Cross-sectional Imaging of the Patellofemoral Joint and Surrounding Structures1 William
F. Conway,
Thomas Landis
Loughran,
MD
Griffeth,
MD,
G. Shellock,
PhD
K.
Frank
MD,
PhD
#{149} Curtis
#{149} William
PhD
W. Hayes,
MD
G. Totty, MD
#{149} Georges
#{149}
#{149}
V. El-Khoury,
MD
#{149}
Computed tomography (CT) and magnetic resonance (MR) imaging are extremely useful in the accurate diagnosis of anterior knee pain, a common complaint arising from numerous causes (including fracture, chondromalacia patellae, and alignment and tracking abnormalities) Plain CT is effective for evaluating intraosseous lesions of the knee. Although CT arthrography provides excellent visualization of the patellar articular cartilage, the technique is expensive and invasive. Cine CT is an excellent method for assessing patellofemoral tracking and alignment. Kinematic MR imaging can also perform this function. In addition, MR imaging can provide valuable information concerning the status of patellar cartilage. Although MR imaging can accurately show high-grade chondromalacia patellae, it is less accurate in the detection of low-grade disease. The authors believe that MR imaging and plain radiography offer radiologists the greatest latitude in making a specific diagnosis of the cause of anterior knee pain; however, CT is a useful alternative. .
INTRODUCTION
U
Anterior knee ages. Common lacia patellae, and inflamed
pain is a frequent, often nonspecific complaint of individuals of all causes of anterior knee pain include patellar fracture, chondromapatellar alignment and tracking abnormalities, patellar tendinitis, infrapatellar synovial plicae. Less common causes include patellar
Abbreviations: Index 452.41
FISP
terms:
Knee,
#{149} Knee.
RadioGraphics I
From
the
injuries, 1991;
Departments
fast
imaging
abnormalities. 452.42. i i : I95-2 ofttadiology
with 453.9
452.485
steady
precession.
#{149} Knee. #{149} Knee.
of Radiology.
Receivedjuly print requests ,
RSNA.
Cedars-Sinai
17, 1990; revision to W.F.C.
arthritis,
fast
452.78
MRstudies,
low.angle
#{149} Knee,
452.1214
CT.
shot. 452.i2i
3D i
= three-dimensional
#{149} Knee,
fractures.
#{149} Patella
1 (W.F.C.,
C.W.H.)
MCV Station, Richmond, VA 23298.06 1 5; Mallinckrodt (W.G.T.. 1KG.); Department of Radiology. University partment
FLASH
Medical requested
Center, August
and
Surgery
Institute oflowa Los Angeles 2 1 and
(T.L.),
Medical
of Radiology, Hospitals and
received
(F.G.S.). October
College
ofVirginia,
Box
University of Washington, Clinics, Iowa City (G.Y.E.K.);
From
the
1989
3 1 ; accepted
RSNA
scientific
November
615,
St Louis and Dcassembly.
5. Address
re-
1991
195
a.
b.
Figure 1. Images of a patient who presented with a warm swollen knee and patellar and penpatellar pain. (a) Plain radiograph of the patella fails to reveal an abnormality. (b) Delayed static bone scintignam shows mild diffuse uptake about the knee and intense uptake in the patella. The presence of a septic joint (Staphylococcus aureus) accounts for the diffuse mild uptake. (c) Axial CT scan through the patella demonstrates a focus of osteomyelitis on Bnodie abscess in the patella, containing a small sequestrum (arrow) find. ings corresponding to the intense uptake seen in the patella in b. ,
osteomyelitis and tumors. In addition, osteonecrosis of the femoral condyles and meniscal tears may refer pain anteriorly. With such diverse causes of pain, accurate diagnosis is essential to treat these disorders effectively. The introduction of cross-sectional imaging
modalities,
specifically
computed
tomogra-
phy (CT) and magnetic resonance (MR) imaging, has greatly expanded the ability of the radiologist to make these diagnoses. We present examples of how both CT and MR imaging have been used to accurately diagnose the various pathologic processes encountered about the knee. Specifically, we describe the use of CT, CT arthrography, cine CT, spin-echo MR imaging, gradient-
C.
echo MR imaging, and MR arthrography in the evaluation of the patellofemoral joint. The images presented are from two sources: cadavenic knee specimens (for which pathologic specimen-image correlation is made) and patients referred to our institutions specifically for evaluation of anterior knee pain.
U
CT
EVALUATION
.
Imaging
OF
KNEE
PAIN
Parameters
CT of the patellofemoral
joint is performed
in the axial plane, with the knee in approximately 50 of flexion. Contiguous 3-mm-thick sections are obtained through the patella
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a. b. Figure 2. CT arthrognams of two cadavenic knee specimens. Approximately 30 mL of air were injected into the knee joint before scanning. (a) Axial image through a normal specimen shows the smooth articulas cartilage surface of the patella. (b) Axial image of the second specimen demonstrates an area of focal chondromalacia patellae (arrow) and overall thinning of the patellar articular cartilage.
with use of a bone algorithm. This permits adequate visualization of intraosseous anatomy and, when CT arthrography is used, the articular cartilage.
CT arthrography
of the knee
of 3 mL of diatrizoate sodiurn meglumine (Renografin 76; Squibb, New Brunswick, NJ) 0 3 mL of epinephrine (1 : 1 ,000 dilution) and 30-50 mL of air into the knee. The actual imaging is performed .
,
within 30-45 minutes ofthe injection. 0then imaging parameters are similar to those used for standard CT of the patellofemoral joint. Cine CT of the knee during flexion can be achieved with use of an ultrafast CT scanner (Imatron, South San Francisco, Calif) (1). The patient is positioned supine within the gantry, and the thigh is supported so that an approximately 45#{176} angle with the horizontal plane is maintained. Section thickness is 10 mm, and nine sections can be obtained in approximately 0.7 seconds. If the scanner is programmed to obtain these images as the knee is moved from 900 of flexion to full extension and back to 90#{176} of flexion, 10 images at each of nine levels (encompassing an 8-cm-length of knee) can be acquired in 7
March
1991
images can be played cine format, which al-
lows for visualization tellofemoral motion.
of active,
real-time
pa-
is performed
after an injection
,
seconds. The processed back in a closed-loop
S
Intraosseous
Lesions
of the
Patella
In isolated cases, CT can be used effectively to evaluate intraosseous lesions of the pate!lofemora! region. Although infrequently used for this purpose, CT can demonstrate radiographica!ly occult Brodie abscesses of the patella (Fig 1). In addition to infection, tumors of the patella also can be evaluated and classified with CT. CT may be particularly valuable in cases of primary tumors, for which the evaluation of marginal of the tumor may ography.
and internal be limited
characteristics with plain radi-
. Chondromalacia Patellae CT can be used in conjunction with routine knee arthrography (CT arthrography) to provide excellent visualization of pate!!ar articular
cartilage
(Fig
2).
Conway
Several
et al
authors
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(2,3)
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veal the luxation.
groove
have
demonstrated
that this technique proand specific evaluation of chondromalacia patellae (see subsection under MR Evaluation for a more detailed discussion of this disease) Criteria for the diag-
flexion
vides
both
to be a significant shortcoming, since abnormalities of both patellar alignment and tracking may be seen only in the first 20#{176} of flexion. (A more detailed discussion of align-
nosis
of chondromalacia
ment
sensitive
.
to those
used
bibition
of contrast
patellae
in regular
are
arthrography
material
similar
(ie,
by cartilage,
imcar-
tilage thinning, and focal defects) The main disadvantages of this technique are its expense and invasiveness. .
#{149} Pateilar Alignment and Tracking There are many methods for obtaining axial plain radiographs of the patella. With all of them, images of the knee in less than 150 of
cannot
be obtained.
and tracking
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Conway
Ct
al
is included
has proved
with
MR
.
and 4 demonstrate a pair of normal (Fig 3) and laterally subluxed (Fig 4) patellae imaged with an ultrafast CT scanner (Imatron). These
images
flexion in different and
represent
of the knee. degrees
processed,
kinematic method od for evaluating
U
This
Evaluation.) As stated above, CT permits axial cross-sectional imaging of the knee in all degrees of flexion from 0#{176}-90#{176} Figures 3
was produced.
198
and no cvi
one
When
position
during
the other
images
of flexion
a cine
ioop
Stanford
were of knee
et a! claim
is the most patellofemoral
Volume
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that this
accurate tracking
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2
In this case,
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MR
EVALUATION
#{149} Pulse With
the patel
(eg,
Ti -weighted 700/20
echo time msec]) cartilage may show diate signal intensity bilaminar sity from
being
KNEE
PAIN
spin-echo
se-
low-angle shot [FLASH]) and with the flip angle (repetition time/echo time/flip angle). For example, three-dimensional (3D) FLASH
Sequences
typical
quences
OF
[repetition time msec/ (Fig 5a) normal articular ,
a homogeneous throughout
appearance, with the basal two-thirds
lower
than
intermeor a subtle
the signal intenof the cartilage
that of the superficial
We found this bilaminar u!ar cartilage to be more disarticulated cadaveric
appearance pronounced specimens;
layer. of articin the the
cause of this appearance is uncertain. When gradient-echo sequences are used, the relative contrast between cartilage and fluid changes imaging with
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1991
with the type of sequence steady precession [FISP]
(fast vs fast
40 images
intensity
show
intermediate
for articular
to high
cartilage
and
signal
slightly
lower signal intensity for fluid (Fig 5b) 3D FISP 40 images also show an intermediate to high signal intensity for articular cartilage but a higher signal intensity for fluid (Fig 5c) 3D FLASH 75 images show a slightly .
.
lower signal intensity for articular cartilage, compared with that seen on 3D FLASH 40 images. This makes distinction between synovial fluid and articular cartilage slightly more difficult (Fig 5d). 3D FISP 75 images show a slightly lower signal intensity for articular
cartilage
than
do 3D FISP 40 images.
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a.
b.
,,
‘
d.
C-
5. Axial MR images through the patellofemoral joint in a patient with a mild effusion. (a) Ti -weighted (700/20) axial image. 3D FLASH Figure
40
(b) and 3D FISP 40 (40/13/40#{176})
(40/13/400)
(c) axial images obtained at the demonstrate mild joint effusion FLASH 75 (40/i3/75#{176}) (d) and i 3/75#{176}) (e) axial images of the equivalent position demonstrate
same location (arrows) . 3D 3D
FISP 75
same knee joint fluid
as a (40/
at an (an-
rows).
permits
greater
and articular
differentiation
cartilage
between
(Fig
fluid
Se).
At present, Ti -weighted axial and sagitta! images are preferred at the Medical College of Virginia for evaluation of pate!lar cartilage when a joint effusion is not present. These images provide adequate contrast and resolution for detection of most surface and internal cartilage lesions. We routinely include
e. Ti-weighted mm-thick
sition)
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axial sections,
with
our
sequences 0.25-mm
usual
(700/20, gap, one
interleaved
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Figure 6. Cadavenic sections and corresponding MR images from healthy volunteers. (a) Axial cadavenic specimen reveals normal, smooth articular cartilage of the patella and the trochlea. (b) Corresponding axial Ti-weighted (700/20) MR image shows the dark line separating the patellar and trochlear articular cartilage (arrows). (C) Sagittal cadavenic section. (d) Corresponding sagittal Ti -weighted (700/20) MR image shows the relative homogeneous nature of the articular cartilage and the distinct line separating the patellar from trochlear cartilage (arrow).
weighted sequences. When fluid is present within the joint, we prefer to use 3D FISP 75 sequences. This sequence maximally enhances the arthrographic effect of the synovia! fluid. A double-echo, proton-density and T2-weighted sequence (2,500/30, 90) is more time consuming to perform, but the resulting images may also show cartilage defects. MR images shown here were obtained with a i .0-T magnet and a receive-only extremity coil (Siemens Medical Systems, Ise!in, NJ).
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#{149} Normal Patellar Cartilage As stated, normal pate!!ar cartilage may show a homogeneous intermediate signal intensity or a subtle bilaminar appearance on Ti weighted images (Fig 6) Morphologic charactenistics of the lateral, medial, and odd facets are best demonstrated on axial images. -
.
The interface cartilage
between
or between
patellar patellar
Conway
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and
fat
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Table
1 ClassifiCations
of Chondromalacia
Grade
Patellae
Pathologic
Based
on Pa thologiC
and
Findings’ swelling
MR Imaging
i
Softening cartilage
and
of articular
2
Blistering ducing
of articular deformity
3
Surface irregularity and cartilage bnillation with minimal, ifany, extension to subchondral bone
4
Ulceration chondral
Focal areas of decreased Ti-weighted images the cartilage surface bone Focal areas of decreased extending to cartilage
cartilage proof the surface
ervation
with exposure bone
fi-
Modified
from
classification
system
by Shahriaree
Findings signal intensity on not extending to or subchondral signal surface
cartilage
intensity with pres-
margin
tella and that of the trochlea Focal areas of decreased signal extending from subchondral
of sub-
used
of sharp
Findings
Focal signal intensity abnormality extending to the articular surface but not the osseous surface of the articular cartilage; loss of the sharp dark margin between the articular cartilage of the pa-
cartilage cartilage bone S
MR Imaging
intensity bone to the
surface over a significant area; is thinned to the subchondral
(4).
should form a thin dark line. Volume averaging may blur this line, especially with sagittal images of the steeper medial pate!lar fac-
et. Evaluation gether helps averaging
of sagittal one avoid
for true
surface
#{149} Chondromalacia Simply put, pathologic
There
Pateliae
is no consensus patellae.
tracking
to-
irregularity.
chondromalacia softening of the
chondromalacia
chanica!
and axial images mistaking volume
patellae patellar
as to the Trauma
abnormalities
is cartilage.
causes and
of me-
are most
fre-
quently cited. The number of cases of anterior knee pain actually caused by chondromalacia patellae is also controversial, since a
Figure
7.
Schematic
lion of chondromalacia definition of the grades).
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of the Shahriaree patellae
(see
Volume
11
classificaTable
1 for
Number
2
b.
a.
Figure 8. Grade 1 chondromalacia patellae. (a) Axial section through the patellofemoral
joint
of a cadaveric specimen shows the area of cartilage softening (arrowheads) as determined with use ofa metallic probe on the specimen. (b) On
the corresponding Ti-weighted (700/20) MR image, no abnormality is seen. (C) Sagittal Tiweighted (700/20) image of a patient with symptomatic grade 1 chondromalacia patellae demonstrates an area of focal, intracartilaginous decreased signal intensity (arrow).
patients,
we
have
great many asymptomatic individuals also show significant chondromalacia patellae at arthroscopy. Several classifications of chondromalacia patel!ae have been proposed on the basis of pathologic findings. We have used the c!assification system by Shahriaree (4), based on arthroscopic findings (Fig 7, Table 1). A three-grade classification system based on MR imaging findings was proposed by Yulish et a! (5). Based on our examination of disarticulated knee specimens and symptomatic
March
1991
a four-grade
sys-
to more closely follow the arthroscopic staging system
Grade
superficial
,
C-
adopted
tern (6) hoping commonly used (Table 1).
ing
1.-The noted
imens
in several
(Fig
on
MR
cal
areas
8a)
images
is not of the
cartilage
disarticulated clearly signal
spec-
demonstrated
specimens
of decreased
softenknee
(Fig intensity
8b)
.
Fo-
are fre-
quently seen in both symptomatic and asymptomatic subjects (Fig 8c). The significance of these focal lesions is not certain at this
point.
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‘,
..-s,
‘
1’ Figure 9- Grade 2 chondromalacia patel!ae. (a) Sagittal section through the patellofemoral joint of a cadavenic specimen demonstrates a blistenlike lesion extending to the cartilage surface (arrow). (b) Corresponding Ti -weighted (700/ 20) MR image demonstrates a focal area of decreased signal intensity extending to and deforming the articular surface of the cartilage (arrow). (c) Sagittal Ti -weighted (700/20) image of a patient with symptomatic grade 2 chondromalacia patellae shows a focal lesion with sharply defined margins (arrow).
Grad. 2.-A blister!ike lesion may extend to the cartilage surface (Fig 9a) and appears on MR images as a low-signal-intensity area at the cartilage surface (Fig 9b) Grade 2 le.
sions extend bulge while (Fig 9c).
to the surface, causing a focal maintaining sharp margins
Grade 3.-Fibrillation ing a “crabmeat”
seen
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on MR images
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of cartilage appearance (Fig
as decreased
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produc1 Oa) is
signal
inten-
C.
sity extending to the surface, with conspicuous loss of the sharp interface at the cartilage surface (the “brush-border” sign of arthroscopic stage 3 changes) (Fig 1 Ob- 1 Od) Significant focal erosions are also classified as grade 3 lesions and may coexist with cartilage fibrillation (Fig 1 Oe, 1 Of). .
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11
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2
b.
e.
f.
Figure
10.
Grade
3 chondromalacia
specimen. Axial 3 chondromalacia
lage
fibrillation
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1991
(curved
Axial
section
through
the
patellofemoral
joint
of a ca.
.
(c) and patellae
no sharp margin is visualized sponding axial Ti -weighted
(a)
fibrillation of the articular cartilage of the lateral facet (arrows) (b) Con(700/20) MR image demonstrates the loss of the sharp margin between arand trochlea (arrows) This is in the same area as the fibrillation seen in the
davenic specimen demonstrates responding axial Ti -weighted ticular cartilage of the patella cadavenic ic grade
patellae.
sagittal show
(arrow). (700/20)
(d) Ti -weighted decreased signal
(700/20) intensity
images extending
Axial section through a cadavenic MR image (f) demonstrate focal
knee erosion
of a patient with to the articular
specimen (straight
symptomatsurface, and
(e) and correarrow) and carti-
arrow).
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a.
b.
Figure 11. Grade 4 chondromalacia patellae. (a) Axial section through a cadavenic knee specimen shows a focal cartilage defect extending from the bone to the articular surface (arrow) Early subchondral cystic changes are also seen. (b) Conresponding Ti-weighted (700/20) MR image shows both the focal cartilaginous (arrow) and subchondral osseous abnormalities. (c) Sagittal Ti -weighted (700/20) MR image of a patient with symptomatic grade 4 chondromalacia pate!lae shows a low-signal-intensity lesion extending from the articular surface to subchondral bone (arrow). .
Grade
4.-Ulceration
extending
to the
sub-
chondral bone (Fig i i a) is seen on MR images as a focal cartilage defect extending to the bone, with decreased signal intensity within the underlying subchondra! bone (Fig i ib). In our experience, grade 3 or 4 chondromalacia patel!ae was virtually always present when a patellar subchondral signal abnormality was detected. A typical grade example is illustrated in Figure 1 ic.
4
C.
Clinical Study oftbe Accuracy ofMR Imaging.-To determine the relative sensitivity and predictive value of MR imaging in the detection of chondromalacia pate!lae, we conducted a prospective study (Table 2) MR imaging was performed in 30 patients complaining of anterior knee pain. Only Tiweighted axial and sagitta! images were eva!uated, since some of the earlier patients did .
not
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3D FISP
75 imaging.
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Table 2 Efficacy of MR Imaging Arthroscopic
Stage
in Detection
Sensitivity and Odd Facets
Medial
0 (normal) 1
of Chondromalacia
83 (5/6) ioo (3/3)
Lateral
Facet
Medial
55 (6/i i) iOO (3/3)
88 (7/8)
iOO (6/6)
iOO (5/5)
iOO
iOO
(2/2)
= true positive/(true positive + false negative). value = true positive/(true positive + false positive).
subsequently underwent arthroscopy, and these results were used as the “gold standard.” In our prospective clinical study, MR imaging was relatively sensitive and had a relatively high predictive value in the detection
(stages
3 and
4) chondromala-
cia patellae. In these cases, the only lesions missed were in the medial facet, probably because of volume averaging of this steeper
Although
the brush-border
stage 3 disease was very casionally nondiagnostic.
was
Facet
78 (7/9) 67 (6/9) 100 (2/2)
88 (7/8)
56 (5/9) iOo (2/2)
of high-grade
Lateral
86 (6/7) iOO (3/3)
70 (7/iO)
(2/2)
(%)t
50 (5/10) 60 (3/5)
3 4
Predictive
ance
Predictive Value and Odd Facets
(%)‘
2
‘Sensitivity
facet.
Patellae
observed
sensitive, A similar
in a normal
MR sign of it was ocappear-
grade fair
(stages
0, i and
decreased in the
2) disease was only MR finding of focal areas of ,
at best.
The
signal detection
intensity
was very
of stage
1 disease since it was
sensitive but also
had
a
low predictive value, seen in patients with normal articular cartilage. Although our clinical results were somewhat disappointing, it is hoped that the addition of 3D FISP 75 sequences to our imaging protocol will and predictive
detection however,
improve value
both the sensitivity of MR imaging in the
of chondromalacia awaits clinical
patellae. verification.
This,
patellofemo-
ral joint due to volume averaging of an oddly shaped facet. The sensitivity and predictive value of MR imaging in the detection of low-
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1991
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CA1-.
) -.
Figure
12.
Congruence
angle.
(a) Schematic
.
S
___
-.
of
the measurements used to evaluate congruence angle (CA). The normal congruence angle is -8#{176} ± 6#{176}. L = lateral, M = medial. (b) Axial Tiweighted (700/20) MR image through the pate!lofemoral joint in a patient with a normal congruence angle. (c) Axial Ti-weighted (700/20) MR image of a patient with a positive congruence angle and a history of recurrent lateral patellar dislocations.
#{149} Patellar Patellar tionship
groove
Alignment
alignment between
patellae
refers to the static relathe patella and trochlear
of the femur.
ods used to evaluate most common are
There
are several
alignment. the measurements
Two
methof the
Congruence is a measurement
of the
the patella.
patellar congruence angle and tilt angle. Abnormalities in patellar alignment have been thought
208
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to be precursors
U
Conway
to chondromalacia
et al
and
frank
the patellofemoral
degenerative
joint Angle.-The of lateral
Abnormal
changes
of
(7,8). congruence
angle
subluxation
congruence
of
angles
have been associated with chondromalacia patellae (7). The congruence angle is formed by a line bisecting the sulcus angle and a second line projecting from the apex the trochlea through the apex of the patella
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11
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of
2
.r’
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b.
(Fig
13. Patellar tilt angle. (a) Schematic of drawn to measure patellar tilt angle (PTA). L = lateral, M = medial. (b) Axial Tiweighted (700/20) MR image through the pate!lofemoral joint in a patient with a normal patellar tilt angle. (c) Axial Ti-weighted (700/20) MR image through the patellofemoral joint in a patient with an abnormal patellar tilt angle (significantly less than 8#{176}). the lines
c.
i 2a).
The
normal
congruence
angle
allel
is
-8#{176}± 6#{176}. Positive congruence angles are sociated with recurrent lateral dislocation. This angle can be easily measured on both axial MR or CT images (Fig i 2b, i 2c).
as-
to the
posterior
aspects
of the
lateral
and medial femoral condyles (8). The normal angle is greater than 8#{176} (Fig i 3a, 1 3b). An abnormal patellar tilt angle (Fig 1 3c) may be associated with excessive lateral pressure syndrome.
Pateilar
is formed et of the
March
pate!lar
TiltAngle.-The
by a line patella
1991
and
paralleling a second
tilt
the lateral line
drawn
angle
facpar.
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ci.
C.
Figure 14. Images taken with the knees femoral joints. (c, d) with the knees in 50
of a woman with a clinical history of bilateral subluxing patellae. in 150 of flexion demonstrate no significant alignment abnormality Axial Ti-weighted (700/20) images through the patellofemoral of flexion, demonstrate laterally subluxing patellae bilaterally.
Figure 1 4 illustrates the efficacy of crosssectional imaging (CT or MR) in the evaluation of patellar alignment. Plain radiographs failed to demonstrate abnormal patellar alignment. MR images demonstrated an abnormal patellar tilt angle and congruence angle. Both patellae were laterally subluxed. Despite this finding, the articular surfaces of the patellae
appeared
intact.
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the same
informa-
lion concerning patellar alignment could have been obtained with CT, additional information about the articular cartilage was
afforded The tamed
by MR imaging. MR images (Fig i 4c, 1 4d) were with the knees in 5#{176} of flexion.
degree
of flexion
was
used
because
the
obThis
effi-
cacy of cross-sectional studies with the joint in relaxed, full extension is controversial. Delgado-Martins believes that slight lateral subluxation
210
Although
(a, b) Launin views of the patellojoints, obtained
when
the
joint
Volume
is in resting
11
Number
full
2
ages of the increments
patellofemoral of passive
joint during early flexion. They
knee
used a special non.ferromagnetic device (Medrad, Pittsburgh) (Fig
positioning for this purpose
15).
Kinematic
MR imaging
of both
pate!lofem-
oral joints was performed in a patient with bilateral anterior knee pain (Fig i 6). MR images showed that the right patella was mcdially subluxed and that the left patella was laterally subluxed through the entire range ofmotion (50300) In addition to demonstrating a useful technique, these images demonstrated a newly
recognized tion
Figure
15. Schematic of the positioning device used to evaluate patellar tracking with MR imaging. The handle (straight anrow) is used to adjust the device (curved anrow) used to flex and extend the knee.
extension is a normal variant (9) cases, isometric contraction of the ceps mechanism usually results in movement of the patella to a more position. .
#{149} Patellar Patellar tionship
groove
refers to the dynamic relathe patella and trochlear
femur.
Abnormalities
of pate!-
lar tracking have also been associated with chondromalacia patellae and degenerative changes of the patellofemoral joint (1 10). As stated previously, some researchers believe that producing a kinematic depiction ,
patella
medial
(right
knee).
and Deese (i 2) observed of patellofemoral joints a! retinacular
release
However, medial
there subluxation
also
occurs
now,
but,
until
is especially of patellar thopedic stabilization
been
a high
in patients
surgery, patellar
performed.
frequency who
suggesting tracking was
important
subluxaHughston
this finding in 93% in which prior later-
had
was
undergone prior type of abnormal
nacular
Tracking
tracking between
of the
In these quadnimedial normal
phenomenon,
of the
not
had
that this commonly
recognized.
to identify
this
It
type
subluxation and to inform the orsurgeon because classical surgical techniques, such as lateral reti-
release
or medial
extensor mechanism, medial displacement tion rather than relief toms.
transposition
of the
can further increase and lead to exacerbaof the patient’s symp-
Kinematic MR imaging of the knee ly suffers from one potential problem. images depiction unclear
of not
currentThe
displayed do not represent a real-time of knee motion. At this point, it is whether this problem will prove to
be of clinical
significance.
of patellofemoral motion may be the most accurate way of evaluating patellar tracking. Recently, Shellock et al (1 0) described their experience using a kinematic MR imaging technique for the assessment of patellar tracking. This involved the acquisition of multiple sequential, Ti-weighted axial im-
March
1991
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C.
Figure 16. Axial Ti-weighted (500/20) MR images (5-mm-thick sections) taken at 5#{176} increments of passive knee flexion from 5#{176} (a) to 30#{176} (f). The patellae are of a Wiberg type I configuration ( 1 1 ) and the tnochlear grooves are shallow. There is a redundant lateral retinaculum of the left knee (arrow in a) which becomes taut at 30#{176} of flexion (I). The night knee shows gradually increasing medial subluxation of the patella with flexion. ,
,
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a.
b.
Figure 17. Radiographically occult fracture of the patella. (a) image demonstrates an irregular transverse fracture of the lower T2-weighted (2,500/90) image demonstrates edema surrounding
#{149} Miscellaneous
Disorders
Radiographically Yao and Lee
found MR imaging
(1 3), ing
OccultFraclure.-Just
occult
in other is capable
fractures
of the
as
parts of the knee of demonstratpateila.
In one
of
our patients, a transverse fracture of the lower pole of the patella that was not evident on plain
radiographs
the
sagittal
(Fig
17).
Infrapatellar
cae
occur
involution
septi.
was
proton-
easily
and
Synovial
within
Infrapatellar
due
to failure
embryologic
synovial
plicae
.
mon and thickened
usually medial
Tendinitis.-Symptomatic
Patellar tendinitis
is relatively
accompanied by central tion of the tendon. The
of
ably
synoviah
are com-
related
ferred mon
to overuse is at the
mal
area
easily of increased
(Fig
RadioGraphics
U
Conway
et al
and
mucoid disorder
to as “jumper’s site
patellar
common
ph-
the normally
U
An inflamed, may produce
anterior pain, clicking, or locking, mimicking a patellofemoral problem or meniscal tear. The medial plica is visualized on axial views as a linear low-signal structure medial to the patella (Fig 18).
MR imaging
214
asymptomatic. patellar phica
on
images
Pllcae.-These
the knee
of normal
identified
T2-weighted
Sagittal proton-weighted (2,500/30) MR pole of the patella (arrows) (b) Sagittal the fracture site (arrows).
is often
degenerais presum-
and
is frequently
re-
knee.”
The
corn-
inferior
pole
of the
demonstrates signal
most
patella.
the abnorintensity
low-signal-intensity
within
tendon
19).
Volume
11
Number
2
a.
Figure
18. Medial synovial plica of the knee. (a) Axial davenic specimen reveals a medial synovial plica (arrow). MR image also shows the plica (arrow).
b. section through the patellofemoral joint of a ca(b) Corresponding axial Ti -weighted (700/20)
a. b. Figure 19. Patellar tendinitis (jumper’s knee). (a) Sagittal Ti -weighted (700/20) MR image shows an area of increased signal intensity within the supeniormost portion of the patellar tendon (arrow) (b) 3D FLASH 40 (40/i 3/40#{176})gradient-echo image through the same area demonstrates the same finding (arrow). .
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1991
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a.
b.
C.
d.
I
Figure 20. MR arthrograms of the patellofemoral joint of a cadavenic specimen obtained after an injection of 500 mol of gadopentetate dimeglumine. (a) Axial Ti -weighted (700/20) MR image shows a focal grade 3 chondromalacia patellae defect in the medial-most aspect of the lateral facet (arrow) (b) On the corresponding proton density (2,500/30) image, the focal defect (arrow) is again noted, but it is not quite as well seen as on a. On the corresponding T2-weighted (2,500/90) image (c), 2D FISP iO (30/i3/iO#{176}) gradientecho image (d), and 2D FISP 40 (30/i3/40#{176}) gradient-echo image (e), the focal defect is not well visualized. (f) Corresponding 2D FISP 75 (30/ i 3/75#{176})gradient-echo image demonstrates the focal defect (arrow) only slightly better than c-C. (g) On the corresponding 2D FLASH 75 (30/ 13/75#{176})gradient-echo image, the focal defect is not well visualized. .
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ARTHROGRAPHY Gyhys-Morin et al (1 4) first demonstrated potential efficacy of MR arthrography U
mography scanning in chondromalacia patellae. Skeletal Radio! i982; 8:i83-i85. Ihara H. Double-contrast CT arthrography of the cartilage of the patellofemoral joint. Clin Orthop Rd Res i985; i98:50-55. Shahniaree H. Chondromalacia. Contemp Orthop 1985; ii:27-39. Yulish BS, MontanezJ, Goodfellow DB, Bryan PJ, Mulopulos GP, Modic MT. Chondromalacia patellae: assessment with MR imaging. Radiology i987; 164:763-766. Hayes CW, Sawyer RW, Conway WF. Detection and staging of patellar cartilage lesions with MR imaging: pathologic correlations. Radiology 1990; 176:479-483. Benquist Th. Imaging oforthopaedic trauma and surgery. Philadelphia: Saunders, 1986; 314. Weissman BNW, Sledge CB. Orthopaedic radiology. Philadelphia: Saunders, 1986; 516. Delgado-Martins H. A study of the position of the patella using computenised tomography. J Bone Joint Sung [Br] 1979; 61 :44 3-
MR
hanced
with
gadopentetate
the en-
dimeglumine
3.
in
the evaluation of focal articular cartilage defects (1 4) Preliminary work with cadavenic specimens at the Medical College of Virginia also suggests possible qualitative enhancement of cartilaginous defects (Fig 20); how-
4
.
.
ever,
further
cadavenic
and
clinical
studies
of
this technique need to be performed. It should be noted that gadopentetate dimeglumine is currently not approved by the Food and Drug Administration for intraarticular injection. If clinical studies are to be per-
formed,
they
will
require
prior
informed
U SUMMARY The introduction of cross-sectional specifically CT and MR, to the
the
patehlofemoral
radiologists’
joint
diagnostic
choice
of which
to use
is strongly
to
is pro-
on
diagnosis in the joint. However,
alternative not
In some intraosseous represent U
to MR imaging
available
or cost
situations lesions the imaging
when
(eg,
.
12
.
13
.
14
.
patient’s
area of the patelloCT can be a useful
is a major
11
modalities the
clinical examination and resulting differential diagnosis. In general, we believe that MR imaging, when combined with the usual plain radiography, offers the clinician and radiologist the greatest latitude in making a specific femoral
444.
1 0.
the
Shellock FG, MinkJH, Deutsch AL, FoxJM. Patellar tracking abnormalities: clinical cxpenience with kinematic MR imaging in 130 patients. Radiology i989; 172:799-804. Wiberg G. Roentgenographic and anatomic studies of the patellofemoral joint with specia! reference to chondromalacia patellae. ActaOrthop[Scand]
The
imaging
predicated
9.
increased
capabilities.
of these
7.
8.
imaging, evaluation of
has greatly
6.
pa-
tient consent and approval by the hospital’s committee on human studies. Although the technique of MR arthrography may improve detection of both meniscal
and articular cartilage lesions, it remains be seen whether this additional advantage worth subjecting patients to an invasive cedure.
5.
148:1 153-i
hatter
1941;
12:319-333.
Hughston JC, Deese M. Medial subluxation of the patella as a complication of lateral nelease. AmJ Sports Med 1988; 16:383-388. Yao L, Lee JK. Occult intraosseous fracture: detection with MR imaging. Radiology 1988; 167:749-751. Gylys-Monin VM, Hajek PC, Sartonis DJ, Resnick D. Articular cartilage defects: detectability in cadaver knees with MR. AJR 1987; 157.
is
consideration.
characterization
of
of the patella), CT may modality of choice.
REFERENCES Stanford W, PhelanJ, Kathol MH, et al. Patellofemoral joint motion: evaluation by ultrafast computed tomography. Skeletal Radiol i988; i7:487-492. 2. Boven F, Bellemans MA, GeartsJ, DeBoeck H, Patvliege R. The value of computed toi
.
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1991
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F. Conway,
Thomas Landis
Loughran,
MD
Griffeth,
MD,
G. Shellock,
PhD
K.
Frank
MD,
PhD
#{149} Curtis
#{149} William
PhD
W. Hayes,
MD
G. Totty, MD
#{149} Georges
#{149}
#{149}
V. El-Khoury,
MD
#{149}
Computed tomography (CT) and magnetic resonance (MR) imaging are extremely useful in the accurate diagnosis of anterior knee pain, a common complaint arising from numerous causes (including fracture, chondromalacia patellae, and alignment and tracking abnormalities) Plain CT is effective for evaluating intraosseous lesions of the knee. Although CT arthrography provides excellent visualization of the patellar articular cartilage, the technique is expensive and invasive. Cine CT is an excellent method for assessing patellofemoral tracking and alignment. Kinematic MR imaging can also perform this function. In addition, MR imaging can provide valuable information concerning the status of patellar cartilage. Although MR imaging can accurately show high-grade chondromalacia patellae, it is less accurate in the detection of low-grade disease. The authors believe that MR imaging and plain radiography offer radiologists the greatest latitude in making a specific diagnosis of the cause of anterior knee pain; however, CT is a useful alternative. .
INTRODUCTION
U
Anterior knee ages. Common lacia patellae, and inflamed
pain is a frequent, often nonspecific complaint of individuals of all causes of anterior knee pain include patellar fracture, chondromapatellar alignment and tracking abnormalities, patellar tendinitis, infrapatellar synovial plicae. Less common causes include patellar
Abbreviations: Index 452.41
FISP
terms:
Knee,
#{149} Knee.
RadioGraphics I
From
the
injuries, 1991;
Departments
fast
imaging
abnormalities. 452.42. i i : I95-2 ofttadiology
with 453.9
452.485
steady
precession.
#{149} Knee. #{149} Knee.
of Radiology.
Receivedjuly print requests ,
RSNA.
Cedars-Sinai
17, 1990; revision to W.F.C.
arthritis,
fast
452.78
MRstudies,
low.angle
#{149} Knee,
452.1214
CT.
shot. 452.i2i
3D i
= three-dimensional
#{149} Knee,
fractures.
#{149} Patella
1 (W.F.C.,
C.W.H.)
MCV Station, Richmond, VA 23298.06 1 5; Mallinckrodt (W.G.T.. 1KG.); Department of Radiology. University partment
FLASH
Medical requested
Center, August
and
Surgery
Institute oflowa Los Angeles 2 1 and
(T.L.),
Medical
of Radiology, Hospitals and
received
(F.G.S.). October
College
ofVirginia,
Box
University of Washington, Clinics, Iowa City (G.Y.E.K.);
From
the
1989
3 1 ; accepted
RSNA
scientific
November
615,
St Louis and Dcassembly.
5. Address
re-
1991
195
a.
b.
Figure 1. Images of a patient who presented with a warm swollen knee and patellar and penpatellar pain. (a) Plain radiograph of the patella fails to reveal an abnormality. (b) Delayed static bone scintignam shows mild diffuse uptake about the knee and intense uptake in the patella. The presence of a septic joint (Staphylococcus aureus) accounts for the diffuse mild uptake. (c) Axial CT scan through the patella demonstrates a focus of osteomyelitis on Bnodie abscess in the patella, containing a small sequestrum (arrow) find. ings corresponding to the intense uptake seen in the patella in b. ,
osteomyelitis and tumors. In addition, osteonecrosis of the femoral condyles and meniscal tears may refer pain anteriorly. With such diverse causes of pain, accurate diagnosis is essential to treat these disorders effectively. The introduction of cross-sectional imaging
modalities,
specifically
computed
tomogra-
phy (CT) and magnetic resonance (MR) imaging, has greatly expanded the ability of the radiologist to make these diagnoses. We present examples of how both CT and MR imaging have been used to accurately diagnose the various pathologic processes encountered about the knee. Specifically, we describe the use of CT, CT arthrography, cine CT, spin-echo MR imaging, gradient-
C.
echo MR imaging, and MR arthrography in the evaluation of the patellofemoral joint. The images presented are from two sources: cadavenic knee specimens (for which pathologic specimen-image correlation is made) and patients referred to our institutions specifically for evaluation of anterior knee pain.
U
CT
EVALUATION
.
Imaging
OF
KNEE
PAIN
Parameters
CT of the patellofemoral
joint is performed
in the axial plane, with the knee in approximately 50 of flexion. Contiguous 3-mm-thick sections are obtained through the patella
196
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a. b. Figure 2. CT arthrognams of two cadavenic knee specimens. Approximately 30 mL of air were injected into the knee joint before scanning. (a) Axial image through a normal specimen shows the smooth articulas cartilage surface of the patella. (b) Axial image of the second specimen demonstrates an area of focal chondromalacia patellae (arrow) and overall thinning of the patellar articular cartilage.
with use of a bone algorithm. This permits adequate visualization of intraosseous anatomy and, when CT arthrography is used, the articular cartilage.
CT arthrography
of the knee
of 3 mL of diatrizoate sodiurn meglumine (Renografin 76; Squibb, New Brunswick, NJ) 0 3 mL of epinephrine (1 : 1 ,000 dilution) and 30-50 mL of air into the knee. The actual imaging is performed .
,
within 30-45 minutes ofthe injection. 0then imaging parameters are similar to those used for standard CT of the patellofemoral joint. Cine CT of the knee during flexion can be achieved with use of an ultrafast CT scanner (Imatron, South San Francisco, Calif) (1). The patient is positioned supine within the gantry, and the thigh is supported so that an approximately 45#{176} angle with the horizontal plane is maintained. Section thickness is 10 mm, and nine sections can be obtained in approximately 0.7 seconds. If the scanner is programmed to obtain these images as the knee is moved from 900 of flexion to full extension and back to 90#{176} of flexion, 10 images at each of nine levels (encompassing an 8-cm-length of knee) can be acquired in 7
March
1991
images can be played cine format, which al-
lows for visualization tellofemoral motion.
of active,
real-time
pa-
is performed
after an injection
,
seconds. The processed back in a closed-loop
S
Intraosseous
Lesions
of the
Patella
In isolated cases, CT can be used effectively to evaluate intraosseous lesions of the pate!lofemora! region. Although infrequently used for this purpose, CT can demonstrate radiographica!ly occult Brodie abscesses of the patella (Fig 1). In addition to infection, tumors of the patella also can be evaluated and classified with CT. CT may be particularly valuable in cases of primary tumors, for which the evaluation of marginal of the tumor may ography.
and internal be limited
characteristics with plain radi-
. Chondromalacia Patellae CT can be used in conjunction with routine knee arthrography (CT arthrography) to provide excellent visualization of pate!!ar articular
cartilage
(Fig
2).
Conway
Several
et al
authors
U
(2,3)
RadioGraphics
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197
veal the luxation.
groove
have
demonstrated
that this technique proand specific evaluation of chondromalacia patellae (see subsection under MR Evaluation for a more detailed discussion of this disease) Criteria for the diag-
flexion
vides
both
to be a significant shortcoming, since abnormalities of both patellar alignment and tracking may be seen only in the first 20#{176} of flexion. (A more detailed discussion of align-
nosis
of chondromalacia
ment
sensitive
.
to those
used
bibition
of contrast
patellae
in regular
are
arthrography
material
similar
(ie,
by cartilage,
imcar-
tilage thinning, and focal defects) The main disadvantages of this technique are its expense and invasiveness. .
#{149} Pateilar Alignment and Tracking There are many methods for obtaining axial plain radiographs of the patella. With all of them, images of the knee in less than 150 of
cannot
be obtained.
and tracking
RadioGraphics
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Conway
Ct
al
is included
has proved
with
MR
.
and 4 demonstrate a pair of normal (Fig 3) and laterally subluxed (Fig 4) patellae imaged with an ultrafast CT scanner (Imatron). These
images
flexion in different and
represent
of the knee. degrees
processed,
kinematic method od for evaluating
U
This
Evaluation.) As stated above, CT permits axial cross-sectional imaging of the knee in all degrees of flexion from 0#{176}-90#{176} Figures 3
was produced.
198
and no cvi
one
When
position
during
the other
images
of flexion
a cine
ioop
Stanford
were of knee
et a! claim
is the most patellofemoral
Volume
obtained motion
that this
accurate tracking
11
meth(1).
Number
2
In this case,
U
MR
EVALUATION
#{149} Pulse With
the patel
(eg,
Ti -weighted 700/20
echo time msec]) cartilage may show diate signal intensity bilaminar sity from
being
KNEE
PAIN
spin-echo
se-
low-angle shot [FLASH]) and with the flip angle (repetition time/echo time/flip angle). For example, three-dimensional (3D) FLASH
Sequences
typical
quences
OF
[repetition time msec/ (Fig 5a) normal articular ,
a homogeneous throughout
appearance, with the basal two-thirds
lower
than
intermeor a subtle
the signal intenof the cartilage
that of the superficial
We found this bilaminar u!ar cartilage to be more disarticulated cadaveric
appearance pronounced specimens;
layer. of articin the the
cause of this appearance is uncertain. When gradient-echo sequences are used, the relative contrast between cartilage and fluid changes imaging with
March
1991
with the type of sequence steady precession [FISP]
(fast vs fast
40 images
intensity
show
intermediate
for articular
to high
cartilage
and
signal
slightly
lower signal intensity for fluid (Fig 5b) 3D FISP 40 images also show an intermediate to high signal intensity for articular cartilage but a higher signal intensity for fluid (Fig 5c) 3D FLASH 75 images show a slightly .
.
lower signal intensity for articular cartilage, compared with that seen on 3D FLASH 40 images. This makes distinction between synovial fluid and articular cartilage slightly more difficult (Fig 5d). 3D FISP 75 images show a slightly lower signal intensity for articular
cartilage
than
do 3D FISP 40 images.
Conway
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a.
b.
,,
‘
d.
C-
5. Axial MR images through the patellofemoral joint in a patient with a mild effusion. (a) Ti -weighted (700/20) axial image. 3D FLASH Figure
40
(b) and 3D FISP 40 (40/13/40#{176})
(40/13/400)
(c) axial images obtained at the demonstrate mild joint effusion FLASH 75 (40/i3/75#{176}) (d) and i 3/75#{176}) (e) axial images of the equivalent position demonstrate
same location (arrows) . 3D 3D
FISP 75
same knee joint fluid
as a (40/
at an (an-
rows).
permits
greater
and articular
differentiation
cartilage
between
(Fig
fluid
Se).
At present, Ti -weighted axial and sagitta! images are preferred at the Medical College of Virginia for evaluation of pate!lar cartilage when a joint effusion is not present. These images provide adequate contrast and resolution for detection of most surface and internal cartilage lesions. We routinely include
e. Ti-weighted mm-thick
sition)
200
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axial sections,
with
our
sequences 0.25-mm
usual
(700/20, gap, one
interleaved
Volume
4acqui-
sagittal
11
Number
Ti-
2
Figure 6. Cadavenic sections and corresponding MR images from healthy volunteers. (a) Axial cadavenic specimen reveals normal, smooth articular cartilage of the patella and the trochlea. (b) Corresponding axial Ti-weighted (700/20) MR image shows the dark line separating the patellar and trochlear articular cartilage (arrows). (C) Sagittal cadavenic section. (d) Corresponding sagittal Ti -weighted (700/20) MR image shows the relative homogeneous nature of the articular cartilage and the distinct line separating the patellar from trochlear cartilage (arrow).
weighted sequences. When fluid is present within the joint, we prefer to use 3D FISP 75 sequences. This sequence maximally enhances the arthrographic effect of the synovia! fluid. A double-echo, proton-density and T2-weighted sequence (2,500/30, 90) is more time consuming to perform, but the resulting images may also show cartilage defects. MR images shown here were obtained with a i .0-T magnet and a receive-only extremity coil (Siemens Medical Systems, Ise!in, NJ).
March
1991
#{149} Normal Patellar Cartilage As stated, normal pate!!ar cartilage may show a homogeneous intermediate signal intensity or a subtle bilaminar appearance on Ti weighted images (Fig 6) Morphologic charactenistics of the lateral, medial, and odd facets are best demonstrated on axial images. -
.
The interface cartilage
between
or between
patellar patellar
Conway
et al
and trochlear cartilage
U
and
fat
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201
Table
1 ClassifiCations
of Chondromalacia
Grade
Patellae
Pathologic
Based
on Pa thologiC
and
Findings’ swelling
MR Imaging
i
Softening cartilage
and
of articular
2
Blistering ducing
of articular deformity
3
Surface irregularity and cartilage bnillation with minimal, ifany, extension to subchondral bone
4
Ulceration chondral
Focal areas of decreased Ti-weighted images the cartilage surface bone Focal areas of decreased extending to cartilage
cartilage proof the surface
ervation
with exposure bone
fi-
Modified
from
classification
system
by Shahriaree
Findings signal intensity on not extending to or subchondral signal surface
cartilage
intensity with pres-
margin
tella and that of the trochlea Focal areas of decreased signal extending from subchondral
of sub-
used
of sharp
Findings
Focal signal intensity abnormality extending to the articular surface but not the osseous surface of the articular cartilage; loss of the sharp dark margin between the articular cartilage of the pa-
cartilage cartilage bone S
MR Imaging
intensity bone to the
surface over a significant area; is thinned to the subchondral
(4).
should form a thin dark line. Volume averaging may blur this line, especially with sagittal images of the steeper medial pate!lar fac-
et. Evaluation gether helps averaging
of sagittal one avoid
for true
surface
#{149} Chondromalacia Simply put, pathologic
There
Pateliae
is no consensus patellae.
tracking
to-
irregularity.
chondromalacia softening of the
chondromalacia
chanica!
and axial images mistaking volume
patellae patellar
as to the Trauma
abnormalities
is cartilage.
causes and
of me-
are most
fre-
quently cited. The number of cases of anterior knee pain actually caused by chondromalacia patellae is also controversial, since a
Figure
7.
Schematic
lion of chondromalacia definition of the grades).
202
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Ct al
of the Shahriaree patellae
(see
Volume
11
classificaTable
1 for
Number
2
b.
a.
Figure 8. Grade 1 chondromalacia patellae. (a) Axial section through the patellofemoral
joint
of a cadaveric specimen shows the area of cartilage softening (arrowheads) as determined with use ofa metallic probe on the specimen. (b) On
the corresponding Ti-weighted (700/20) MR image, no abnormality is seen. (C) Sagittal Tiweighted (700/20) image of a patient with symptomatic grade 1 chondromalacia patellae demonstrates an area of focal, intracartilaginous decreased signal intensity (arrow).
patients,
we
have
great many asymptomatic individuals also show significant chondromalacia patellae at arthroscopy. Several classifications of chondromalacia patel!ae have been proposed on the basis of pathologic findings. We have used the c!assification system by Shahriaree (4), based on arthroscopic findings (Fig 7, Table 1). A three-grade classification system based on MR imaging findings was proposed by Yulish et a! (5). Based on our examination of disarticulated knee specimens and symptomatic
March
1991
a four-grade
sys-
to more closely follow the arthroscopic staging system
Grade
superficial
,
C-
adopted
tern (6) hoping commonly used (Table 1).
ing
1.-The noted
imens
in several
(Fig
on
MR
cal
areas
8a)
images
is not of the
cartilage
disarticulated clearly signal
spec-
demonstrated
specimens
of decreased
softenknee
(Fig intensity
8b)
.
Fo-
are fre-
quently seen in both symptomatic and asymptomatic subjects (Fig 8c). The significance of these focal lesions is not certain at this
point.
Conway
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203
‘,
..-s,
‘
1’ Figure 9- Grade 2 chondromalacia patel!ae. (a) Sagittal section through the patellofemoral joint of a cadavenic specimen demonstrates a blistenlike lesion extending to the cartilage surface (arrow). (b) Corresponding Ti -weighted (700/ 20) MR image demonstrates a focal area of decreased signal intensity extending to and deforming the articular surface of the cartilage (arrow). (c) Sagittal Ti -weighted (700/20) image of a patient with symptomatic grade 2 chondromalacia patellae shows a focal lesion with sharply defined margins (arrow).
Grad. 2.-A blister!ike lesion may extend to the cartilage surface (Fig 9a) and appears on MR images as a low-signal-intensity area at the cartilage surface (Fig 9b) Grade 2 le.
sions extend bulge while (Fig 9c).
to the surface, causing a focal maintaining sharp margins
Grade 3.-Fibrillation ing a “crabmeat”
seen
204
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on MR images
U
of cartilage appearance (Fig
as decreased
Conway
et al
produc1 Oa) is
signal
inten-
C.
sity extending to the surface, with conspicuous loss of the sharp interface at the cartilage surface (the “brush-border” sign of arthroscopic stage 3 changes) (Fig 1 Ob- 1 Od) Significant focal erosions are also classified as grade 3 lesions and may coexist with cartilage fibrillation (Fig 1 Oe, 1 Of). .
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b.
e.
f.
Figure
10.
Grade
3 chondromalacia
specimen. Axial 3 chondromalacia
lage
fibrillation
March
1991
(curved
Axial
section
through
the
patellofemoral
joint
of a ca.
.
(c) and patellae
no sharp margin is visualized sponding axial Ti -weighted
(a)
fibrillation of the articular cartilage of the lateral facet (arrows) (b) Con(700/20) MR image demonstrates the loss of the sharp margin between arand trochlea (arrows) This is in the same area as the fibrillation seen in the
davenic specimen demonstrates responding axial Ti -weighted ticular cartilage of the patella cadavenic ic grade
patellae.
sagittal show
(arrow). (700/20)
(d) Ti -weighted decreased signal
(700/20) intensity
images extending
Axial section through a cadavenic MR image (f) demonstrate focal
knee erosion
of a patient with to the articular
specimen (straight
symptomatsurface, and
(e) and correarrow) and carti-
arrow).
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a.
b.
Figure 11. Grade 4 chondromalacia patellae. (a) Axial section through a cadavenic knee specimen shows a focal cartilage defect extending from the bone to the articular surface (arrow) Early subchondral cystic changes are also seen. (b) Conresponding Ti-weighted (700/20) MR image shows both the focal cartilaginous (arrow) and subchondral osseous abnormalities. (c) Sagittal Ti -weighted (700/20) MR image of a patient with symptomatic grade 4 chondromalacia pate!lae shows a low-signal-intensity lesion extending from the articular surface to subchondral bone (arrow). .
Grade
4.-Ulceration
extending
to the
sub-
chondral bone (Fig i i a) is seen on MR images as a focal cartilage defect extending to the bone, with decreased signal intensity within the underlying subchondra! bone (Fig i ib). In our experience, grade 3 or 4 chondromalacia patel!ae was virtually always present when a patellar subchondral signal abnormality was detected. A typical grade example is illustrated in Figure 1 ic.
4
C.
Clinical Study oftbe Accuracy ofMR Imaging.-To determine the relative sensitivity and predictive value of MR imaging in the detection of chondromalacia pate!lae, we conducted a prospective study (Table 2) MR imaging was performed in 30 patients complaining of anterior knee pain. Only Tiweighted axial and sagitta! images were eva!uated, since some of the earlier patients did .
not
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3D FISP
75 imaging.
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Table 2 Efficacy of MR Imaging Arthroscopic
Stage
in Detection
Sensitivity and Odd Facets
Medial
0 (normal) 1
of Chondromalacia
83 (5/6) ioo (3/3)
Lateral
Facet
Medial
55 (6/i i) iOO (3/3)
88 (7/8)
iOO (6/6)
iOO (5/5)
iOO
iOO
(2/2)
= true positive/(true positive + false negative). value = true positive/(true positive + false positive).
subsequently underwent arthroscopy, and these results were used as the “gold standard.” In our prospective clinical study, MR imaging was relatively sensitive and had a relatively high predictive value in the detection
(stages
3 and
4) chondromala-
cia patellae. In these cases, the only lesions missed were in the medial facet, probably because of volume averaging of this steeper
Although
the brush-border
stage 3 disease was very casionally nondiagnostic.
was
Facet
78 (7/9) 67 (6/9) 100 (2/2)
88 (7/8)
56 (5/9) iOo (2/2)
of high-grade
Lateral
86 (6/7) iOO (3/3)
70 (7/iO)
(2/2)
(%)t
50 (5/10) 60 (3/5)
3 4
Predictive
ance
Predictive Value and Odd Facets
(%)‘
2
‘Sensitivity
facet.
Patellae
observed
sensitive, A similar
in a normal
MR sign of it was ocappear-
grade fair
(stages
0, i and
decreased in the
2) disease was only MR finding of focal areas of ,
at best.
The
signal detection
intensity
was very
of stage
1 disease since it was
sensitive but also
had
a
low predictive value, seen in patients with normal articular cartilage. Although our clinical results were somewhat disappointing, it is hoped that the addition of 3D FISP 75 sequences to our imaging protocol will and predictive
detection however,
improve value
both the sensitivity of MR imaging in the
of chondromalacia awaits clinical
patellae. verification.
This,
patellofemo-
ral joint due to volume averaging of an oddly shaped facet. The sensitivity and predictive value of MR imaging in the detection of low-
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CA1-.
) -.
Figure
12.
Congruence
angle.
(a) Schematic
.
S
___
-.
of
the measurements used to evaluate congruence angle (CA). The normal congruence angle is -8#{176} ± 6#{176}. L = lateral, M = medial. (b) Axial Tiweighted (700/20) MR image through the pate!lofemoral joint in a patient with a normal congruence angle. (c) Axial Ti-weighted (700/20) MR image of a patient with a positive congruence angle and a history of recurrent lateral patellar dislocations.
#{149} Patellar Patellar tionship
groove
Alignment
alignment between
patellae
refers to the static relathe patella and trochlear
of the femur.
ods used to evaluate most common are
There
are several
alignment. the measurements
Two
methof the
Congruence is a measurement
of the
the patella.
patellar congruence angle and tilt angle. Abnormalities in patellar alignment have been thought
208
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to be precursors
U
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to chondromalacia
et al
and
frank
the patellofemoral
degenerative
joint Angle.-The of lateral
Abnormal
changes
of
(7,8). congruence
angle
subluxation
congruence
of
angles
have been associated with chondromalacia patellae (7). The congruence angle is formed by a line bisecting the sulcus angle and a second line projecting from the apex the trochlea through the apex of the patella
Volume
11
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of
2
.r’
I
b.
(Fig
13. Patellar tilt angle. (a) Schematic of drawn to measure patellar tilt angle (PTA). L = lateral, M = medial. (b) Axial Tiweighted (700/20) MR image through the pate!lofemoral joint in a patient with a normal patellar tilt angle. (c) Axial Ti-weighted (700/20) MR image through the patellofemoral joint in a patient with an abnormal patellar tilt angle (significantly less than 8#{176}). the lines
c.
i 2a).
The
normal
congruence
angle
allel
is
-8#{176}± 6#{176}. Positive congruence angles are sociated with recurrent lateral dislocation. This angle can be easily measured on both axial MR or CT images (Fig i 2b, i 2c).
as-
to the
posterior
aspects
of the
lateral
and medial femoral condyles (8). The normal angle is greater than 8#{176} (Fig i 3a, 1 3b). An abnormal patellar tilt angle (Fig 1 3c) may be associated with excessive lateral pressure syndrome.
Pateilar
is formed et of the
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pate!lar
TiltAngle.-The
by a line patella
1991
and
paralleling a second
tilt
the lateral line
drawn
angle
facpar.
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ci.
C.
Figure 14. Images taken with the knees femoral joints. (c, d) with the knees in 50
of a woman with a clinical history of bilateral subluxing patellae. in 150 of flexion demonstrate no significant alignment abnormality Axial Ti-weighted (700/20) images through the patellofemoral of flexion, demonstrate laterally subluxing patellae bilaterally.
Figure 1 4 illustrates the efficacy of crosssectional imaging (CT or MR) in the evaluation of patellar alignment. Plain radiographs failed to demonstrate abnormal patellar alignment. MR images demonstrated an abnormal patellar tilt angle and congruence angle. Both patellae were laterally subluxed. Despite this finding, the articular surfaces of the patellae
appeared
intact.
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the same
informa-
lion concerning patellar alignment could have been obtained with CT, additional information about the articular cartilage was
afforded The tamed
by MR imaging. MR images (Fig i 4c, 1 4d) were with the knees in 5#{176} of flexion.
degree
of flexion
was
used
because
the
obThis
effi-
cacy of cross-sectional studies with the joint in relaxed, full extension is controversial. Delgado-Martins believes that slight lateral subluxation
210
Although
(a, b) Launin views of the patellojoints, obtained
when
the
joint
Volume
is in resting
11
Number
full
2
ages of the increments
patellofemoral of passive
joint during early flexion. They
knee
used a special non.ferromagnetic device (Medrad, Pittsburgh) (Fig
positioning for this purpose
15).
Kinematic
MR imaging
of both
pate!lofem-
oral joints was performed in a patient with bilateral anterior knee pain (Fig i 6). MR images showed that the right patella was mcdially subluxed and that the left patella was laterally subluxed through the entire range ofmotion (50300) In addition to demonstrating a useful technique, these images demonstrated a newly
recognized tion
Figure
15. Schematic of the positioning device used to evaluate patellar tracking with MR imaging. The handle (straight anrow) is used to adjust the device (curved anrow) used to flex and extend the knee.
extension is a normal variant (9) cases, isometric contraction of the ceps mechanism usually results in movement of the patella to a more position. .
#{149} Patellar Patellar tionship
groove
refers to the dynamic relathe patella and trochlear
femur.
Abnormalities
of pate!-
lar tracking have also been associated with chondromalacia patellae and degenerative changes of the patellofemoral joint (1 10). As stated previously, some researchers believe that producing a kinematic depiction ,
patella
medial
(right
knee).
and Deese (i 2) observed of patellofemoral joints a! retinacular
release
However, medial
there subluxation
also
occurs
now,
but,
until
is especially of patellar thopedic stabilization
been
a high
in patients
surgery, patellar
performed.
frequency who
suggesting tracking was
important
subluxaHughston
this finding in 93% in which prior later-
had
was
undergone prior type of abnormal
nacular
Tracking
tracking between
of the
In these quadnimedial normal
phenomenon,
of the
not
had
that this commonly
recognized.
to identify
this
It
type
subluxation and to inform the orsurgeon because classical surgical techniques, such as lateral reti-
release
or medial
extensor mechanism, medial displacement tion rather than relief toms.
transposition
of the
can further increase and lead to exacerbaof the patient’s symp-
Kinematic MR imaging of the knee ly suffers from one potential problem. images depiction unclear
of not
currentThe
displayed do not represent a real-time of knee motion. At this point, it is whether this problem will prove to
be of clinical
significance.
of patellofemoral motion may be the most accurate way of evaluating patellar tracking. Recently, Shellock et al (1 0) described their experience using a kinematic MR imaging technique for the assessment of patellar tracking. This involved the acquisition of multiple sequential, Ti-weighted axial im-
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Figure 16. Axial Ti-weighted (500/20) MR images (5-mm-thick sections) taken at 5#{176} increments of passive knee flexion from 5#{176} (a) to 30#{176} (f). The patellae are of a Wiberg type I configuration ( 1 1 ) and the tnochlear grooves are shallow. There is a redundant lateral retinaculum of the left knee (arrow in a) which becomes taut at 30#{176} of flexion (I). The night knee shows gradually increasing medial subluxation of the patella with flexion. ,
,
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a.
b.
Figure 17. Radiographically occult fracture of the patella. (a) image demonstrates an irregular transverse fracture of the lower T2-weighted (2,500/90) image demonstrates edema surrounding
#{149} Miscellaneous
Disorders
Radiographically Yao and Lee
found MR imaging
(1 3), ing
OccultFraclure.-Just
occult
in other is capable
fractures
of the
as
parts of the knee of demonstratpateila.
In one
of
our patients, a transverse fracture of the lower pole of the patella that was not evident on plain
radiographs
the
sagittal
(Fig
17).
Infrapatellar
cae
occur
involution
septi.
was
proton-
easily
and
Synovial
within
Infrapatellar
due
to failure
embryologic
synovial
plicae
.
mon and thickened
usually medial
Tendinitis.-Symptomatic
Patellar tendinitis
is relatively
accompanied by central tion of the tendon. The
of
ably
synoviah
are com-
related
ferred mon
to overuse is at the
mal
area
easily of increased
(Fig
RadioGraphics
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et al
and
mucoid disorder
to as “jumper’s site
patellar
common
ph-
the normally
U
An inflamed, may produce
anterior pain, clicking, or locking, mimicking a patellofemoral problem or meniscal tear. The medial plica is visualized on axial views as a linear low-signal structure medial to the patella (Fig 18).
MR imaging
214
asymptomatic. patellar phica
on
images
Pllcae.-These
the knee
of normal
identified
T2-weighted
Sagittal proton-weighted (2,500/30) MR pole of the patella (arrows) (b) Sagittal the fracture site (arrows).
is often
degenerais presum-
and
is frequently
re-
knee.”
The
corn-
inferior
pole
of the
demonstrates signal
most
patella.
the abnorintensity
low-signal-intensity
within
tendon
19).
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11
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2
a.
Figure
18. Medial synovial plica of the knee. (a) Axial davenic specimen reveals a medial synovial plica (arrow). MR image also shows the plica (arrow).
b. section through the patellofemoral joint of a ca(b) Corresponding axial Ti -weighted (700/20)
a. b. Figure 19. Patellar tendinitis (jumper’s knee). (a) Sagittal Ti -weighted (700/20) MR image shows an area of increased signal intensity within the supeniormost portion of the patellar tendon (arrow) (b) 3D FLASH 40 (40/i 3/40#{176})gradient-echo image through the same area demonstrates the same finding (arrow). .
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a.
b.
C.
d.
I
Figure 20. MR arthrograms of the patellofemoral joint of a cadavenic specimen obtained after an injection of 500 mol of gadopentetate dimeglumine. (a) Axial Ti -weighted (700/20) MR image shows a focal grade 3 chondromalacia patellae defect in the medial-most aspect of the lateral facet (arrow) (b) On the corresponding proton density (2,500/30) image, the focal defect (arrow) is again noted, but it is not quite as well seen as on a. On the corresponding T2-weighted (2,500/90) image (c), 2D FISP iO (30/i3/iO#{176}) gradientecho image (d), and 2D FISP 40 (30/i3/40#{176}) gradient-echo image (e), the focal defect is not well visualized. (f) Corresponding 2D FISP 75 (30/ i 3/75#{176})gradient-echo image demonstrates the focal defect (arrow) only slightly better than c-C. (g) On the corresponding 2D FLASH 75 (30/ 13/75#{176})gradient-echo image, the focal defect is not well visualized. .
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ARTHROGRAPHY Gyhys-Morin et al (1 4) first demonstrated potential efficacy of MR arthrography U
mography scanning in chondromalacia patellae. Skeletal Radio! i982; 8:i83-i85. Ihara H. Double-contrast CT arthrography of the cartilage of the patellofemoral joint. Clin Orthop Rd Res i985; i98:50-55. Shahniaree H. Chondromalacia. Contemp Orthop 1985; ii:27-39. Yulish BS, MontanezJ, Goodfellow DB, Bryan PJ, Mulopulos GP, Modic MT. Chondromalacia patellae: assessment with MR imaging. Radiology i987; 164:763-766. Hayes CW, Sawyer RW, Conway WF. Detection and staging of patellar cartilage lesions with MR imaging: pathologic correlations. Radiology 1990; 176:479-483. Benquist Th. Imaging oforthopaedic trauma and surgery. Philadelphia: Saunders, 1986; 314. Weissman BNW, Sledge CB. Orthopaedic radiology. Philadelphia: Saunders, 1986; 516. Delgado-Martins H. A study of the position of the patella using computenised tomography. J Bone Joint Sung [Br] 1979; 61 :44 3-
MR
hanced
with
gadopentetate
the en-
dimeglumine
3.
in
the evaluation of focal articular cartilage defects (1 4) Preliminary work with cadavenic specimens at the Medical College of Virginia also suggests possible qualitative enhancement of cartilaginous defects (Fig 20); how-
4
.
.
ever,
further
cadavenic
and
clinical
studies
of
this technique need to be performed. It should be noted that gadopentetate dimeglumine is currently not approved by the Food and Drug Administration for intraarticular injection. If clinical studies are to be per-
formed,
they
will
require
prior
informed
U SUMMARY The introduction of cross-sectional specifically CT and MR, to the
the
patehlofemoral
radiologists’
joint
diagnostic
choice
of which
to use
is strongly
to
is pro-
on
diagnosis in the joint. However,
alternative not
In some intraosseous represent U
to MR imaging
available
or cost
situations lesions the imaging
when
(eg,
.
12
.
13
.
14
.
patient’s
area of the patelloCT can be a useful
is a major
11
modalities the
clinical examination and resulting differential diagnosis. In general, we believe that MR imaging, when combined with the usual plain radiography, offers the clinician and radiologist the greatest latitude in making a specific femoral
444.
1 0.
the
Shellock FG, MinkJH, Deutsch AL, FoxJM. Patellar tracking abnormalities: clinical cxpenience with kinematic MR imaging in 130 patients. Radiology i989; 172:799-804. Wiberg G. Roentgenographic and anatomic studies of the patellofemoral joint with specia! reference to chondromalacia patellae. ActaOrthop[Scand]
The
imaging
predicated
9.
increased
capabilities.
of these
7.
8.
imaging, evaluation of
has greatly
6.
pa-
tient consent and approval by the hospital’s committee on human studies. Although the technique of MR arthrography may improve detection of both meniscal
and articular cartilage lesions, it remains be seen whether this additional advantage worth subjecting patients to an invasive cedure.
5.
148:1 153-i
hatter
1941;
12:319-333.
Hughston JC, Deese M. Medial subluxation of the patella as a complication of lateral nelease. AmJ Sports Med 1988; 16:383-388. Yao L, Lee JK. Occult intraosseous fracture: detection with MR imaging. Radiology 1988; 167:749-751. Gylys-Monin VM, Hajek PC, Sartonis DJ, Resnick D. Articular cartilage defects: detectability in cadaver knees with MR. AJR 1987; 157.
is
consideration.
characterization
of
of the patella), CT may modality of choice.
REFERENCES Stanford W, PhelanJ, Kathol MH, et al. Patellofemoral joint motion: evaluation by ultrafast computed tomography. Skeletal Radiol i988; i7:487-492. 2. Boven F, Bellemans MA, GeartsJ, DeBoeck H, Patvliege R. The value of computed toi
.
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