DOI:10.2214/AJR.04.1024
AJR 2005; 185:1429-1434
© American Roentgen Ray Society
Radial Meniscal Tears: Significance, Incidence, and MR Appearance
Keith W. Harper1,2,
Clyde A. Helms1,
H. Stanley Lambert, III3 and
Laurence D. Higgins4
1 Department of Radiology, Division of Musculoskeletal Radiology, Duke
University Medical Center, Durham, NC 27701.
3 Department of Radiology, Duke University Medical Center, Durham, NC.
4 Department of Surgery, Division of Orthopedic Surgery, Duke University Medical
Center, Durham, NC.
Received July 27, 2004;
accepted after revision December 7, 2004.
Address correspondence to K. W. Harper.
2 Present address: Catawba Radiological Associates, 18 13th Ave., Hickory, NC
28601.
Abstract
OBJECTIVE. The purpose of this study was to assess the prevalence of
radial meniscal tears at arthroscopy and the ability of MRI to detect radial
tears preoperatively. In addition, the ability of four radiologic signs to
detect radial tears was assessed. Those signs are the truncated triangle,
cleft, marching cleft, and ghost meniscus signs.
MATERIALS AND METHODS. Arthroscopy of the knee was performed by a
single orthopedic surgeon on 196 consecutive patients. The surgeon noted each
radial tear he encountered. The MR images that were obtained at our
institution were reviewed, whereas those patients who were imaged elsewhere
were excluded. The preoperative MRI reports were reviewed to assess the
ability to prospectively identify radial meniscal tears. In addition, a
retrospective analysis of the MRI studies was performed by two radiologists in
which four radiologic signs were applied to detect radial tears.
RESULTS. Twenty-nine patients (15%) had radial tears at arthroscopy.
Eighteen of the 29 patients had their imaging performed at our institution and
were selected for review. There were 19 radial tears found at surgery. Seven
(37%) of the 19 tears were identified as radial prospectively.
Retrospectively, using the four signs for radial tears, reviewers identified
17 (89%) of 19 radial tears.
CONCLUSION. A more accurate preoperative diagnosis may be rendered
using the four described signs to detect radial tears, thus allowing
informative preoperative counseling and consideration of new therapies that
are available for radial meniscal repair.
Introduction
MRI has high accuracy in the identification of meniscal tears
[1]. Meniscal conservation and
meniscal repair have been advocated when practicable
[2]. Preoperative
characterization of meniscal tears can have an impact on operative planning,
preoperative counseling, and prognosis
[2,
3]. Some types of tears, such
as radial tears, may not be considered to be repairable. Radial tears are
considered less common than some other types of meniscal tears
[4] and can impair the function
of the meniscus, leading to increased wear and degenerative changes in the
affected joint [4,
5]. Radial tears are frequently
treated with débridement. Repair of radial tears is infrequently
attempted, and precise description of this type of tear can alert the
clinician and allow better preoperative planning
[3,
6]. The ability to
preoperatively identify patients suitable for meniscal repair would be ideal
[2].
The purpose of this study was to assess the prevalence of radial meniscal
tears at arthroscopy and to assess the ability to detect and characterize
radial tears on preoperative MRI. We also compare our data with data of other
studies in the literature.
Some radiologic signs for the detection of radial tears on MRI have been
described previously in the literature. During the course of this study, four
radiologic signs that aided greatly in the prospective identification of
radial tears were detected. These signs were retrospectively applied to the MR
examinations, and the ability of each sign to detect radial tears was
assessed.
Materials and Methods
Arthroscopy of the knee was performed by a single orthopedic surgeon in 196
consecutive patients during a 1-year period. The orthopedic surgeon is a
fellowship-trained sports medicine specialist and accomplished arthroscopist
with 10 years of experience who had specific training in meniscal repair and
cartilage repair and who is the orthopedic team physician for a major
university sports program. Twenty-nine (15%) of those 196 patients had radial
tears found at arthroscopy. The surgeon made note of the exact location of
each radial tear detected using meniscal diagrams completed immediately after
surgery. Of the 29 patients with radial tears, 18 had knee MRI performed at
our institution preoperatively. These 18 studies are the basis of this
report.
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Fig. 2 —Truncated triangle sign indicates radial meniscal tear.
T2-weighted fast spin-echo sagittal image (TR/TE, 4,000/70) with fat
saturation shows abrupt termination (arrow) of normal triangular
meniscal contour at tip of free edge of meniscus indicating radial tear in
49-year-old man.
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All of the studies were performed using a 1.5-T scanner (Signa, GE
Healthcare). MRI was performed using a standard knee protocol. Sagittal,
coronal, and axial fast spin-echo T2-weighted (TR/TE, 4,000/70) and sagittal
conventional proton density-weighted (2,000/20) images were obtained. Fat
saturation was used on each sequence. The field of view was 16 cm, and the
matrix was 256 x 192. The number of excitations was 2 for the fast
spin-echo images and 1 for the proton density images.
The initial interpretation of each study was performed prospectively by one
of five experienced musculoskeletal radiology staff at a major academic
medical center. The MRI reports were reviewed to assess the prospective
accuracy of MRI for the detection of radial tears. The corresponding
arthroscopic reports were reviewed to note the exact location of each radial
tear.
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Fig. 3A —Cleft sign indicating radial meniscal tear. T2-weighted fast
spin-echo coronal images (TR/TE, 4,000/70) with fat saturation show vertical
high signal extending through menisci (arrows), revealing radial
tears.
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Fig. 3B —Cleft sign indicating radial meniscal tear. T2-weighted fast
spin-echo coronal images (TR/TE, 4,000/70) with fat saturation show vertical
high signal extending through menisci (arrows), revealing radial
tears.
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Fig. 3C —Cleft sign indicating radial meniscal tear. T2-weighted fast
spin-echo coronal images (TR/TE, 4,000/70) with fat saturation show vertical
high signal extending through menisci (arrows), revealing radial
tears.
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In addition, a retrospective analysis of the MRI studies was performed by
two radiologists, including an experienced musculoskeletal radiology staff
member who was among the original group of five radiologists and a
musculoskeletal radiology fellow, who interpreted the examinations in
consensus. In the retrospective analysis, four radiologic signs were used to
detect radial tears: truncated triangle, cleft, marching cleft, and ghost
meniscus signs (Figs. 1A,
1B,
1C, and
1D).
The posterior horn and anterior meniscal horns appear triangular and have
low signal on sagittal MR images, whereas the body of the meniscus has a
triangular appearance on coronal images. The truncated triangle sign was
defined as the abrupt termination of the normal triangular meniscal contour at
its tip on a sagittal or coronal image
(Fig. 2). The cleft sign was
defined as linear, vertical high signal extending through the meniscus on a
coronal or sagittal image (Figs.
3A,
3B, and
3C). Similarly, the marching
cleft sign was defined as a cleft that was identified on consecutive sagittal
or coronal images that "marched" centrally or peripherally on each
adjacent image (Figs. 4A,
4B, and
4C). The ghost meniscus sign
was defined as the absence of identifiable meniscus on a given coronal or
sagittal image or the visible triangular form of the meniscus but high signal
replacing the normal dark meniscal signal, with normal meniscus seen on the
immediately adjacent images (Figs.
5A,
5B, and
5C). The incidence of each
sign was recorded.
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Fig. 4A —Marching cleft sign in discoid lateral meniscus indicates
radial meniscal tear in 21-year-old man. Conventional sagittal proton density
image (TR/TE, 2,000/20) with fat saturation shows partial cleft
(arrow) in most peripheral body segment.
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Fig. 4B —Marching cleft sign in discoid lateral meniscus indicates
radial meniscal tear in 21-year-old man. Conventional sagittal proton density
images (2,000/20) with fat saturation show vertical high signal
(arrows) extending through adjacent two body segments, indicating
cleft marching centrally and anteriorly indicating radial tear.
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Fig. 4C —Marching cleft sign in discoid lateral meniscus indicates
radial meniscal tear in 21-year-old man. Conventional sagittal proton density
images (2,000/20) with fat saturation show vertical high signal
(arrows) extending through adjacent two body segments, indicating
cleft marching centrally and anteriorly indicating radial tear.
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Fig. 5A —Ghost meniscus sign indicates radial meniscal tear.
T2-weighted fast spin-echo sagittal image (TR/TE, 4,000/70) with fat
saturation shows abnormal high signal in triangular shape (arrow) in
place of normally low-signal posterior horn of meniscus.
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Fig. 5B —Ghost meniscus sign indicates radial meniscal tear.
Conventional sagittal proton density image with fat saturation shows similar
findings of high signal in shape of posterior horn of meniscus.
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Fig. 5C —Ghost meniscus sign indicates radial meniscal tear.
T2-weighted fast spin-echo coronal image (4,000/70) shows cleft of high signal
(arrows) traversing posterior horn of meniscus corresponding to same
radial tear seen in orthogonal plane.
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Results
In the 18 MR studies that were available, 19 radial tears were identified
at arthroscopy (one patient had two radial tears). Seven (37%) of 19 were
identified as radial on MRI prospectively. The remaining tears were classified
as tears other than radial. These were simply identified as tears or as
complex tears. The location of the tears was as follows: posterior horn of the
medial meniscus (n = 10), posterior horn of the lateral meniscus
(n = 5), midbody of the lateral meniscus (n = 3), and
anterior horn of the lateral meniscus (n = 1)
(Fig. 6).
Retrospectively, using the four described signs to detect radial tears,
reviewers identified 17 (89%) of 19 radial tears. This represents a greater
than twofold increase in the number of radial tears detected (7 vs 17).
Although meniscal tears were clearly present on the two cases that were not
retrospectively identified as radial tears, none of the four signs to detect
radial tears was present in either case. The simultaneous presence of the
truncated triangle and cleft signs detected 13 radial tears, whereas each of
the four signs in isolation detected a single tear, respectively
(Table 1).
Discussion
The menisci serve several important biomechanical functions in the knee.
The menisci absorb shock, distribute load during dynamic loading, and assist
in joint lubrication. They also provide stability to the injured knee when the
cruciate ligament or other primary stabilizers are deficient. Menisci
distribute stresses over a broad area of articular cartilage that, in turn,
distributes the forces more evenly over the underlying bone. Together, these
functions enhance the ability of articular cartilage to provide a near
frictionless articulation that can perform extensive biomechanical maneuvers
while minimizing stress to the joint
[7]. It is estimated that up to
50-70% of the body's weight is transmitted through the menisci in extension
and up to 85-90% in flexion [2,
5].
Incongruity between the semicircular-shaped femoral condyles and the
comparably flat tibial plateau is compensated for by the congruent upper and
lower meniscal surfaces. This significantly increases the contact area of the
tibiofemoral joint and reduces stress on tibial and femoral cartilage. The
circumferential fibers of the meniscus, in concert with the firm attachments
to bone, or entheses, on each end of the meniscus allow the axial load to be
transformed into so-called "hoop-stresses" at the meniscal
periphery [2,
5].
Radial tears of the meniscus are significant in that radial transection of
the meniscus will completely disable the load-bearing function of the meniscus
and will instead allow the meniscus to be extruded under axial loading
[2,
5]. This exposes the
incongruent articular surfaces of the femoral condyles and tibial plateaus to
contact each other, resulting in overload and subsequent damage to the
articular cartilage and ultimately leading to accelerated wear and
degeneration. In addition, spontaneous osteonecrosis has been reported to be
more common in patients with radial tears
[4].
Treatment of meniscal tears is dependent on their configuration, size, and
location. Four alternatives exist for treatment of meniscal tears: no meniscal
surgery, meniscal repair, partial meniscectomy, and complete meniscectomy. For
more than 50 years, the practice of total meniscectomy has been known to
accelerate degeneration of the knee and cause remodeling of the articular
surfaces [5]. Loss of all or
part of the meniscus results in point loading. Thus, the practice of total
meniscectomy has been largely discarded. Enhanced understanding of the
biomechanics of the knee has led to a shift toward preservation of the menisci
[2].
For most types of meniscal tears, stress on the weight-bearing portions of
the tibial joint surface after partial meniscectomy was found to be directly
proportional to the amount of meniscal tissue resected. For this reason, the
goal of any surgical resection is to preserve as much meniscal material as
possible. Most important is preservation of the peripheral circumferential
collagen fibers [5]. In radial
tears, however, loss of function may be out of proportion to the amount of
residual meniscal tissue. Although radial tears involving the peripheral
fibers may not cause significant meniscal volume loss, they likely will render
the meniscus completely nonfunctional through an inability to resist hoop
stresses [2].
Longitudinal and oblique tears are usually amenable to repair, whereas
radial tears, horizontal tears, and complex tears (of which there is
frequently a radial component) generally cannot be repaired and usually
require partial meniscectomy
[6]. Thus, characterization of
the tear can help the surgeon and patient understand the preoperative
likelihood of repair versus resection
[2,
5]. This aids in preoperative
planning, patient counseling, and rehabilitation planning. For repairable
meniscal tears, the timing of surgery is important because outcome is improved
if surgery is performed within 8 weeks of injury
[3]. Stratification of
irreparable meniscal tears, such as radial tears and complex tears with a
radial component, from those that are potentially repairable takes on greater
significance.
Thus, proper preoperative characterization of meniscal tears is important.
Radial tears present unique challenges and entail special consideration.
Correct preoperative characterization of radial tears can allow better
operative planning and preoperative patient counseling.
Radial tears were found in 15% (29/196) of the studied patients undergoing
arthroscopy. Although all the radial tears in this study had been identified
as meniscal tears preoperatively by the five musculoskeletal radiologists
using subjective criteria (100% MR detection for these meniscal tears), the
prospective identification of the tear as radial was only 37%. It was thought
that the use of more objective signs for MR identification of radial meniscal
tears should improve prospective identification of radial meniscal tears with
MRI.
The application of the four described signs, including truncated triangle,
cleft, marching cleft, and ghost meniscus signs, increased the observers'
ability to detect radial tears in our retrospective review. The two most
effective signs were the cleft and the truncated triangle signs. The use of
only these two signs increased detection of radial meniscal tears to 76%. The
use of all four signs increased the detection rate for radial tears to
89%.
Tuckman et al. [4] described
similar findings in radial tears a decade ago. Among these findings was
complete absence of meniscus on MR images with meniscus seen on adjacent
images on either side of the tear. This is similar to the ghost meniscus sign;
however, due to volume averaging, the images reviewed in this study seldom
showed a complete absence of the meniscus, but rather showed the form of the
meniscus, but with high signal not representative of meniscus signal or the
so-called "ghost."
In the interval since the data from our study were originally presented,
other authors have confirmed several of our findings. A subsequent study by
Magee et al. [8] found radial
tears present in 14% (28/200) of radial meniscal tears at arthroscopy. In
addition, those authors, using criteria of abnormal morphology and truncation,
found 68% prospective identification of radial meniscal tears. This detection
rate is substantially better than the 37% prospective detection rate we found
using only subjective evaluation. Magee et al. added an additional criterion
to their evaluation described as "abnormal increased signal in the
meniscus on fat-saturated T2-weighted and proton density sequences," to
the previously mentioned criteria. This addition resulted in the detection of
89% of radial meniscal tears. This is identical to our calculated detection
rate of 89% when using the four radiographic signs for radial meniscal tears.
Although truncation is clearly analogous to the truncated triangle sign used
in our study, it is uncertain to what degree "abnormal morphology"
or "abnormal increased signal in the meniscus" corresponds to the
other criteria used in our study. It is likely that these were similar because
both methods resulted in an identical detection rate (89%).
Jee et al. [6] cited a
detection rate between 45% and 73% for MR identification of radial tears and a
prospective ability to distinguish repairable versus nonrepairable meniscal
tears 56-73% of the time. Matava et al.
[9], using high-field-strength
MRI evaluation, found that the correct type of meniscal tear could be
estimated in only 14-73% of the cases with only moderate ability to correctly
predict meniscal reparability.
We think that the four signs we describe, although similar in overall rate
of detection of meniscal tears to some described in previous studies, may be
more easily understood, recognized, and thus used by practicing radiologists.
Through the use of these four signs, we hope that practicing radiologists will
be able to increase their ability to detect radial meniscal tears during
everyday practice and improve the preoperative prediction of radial meniscal
tears. This can help improve characterization of meniscal reparability and aid
in preoperative planning.
Limitations of our study include the retrospective nature of the study. The
five original observers did not use objective criteria during their original
interpretation and did not always characterize the type of meniscal tear that
they thought was present. This may have artificially lowered the sensitivity
of the original interpretations and may artificially magnify the difference
between the original interpretations and the subsequent reinterpretations
using the four radiologic signs of radial meniscal tears.
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Abstract
Introduction
