Musculoskeletal Georges Thomas

Y. El-Khoury, MD #{149}Raymund L. Wira, MD L. Pope, Jr, MD #{149} Johnny U. V. Monu, MD

MR

Imaging

ofPatellar

To identify magnetic resonance (MR) imaging characteristics of normal patellar tendons and those affected by tendinitis, the authors evaluated MR images obtained in 10 healthy volunteers, in 50 patients who underwent MR imaging for evaluation of knee structures other than the patellar tendon, in 11 patients with patellar tendinitis, and in two athletes with patellar tendon injuries. Normal tendons had uniformly low signal intensity on Ti-, T2-, and proton-densityweighted images and displayed distinct margins, and the anteropostenor (AP) diameter slightly increased proximally to distally. It was concluded that the AP diameter of a normal tendon, in its proximal porlion, should not exceed 7 mm. In patellar tendinitis, the tendon showed increased signal intensity on Ti-, T2-, and proton-density-weighted images and increased AP diameter proximally. The margins of affected tendons were indistinct, especially postenor to the thickened segmenL In all groups studied, women had thicker proximal tendons than did men. Knee,

#{149}

MR.

S. Berbaum,

PhD

Tendinitis’

P

tendinitis is a potentially disabling condition affecting athletes whose sports require them to perform sudden extension of the knee or repetitive peak strain to their patellar tendon. Such activities indude running, jumping, and kicking (1-4). Year-round strength and speed training has increased the incidence of patellar tendinitis (1,2). Clinically, patellar tendinitis is first seen as a ATELLAR

spectrum

of symptoms

verity tivity

from pain to complete

riceps

ranging

in se-

only after sports acfailure of the quad-

mechanism

due

to rupture

of

the patellar tendon (1,3,4). Mild forms of the disease are treated with cessalion of the offending antiinflammatory

activity,

rest,

soft-tissue

radiography,

xeroradiogra-

phy, ultrasonography (US), radionuclide bone scanning, and computed tomography (CT) (1,4-10). MR imaging, with its superior soft-tissue conallows

evaluation

of many

biga-

ments and tendons (10-14). Recently, MR imaging has been shown to be useful in diagnosis of patellar tendinitis (6,15).

Radiology

1992;

184:849-854

most cus

commonly tear

There range,

patients affected

underwent men

knees) years).

knees)

In this study, we attempt to define the normal and abnormal appearance of the patelbar tendon and to quantify patellar tendinitis by using MR imaging.

I From the Department of Radiology, University oflowa College of Medicine, Iowa City

(G.Y.E.K., R.L.W., K.S.B.), and the Department of Radiology, Bowman Gray School of Medicine, Winston-Salem, NC (T.L.P.,J.U.V.M.).

From the 1991 RSNA scientific assembly. Received February 20, 1992; revision requested March 24; revision received April 16; accepted April

27. Address

University Hawkins C

RSNA,

reprint

requests

to G.Y.E.K.,

oflowa Hospitals and Clinics, Dr, Iowa City, IA 52242. 1992

200

We

AND

obtained

volunteers.

MR

None

images

in 10 healthy

volunteers

a history of knee injury, prolonged pain, or knee surgery. There were men

years;

and

five

average,

A second

women

(age

range,

had knee five 21-35

28 years). “control”

group

of MR

There

three

obtained

were

women

eight

(three

(average, 21 MR images

in a 19-year-old

that

male

(2,000-2,150/17-20

[repetition time msec/echo time msec]) and T2-weighted (2,000-2,150/80) images designed to optimize visualization of the anterior cruciate ligament (16), as well as a coronal T1-weighteu SE sequence (350567/15). In addition, straight sagittal images were obtained in four volunteers, to determine whether there is a difference in measurement of anteroposterior (AP) tendon thickness when straight sagittal seclions versus minimally oblique sagittal sections are used. All images were obtained with a 1.5-1 unit (Signa; GE Medical Systems, Milwaukee) by using a 256 x 192

two signal

matrix,

averages,

field of view. The knee surface coil, and 3-mm

with

1-mm

and a 16-cm

was positioned section thickness

intersection

in a

gap was selected.

Measurements of the pateblar tendon thickness in the AP dimension were made at the proximal, middle, and distal portions of the tendon (Fig 1). Margin distinctness and signal characteristics of the were

recorded.

Two

radiologists

(G.Y.E.K., R.L.W.) made all measurements and observations in conference. Statistical methods included analysis

METHODS

of these

and

were

gymnast with acute patellar tendon niphire and a 22-year-old male basketball player with chronic patellar tendinitis and a previously ruptured, surgically repaired tendon. Our routine MR imaging protocol includes obtainment of minimally oblique (less than 15#{176}) sagittal spin-echo (SE) pro-

tendon

PATIENTS

with 13 knees that by patellar tendinitis

aged 16-34 years We also evaluated been

injury.

and 15 women (age average, 29 years).

MR imaging.

(10

of a menis-

ligament

were 35 men 16-72 years;

Eleven clinically

had

for evaluation

or a cruciate

ton-density-weighted

drugs, and physical therapy. More severe forms are treated surgically (1,3,4). Before the advent of magnetic resonance (MR) imaging, techniques used to study patellar tendinitis included

trast, Index terms: Knee, injuries, 4528.253 ligaments and menisci, 4528.253 #{149}Knee, 45.1214 #{149}Tendons, CT, 4528.1211

#{149} Kevin

Radiology

images

was obtained from 50 knee studies randomly selected from our patient ifies. The studies were performed for evaluation of structures other than the patellar tendon,

variance

(ANOVA),

which

was

used

of to

compare the two control groups (normal volunteer and retrospective review group) and controls and patients. Whether proximab tendon thickness is related to gender was also assessed by means of ANOVA.

Abbreviations:

ance, AP

ANOVA =

anteroposterior,

=

analysis

SE

=

spin

of vanecho.

849

3.7 ± 1 .2

mm

4.3±1.1mm mm

5.6±1.1

Figure

1.

mal

Sites

patellar

crease distal

of measurement

tendon.

in the AP is evident.

of the

A mild

and

dimension

gradual

from

nor-

in-

proximal

to

a.

b.

Figure 2. Normal variations. (a) Proton-density-weighted 17) MR image obtained in a healthy volunteer shows

We

moderately

RESULTS that the AP diameter

found

proximal

of a

sequences

used,

the

ton-density-weighted

:

images

(Fig

2a).

We occasionally found minimally increased signal intensity in the central portion of the distal tendon, near its caudab insertion (Fig 2b). The margins of the tendon were always distinct from the surrounding areolar tissue. Data

the

analysis

two

of measurements

control

statistically

groups

significant

showed difference

from

no

N

20

Radiology

shows

3.7 Male Female

PatIents Patients

Male Controls 10

b

-

Patients

I

:

5

Mean SD=2.3

t

=

Female

Controls

10.9

S

0 0

1 2 3 4 5 6 7 8 910111213141516

(mm)

AP Diameter

mal

#{149}

=

LIII

;

teristics

850

Mean

1

The

were also identical. proximal tendon of patients with patelbar tendinitis showed a greater AP diameter (mean, iO.9 mm) than that of subjects in the control group (mean, 3.7 mm) (Fig 3). ANOVA

volunteer

signal intensity within the subproximal to its insertion on the

15

r

When the oblique sagittal and straight sagittal images obtained in four normal volunteers were compared, there was always less than 1 mm of difference between the AP measurements of the patellar tendon. The internal signal intensity charactendons The

increased (arrowhead)

(b) Proton-density-

in a healthy

SD=1.2

be-

of the

(arrow).

obtained

of to the

Controls

In

Figure

definition

tendon

image

immediately

U

trobs.

margin

of the

(2,150/17)

intensity

2b

tween the AP diameter of the proximal tendon in healthy volunteers and that of tendons in retrospective con-

and

signal

ill-defined, minimally stance of the tendon tibial tubercle.

tendon

extended, as a homogeneous band of low signal intensity, from the lower pole of the patella to the tibiab tubercle. A thin band of higher signal intensity immediately posterior to the proximal portion of the tendon was frequently seen on Ti-, T2-, and pro-

portion

weighted

normal pateblar tendon slightly increases proximally to distally (Fig 1). The mean AP diameter (± 1 standard deviation) of the proximal portion of the tendon was 3.7 mm ± 1.2. With all SE pulse

increased

(2,000/

a band posterior

3. cutoff

women

Plot point

to have

showed

the

tendon

significantly

of the AP diameter of 7 mm separates

a thicker

AP

proximal

diameter

in patients different

of the proximal tendon the patients from the

tendon

of the

than

proxi-

to be highly from

that

in

the control group (F[i,69] = 263.48; P < .0001). In fact, there was no overlap in the measurements between the patients and the control group. Review of the data in the bar graph

men

(Fig

in the healthy

control controls.

and patient groups. The tendency for

is evident.

3) shows

that

off point

between

of normal tendons

and would

a reasonable

the

cut-

AP diameter

abnormal be 7 mm.

proximal The proxi-

mal tendon of women in both the control and patient groups had a larger mean AP diameter than that of men. This was statistically signifiSeptember

1992

Figures 4, 5. (4) MR imaging The proximal tendon measures irregular margin (arrowheads). evident. gymnast.

The margin MR imaging

intensity

throughout

image

cant

also

(F[1,69J

difference

is indistinct at the thickened portion (arrowheads). (5) MR imaging was performed 3 hours after the injury. (a) Proton-density-weighted the

shows

proximal

increased

14.17;

=

patients for men

two-thirds

signal

P

in AP diameter

controls and women than P = .0102).

findings of patellar tendinitis in a 21-year-old male track runner. (a) Proton-density-weighted (2,000/17) image. 14 mm in its AP diameter. The thickened portion shows increased signal intensity, as well as an indistinct and (b) T2-weighted image (2,000/80). Again, thickening and increased signal intensity of the proximal tendon are

=

.0003).

The

between

was greater (F[i,69] =

for 6.97;

The increased AP diameter was not limited to the proximal tendon, especially in more severe cases. In four patients, the enlargement of the tendon extended into the middle portion. Inhomogeneous high signal intensity accompanied the tendon enlargement. Proton-densityand T2-weighted images demonstrated this increased signal intensity better than did Tiweighted images. The affected tendons showed indistinct margins, especially posterior to the thickened areas (Fig 4). Images obtained in the patient with acute

tendon

rupture

showed

discon-

of the tendon and a wavy tendon contour. The signal intensity was inhomogeneously high (Fig 5). Images obtained in the patient with tendon rupture secondary to chronic tendinitis with subsequent repair revealed marked thickening and intinuity

Volume

184

Number

#{149}

3

of the

and

intensity

wavy

tendon.

contour

The visualized tendon of the tendon.

is thin

findings of acute tendon rupture (2,000/20) image demonstrates

and

homogeneous high signal intensity through most of the tendon. The tendon margins were indistinct posteriorly, and the surrounding soft tissues appeared edematous (Fig 6e).

has a wavy

The patellar tendon rarely ruptures in healthy individuals (17-19). Rupture usually is the end stage of patebbar tendinitis and results from the cumulative effect of repetitive trauma and microtearing of the patellar tendon (17,20). In patients with tendinitis and partial tears of the patellar tendon, King et al (21) and Karlsson et al (22) described thickening of the tendon and lack of distinction between the posterior proximal aspect of the tendon and the adjacent soft tissues. These findings can, to a great extent, be demonstrated noninvasively with

MR imaging

(6,15).

Such

information

is of assistance to the surgeon in that the exact location and extent of the disease are pointed out and because patellar tendinitis is differentiated from other clinical conditions that can

(b) T2-weighted

(2,000/80)

mimic it, such as bursitis and dromabacia (3). Patelbar tendinitis is probably

nomer,

since

in fact,

a ligament

ferior DISCUSSION

contour.

in a 19-year-old male increased signal

pole

the of the

patellar

chon-

connecting

patella

a mis-

“tendon”

is,

the

to the

in-

tibial

tubercle (bone to bone) (23,24). Furthermore, histologic studies of specimens removed at surgery reveal microtearing within the ligament, mucoid degeneration, and fibrinoid necrosis (3,15,24). Inflammation is found in conjunction with the repair process rather than as a primary condition. Areas of regeneration with fibroblast proliferation and thin-walled vessels are also present (4). The term patellar tendinitis is deeply entrenched in the literature, but probably a better term might be “incomplete pateblar ligament tear” or “chronic microtearing of the patellar ligament.” Patients with patelbar tendinitis usually present with typical clinical symptoms. In the early stages, patients complain of pain inferior to the patella after athletic activity. In later stages, the pain becomes persistent

Radiology

851

#{149}

rn.

U.

Figure 17-20). margin

6. Spectrum of MR imaging findings in a variety (a) Mild patellar tendinitis with minimal thickening is indistinct in the thickened portion. (b) Moderate

evident.

(c) Moderately

advanced

changes.

Thickening

of patients (9 mm) changes

with patellar and increased in proximal

of the proximal

tendinitis. All images are proton density signal intensity of the proximal tendon. tendon. Signal intensity is increased, and

tendon

(13 mm)

is pronounced,

and

signal

weighted (2,000/ The posterior tendon thickening (10 mm)

intensity

is increased

is

(Fig 6

CO?lti?ZUCS).

and severe and begins during, rather than after, activity. Finally, the tendon ruptures, resulting in the inability

to extend

athlete

the

with

pairment.

there

knee,

leaving

complete

at or just

of the

symptoms. a defect

partial

or complete The

inferior

Quadriceps

chronic palpate 4,21).

the

frequently

strates

tender-

below

patella.

atrophy

im-

examination,

is webb-circumscribed

ness

the

functional

At physical

muscle

accompanies The examiner in patients with

tendon

clinical

staging

may a

tear

(1-

proposed

and

perform

after

activity,

at a satisfactory

3-pain

during

more

prolonged,

patient

sively

increasing

difficulty

ing

at a satisfactory

Although niques have

the the

and

by

clear (1-3). This clinical predictors,

852

Radiology

#{149}

able

after

activity

has

to

phase and

progres-

in perform-

level.

several been

treatment indications

still

level;

surgical recommended

techfor

of patellar tendinitis, for surgery are not is probably at least

because in the mild

that,

between

normal

normal tendons, there difference in proximal addition to differences

pole

Blazina et ab (1) is widely used: Phase 1-pain after activity only, no undue functional impairment; phase 2-pain during

and moderate cases, are unable to albow differentiation of patients who require only conservative therapy from those who require surgical intervention. This investigation demonand

ab-

is a definite thickness, in in signal inten-

sity characteristics and margin distinctness. None of the AP diameters of normal tendons measured more

than 7 mm proximally, whereas all the tendons involved with patellar tendinitis measured more than 7 mm. Therefore, 7 mm is suggested as the upper limit for normal AP diameter of the proximal tendon. Most studies of patellar tendinitis report a male preponderance, and this study is no exception (4,17,22, 25,26). Our data demonstrated a statisticabby significant difference in the thickness of the proximal tendon between men and women in both the

healthy control group and the patient population. Women generally have a thicker

tulate

tendon.

that

since

It is reasonable

patellar

tendinitis

to pos-

histologically represents microtearing of the tendon, the added thickness of the tendon in women could be protective. It may be argued, however, that men are more actively involved with sports than women, but this argument may not hold true at the present time. Because of expense, we currently reserve MR imaging for athletes with patellar tendinitis who fail conservative therapy. Our surgeons use the information from the MR imaging examination to assess the severity of the disease and to determine how much of the tendon to excise at surgery. With faster pulse sequences, such as fast SE and echo-planar sequences, it is hoped that limited MR studies tailored to a specific problem could become more affordable.

The information gleaned from MR imaging could be helpful in confirmation nitis with

of the diagnosis of patellar tendiand in the follow-up of patients this condition. It may also allow

differentiation

surgery conservative

of

from

patients

those therapy.

requiring

requiring only To achieve this

September

1992

tendon

thickening

tients,

but

in 14 of 16 pa-

only

nine

(56%)

showed

increased signal intensity within the tendon on Ti-weighted images, and 10 (63%) showed increased signal intensity on T2-weighted images. Shorttau

inversion

recovery

and

partial

saturation images, however, demonstrated increased signal intensity within all diseased tendons. The increased signal intensity in the affected segment of the tendon is thought to represent regions of fibrinoid necrosis,

inflammation,

and

synovial

probif-

eration (i5). Signal changes within the fat posterior to the tendon are also likely to be caused by inflammation (6). Although we found few MR imaging signs that indicated the presence of patellar tendinitis, the most useful was enlargement of the proximal tendon in the AP dimension (Fig 3). Another important finding in our series was the absence of any detectable difference in the tendon thickness and signal intensity characteristics on the oblique sagittal and straight sagittab scans.

d.

e.

Figure

sures

(continued).

6

15 mm,

and

(d) Changes the posterior

formed 10 months after to competitive basketball

goal,

however,

to diagnose tendinitis, ity of the surgeons symptoms

Blazina

the

ruptured

tendon

at the collegiate

it is necessary

was

level,

not

only

the presence of patellar but also to judge the severdisease. Unfortunately, our did not stage the severity of by using the criteria of

et al (1). For

could

of advanced patellar tendinitis. The tendon margin is ill defined proximally. (e) Image from

not

create

an

this MR

reason, imaging

repaired.

The

structure

stag-

attenuation.

The

abnormal

riorly

and

rare

in the

early

radiographs

are

disease,

and

usually

rior

(8) reported

increased

of radionuclide pole of the

tella

patients

with

At US, the

normal

in three

tendinitis. is described

Volume

as a hypoechoic

184

Number

#{149}

3

patellar

tendon linear

pole

of the

abnormal

at the

patella,

extending

length

down

the

tendon has

tendon

expansion

a clearly

infe-

for

tendon.

pa-

US. Bodne et al (15) used to evaluate seven knees

substance the

that

those

apy

have

patelbar tendinidisease.

They found varying degrees of tendon thickening and increased signal intensity on Ti- and T2-weighted images. Davies et al (6), with a bow-fieldstrength magnet (0.15 T), reported

posterior

and

poor

margins, proximal

patelbar

tendinitis.

needing

must

def-

particmargin.

The

role

only

await

conservative

further

ther-

study.

#{149}

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ME,

Kerlan

vS, Carlson Clin

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GJ. Am

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patebbar detected

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(4).

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With bong-standing symptoms, bone rarefaction, fragmentation, and sometimes elongation of the inferior patellar pole may appear (1,3-5). Kahn and Wilson

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i992