DOI:10.2214/AJR.05.0339
AJR 2006; 187:364-370
© American Roentgen Ray Society
Meniscal Flounce on Knee MRI: Correlation with Meniscal Locations After Positional Changes
Ji Seon Park1,
Kyung Nam Ryu1 and
Kyoung Ho Yoon2
1 Department of Diagnostic Radiology, Kyung Hee University Hospital, 1,
Heokidong Dongdaemun-ku, Seoul, South Korea 130-702.
2 Department of Orthopaedic Surgery, Kyung Hee University Hospital, Seoul, South
Korea.
Received February 27, 2005;
accepted after revision April 25, 2005.
Address correspondence to K. N. Ryu
(t2star{at}naver.com).
Abstract
OBJECTIVE. The purpose of our study was to illustrate the MRI
features of meniscal flounce and the meniscal locations on the tibial plateau
after positional changes without external force and to evaluate the
correlation of the presence of flounce with meniscal location.
SUBJECTS AND METHODS. For 8 months, 441 knee MR images were
prospectively studied for meniscal flounce. Routine MRI was performed on a
10° flexed knee, and flounce was seen in 22 medial menisci (5%). In all 22
of the patients with flounce, additional sagittal proton density-weighted MR
images were obtained while the knees were both maximally flexed and maximally
extended in a knee surface coil. We evaluated and compared the changes of
degree of flounce and meniscal location on the tibial plateau among the three
positions.
RESULTS. With the maximally extended knee, the flounce disappeared
in all cases but one. With the maximally flexed knee, the flounce disappeared
in nine cases (9/22, 41%), was slightly released in 11 (11/22, 50%), and was
accentuated in two (2/22, 9%). As the knees were more extended, the anterior
horns of the menisci migrated more anteriorly, the posterior horns revealed
subtle movement without a regular pattern, and the flounce was slightly
released or disappeared.
CONCLUSION. Active knee positioning in the knee surface coil changed
the degree of meniscal flounce and the meniscal location on the tibial
plateau. The meniscal flounce is thought to be a transient physiologic
distortion and may be related to meniscal locations on the tibial plateau. It
may be changed by varying the knee position.
Keywords: anatomy • knee • meniscus • MRI • musculoskeletal imaging
Introduction
Ameniscal flounce is considered a normal positional variant characterized
by a single symmetric fold along the free edge of the meniscus. Zarins and
McInerney [1] described this
phenomenon in arthroscopy and considered it to be a meniscal variant induced
by external force [1]. A few
literature articles regarding arthroscopy or arthrography also relate that the
meniscal flounce can be commonly found when an external force, including
flexion, valgus, and external rotation, is simultaneously applied to the
posteromedial compartment of the knee during the procedure
[2,
3]. In addition, relaxation by
anesthesia or iatrogenic distention with fluid during a procedure has been
thought to contribute to the appearance of meniscal flounce. However, with the
advent of MRI, this flounce was observed when no predisposing factors such as
external force were present, although the flounce was observed far less often
than on arthroscopy [4,
5]. Regarding this observation,
previous studies have explained that the valgus deformity and increased
mobility caused by ligamentous injuries or joint effusion may predispose the
meniscus to folding
[4-6].
However, in clinical practice, we rarely observe the meniscal flounce on
the knee MR images of patients who have neither the application of external
force nor a clinically significant internal derangement; and, in those cases,
the location of either horn on the tibial plateau is changed with regard to
the degree of flexion of the knee joint. We believe that the evaluation of
flounce cause based on the arthroscopic concept has a few limitations. First,
the locations of the meniscal horns on the tibial plateau cannot be externally
visualized, so the anatomic relationship of the meniscus to adjacent
structures is not completely evaluated. Second, the posterior horn of the
medial meniscus is seen only with tibial rotation, and it is not known whether
this phenomenon persists when the tibia is not rotated. Furthermore, the
previous MRI studies related to meniscal flounce also focused on the
predisposing factors in arthroscopy and the differences between a flounce and
a true meniscal tear
[4-6].
Thus, we attempted to analyze on MRI the occurrence and disappearance of the
meniscal flounce in view of the anatomic changes associated with active
positioning because MRI can depict meniscal configuration and its location
with the knee in any position. We hypothesized that the active knee positions
when there is no external force may alter the anatomic relationship of the
meniscus with surrounding structures—the meniscal location on the tibial
plateau, the contact surface with the femoral condyle—and lead to
meniscal flounce at a certain point in the course of movement. To our
knowledge, few MRI studies have described the changes of meniscal flounce by
different positions in the absence of external force and the relationship of
flounce to meniscal locations in different positions, although many
investigators have described the meniscal movement in various positions
[7-12].
The purpose of this study was to illustrate the positional changes of
meniscal flounce on MR images when no external force is applied. In addition,
in the knees with flounce, the meniscal locations on the tibial plateau
related to different knee positions were evaluated on MR images and were
correlated with the existence or degree of flounce in each knee.
Subjects and Methods
Between August 2003 and March 2004, a total of 441 knee MR images were
prospectively evaluated for the presence of meniscal flounce. Meniscal flounce
was defined as a wavy, undulating, or S-shaped redundancy along the free edge
of the meniscus. Routine knee MR images were obtained with the knee placed at
about 10° of flexion in a knee surface coil because this position has been
thought to accurately show the injury of the anterior cruciate ligament (ACL),
which is the most common form of internal knee derangement
[13]. This position is
referred to in this article as the "neutral" position. A 1.5-T MR
scanner (Magnetom Vision, Siemens Medical Solutions) was used with the
following parameters: acquisition matrix of 512 x 180, a field of view
of 16 cm, 1-2 excitations, a slice thickness of 4 mm, and an interslice gap of
0.2 mm. For the evaluation of meniscal flounce, we observed the proton
density-weighted (TR/TE, 3,300/16) and T2-weighted sagittal images
(3,300/98).
Of 441 patients, 22 patients (5%) were identified as showing the meniscal
flounce on routine MRI, all of which occurred in the medial meniscus. The
patients were 18 men and four women whose ages ranged from 20 to 54 years
(mean age, 33.3 years). The patients had pain or discomfort of the knee and
findings suspicious for internal knee derangement on physical examination. All
22 patients with flounce underwent additional MRI studies with the knee in two
different positions immediately after the routine MRI examination. This study
was approved by the hospital's review board, and all patients gave informed
consent to participate in the study.
First, patients were asked to perform maximum knee flexion in the surface
coil by themselves, with a sponge pad placed beneath the knee, and proton
density-weighted and T2-weighted sagittal MR images were obtained. This
position is referred to in this article as the "flexed" position.
Next patients were asked to perform maximum knee extension in the surface coil
by themselves, and proton density-weighted sagittal MR images were obtained.
This position is termed the "extended" position. The other
parameters used on additional MRI studies were the same as for the routine MRI
studies.
Two experienced musculoskeletal radiologists who were aware of the patient
positions used reviewed the MR images on a PACS monitor and interpreted the
images by consensus. In each patient, the angle between the femur and the
tibia was measured on midsagittal images of three positions (neutral, flexed,
and extended). The differences in the angles of the knee joint among the three
positions were statistically analyzed using an analysis of variance test
(SPSS, version 11.0). On comparison with the neutral position of the knee, the
changes of flounce configuration in both flexed and extended positions were
classified into three types: disappeared, slightly released but still evident,
and accentuated. The meniscal location in relation to the tibial plateau was
assessed on the first medial sagittal image, in which both horns of the medial
meniscus were separated with no bowtie appearance. Base lines were drawn along
the inferior meniscal surfaces of both the anterior and posterior horns, and
then perpendicular lines were drawn through the peripheral meniscal margin and
the tibial margin (Fig. 1). The
distances (in millimeters) between the peripheral meniscal margin and the
tibial margin were measured along those lines. If the peripheral meniscal
margin was within the tibial plateau, the distance was expressed as a positive
value, whereas if it was outside the tibial plateau, the distance was reported
as a negative value. If the meniscal margin corresponded to the tibial margin,
the distance was given as 0. The changes of meniscal location on the tibial
plateau among the three positions were statistically analyzed using an
analysis of variance test (SPSS, version 11.0). A p value of less
than 0.05 was considered a statistically significant difference. We also
evaluated the correlation of the configurations of the meniscal flounce with
meniscal location according to positional changes in each patient. For the
meniscal location of this analysis, the migrations of both the anterior and
posterior horns were simultaneously considered from a viewpoint of direction
and distance, reflecting the distance between the anterior and posterior
horns.
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Fig. 1 —Diagram shows measurement for anterior (A) and posterior (P)
distances from peripheral meniscal margin to tibial margin for both anterior
and posterior horns, indicating meniscal location on tibial plateau. Lines
through both peripheral meniscal margin and outermost tibial margin were set
perpendicular to baseline along inferior meniscal surface of both anterior and
posterior horns, respectively. Anteroposterior distances between these two
lines were measured in millimeters.
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In addition, we recorded the presence of any associated
abnormalities—particularly ligamentous or meniscal lesions, significant
amounts of joint effusion, and osteochondral lesions—in the knees with
meniscal flounce. Finally, in four patients who underwent arthroscopic surgery
within 1 month of MRI, we observed in which positions the flounce was induced
or released.
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Fig. 2A —Medial meniscal flounce on routine left knee MR images of
43-year-old man with anterior cruciate ligament tear, lateral meniscus tear,
and medial meniscus degeneration. Sagittal proton density-weighted (TR/TE,
3,300/16) images show bowtie appearance and next lateral image in neutral
(A), maximally extended (B), and maximally flexed (C)
knee in a surface coil. From neutral to maximally extended position, flounce
disappears, with anterior migration of anterior horn and slightly posterior
migration of posterior horn. With maximally flexed knee, flounce is slightly
released but is still evident, with posterior migration of both horns.
Distances between anterior horn margin and anterior tibial margin (A in
Fig. 1) are 5.19 mm in
A, 0 mm in B, and 7.74 mm in C, representing anterior
migration of anterior horn as knee is extended farther. Distances between
posterior horn margin and posterior tibial margin (P in
Fig. 1) are 6.64 mm in
A, 4.7 mm in B, and 4.2 mm in C.
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Fig. 2B —Medial meniscal flounce on routine left knee MR images of
43-year-old man with anterior cruciate ligament tear, lateral meniscus tear,
and medial meniscus degeneration. Sagittal proton density-weighted (TR/TE,
3,300/16) images show bowtie appearance and next lateral image in neutral
(A), maximally extended (B), and maximally flexed (C)
knee in a surface coil. From neutral to maximally extended position, flounce
disappears, with anterior migration of anterior horn and slightly posterior
migration of posterior horn. With maximally flexed knee, flounce is slightly
released but is still evident, with posterior migration of both horns.
Distances between anterior horn margin and anterior tibial margin (A in
Fig. 1) are 5.19 mm in
A, 0 mm in B, and 7.74 mm in C, representing anterior
migration of anterior horn as knee is extended farther. Distances between
posterior horn margin and posterior tibial margin (P in
Fig. 1) are 6.64 mm in
A, 4.7 mm in B, and 4.2 mm in C.
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Fig. 2C —Medial meniscal flounce on routine left knee MR images of
43-year-old man with anterior cruciate ligament tear, lateral meniscus tear,
and medial meniscus degeneration. Sagittal proton density-weighted (TR/TE,
3,300/16) images show bowtie appearance and next lateral image in neutral
(A), maximally extended (B), and maximally flexed (C)
knee in a surface coil. From neutral to maximally extended position, flounce
disappears, with anterior migration of anterior horn and slightly posterior
migration of posterior horn. With maximally flexed knee, flounce is slightly
released but is still evident, with posterior migration of both horns.
Distances between anterior horn margin and anterior tibial margin (A in
Fig. 1) are 5.19 mm in
A, 0 mm in B, and 7.74 mm in C, representing anterior
migration of anterior horn as knee is extended farther. Distances between
posterior horn margin and posterior tibial margin (P in
Fig. 1) are 6.64 mm in
A, 4.7 mm in B, and 4.2 mm in C.
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Results
The flounce of the medial meniscus showed a wavy or S-shaped deformity
along the free edge of the posterior horn and the mid horn on one or two
sagittal images of routine MR studies.
The mean angle between the femur and tibia was 168.15° (range,
160.8-174.2°) in the neutral position of the routine MR images,
156.37° (147.1-169.6°) in the flexed position, and 180.71°
(175.4-192.6°) in the extended position on additional MR images. Despite
individual variations, a statistically significant difference in the angles of
the knee joint among the three positioning groups was seen (p <
0.001); on average, the difference was approximately 12° between the
maximally flexed and neutral groups and between the neutral and maximally
extended groups.
Compared with the flounce visualized on routine MR images, the degree of
flounce in two different positions on additional MR studies was assessed in
each patient. With the maximally extended knee, the flounce disappeared in all
cases (Figs. 2B,
3B, and
4B) but one, which showed the
flounce slightly released but still evident in comparison with the neutral
position. On the other hand, with the maximally flexed knee, the flounces
disappeared in nine patients (41%, Fig.
3C), was slightly released but still evident in 11 (50%,
Fig. 2C), and was accentuated
in two (9%, Fig. 4C). In nine
patients in whom the flounce disappeared in the flexed position, routine knee
MRI identified the various associated findings: lateral meniscus tear in one
patient, medial collateral ligament tear in two, medial collateral ligament
and lateral collateral ligament tears in one, lateral meniscus and lateral
collateral ligament tears in one, ACL tear in one, and normal in three
patients. In 11 patients with a slightly released but still evident flounce in
the flexed position, routine knee MRI revealed the various associated
findings: medial meniscus degeneration in three patients, ACL tear in one,
posterior cruciate ligament degeneration in one, lateral meniscus and ACL
tears in one, medial collateral ligament tear in one, lateral meniscus tear in
one, posterior cruciate ligament degeneration in one, synovitis in one, and
normal in one. Two patients with an accentuated flounce in the flexed position
sustained an osteochondral lesion and a medial collateral ligament tear,
respectively.
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Fig. 3B —Medial meniscal flounce on routine knee MR images of
23-year-old man with no abnormality. Two continuous sagittal proton
density-weighted (TR/TE, 3,300/16) images in neutral (A), maximally
extended (B), and maximally flexed (C) knee in surface coil.
From neutral to maximally extended position, flounce disappears with anterior
migration of anterior horn. On maximally flexed knee, flounce also disappears
with posterior migration of both horns. Distances representing anterior
migration of anterior horn with more extension of knee (A in
Fig. 1) are 0 mm in A,
-2.1 mm in B, and 4.25 mm in C. Distances between posterior horn
margin and posterior tibial margin (P in
Fig. 1) are 5.31 mm in
A, 5.35 mm in B, and 3.98 mm in C.
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Fig. 4B —Medial meniscal flounce on routine knee MR images of
34-year-old man with medial collateral ligament tear. Sagittal proton
density-weighted (TR/TE, 3,300/16) images in neutral (A), maximally
extended (B), and maximally flexed (C) knee in a surface coil.
From neutral to maximally extended position, flounce disappears. On maximally
flexed knee, flounce is accentuated, with posterior migration of anterior horn
and slightly anterior migration of posterior horn.
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Fig. 3C —Medial meniscal flounce on routine knee MR images of
23-year-old man with no abnormality. Two continuous sagittal proton
density-weighted (TR/TE, 3,300/16) images in neutral (A), maximally
extended (B), and maximally flexed (C) knee in surface coil.
From neutral to maximally extended position, flounce disappears with anterior
migration of anterior horn. On maximally flexed knee, flounce also disappears
with posterior migration of both horns. Distances representing anterior
migration of anterior horn with more extension of knee (A in
Fig. 1) are 0 mm in A,
-2.1 mm in B, and 4.25 mm in C. Distances between posterior horn
margin and posterior tibial margin (P in
Fig. 1) are 5.31 mm in
A, 5.35 mm in B, and 3.98 mm in C.
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Fig. 4C —Medial meniscal flounce on routine knee MR images of
34-year-old man with medial collateral ligament tear. Sagittal proton
density-weighted (TR/TE, 3,300/16) images in neutral (A), maximally
extended (B), and maximally flexed (C) knee in a surface coil.
From neutral to maximally extended position, flounce disappears. On maximally
flexed knee, flounce is accentuated, with posterior migration of anterior horn
and slightly anterior migration of posterior horn.
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As the knees were more extended, the numeric values of distances between
the meniscal margin of the anterior horn and the anterior tibial margin,
marked as positive or negative signs according to meniscal location, decreased
(Table 1). Apparently the
anterior horns of the menisci migrated more anteriorly as the knees were more
extended (Figs. 2A,
2B, and
2C), with a statistical
confidence of p < 0.001. On the other hand, the posterior horn
showed a slight posterior migration in the extended position, and posterior
migration occurred to a large degree in the flexed position (Figs.
2A,
2B, and
2C) as compared with the
neutral position (Table 1).
These findings mean that the positional changes of the posterior horn location
revealed a statistical significance (p = 0.041) but in a nonuniform
pattern.
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TABLE 1: Mean Distances Between Peripheral Meniscal Margin and Tibial Margin for
the Two Horns in Three Positions
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Fig. 3A —Medial meniscal flounce on routine knee MR images of
23-year-old man with no abnormality. Two continuous sagittal proton
density-weighted (TR/TE, 3,300/16) images in neutral (A), maximally
extended (B), and maximally flexed (C) knee in surface coil.
From neutral to maximally extended position, flounce disappears with anterior
migration of anterior horn. On maximally flexed knee, flounce also disappears
with posterior migration of both horns. Distances representing anterior
migration of anterior horn with more extension of knee (A in
Fig. 1) are 0 mm in A,
-2.1 mm in B, and 4.25 mm in C. Distances between posterior horn
margin and posterior tibial margin (P in
Fig. 1) are 5.31 mm in
A, 5.35 mm in B, and 3.98 mm in C.
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In each case, the morphologic changes of meniscal flounce in two different
positions were correlated with the meniscal locations on the tibial plateau.
The disappearance or release of flounce while the knee was maximally extended
involved both the anterior migration of the anterior horn and the slightly
posterior migration of the posterior horn in all patients except two. In those
two patients, both horns migrated anteriorly and the anterior migration of the
anterior horns was less than that of the posterior horns, although the
flounces disappeared. In other words, in most cases the maximal extension of
the knee led to the widened distance between both horns, allowing the release
of the flounce. On the other hand, the flounce changes while the knee was
maximally flexed were explained by the pattern of meniscal movement in only
half the cases; release with various degrees was coincident with widened
distance between both horns. Only one of two cases with accentuated flounce
during maximal flexion was attributed to meniscal location—posterior
migration of anterior horn and anterior migration of posterior horn. The
degree of release of meniscal flounce in the maximally flexed position did not
show a linear relationship to the distance between the two horns.
In the four patients who underwent arthroscopic surgery, intact medial
menisci without tear were confirmed, whereas associated injuries such as an
ACL tear in one patient, lateral meniscus tear in one, and osteochondral
lesions in two were identified. Furthermore, arthroscopy revealed that the
meniscal flounce developed during external rotation, valgus stress, and
flexion of the knee. However, as the knees became more flexed, the flounce
disappeared, in a manner similar to our MRI finding.
Discussion
According to biomechanical theory, the periphery of either of the horns of
the medial meniscus is firmly attached to the tibial plateau by a capsule,
whereas the inner edge is free. Also, tibial rotation can induce the periphery
of the meniscus to be pulled in different directions, leading to waviness or
buckling of the free inner edge
[4]. However, the kinetic
linkage in relation to the knee joint is complex, and when and why the flounce
is developed or released have not been clearly identified.
Meniscal flounce during knee MRI without the application of any external
force has been thought to be created by joint laxity with ligamentous
injuries, large effusion, and mild external rotation by positioning in the
surface coil, which simulate the arthroscopic condition
[4]. However, this theory is
not unanimously accepted, and a few MRI studies have reported some cases
suggesting that the flounce could be more than a simple rotational deformity
by joint laxity [5,
6]. Yu et al.
[5] presented evidence that
half the patients in a study group did not have a clinically significant
ligamentous injury, and 40% did not have a significant joint effusion. Kim et
al. [6] showed a case of
flounce with no ligament injury. Those authors stated that the flounce was not
as prominent as the cases with ligamentous injury and might be induced by a
mild external rotation of the tibia in the magnet. Furthermore, joint
effusion, according to these two previous studies, was not necessary to cause
the flounce. Our study of 22 flounces showed results coincidental with these
two studies; significant ligamentous injuries were identified in nine cases
(41%), and joint effusion with clinical significance was seen in only two
cases (9%).
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Fig. 4A —Medial meniscal flounce on routine knee MR images of
34-year-old man with medial collateral ligament tear. Sagittal proton
density-weighted (TR/TE, 3,300/16) images in neutral (A), maximally
extended (B), and maximally flexed (C) knee in a surface coil.
From neutral to maximally extended position, flounce disappears. On maximally
flexed knee, flounce is accentuated, with posterior migration of anterior horn
and slightly anterior migration of posterior horn.
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The meniscal location related to positional change has been described in a
few in vivo or in vitro MRI studies
[7-12].
According to a previous report using cadaveric knees
[7], the meniscus can show
migration in either an anteroposterior direction or a lateromedial direction
during flexion and extension. These MR studies agreed that knee flexion leads
to posterior movement of either horn of the menisci and shortening of the
distance between the two horns
[8,
9]. In addition, the movement
is greater in the anterior horn than in the posterior horn
[10,
11]. The movement direction of
the medial menisci viewed in our study is coincident with previous
descriptions except for a few points. First, in our study the posterior horns
migrated posteriorly during knee motion from the neutral to the maximally
extended position in a surface coil in 14 cases (63.6%), but it was too subtle
(mean, 0.6 mm) for the posterior migration on extension to reach statistical
significance. Second, the considerable migration of the anterior horn compared
with the posterior horn was observed from the neutral to the extended position
but was not significant from the neutral to the flexed position. We consider
that this discrepancy may be related to the range and degree of motion. This
is supported by the kinematic MRI study using cadaveric knees by Muhle et al.
[12]. Those authors proposed
that the transverse ligament has a restricting effect on the anteroposterior
excursion of the anterior horn of the medial meniscus at lower degrees (<
30°) of knee flexion but not at greater degrees (> 60°) of
flexion.
Our MRI study presented evidence that the meniscal flounce is a transient
phenomenon changed by active positioning. It was observed in a neutral
position and was slightly released or eliminated by a maximally flexed or
extended position in almost all cases. Although the differences in joint angle
in relation to the positions were not large because of limitations of the knee
surface coil, a maximally extended knee in the surface coil induced the
disappearance of flounce, significant anterior migration of the anterior horn,
and subtle posterior migration of the posterior horn in almost all cases. This
suggests that knee extension separates the anterior horn from the posterior
horn, followed by the release of flounce. On the other hand, a maximally
flexed knee in the surface coil induced significant posterior migration of the
anterior horn and subtle posterior migration of the posterior horn and
resulted in a slightly released but still evident flounce in half of the
patients, completely released flounce in 41% (9/22), and even accentuated
flounce in 9% (2/22).
In the flexed position, the migration distances of both horns did not
correlate with the positional changes of configuration or the degree of
release of flounce; of the 20 patients with a partial or complete release of
flounce, half (10/20) showed a decreased distance between the two horns.
Furthermore, the distance between the two horns was not proportional to the
degree of release of flounce, on comparison between the disappeared and the
slightly released but still evident groups. These findings suggest that the
changes in meniscal flounce from the neutral to the maximally flexed position
could be related to other anatomic factors in addition to meniscal location,
whereas the maximally extended position ensures the release of the meniscal
flounce because of the meniscal location. In view of meniscal dynamics, knee
flexion allows the femorotibial contact point to migrate posteriorly,
resulting in posterior horn impingement and the pressing of the free edge of
the meniscus between the femoral and tibial condyles
[8]. This meniscal impingement
during knee flexion ensures maximal congruency with the articular surfaces for
preventing injury. We unexpectedly observed that the posterior horn of the
meniscus was tightly interposed between the femoral and tibial condyles during
knee flexion, in contrast to the floating meniscus on the tibial plateau with
intervening fluid signal seen on T2-weighted sagittal images during knee
extension, as consistent with previous reports
[8,
10]. According to these
findings, we believe that the impact of the relatively thin and long posterior
horn against the posterior femoral condyle during knee flexion may result in
the meniscus conforming to the tibial plateau and may account for this
phenomenon of flounce release or disappearance in progressive degrees of
flexion.
The meniscal flounce has been reported to be a rare phenomenon—seen
in 0.2-6% of patients
[4-6]—on
MRI as compared with arthroscopy, because of the lack of external stress in
MRI studies. In our experience, the prevalence of meniscal flounce was 5%,
which appeared to be slightly more frequent than in previous MR reports
[4,
5]. Furthermore, we found that
the flounce in the 10° flexed position was retained in 59% of maximally
flexed knees in the surface coil. We believe that this occurrence rate of
flounce in our study could be related to the 10° flexed knee positions on
our routine MR images, contrary to the usual knee MRI studies with a 10°
external rotation of knee
[14]. Also, the active knee
flexion with no external force may provide a condition more vulnerable to
meniscal flounce because of the decreased distance between the two horns
during knee flexion.
Our study has a few limitations. First, the various and practical types of
knee motions could not be thoroughly visualized because of the closed MR
scanner and the number of sequences. This limitation of meniscal kinematic
assessment may be overcome with the use of advanced imaging techniques such as
3D MRI reconstruction. Second, in the measurement and comparison of meniscal
movement in three positions, the positional changes in limb orientation in the
surface coil and non-realtime examinations could not ensure a constant
scanning plane. However, the direction and pattern of meniscal movement were
recorded with reference to two more planes adjacent to the selected sagittal
section. Third, the meniscal locations on positional changes were evaluated on
sagittal planes, not on coronal planes.
In conclusion, the meniscal flounce is thought to be a transient
physiologic distortion, and its degree can be changed with the meniscal
location on the tibial plateau and the anatomic knee position.
References
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Abstract
Introduction
