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.

thology.

David Dillard, Jean Snow for Chazo for suShackelford

II. Chondromalacia

Outerbridge

RE.

dromalacia patellae. 1961; 43:752-757. RE.

#{149} Number

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patellae.

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on

[Br]

etiology of chondromalacia patellae. Bone Joint Surg [Br] 1964; 46:179-190. Outerbridge RE. The problem of chon-

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1975; 110:177-196. Shahriaree H. Chondromalacia.

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Radiology

#{149} 483

Patellar cartilage lesions: in vitro detection and staging with MR imaging and pathologic correlation.

Fourteen freshly disarticulated knee specimens were studied to assess the usefulness of magnetic resonance (MR) imaging in the detection and correct s...
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