AJR 2003; 180:1443-1447
© American Roentgen Ray Society
MR Imaging of Infrapatellar Plica Injury
R. Lee Cothran1,
Philip M. McGuire1,2,
Clyde A. Helms1,
Nancy M. Major1 and
David E. Attarian3
1 Department of Radiology, Box 3808, Duke University Medical Center, Durham, NC
27710.
2 Present address: Radiology Alliance, P.A., 210 25th Ave. N., Ste. 602,
Nashville, TN 37203.
3 Division of Orthopaedic Surgery, Duke University Medical Center, Durham, NC
27710.
Received October 25, 2001;
accepted after revision October 11, 2002.
Address correspondence to R. L. Cothran.
Abstract
OBJECTIVE. Injury to the infrapatellar plica (ligamentum mucosum)
has not been previously described in the radiology literature to our
knowledge. This article shows the MR imaging appearance of injury to the
infrapatellar plica.
CONCLUSION. Injury to the infrapatellar plica is uncommon but should
be considered as a potential source of knee pain, especially if no other
evidence indicates internal derangement. MR imaging can reveal a typical
appearance for infrapatellar plica injury.
Introduction
The plicae of the knee are normal synovial folds that are remnants from the
embryologic development of the knee
[1]. At arthroscopy a normal
infrapatellar plica has a variable appearance. It is a thin, pliable fold of
synovial tissue with elastic and areolar components. The infrapatellar plica
may be a complete septum or may be partially attached to the anterior cruciate
ligament. The infrapatellar plica may be split, fenestrated, or absent
[2,
3]. Plica syndrome is a
well-known clinical entity whereby the normally thin, pliable synovial plica
becomes abnormally thickened, edematous, or fibrotic, leading to clinical
symptoms. This syndrome usually involves the mediopatellar plica or,
sometimes, the suprapatellar plica
[4].
Traditionally, the infrapatellar plica has been thought to be incidental
and not a source of symptoms
[2]. However, some orthopedic
surgeons at our institution have told us that they have encountered abnormal
infrapatellar plicae, sometimes thickened, fibrotic, or acutely ruptured with
hemarthrosis (Feagin J, personal communication). We retrospectively reviewed
the preoperative MR images from one of these patients and noted a high T2
signal along the course of the infrapatellar plica. This finding led us to
perform a database search for other patients who had signal abnormality
reported in this region on knee MR imaging. The purpose of this article is to
show the MR imaging appearance of abnormal infrapatellar plicae and to
clinically correlate these findings with the patients' symptoms and
arthroscopy findings.
Materials and Methods
Our MR imaging database was retrospectively searched for MR imaging knee
examinations performed between January 1995 and April 2001, in which signal
abnormality was reported in the approximate region of the infrapatellar plica.
Of 5237 MR imaging studies of the knee, nine knees were interpreted
prospectively as having curvilinear signal abnormality associated with the
infrapatellar plica. The prospective interpretation was performed in the scope
of daily dictation during this period by one of six musculoskeletal
radiologists. The cases prospectively interpreted as containing a high T2
signal in the region of the infrapatellar plica were then reexamined in a
retrospective manner by two musculoskeletal radiologists; confirmation of the
abnormal signal in the region of the infrapatellar plica was by consensus. An
additional case was submitted by an orthopedic surgeon after arthroscopy
revealed an abnormally thickened, hypertrophic infrapatellar plica. These
images revealed abnormal signal along the infrapatellar plica on retrospective
review but were not prospectively interpreted as having an abnormal
infrapatellar plica.
The MR imaging findings were correlated with clinic notes, arthroscopic
reports (five knees in four patients), and discussion with the orthopedic
surgeons. All patients were imaged on a 1.5-T MR imaging system (Signa;
General Electric Medical Systems, Milwaukee, WI) with a routine knee protocol
including sagittal fat-suppressed spin-echo proton density–weighted
images (TR/TE, 20/2000) and sagittal, axial, and coronal fast spin-echo
T2-weighted images with fat suppression (TR range/TE range,
3500–5000/65–75). The sagittal fast spin-echo T2-weighted images
with fat suppression were the primary images used to evaluate the
infrapatellar plica. The signal abnormality could also be seen on the fast
spin-echo T2-weighted axial and coronal images and on the proton
density–weighted sagittal sequence, but the sagittal T2-weighted
sequence best showed the signal abnormality. The infrapatellar plica was
considered abnormal when a high T2 signal extended along the course of the
infrapatellar plica. Only those five knees in four patients who had been
examined arthroscopically at the time of retrospective review are included in
the results and discussion.
Results
On MR imaging, a normal infrapatellar plica is best appreciated on sagittal
images as a thin, low-signal, curvilinear structure coursing between the
intercondylar notch and the inferior pole of the patella or adjacent fat
[5] (Figs.
1A,
1B and
1C). The infrapatellar plica is
normally isointense to other ligaments on all sequences
[5,
6].
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Fig. 1A. —Normal infrapatellar plica. Schematic drawing of knee in
sagittal section through intercondylar notch shows infrapatellar plica
(black arrow) extending from inferior pole of patella (P) or
immediately adjacent fat, through Hoffa's fat pad, to intercondylar notch of
femur anterior to anterior cruciate ligament (white arrow).
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Fig. 1B. —Normal infrapatellar plica. Sagittal fast spin-echo
T2-weighted MR image (TR/TE, 4000/72) with fat suppression through
intercondylar notch shows normal infrapatellar plica as thin, linear
low-signal-intensity structure (black arrow) in Hoffa's fat with more
prominent intercondylar component (straight white arrows) lying
anterior to anterior cruciate ligament (curved white arrows),
proximal attachment in intercondylar portion of femur, and distal visualized
portion attaching to prominent transverse ligament.
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Fig. 1C. —Normal infrapatellar plica. Sagittal fast spin-echo
T2-weighted MR image (4000/72) with fat suppression through intercondylar
notch shows partially resorbed or less prominent intercondylar infrapatellar
plica (arrows), with portion in Hoffa's fat as only visible component
on MR image.
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On MR imaging, all five knees had a high T2 signal associated with the
infrapatellar plica that extended into the Hoffa fat pad, suggesting injury to
the plica. The signal abnormality was typically curvilinear, but two knees
also had a globular component. The studies included one male and three
females—one patient had bilateral infrapatellar plica abnormalities
(Figs. 2A,
2B). All patients were young,
ranging in age from 14 to 38 years (average age, 24.8 years). A history of
prior sports-related trauma was noted for four of the five knees. Return to
the sporting activity before injury is known to have occurred in three of
these four knees (two of these knees were in a single individual). The knee
without a known history of prior sports trauma did have a history of prior
arthroscopic surgery for cartilage débridement. Three of the five knees
exhibited a limitation to extension without history of prior surgery. In two
of these cases, redundant tissue was seen anterior to the anterior cruciate
ligament (Fig. 3). This tissue
was resected at arthroscopy, which confirmed infrapatellar plica injury in
four of the five knees. Four of five knees had other findings that were
addressed at arthroscopy (Table
1).
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Fig. 2A. —18-year-old woman soccer player with anterior knee pain.
Sagittal fast spin-echo T2-weighted MR image (TR/TE, 4000/69) with fat
suppression through intercondylar notch shows curvilinear high T2 signal along
course of infrapatellar plica (arrow). Fluid signal immediately
anterior to anterior cruciate ligament in intercondylar notch may be related
to infrapatellar plica avulsion or may simply represent joint fluid. Other
findings on MR imaging included discoid lateral meniscus and mediopatellar
plica (not shown). At arthroscopy (not shown), infrapatellar plica was
thickened and avulsed from its femoral attachment, and redundant infrapatellar
plica interfered with full extension. Infrapatellar plica was resected; after
surgery, patient was asymptomatic and resumed playing soccer.
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Fig. 2B. —18-year-old woman soccer player with anterior knee pain. One
year later patient injured her contralateral knee and suffered bucket-handle
tear of discoid lateral meniscus. Sagittal fast spin-echo T2-weighted MR image
(4000/70) with fat suppression through intercondylar notch shows fluid signal
along course of infrapatellar plica (white arrows), which was
interpreted as injury to infrapatellar plica. Infrapatellar plica was
arthroscopically resected, and meniscus was débrided. Fragment from
bucket-handle meniscus tear can be seen in posterior joint (black
arrow).
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Fig. 3. —38-year-old woman with skiing injury. Sagittal fast spin-echo
T2-weighted MR image (TR/TE, 4000/67) with fat suppression through knee 6
months after injury shows fluid signal along course of infrapatellar plica
(arrows) interpreted as torn anterior cruciate ligament with
associated rupture of infrapatellar plica. At arthroscopy 2 months later (not
shown), scar tissue was found in expected position of infrapatellar plica,
suggesting that plica had been injured.
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Discussion
Some debate exists as to the origin of the plicae of the knee. A common
theory is that the plicae are inconstant synovial remnants from the
embryologic development of the knee. The knee joint is believed to be
originally composed of three compartments during embryologic development:
medial, lateral, and suprapatellar. A recent embryologic study suggests that
in the first trimester, multiple cavities exist, which coalesce to form larger
cavities, and by 10.5 weeks the knee joint consists of a single cavity with
synovial lining. After coalescence of the small cavities, a small amount of
mesenchymal tissue may persist as a plica, especially in the supra-, infra-,
and mediopatellar regions. These synovial folds usually partially or totally
regress, and they infrequently cause symptoms in the adult. Rarely, the
suprapatellar or infrapatellar plicae may persist in their entirety, which
leads to persistent complete compartmentalization of the joint
[1].
The plicae are usually of no clinical significance, with a normal plica in
the adult being a thin, pliable asymptomatic synovial fold containing abundant
elastic and areolar tissue. The presence of elastic tissue allows changes in
shape and length as the plica glides over bony structures. Occasionally,
however, the plicae may give rise to clinical symptoms. The mediopatellar
plica is most commonly symptomatic, becoming thickened, edematous, and
eventually fibrotic. This change in morphology may lead to a snapping sound as
the plica moves over a bony protuberance. Associated mechanical or
inflammatory synovitis may also occur
[2]. The suprapatellar plica
may cause symptoms if it is imperforate or has a one-way communication causing
fluid to become loculated in the most superior aspect of the suprapatellar
pouch cephalad to the suprapatellar plica.
The infrapatellar plica, or ligamentum mucosum, is a vestigial remnant of
the embryonic tissue and is typically not thought to be a source of clinical
symptoms. The infrapatellar plica has a narrow femoral attachment in the
intercondylar notch of the femur. The infrapatellar plica attaches just
anterior to the anterior cruciate ligament and parallels that ligament for a
short distance. The infrapatellar plica then curves gently upward to attach to
the infrapatellar fat pad or inferior pole of the patella. The alar folds
continue laterally to cover the Hoffa fat pad
[4,
5]. On occasion, partial
attachment to the anterior cruciate ligament or anterior horn lateral meniscus
may be seen [3].
The prevalence of plicae reported in the literature varies according to the
method of detection; plicae are easier to see and thus more commonly reported
on arthroscopy than on arthrography. On double-contrast arthrography, the
infrapatellar plica was detected in only 10% of knees
[7]. On cadaveric dissection,
the infrapatellar plica was seen in 65% of patients
[5]. On arthroscopy, the
infrapatellar plica has been reported as being frequently present
[5]. On MR imaging, the
infrapatellar plica is best seen on sagittal images, with a curvilinear
appearance as it courses in an anteroposterior orientation
[3,
4,
5]. An injured or diseased
infrapatellar plica is suggested when a significant amount of curvilinear high
T2 signal is seen along the expected course of the infrapatellar plica, or if
a markedly thickened plica is visualized. Patel et al.
[8] reported seeing a
horizontal cleft in the infrapatellar fat pad on MR imaging in 90% of knees,
with the infrapatellar plica forming the roof of the cleft. This cleft did not
account for the abnormal signal along the infrapatellar plica in the cases we
have described, because the signal in our series was more extensive along the
course of the infrapatellar plica, and slightly cephalad in location relative
to the horizontal cleft.
To our knowledge, abnormalities of the infrapatellar plica have not been
described in the radiology literature. The orthopedic literature contains a
report of two cases, with the infrapatellar plica described as thickened,
fibrotic, impinging on the notch, and preventing full extension. Resection led
to improved range of motion
[9]. Also found in the
orthopedic literature is an anatomic and clinical study that describes a torn
infrapatellar plica as the only abnormality in three of 57 patients with
posttraumatic hemarthrosis and a clinically stable joint
[10]. That same article also
describes the presence of a small artery in the infrapatellar synovial fold in
five of 12 cadaveric knee dissections
[10].
Abnormal lesions of Hoffa's fat pad as seen on MR imaging have been
described previously, including Hoffa's disease or Hoffa's syndrome
[11]. In addition, the
clinical and histologic findings have been reported in cases of Hoffa's
disease, in which there is injury to, or hemorrhage within, Hoffa's fat pad,
usually related to trauma. This injury then results in impingement of portions
of the fat in extension, which results in pain and functional impairment.
Chronically, such an injury may result in patellar crepitus
[12]. Magi et al.
[12] also state in their
conclusion, "It is a wellknown fact that many cases of Hoffa disease
have been misdiagnosed and incorrectly treated as meniscal syndromes."
Possibly the abnormal signal we are seeing around the infrapatellar plica is
related to Hoffa's disease or Hoffa's syndrome. Infrapatellar plica injury of
an acute or chronic nature would likely be associated with injury to Hoffa's
fat pad. In fact, Smillie [13]
writes of the infrapatellar plica: "The clinical importance of the fold,
apart from a source of haemorrhage if divided, is that by anchoring the fat
pad it may limit expansion in a forward direction when swelling occurs and
thus may be responsible for the compression of the synovial membrane."
Reports of the MR imaging appearance of Hoffa's disease are relatively few,
but imaging findings have tended to be more dramatic than the findings in our
series, which leads us to suggest that, if they are related, the findings in
our series may represent a less uncommon or more subtle imaging presentation
of what was once thought to be a relatively uncommon clinical problem.
We believe that abnormal increased signal along the infrapatellar plica at
MR imaging may be indicative of direct trauma to the plica or to inflammation
of the plica that is possibly related to Hoffa's disease or syndrome. Also, an
acute rupture of the infrapatellar plica may mimic an anterior cruciate
ligament rupture with a painful pop and hemarthrosis, with MR imaging showing
the anterior cruciate ligament to be intact and a high T2 signal along the
course of the infrapatellar plica. However, because abnormality of the
infrapatellar plica appears to be uncommon in isolation, we recommend close
correlation with the clinical symptoms and exclusion of other internal
derangement before suggesting injury to the infrapatellar plica as a sole
cause for knee symptoms. We have seen isolated abnormal signal in the
infrapatellar plica in a collegiate basketball player with no other
abnormalities detected on MR imaging (Fig.
4). Examination by an experienced orthopedic surgeon confirmed the
anterior location of the pain, and an abnormal or injured infrapatellar plica
was thought by the examiner to be the probable cause after review of the MR
images.
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Fig. 4. —22-year-old male collegiate basketball player with bilateral
anterior knee pain. Sagittal fast spin-echo T2-weighted MR image (TR/TE,
4000/73) with fat suppression through left intercondylar notch shows
curvilinear high signal intensity along course of infrapatellar plica
(arrows). Knee was otherwise normal.
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In summary, injury to the infrapatellar plica should be considered as a
potential cause of knee pain or hemarthrosis, particularly in patients with
signal abnormality of the infrapatellar plica and no other evidence of
internal derangement.
References
- Ogata S, Uhthoff H. The development of synovial plicae in human
knee joints: an embryologic study. Arthroscopy
1990;6:315
–321[Medline]
- Hardaker W, Whipple T, Basset F. Diagnosis and treatment of the
plica syndrome of the knee. J Bone Joint Surg Am
1980;62:221
–225[Abstract/Free Full Text]
- Kim S, Min B, Kim H. Arthroscopic anatomy of the infrapatellar
plica. Arthroscopy
1996;12:561
–564[Medline]
- Apple JS, Martinez S, Hardaker WT, Daffner RH, Gehweiler JA.
Synovial plicae of the knee. Skeletal Radiol
1982;7:251
–254[Medline]
- Kosarek FJ, Helms CA. The MR appearance of the infrapatellar plica.
AJR
1999;172:481
–484[Abstract/Free Full Text]
- Boles CA, Martin DF. Synovial plicae in the knee.
AJR
2001;177:221
–227[Free Full Text]
- Brody GA, Pavlov H, Warren RF, Ghelman B. Plica synovialis
infrapatellaris: arthrographic sign of anterior cruciate ligament disruption.
AJR
1983;140:767
–769[Abstract/Free Full Text]
- Patel SJ, Kaplan PA, Dussault RG, Kahler DM. Anatomy and clinical
significance of the horizontal cleft in the infrapatellar fat pad of the knee:
MR imaging. AJR
1998;170:1551
–1555[Abstract/Free Full Text]
- Kim S, Choe W. Pathological infrapatellar plica: a report of two
cases and literature review. Arthroscopy
1996;12:236
–239[Medline]
- Kohn D, Deiler S, Rudert M. Arterial blood supply of the
infrapatellar fat pad: anatomy and clinical consequences. Arch
Orthop Trauma Surg
1995;114:72
–75
- Jacobson JA, Lenchik L, Ruhoy MK, Schweitzer ME, Resnick D. MR
imaging of the infrapatellar fat pad of Hoffa.
RadioGraphics
1997;17:675
–691[Abstract]
- Magi M, Branca A, Bucca C, Langerame V. Hoffa disease.
Ital J Orthop Trauma
1991;17:211
–216[Medline]
- Smillie I. Diseases of the knee joint, 2nd
ed. New York: Churchill Livingstone, 1980:162
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Abstract
Introduction
