AJR 2001; 177:911-917
© American Roentgen Ray Society
MR Imaging of the Medial Collateral Ligament Bursa
Findings in Patients and Anatomic Data Derived from Cadavers
Michel De Maeseneer1,
Maryam Shahabpour1,
Frans Van Roy2,
Anita Goossens3,
Filip De Ridder1,
Jan Clarijs2 and
Michel Osteaux1
1
Department of Radiology, Vrije Universiteit Brussel, Laerbeeklaan 101, 1090
Jette, Belgium.
2
Department of Experimental Anatomy, Vrije Universiteit Brussel, Jette,
Belgium.
3
Department of Pathology, Vrije Universiteit Brussel, Jette, Belgium.
Received October 9, 2000;
accepted after revision April 17, 2001.
Address correspondence to M. De Maeseneer.
Abstract
OBJECTIVE. The purpose of this work was to define the MR imaging
findings of fluid collections confined to the medial collateral ligament (MCL)
bursa and to correlate these findings with anatomic features shown in
cadaveric specimens.
MATERIALS AND METHODS. The anatomic location of the MCL bursa was
investigated by MR—anatomic correlation in seven cadaveric knees. The MR
imaging studies and clinical charts of six patients with fluid collections
confined to the MCL bursa were reviewed.
RESULTS. On anatomic sections, the MCL bursa was located between the
superficial and deep portions of the MCL. Separate femoral and tibial
compartments were seen in most specimens.
CONCLUSION. The anatomy of the MCL bursa is shown with MR imaging in
cadaveric specimens and patients. Understanding the compartmentlike
distribution of fluid in the MCL bursa at MR imaging allows accurate diagnosis
and differentiation from other conditions.
Introduction
Bursae are typically interposed between bony surfaces and ligaments or
tendons in areas where friction takes place. Brantigan and Voshell
[1] found evidence of the
medial collateral ligament (MCL) bursa in 52 (91%) of 57 dissected knees.
Despite this high prevalence, to our knowledge, only one article in the
radiological literature refers to the MCL bursa
[2]. Both Stuttle
[3] and Kerlan and Glousman
[4] reported that the clinical
condition referred to as MCL bursitis may result when the MCL bursa is
inflamed and distended by fluid. These authors consider MCL bursitis an
important cause of medial knee pain that should be differentiated from other
conditions such as MCL injuries and meniscal tears.
The medial supporting structures of the knee can be divided into three
layers [5]. Layer I consists of
the crural fascia, layer II is made up of the superficial portion of the MCL,
and layer III is made up of the joint capsule and the deep portion of the MCL
that includes the meniscotibial and meniscofemoral extensions. Along the
anterior edge of the superficial portion of the MCL, layer II is
discontinuous. The discontinuity in layer II and the presence of the MCL bursa
allow the MCL to glide over the bony surfaces of the tibia and femur with knee
flexion [1,
5] (Figs.
1 and
2). Along the posterior third
of the medial side of the knee, the superficial and deep portions of the MCL
are fused and tend to fold rather than glide over the bony surfaces when the
knee is flexed [1,
5].
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Fig. 1. —Line drawing represents anteromedial aspect of knee. Clamp
(C) elevates anterior edge of superficial portion of medial collateral
ligament (MCL). MCL bursa (black area) is seen between superficial (S) and
deep MCL. Meniscofemoral (F) and meniscotibial (T) extensions are part of deep
MCL. Also note posterior oblique (O) portion of MCL.
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Fig. 2. —Line drawing represents axial section of medial side of knee.
Note three distinct layers (I, II, and III). Layer I corresponds to crural
fascia, layer II contains superficial portion of medial collateral ligament
(MCL), and layer III contains deep portion of MCL. MCL bursa (black area, B)
is located between superficial and deep portion of MCL. Also note split in
layer II along anterior margin of superficial MCL (arrowheads).
Anteriorly, layer I is fused with layer II (curved arrow), whereas
posteriorly, layer II joins layer III (short arrows). Sartorius
tendon is embedded in layer I (S).
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The MCL bursa may become apparent at MR imaging when filled with fluid
[2]. The purpose of our study
was to describe the normal imaging anatomy of the MCL bursa by using cadaveric
correlation and contrast opacification of the bursa. The second aim of our
article was to evaluate the clinical and MR imaging findings in patients with
fluid collections confined to the MCL bursa.
Materials and Methods
Cadaveric Study
Seven cadaveric knees were obtained from non-embalmed fresh cadavers and
were immediately deep-frozen at -30°C. The knees belonged to three men and
four women whose age at death ranged from 50 to 91 years. The specimens were
thawed in saline solution at room temperature for 18 hr before imaging. In six
specimens, MR images were obtained in the transverse and coronal imaging
planes with a 1.5-T clinical system (Vision; Siemens, Erlangen, Germany). The
specimens were placed in supine position in a dedicated knee coil. The imaging
parameters are listed in Table
1. In two specimens, we attempted to inject the MCL bursa with a
mixture of dye and contrast agent. A mixture of 1 mL of dye and 10 mL of
gadopentatate dimeglumine solution (Magnevist [1 mL in 200 mL of saline
solution]; Schering, Berlin, Germany) was injected into the MCL bursa using
sonographic guidance (Prosound 5500 [7.5-Mhz probe]; Aloka, Tokyo, Japan). For
injection of the MCL bursa, an 18-gauge spinal needle was advanced obliquely
through the skin until the needle tip was positioned deep in relation to the
superficial portion of the MCL. The needle was placed at about 1.5 cm above
and below the level of the joint space, adjacent to the femoral cortex and
tibial cortex, respectively. Filling of the bursa could be observed in real
time using sonography. Subsequently, MR images were obtained using the
parameters listed in Table
1.
In one specimen, the medial aspect of the knee was dissected and the MCL
bursa was opened. The other six specimens were refrozen and sectioned with a
band saw (NSV; Modena, Italy) into slices 3-4 mm thick that correlated with MR
images. Three specimens were sectioned along the coronal plane and three
others along the transverse plane. The region of the MCL bursa was examined by
consensus of an anatomist and a musculoskeletal radiologist. This assessment
included evaluation of separate femoral and tibial components of the MCL
bursa, measurement of the size of these compartments, and evaluation of the
distribution of injected dye. Microscopic examination of the MCL bursa was
performed in a randomly selected tissue sample that included the superficial
and deep portions of the MCL. Histologic staining included H and E staining
and immunological staining with epithelial membrane antigen (Dako A/S;
Glostrup, Denmark). The microscopic slides were examined by a senior
pathologist who was unaware of the results of gross anatomy and MR
imaging.
Clinical Study
The reports of all MR examinations of the knee performed in 1998 and 1999
at our institution (n = 2454) were retrospectively reviewed. The
details of typical MR imaging protocols are shown in
Table 1. The initial reports
had been made by one of two senior musculoskeletal radiologists. Both
radiologists used consistent criteria for diagnosing fluid in the MCL bursa,
based on previously published data in the literature
[2]. These criteria included
presence of a collection with high signal intensity on short tau inversion
recovery—weighted MR images, or signal intensity higher than that of fat
on T2-weighted MR images, located deep in relation to the superficial portion
of the MCL is distinguishable from intraarticular joint fluid by the
interposition of the deep layer of the MCL. The records of all patients with a
fluid collection confined to the MCL bursa were selected. Patients with MR
imaging signs of MCL tears were not included. MR imaging signs of MCL tears
included visualization of a tear, nonvisualization of a portion of the MCL,
edema in the substance of the MCL or periligamentous edema, and characteristic
bone contusions. In addition, 20 patients with a meniscal tear on MR images or
at arthroscopy were not included in the further analysis.
The imaging studies and clinical charts of six patients (three men, three
women) with fluid confined to the MCL bursa were reviewed by consensus of two
musculoskeletal radiologists. This evaluation included an assessment of the
size and location of the MCL bursa, as well as presence of other MR imaging
findings (ligament tear, osteoarthritis, edema, and others). Criteria used for
diagnosis of osteoarthritis included joint space narrowing, signal changes and
ulcerations of cartilage, osteophytes, meniscal subluxation, and subchondral
bone changes. The length and thickness of the MCL bursa were measured on the
coronal MR image best showing the superficial portion of the MCL. On the axial
MR image, the anteroposterior dimensions of the femoral and tibial
compartments were measured.
Results
Cadaveric Study
The MCL bursa was not apparent on MR images obtained from the cadaveric
specimens without intrabursal contrast injection (Fig.
3A,3B).
In one specimen, the tibial portion of the MCL bursa could be outlined on MR
images after intrabursal injection of contrast medium. The intrabursal
location of dye was shown on the anatomic slices. In another specimen, the
injection was unsuccessful but the MCL bursa was shown to be present at
macroscopic inspection.
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Fig. 3A. —Cadaveric study. Coronal proton density—weighted MR
image (TR/TE, 2900/15) reveals superficial medial collateral ligament (MCL,
short arrows), as well as meniscofemoral and meniscotibial portions
of deep MCL (curved arrows). MCL bursa is not seen.
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At macroscopic inspection of the specimens, the MCL bursa corresponded to a
vertically elongated compartment located between the superficial and the deep
portions of the MCL. The MCL bursa was located at the level of the middle
third of the medial side of the knee (Figs.
3A,3B
and
4A,4B,4C).
A femoral component of the MCL bursa was found in five (71%) of seven
specimens, whereas a tibial component was observed in all specimens. The
dimensions of the MCL bursa, measured on anatomic sections, are listed in
Table 2. The mediolateral
dimension was not recorded in specimens because this measurement depends on
the amount of fluid injected. At microscopic inspection, a thin layer of
flattened mesothelial cells was seen lining both sides of the cavity between
the superficial and deep MCLs (Figs.
5 and
6). Staining with epithelial
membrane antigen showed uptake in this cell layer.
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Fig. 4A. —Cadaveric study. Coronal T1-weighted MR image (TR/TE, 740/14)
with fat saturation technique obtained after injection of gadolinium-based
contrast medium mixed with dye into medial collateral ligament (MCL) bursa
reveals MCL bursa (arrows).
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Fig. 5. —Photograph of histologic section along coronal plane of
cadaveric tissue sample from medial side of knee including superficial and
deep medial collateral ligaments (MCLs) shows thin layer of cells
(arrowheads) along wall of MCL bursa (B). (H and E, x400)
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Clinical Study
The patients ranged in age from 16 to 58 years (mean age, 41 years). The
right knee was involved in two patients and the left knee was affected in four
patients. Five patients had medial knee pain. One patient, a 33-year-old man,
was asymptomatic; he was found to have an effusion in the MCL bursa in his
asymptomatic knee (Fig. 7). In
our institution, the contralateral knee is examined in patients undergoing MR
assessment of joint injuries in the setting of lawsuits. On MR images, a
femoral component of the MCL bursa was observed in four of six patients (Figs.
8 and
9A,9B),
whereas a tibial component was observed in two of six patients. In one
patient, both the femoral and tibial portions of the MCL bursa contained
fluid. One patient had no separation between femoral and tibial compartments,
and the MCL bursa in that patient spanned the joint line. The dimensions of
the MCL bursa, measured on MR images of patients, are shown in
Table 1. Medial osteoarthritis
was seen in three of six patients with fluid confined to the MCL bursa. In
three of six patients, fluid confined to the MCL bursa was the only MR imaging
finding.
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Fig. 7. —Axial T2-weighted MR image (TR/TE, 4700/93) in 33-year-old
asymptomatic man undergoing imaging in medicolegal setting shows fluid
confined to medial collateral ligament bursa in a perimeniscal location
(arrows). No MR evidence of meniscal tear exists.
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Fig. 8. —Coronal short tau inversion recovery—weighted MR image
(TR/TE, 5920/60; inversion time, 120 msec) in overweight 52-year-old man with
medial knee pain and osteoarthritis shows fluid collection in femoral portion
of medial collateral ligament (MCL) bursa (short arrows) located
between superficial MCL (s) and meniscofemoral extension of deep MCL (d). Also
note intraarticular joint fluid (long arrow).
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Fig. 9A. —58-year-old woman with medial knee pain and osteoarthritis.
Coronal MR image (TR/TE, 4700/93) shows fluid collection in femoral portion of
medial collateral ligament (MCL) bursa (B). Meniscofemoral portion of deep MCL
is also seen (arrow).
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Fig. 9B. —58-year-old woman with medial knee pain and osteoarthritis.
Axial MR image shows MCL bursa between superficial (s) and deep (d) MCL. Note
free anterior edge of MCL (e) and posterior junction (j) of superficial and
deep MCL. B = MCL bursa.
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Discussion
Brantigan and Voshell [1],
in 1943, showed by their anatomic dissections that a bursa was present deep in
relation to the MCL in most patients. Our observations in anatomic specimens
confirmed these findings, although some variations in the location and
dimensions of the bursa occurred. Often separate femoral and tibial
compartments were shown, a finding that was also reported by Brantigan and
Voshell. The femoral component is located adjacent to the femoral cortex,
whereas the tibial component is located adjacent to the tibial cortex.
Histologically, the MCL bursa was lined by a single layer of mesothelial
cells. Results from immunologic staining showed that these cells had an
epithelial origin. Both findings indicate that the MCL bursa is lined by
epithelial cells. Because these cells exhibit a flattened appearance, they
resemble the type of cell usually seen in the wall of ganglion cysts. On the
basis of these findings, it remains uncertain whether the MCL bursa
corresponds to a primary bursa that was present at birth or to a secondary
bursa formed as a result of chronic friction. Both types of bursa may be lined
by epithelial cells [6].
Histologic and immunohistochemical examination of a fetal specimen would
likely provide the definite answer.
Reported clinical findings of MCL bursitis include pain along the medial
side of the knee over the MCL and the presence of a palpable nodule along the
anterior edge of the femoral portion of the MCL
[3,
4]. The pain may be increased
by applying valgus stress to the knee. Stuttle
[3] reported that patients with
MCL bursitis tend to respond favorably to injections of corticosteroids in the
superficial soft tissues, but not to intraarticular injections. Our findings
in patients suggest that fluid confined to the MCL bursa as the single finding
is extremely uncommon in a patient population undergoing MR imaging of the
knee. In only three (0.1%) of 2454 MR examinations, fluid in the MCL bursa was
reported as the single MR imaging finding. The first of these patients had
severe genu valgus deformity, the second patient had gouty arthritis, and the
third patient was asymptomatic. Genu valgus has been reported previously as a
cause of MCL bursitis [3,
4]. Other conditions that have
been implicated as causes of MCL bursitis include trauma, osteophytic spurs,
rheumatoid disorders, and flatfoot deformity
[2,3,4].
MCL bursitis may also be encountered in professional athletes involved in
horseback riding and motorcycling, because of the friction applied to the
medial aspect of the knee (Plenevaux P, unpublished data).
In this study, medial joint osteoarthritis was present in three of six
patients with fluid in the MCL bursa. The fluid in the MCL bursa in these
patients may be caused by the osteoarthritis, and the contribution of the
fluid to the clinical symptoms may be questionable. In osteoarthritis,
marginal osteophytes may impinge on the MCL and lead to inflammation and
distension of the MCL bursa
[3].
Our observations in cadaveric specimens indicate that the MCL bursa is not
identifiable at MR imaging in the absence of a fluid effusion. When distended
by fluid, however, the MCL bursa can be depicted as a vertically elongated
compartment exhibiting high signal intensity on T2-weighted MR images and low
signal intensity on T1-weighted MR images. On anatomic slices and MR images,
the MCL bursa was shown to be located between the superficial and deep
portions of the MCL. On axial anatomic slices and MR images, the anterior
margin of the MCL bursa is located adjacent to the anterior edge of the
superficial portion of the MCL (Fig.
2). The posterior margin of the MCL bursa is outlined by the
junction between the superficial and deep portions of the MCL
(Fig. 2).
Our results show the compartmentlike distribution of fluid confined to the
MCL bursa. These findings may be helpful in differentiating fluid in the MCL
bursa from other cystic lesions located along the medial aspect of the knee.
As a basic rule, a fluid collection that is located superficially, anteriorly
or posteriorly with regard to the anterior superficial portion of the MCL, is
unlikely to correspond to fluid in the MCL bursa
(Fig. 2). The pes anserinus
bursa is located inferiorly with respect to the tibial component of the MCL
bursa. Ganglion cysts often show a septate and lobulated appearance and may
occur in various periarticular locations; they are unlikely to be confined to
the normal location of the MCL bursa
[7]. Peripheral meniscal tears
and meniscocapsular separation may lead to high signal intensity on
T2-weighted MR images in the meniscal periphery or perimeniscal tissues
[8]. However, high signal
intensity in these conditions tends to be ill defined and is located in or
adjacent to the meniscus. Fluid in the MCL bursa, in contradistinction, tends
to be well defined and extends adjacent to the femoral and tibial cortexes. In
addition, meniscal tears and meniscocapsular separation predominantly involve
the posterior horn of the medial meniscus and thus are located posteriorly
with respect to the normal location of the MCL bursa.
Meniscal cysts represent the most realistic differential diagnostic
consideration of fluid in the MCL bursa
[9,
10]. Our review of imaging
reports yielded 20 patients with fluid collections confined to the normal
boundaries of the MCL bursa, but with an adjacent meniscal tear
(Fig. 10). The differentiation
of bursal fluid from a meniscal cyst remains difficult. Neither type of fluid
collection is visualized at arthroscopy because of their extraarticular
location. In addition, only the large meniscal cysts are surgically removed;
therefore, histologic proof is seldom obtained. Meniscal cysts tend to occur
in a posteromedial location, and thus posteriorly with respect to the MCL
bursa, although this is not a general rule. In the case of meniscal cysts, a
direct communication with a meniscal tear or area of intrameniscal
degeneration may be present.
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Fig. 10. —Coronal T2-weighted MR image (TR/TE, 4500/93) in 57-year-old
woman with medial knee pain and medial meniscal tear (not shown) that was
arthroscopically treated reveals fluid in medial collateral ligament bursa
(arrows) spanning joint line.
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Some limitations of our investigation should be considered. First, the
number of specimens examined was limited and this small sample may not take
into account normal anatomic variation. It might be argued that, in our
investigation, injections of dye and the freezing and thawing of specimens may
have created an artificial cleavage plane between the superficial and deep
MCLs [11]. However,
macroscopic and histologic observations were consistent with a preexisting
compartment. Our retrospective selection of cases also represents a limitation
of our study. Nevertheless, the radiologists who made the initial reports were
familiar with previously described MR signs of fluid in the MCL bursa
[2] and used consistent
criteria. Because our analysis was retrospective, patients with MCL bursitis
who might have been treated conservatively and not referred for MR imaging by
clinicians would not have been included. In addition, clinicians may not have
looked specifically for clinical signs suggestive of MCL bursitis in all
patients. We did not include patients with tears of the MCL in our study,
although we acknowledge that periligamentous high signal intensity may be
observed on T2-weighted images in patients with proximal or distal MCL tears
[12]. However, other signs of
MCL tear are present in most patients and allow a correct diagnosis. In
addition, patients with fluid collections confined to the typical site of the
MCL bursa but with associated meniscal tears were not included in further
analysis. Although several of these patients may have had MCL bursitis, we
could not exclude the possibility that these collections represented meniscal
cysts.
In summary, the MCL bursa is located along the middle third of the medial
aspect of the knee between the superficial and deep portions of the MCL.
Although commonly observed in anatomic specimens of elderly patients, MCL
bursitis is infrequently found in a patient population undergoing MR imaging
of the knee. Understanding the normal anatomic location of the MCL bursa on MR
images may help to differentiate fluid in the MCL bursa from other conditions
causing fluid collections on the medial side of the knee.
Acknowledgments
We thank E. Broodtaerts for photographic work; K. Vanderdood for help in
image interpretation; M. Pauwels for performing histologic preparations; F.
Grignard and J. de Mey for assistance with injections; E. Barbaix for anatomic
research; and J. M. Annaert, P. Oger, and T. Scheerlinck for clinical
correlations.
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Abstract
Introduction
