confuse it with meniscal tear. In addition, the lack of histologic follow-up from the affected region of meniscus is a limitation. However, there is little indication for removing an otherwise normal-appearing segment of meniscus on arthroscopy, and therefore histologic proof is difficult to obtain.

In summary, we believe that meniscal contusion may represent an important potential source for false-positive results in the evaluation of meniscal tears in the setting of acute trauma. We postulate a compressive mechanism because of the location of abnormal signal and the association of adjacent bone contusion and ACL tears in almost all the patients. The pathophysiology and the long-term implications of this injury are not known. However, the absence of a meniscal tear on arthroscopy and the resolution, improvement, or lack of progression of the abnormal signal on follow-up imaging suggest that the prognosis for meniscal contusion in the short term is better than it is for a complete meniscal tear. Recognition of this entity may help to explain areas of abnormal signal that do not fit well into previously recognized patterns and may improve interpretation accuracy in the preoperative evaluation of the knee in the setting of acute trauma. In addition, recognition of meniscal contusion may prevent unnecessary surgery because the presence or absence of a meniscal tear may be the determining factor for surgery in some patients whose only other injury is an ACL tear.


References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Mandelbaum BR, Finerman GA, Reicher MA, et al. Magnetic resonance imaging as a tool for evaluation of traumatic knee injuries: anatomical and pathoanatomical correlations. Am J Sports Med 1986;14:361 -370[Abstract/Free Full Text]
  2. Justice WW, Quinn SF. Error patterns in the MR imaging evaluation of menisci of the knee. Radiology 1995;196:617 -621[Abstract/Free Full Text]
  3. Lotysch M, Mink J, Crues JV, Schwartz SA. Magnetic resonance imaging in the detection of meniscal injuries. (abstr) Magn Reson Imaging 1986;4(P):185
  4. Dillon EH, Pope CF, Jokl P, Lynch K. The clinical significance of stage 2 meniscal abnormalities on magnetic resonance knee images. Magn Reson Imaging 1990;8:411 -415[Medline]
  5. Kaplan PA, Nelson NL, Garvin KL, Brown DE. MR of the knee: the significance of high signal in the meniscus that does not clearly extend to the surface. AJR 1991;156:333 -336[Abstract/Free Full Text]
  6. Stoller DW, Martin C, Crues JV, Kaplan L, Mink JH. Meniscal tears: pathologic correlation with MR imaging. Radiology 1987;163:731 -735[Abstract/Free Full Text]
  7. Kaplan PA, Gehl RH, Dussault RG, Anderson MW, Diduch DR. Bone contusions of the posterior lip of the medial tibial plateau (contrecoup injury) and associated internal derangements of the knee at MR imaging. Radiology 1999;211:747 -753[Abstract/Free Full Text]
  8. Arnoczky SP, Warren RF. Microvasculature of the human meniscus. Am J Sports Med 1982;10:90 -95[Abstract/Free Full Text]
  9. Arnoczky SP, Warren RF. The microvasculature of the meniscus and its response to injury: an experimental study in the dog. Am J Sports Med 1983;11:131 -141[Abstract/Free Full Text]

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