Curtis
W. Hayes,
MD
#{149} Rae
W. Sawyer,
MD2
#{149} William
F. Conway,
Patellar Cartilage Lesions: Detection and Staging with and Pathologic Correlation’
Fourteen freshly disarticulated knee specimens were studied to assess the usefulness of magnetic resonance (MR) imaging in the detection and correct staging of patellar chondral lesions. Axial and sagittal images were obtained; Ti-weighted spinecho sequences were found satisfactory for defining cartilage morphology. Specimens were sectioned and examined grossly for cartilage changes such as softening, blistering, fibrillation, fissuring, and frank subchondral bone exposure. In a side-by-side comparison, all lesions classified grossly in the Shahriaree system as stage II or higher showed MR changes. Stage I changes could not be identified in disarticulated specimens. Stage III lesions showed cartilage irregularity (ulceration) or a loss of the normal, sharply defined margin between coapted cartilage, which represented “crabmeat” fibrillation. Stage IV lesions showed ulceration to bone, sometimes with subchondral bone changes. In this in vitro, preliminary study, MR imaging was found to be an accurate means for detecting and staging moderate and advanced patellar cartilage lesions. Index
terms:
normalities,
Cartilage, 452.4851
#{149} Knee, MR studies,
ab-
4521.4851
Knee,
#{149}
From
I
cal
1990;
the
College
Department
Richmond,
of Radiology, Box
VA 23298-0615.
RSNA
annual
1989;
revision
meeting.
March
23, 1990;
Address
reprint
requests
Current
Imaging
,c RSNA,
address: Associates, 1990
From October
received 2
615,
Received
requested
tilage problem
of the patebbar is a common orthopedic
in both
young
and
old
campa-
tients. The term chondromalacia patellae has been used to describe both pathologic patellar cartilage softening and the syndrome of patebbofemoral pain frequently encountered in adolescents and young adults. Whether chondmomalacia pateblae is a separate pathologic entity or simply an early stage in the broader spectnurn of patelbofernomab osteoarthnitis is controversial.
proposed generation
Goodfelbow
et al (1)
that patellam cartilage demay be separated into two
distinct
entities-basal
degeneration
and superficial degeneration
degeneration. affects adolescents
young
and
adults
may
Basal and
be initiated
by
disruption of the vertical coblagenous fibers in the basal layer of the anticulam cartilage. Many causes have been proposed, including trauma, malalignment, and inherited metabolic disturbances (2-5). Surface degeneration is found in older patients thought to be due to repetitive
clinical trauma-wear leading to breakdown cial cartilage layer, may result thnitis.
and is sub-
Medi-
MCV
the
Station,
evabuause in derncartilage
1988
September 27;
Kilrnamnock,
Diagnostic Va.
54% of patients
revision
accepted March to C.W.H.
Rappahanock
7,
changes in the subchondmal (8,9). Radionuclide bone may give positive results
30.
is nonspecific
with (10).
bone scanning in up to
patellar Currently,
pain ortho-
pedists usually resort to anthroscopy to confirm the presence of significant chondrab lesions.
symptoms
of chondrornalacia
patel-
lae. Those authors found good agreement in cases of moderate and advanced chondral changes and proposed an MR grading system for such lesions.
purpose assess
ness
of MR
and
classifying
of our study the theoretical imaging
for
was to useful-
detecting
chondral besions through correlation of MR and pathologic findings in fresh, disanticubated knee specimens.
osteoar-
radiographic
been of limited patelbofemoral
Magnetic resonance (MR) imaging has proved useful in the noninvasive detection of meniscal, ligamentous, and other soft-tissue injuries of the knee (1 1-16). Osteochondral fractunes and other occult bone changes are readily seen as well (17). MR signab changes within menisci have been shown to correlate with pathologic changes of mucoid degeneration in histologic specimens (18). The ability of MR imaging to demonstrate the anticular cartilage in a multiplanar fashion makes this modality well suited for the irregularly shaped patellam cartilage. MR imaging is capabbe of depicting cartilage defects, internal chondrab signal changes, and subchondrab bone changes (1921). Recently, Yulish et ab (22) cornpared MR results with anthroscopic findings in young patients with
The further
and tearof the superfiand eventually
in patebbofernoral
Historically,
PhD
In Vitro MR Imaging
abnormalities. Plain radiographic imaging of the patebbofernoral joint is not sensitive to early cartilage changes (6,7). Conventional anthrognaphy and especially computed tomographic anthrognaphy have been shown to be more valuable but are invasive and insensitive to early
176:479-483
of Virginia,
EGENERATION
tion has onstrating
452.1214
Radiology
D
MD,
but
patebbar
MATERIALS
AND
METHODS
Fourteen freshly disarticulated knee specimens were evaluated. All specimens were obtained immediately after aboveknee amputations performed on patients aged 30-95 years (median, 62 years). Imaging was performed within 24 hours in most cases; specimens were refrigerated at 35#{176}F (1.6#{176}C)until 4 hours prior to imaging, at which time they were allowed to warm slowly to room temperature for best imaging results. Whenever possible, specimens were securely mounted in full or
near-full
Imaging unit
extension
was
(Magnetom;
for
performed Siemens,
imaging.
with Iselin,
a 1.0-T NJ).
In 479
a.
b.
1. Normal cartilage. (a) Gross pathologic axial section shows uniform, smooth anticular cartilage. Lateral (L), medial (M), and odd (0) facets are all demonstrated. (b) Comesponding Ti-weighted MR image shows a sharp line between the coapted surfaces of the patebiar and trochlear cantilages (arrows). Marked bilaminar appearance of the outer third of the articular cartilage can be seen. Figure
10 cases, a 12.7-cm circular surface coil placed directly over the patella was used for imaging. In four cases, a commercial transmit-receive extremity coil was used. Ti-weighted axial and sagittal spin-echo 700/17 (repetition time msec/echo time msec) images were obtained with the following imaging parameters: 4-mm thickness, i-mm intersection gap, 256 X 256 matrix, two acquisitions. Imaging time per sequence was approximately 6 mmutes. T2-weighted 2,500/90 and gradientecho 30/12 three-dimensional fast imaging with steady precession (75#{176} flip angle) sequences were also used on initial specimens. For depicting cartilage momphobogy, Ti-weighted images were preferred for their superior spatial resobution. Specimens were frozen immediately aften imaging, in the same position, and
were
sectioned
with
band-saw
a. Figure
b. 2.
Stage
of the articular
I surface cartilage
(b) Corresponding
degeneration. (arrows),
Ti-weighted
(a) Gross which
MR
specimen
corresponded
image
showed
shows to
no
palpably
corresponding
superficial soft
superficial
discoloration cartilage.
abnormalities.
technique
in 4-mm-thick slices, corresponding to MR images (iO axially, four sagittably). Each slice was inspected grossly for regional cartilage thickness and cartilage defects: softening, blistering, fibrillation, fissuring,
and
frank
erosions.
Cartilage
defects were staged pathologically on a scale of I-IV, according to the pathologic staging system described by Shahriaree (5) (Table 1). Since our specimens were obtained from patients who varied wideby in age but were generally olden, the staging systems for cartilage changes of both basal degeneration and superficial degeneration were used in grading mdividual lesions. Table 1 summarizes the features of basal and superficial degeneration. Early stages of these two entities differ slightly: Stages I and II of basal degeneration show softening and blister formation in the deep cartilage layer. Stages I and II of superficial degeneration, in contrast, consist of fine surface fibnillation, discoloration, and minor fissuning involving the superficial layer of the cartilage. According to Shahniaree (5), the more advanced stages III and IV are quite similar at gross examination. Abnormalities found at gross examination of specimens were individually
480
#{149} Radiology
staged and plotted topographically by location. In a nonblinded, side-by-side fashion, MR images were then compared with gross specimens to determine MR criteria
for
lesion
characterization.
RESULTS Five of 14 specimens be normal or to have lation or focal softening
were found to only mild fibnil(stage I) at
gross examination. On Ti-weighted images, normal cartilage showed eithem homogeneous intermediate signal characteristics or, more often in our specimens, a bilarninar appearance showing lower signal intensity in the basal layer with a thin highersignal-intensity superficial layer (Fig 1). The cartilage surface normally demonstrated a smooth, sharp edge, and a clear distinction between co-
August
1990
pathologically On side-by-side these lesions MR
changes A single
as stage II on higher. comparison, all of showed corresponding (Table pathologic
2). stage
H blister-
like lesion was found. This lesion measured 4 mm in diameter, was characterized internally by fibrillated cartilage, and extended to, but not through, the superficial margin of the cartilage. MR images in this case showed a corresponding focal lowsignal-intensity region that appeared to deform the surface of the cartilage (Fig
a. Figure
b. 3.
Stage
II lesion.
(a) Sagittal
anatomic
section
demonstrates
sion (arrow), which was found to be filled with fibrillated vertical ing Ti-weighted MR image shows focal decreased signal intensity sponding to the blistenlike lesion (arrow). Underlying subchondnal larity.
a.
blistenlike
le-
cartilage. (b) Correspondwithin cartilage comebone shows mild imregu-
b.
Figure
4.
arrow)
and
spectively.
Stage
lIlA
crabmeat
and
IIIB
changes.
(a) Gross
(curved arrow) Ti-weighted
lesion
(b) Corresponding
ty corresponding tnochbean cartilages
to ulceration (large is seen at the site
specimen
involving MR image
shows
focal
ulceration
(straight
apex and lateral facet of patella, shows subtly decreased signal
arrow). Loss of normal sharp line of crabmeat changes (small arrows).
a. Figure
a focal,
between
meintensi-
patellar
and
b. 5.
involving age shows
Stage IIIB changes. (a) Gross specimen shows large area the entire lateral patellar facet (arrows). (b) Corresponding complete loss of the line between patellan and trochlear
of crabmeat fibrillation Ti-weighted MR cantibages (arrows).
im-
3).
Stage commonly
III lesions detected
Two distinct gross appearances differing MR characteristics found. Four focal cartilage extending to MR imaging, actenized by free cartilage irregularities subchondral quite subtle. lesion measured mm in diameter We subclassified lilA lesions. Five lesions
At gross inspection, these lesions were considered to represent superficial degeneration, as opposed to true basal degeneration seen in young patients. There were no lesions that
Volume
176
#{149} Number
2
could be classified as representing true early basal degeneration (ie, softening to palpation involving the deep layer of cartilage). The most common site for stage I lesions was along the ridge separating the medial and odd facets. None of these superficial stage I lesions was detected with
MR the showed
Of
all
imaging remaining at least
(Fig 2). nine specimens, one lesion graded
with were
lesions grossly showed surface ulcerations not subchondmal bone. With these lesions were charfocal irregularity of the margin (Fig 4). These did not extend to the bone and were often The smallest visualized approximately 3-4 and 2 mm in depth. this group as stage showed
the
well-de-
scnibed gross pathologic crabmeat appeanance. According to Goodfelbow et al (1), these changes are due to sepanation of the deeper vertical collagen fibers of the cartilage with extension to the surface and resultant gross fibrillation. These lesions were generally larger than stage lilA besions, often involving a large portion of the involved facet. Corresponding MR images showed a loss of the normal sharp free margin of the cartilage, such that the distinction between the coapted patellar and trochlean cartilages was lost (Fig 5). This pattern was termed stage IIIB. This appearance (loss of the line separating the coapted cartilage surfaces) was occasionally mimicked by volurne-averaging artifact when the cartilage surfaces were oriented oblique-
by relative
to the
avoid false-positive was considered apted patellar and tmochlean cartilage could be made in at least one projection (sagittal on axial). Six separate stage I lesions were found; all grossly involved the superficial third of the articulam cartilage.
were the most abnormalities.
imaging
plane.
To
interpretations, important to refer
it
carefully to both axial and sagittal images when this type of lesion was considered. In spite of this, two falsepositive MR stage III interpretations were made, involving the periphery of the patelbar cartilage in both cases. Three pathologic stage IV lesions were found. These lesions measured 9, 12, and 20 mm, respectively. With MR imaging, these showed decreased signal intensity or erosion of carti-
Radiology
. 481
lage extending to the subchondmal bone. One focal stage IV lesion also showed decreased signal intensity within the subchondmab bone comesponding to an area of erosion and early cyst formation (Fig 6). All stage II-IV lesions were plotted by location (Fig 7). The highest frequency
occurred
just
lateral
to the
median longitudinal ridge of the patella in the middle third. Stage III and IV lesions were more common on the lateral facet. Lesions were least common at the periphery of the patelba.
a.
Figure
b. 6.
Stage
lan facet
(curved
sclerosis
are
decreased decreased
in spite
DISCUSSION
IV changes.
arrow)
present
signal signal
(a) Gross
extending
(small
intensity intensity
of producing
specimen
to subchondral
arrows).
(b)
the
in vitro
fo-
cal erosions along the femoral condyles and did not examine patellar lesions per se. It is possible that these sharp, experimentally produced besions may produce signal changes different from those from naturally occurring chondrab lesions. In our study, we found that Tiweighted spin-echo images allowed the discrimination of focal cartilage lesions, the smallest of which measured 3-4 mm in diameter. Tiweighted images also correctly showed areas of diffuse thinning. Although contrast between joint fluid and cartilage was not as high as with T2- on T2*weighted images, it was adequate to permit visualization of stage II-IV lesions in specimens. On our initial five specimens, T2-weighted spin-echo 2,500/90-100 images were obtained in addition to Tiweighted images. These images produced less satisfactory spatial nesolution than Ti-weighted images, lacked contrast between subchondmal contical bone and cartilage, and were not useful in examining for internal camtilage signal differences. Therefore, 482
#{149} Radiology
study
and
therefore
may
not
reflect the accuracy that MR imaging can currently attain in clinical imaging. The technique used was designed to maximize spatial resolution and may not be practical in clinical situations. consideration
Motion artifact-not in this study-may
a
cause some degradation of image quality in living subjects. In spite of the optimal imaging parameters used in this study, many of the lesions showed only subtle changes, some of which may have been missed in a prospective analysis. Clearly, themefore, a prospective study comparing MR imaging with a thorough anthroscopic examination of the patebbofemoral joint will be necessary before the clinical accuracy of MR imaging can be determined. In our specimens, MR images dernonstrated no focal stage I internal cartilage
signals
scnibed clinical
by Yulish experience,
cur commonly both symptomatic
such
as were
de-
et al (22). In our such changes ocin young and
Our specimens, however, mived from a significantly
on
cystic
Ti-weighted
MR
arrow).
the
lateral
patel-
changes
image
Small
with
shows
arrows
focal
denote
desirable
study,
produced
ulceration
Subchondral
Corresponding
The utility of MR imaging in the evaluation of anticular cartilage abnonmalities has been examined mecently by several authors. In a study of patients with clinically symptomatic and arthoscopicalby proved chondrornalacia patellae, Yulish et al (22) concluded that MR imaging was an accurate means of detecting lesions classified as at beast stage II. Both Tiand T2-weighted images were considered useful-the former for anatomic detail and the latter for their “anthrograrn effect” when joint fluid was present. In contrast, Gylys-Momin et al (19) examined the detectability of experimentally produced cartilage lesions and found that Ti-weighted images alone were inadequate for use in detecting focal lesions. In that investigators
a focal
bone.
in area of cartilage ulceration (large indicative of subchondral changes.
anthrogmam effect, T2-weighted irnages were considered to be less informative than Ti-weighted images overall and were not obtained on the remaining specimens. Ultimately, other imaging sequences may prove more sensitive for overall cartilage evaluation than Ti-weighted irnaging. T2-weighted sequences, certain gradient-echo sequences, and particularly Ti-weighted sequences penformed with intnaarticulam injection of gadolinium produce high cartibage-fbuid contrast and may allow detection of smaller surface lesions than Ti-weighted spin-echo sequences. The relative sensitivity of these sequences in the detection of internal cartilage changes, however, has yet to be examined. It should be noted that this was an
the
shows
patients, asymptomatic.
were older
depa-
Figure
7.
Topographic
plotting
of
the
fre-
quency of stage II-IV patellar chondral lesions in this group of 14 specimens. Vertical and curvilinear lines represent major ridges in the patella. MED medial, LAT lateral. Darker shaded areas denote frequency of lesions.
apex were
Note
concentration
of the patella. found around
of
lesions
No significant the perimeter
near
tella. Lightly shaded area at inferior represents that portion of the patellar
face that
is not covered
the
lesions of the pa-
by articular
pole (*) sum-
carti-
lage.
tient population, in whom the early changes of superficial degeneration are much more common than those of basal degeneration. It is possible that with increased age desiccation of cartilage (particularly the outer third) produces an evening out of the MR signal from the basal two-thirds of the cartilage and accentuates the difference between that portion and the superficial third, producing the prominent bibaminar appearance. The histologic correlation of these early intemnab changes remains in question. Finally, only a single, 4-mm, stage
II blisterbike
lesion
was
observed.
In
spite of the fact that this lesion showed a corresponding focal abnormabity on MR images, this type of besion cannot be categorized adequateby on the basis of a single case. Confirmation of more stage I and II lesions will be necessary before conclusions cartilaginous
regarding lesions
these can
early, intrabe made.
August
1990
In summary, Ti-weighted spinecho MR images enabled detection of moderate and advanced naturally occurning chondral lesions of the patellam cartilage in freshly disarticuiated knee specimens. Lesions with stage III pathologic changes showed focal defects not extending to subchondmal bone on a loss of the normal sharp cartilage
margin
in areas
of signifi-
cant fibrillation. Superficial pathologic stage I lesions were not detected with MR imaging. The internal signal changes described as “MR stage 1” by Yulish et a! (22) were not demonstrated in this series. This may be due to the advanced age of the subjects from whom knee specimens were obtained in this study or possibly
an
artifact
caused
by
Acknowledgments: Pat Nofsinger, their technical perb photography;
We thank Max Russell, and assistance; Carlos and Sharron
for manuscript
preparation.
1.
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