Pekka

A. Kannus,

MD,

PhD

Long Patellar ofPatellofemoral A Prospective

Tendon: Pain Study’

The position of the patebla was studied prospectively in both knees of 45 consecutive patients (21 male and 24 female patients aged 16-48 years who were competitive En 17J or recreational [n = 28] athletes) who had unilateral patellofemoral pain syndrome

without

symptoms

or signs

of

patellar instability at initial examination. In each knee, standardized anteroposterior, lateral, and tangential radiographs were obtained and six indexes

of patellar

position

(the

ratio

of the patellar tendon to the greatest diagonal length of the patella, sulcus angles, lateral patelbofemoral angle, lateral patellar displacement, patelbofemoral index, and knee angle) were

measured.

When

healthy

and

affected knees were compared, high riding of the patella due to a long patellar tendon (patella alta) was the only definite finding in the affected knees. The shape of the intercondybar sulcus and the mediolateral position of the patella were identical in both knees, providing no evidence for patelbofemoral incongruence or lateral patellar tilt. Results of this study strongly suggest that idiopathic retropatellar pain is closely associated with patella alta. Index terms: Athletic injuries, 4528.4859, 458.4859 #{149} Knee, injuries, 4528.4859, 458.4859 Knee, radiography, 458.11 #{149}Patella, 453.4859 Radiology

1992;

185:859-863

P

Radiographic Syndrome

ATELLOFEMORAL

(otherwise

malacia defined

pain

known

Sign

syndrome

as chondro-

or chondropathia

patellae)

is

as retropatellar pain and during physical activity

crepitation such as running,

these

jumping, squatting, and ascending or descending stairs (1-3). Often the patient has pseudolocking and snapping sensations of the patella, as well as knee stiffness and periodic effusions. At clinical examination, pain and crepitation become evident in the compression, grinding, and apprehension tests of the patella (i,3). Patellofemoral pain syndrome is one of the most frequent musculoskeletal disorders in physically active people (1-3). In sports injury clinics it may account for almost 10% of all visits (4). Once started, it frequently becomes a chronic state of pain, forcing the

patient

to stop participation in all other similar activities. Recently, Minkoff and Fein (3) published a large review on the use of radiography in evaluation of the

sports

and

patellofemoral pain syndrome. As suspected, great variation and confusion existed in definitions of this syndrome

and

in the

radiobogic

criteria

establish

the

criteria

for

inclusion

I

From

the

Tampere

Research

Station

of

Sports Medicine, President Urho Kaleva Kekkonen Institute, Kaupinpuistonkatu 1, SF33500 Tampere, Finland. Received March 17, 1992; revision requested May 4; revision received July 16; accepted July 22. Supported in part by a grant from the Research Council for Physical Education and Sport, Ministry of Education, Finland; and Emil Aaltonen Research Foundation, Tampere. Address reprint requests to the author. RSNA, 1992

,

to

establish the “pathologic” position of the patella. It became evident that three factors are of great importance for further studies: (a) The study design must be prospective to adequately define the study group (ie, to adequately

of patients), (b) the disease must be unilateral so that each radiographic value in the affected knee can be properly controlled by the corresponding value in the healthy knee (ie, the large intersubject variation observed

as in patients

in

The purpose of this prospective study was to examine the position of the patella in the unilateral patellofemoral pain syndrome and avoid three

sources

of confusion.

MATERIALS Study

AND

Group

Forty-five consecutive derwent examination nod (December 1987 Tampere

cine,

METHODS

Research

Tampere,

Station

of Sports

Finland,

teristic

unilateral

drome

were

enrolled

study.

Each

patient

lowing

patients who unduring a 3-year peto November 1990) at

because

patelbofemoral

inclusion

pain

in this had

Medi-

of characsyn-

prospective

to meet

the

fol-

criteria:

1. Characteristic history and symptoms of the patellofemoral pain syndrome in one extremity, including (a) retropatellar pain of at least physical activity ning,

2 months duration such as jumping,

squatting,

scending

and

ascending

or

(h) characteristic

stairs,

crepitation

during run-

during

squatting

de-

patellar and

a posi-

tive “movie sign” (ie, retropatellar pain that occurred while the knee remained flexed for a prolonged period and that was relieved immediately after extension of the knee), and (c) a possibility of one or more of the following symptoms associated with physical activity: patellar snapping,

pseudobocking,

odic

knee

stiffness,

2. Characteristic

patellofemoral tremity,

and

and

pen-

effusions. clinical

pain

including

crepitation

pression,

signs

syndrome

of the

at one ex-

(a) retropatellar

in the

grinding,

and

patella

pain

during

apprehension

comtests

and (b) retropatellar pain in one-leg squatting. All patients with symptoms and clinical signs of patellar subluxation or luxation were excluded from this study. 3. Symptoms

and

tive for the following: ligaments (instability),

clinical

findings

nega-

abnormality of knee menisci (tears), and

subjects as well can be controlled with comparisons), and healthy

side-to-side (c) only a limited number of well-established radiographic criteria should

be used (ie, the study should trate on a few well-selected variables).

concenoutcome

Abbreviations:

LP = greatest diagonal length of the patella, LPA = lateral patellofemoral angle, LPD = lateral patellar displacement, LI = length of the patellar tendon, PFI = pateHofemoral index, SA = sulcus angle, SD = standard deviation.

859

bursae

and

Hoffa

disease

and tion

synovial

plicae

(rupture

abnormality syndrome)

(inflammation);

and

inflammation);

of the iliotibial and hamstring,

ceps, and patellar

tendons

band (fricquadri-

and their

inser-

tions (rupture and inflammation). 4. Findings negative for osteoarthntis, osteochondritis dissecans, or loose bodies in the patelbofemoral and tibiofemoral joints on radiographs of the knee (anteroposterior

and

lateral

views

ing weight-bearing, tangential

obtained

a tunnel

patellar

view

of the

and

knee

5. No

general

illnesses

and

fected

only

one

tic symptoms months, and

no

a

at 30#{176}

with

closed

that

the

af-

or signs

of patellar

study

group

and 24 female (mean

age,

consisted

subjects

27 years).

Their

distance

the

was 110 cm

lateral,

and

i20

radiographs. The 50 kV and 50 mA graphs and 45 kV radiographs. The

three

cm

for

and the

tunnel

tangential

exposure variables were for the former radioand 25 mA for the latter field size was 25 x 35 cm

radiographs,

lateral

18 x

radiographs,

i8 x i3

pain crepita-

instability

greatest

with

length

measured

method,

use of

described

by Insall

and

(Fig 1). In the

described

(14),

patella

(LP)

Salvati

of the LT to the LP (LT/LP)

ascertained

method,

of the

(Fig 1). In the second

(i3), the ratio was

measured

diagonal

were

by

the shortest

Blackburne

distance

1. Methods of measuring the height of the patella on a lateral radiograph. The Figure

third and

between

Peel

the

lower pole of the patellar articular cartilage and tibial plateau was divided by the articular length of the patella (A/B) (Fig 1). On the tangential radiographs, four indexes were measured to characterize the shape

symptoms

was

methods. In the first method, the of the patellar tendon (LT) and the

length

of 21 male 16-48 years

aged

in

with

the intercondy-

anteroposterior,

radiographs

characteris-

idiopathic patellofemoral (retropatellar pain and

knees

cm for the tunnel radiographs, and 30 x 7 cm for the tangential radiographs. The height of the patella on the lateral

epiphy-

the syndrome

knee,

separately

of the femur.

24 cm for the

excluded.

Our

20#{176} to display

flexed

obtained

unaffected

for the anteroposterior

adminis-

tion during activity without symptoms or signs of patellar subluxation or luxation), all patients with a history of symptoms of were

knee

radiographs

had existed at least 2 that the clinical examination

giving-way

and

for the

and radiographs revealed no other abnormality in the affected knee. Because the purpose of this study was to examine the so-called syndrome

were

the affected

The focus-to-film

of flexion). tration of medication. 6. Age 15-50 years, seal growth plates. We made sure that

radiographs

bar notch

dur-

view,

to the anterior border of the tibia and patelbofemoral interspace and perpendicubar to the casette (ii). Finally, the tunnel

of the intercondylar

sulcus

and

of the

LT

index (14) is the ratio of the shortest distance between the lower pole of the patellar articular cartilage and tibial plateau (A) to the articular length of the patella (B).

the

mediolateral

demonstrate the possible patellar malposition and lateral patellar tilt: (a) the sulcus angle (SA, expressed in degrees) (i5) (Fig 2a), (b) the lateral patellofemoral angle

affected knees, the statistical calculations between the differences of means were performed with the Student t test and between the differences of medians with the Mann-Whitney U test. The differences in

reational

(LPA, expressed

data

athletes.

Because

pain

arthroscopy

had

of persistent

and crepitation, been

performed

tients before the study. dance with the findings ports (5-10), only showed abnormality

eight

the

in 17 pa-

was found and

the

expressed (d) the

of these 17 patients in the patellar carti-

symptoms

in degrees)

(c) the lateral

In good accorin previous re-

lage, and no correlation tween

knee

be-

arthroscopic

patellar

in millimeters)

(ii) index

radiographs (n = 8) and

were obtained six well-established

criteria

were

position

of the

patebla.

obtained

in both knees radio-

used

The anteroposterior knees

and rec-

of Laurin et al (ii), Kujala Minkoff and Fein (3), four

graphic

to measure

radiographs

during

the of the

weight-bearing

were

obtained simultaneously in both knees in full extension. The lateral radiographs

of the

knees

weight-bearing in the affected

muscles

source

was

directed

860

(Fig

of the

Statistical a probability

tibia

and

the

femur

deformity

to detect

of the knees

possi-

(17).

measurements

obtained

was

obtained

in the

affected

was

Radiology

The

beam

The and

was

x-ray was

parallel

were

tested

test for variability. levels reported herein tests. The results are

with with

plus or

minus

standard

95% confidence range throughout

limits the

study.

significance was defined as of a type I error (alpha) of less than 5% (P < .05). The sample size (n = 45) was calculated to give a 90% statistical power for the study (type II error, .10).

healthy

used

in the analysis.

reading, phase

For the

all the lines drawn were

wiped

second

in the first

off immediately

after

the first reading, and new lines were drawn in the second phase. The Pearson product-moment correlation coefficient between

two

the

readings

averaged

0.9i.

during

relaxed (3,11,12). below the tabletop

(variances) F

as mean

deviation (SD) and as median

knee. The radiographs were read twice (2 weeks apart) by the same observer (P.A.K.), and the average value or the

separately Statistics knees at 30#{176} radiographs All the data

cephalad.

#{149}

(ii)

were obtained and unaffected

of flexion. The tangential were obtained simultaneously in both patellofemoral joints with the patient supine, the knees flexed 30#{176}, and the quadriceps

(Fig 2c), and (PFI)

distributions

with the Levene The significance refer to two-tailed

reported

der analysis

to the instructions

ommendations et al (12), and

(LPD,

were performed on a blind basis without knowledge of whether the radiograph un-

Analysis

According

(Fig 2b),

2d). On the anteroposterior radiographs the knee angle (KA) (degrees of valgus position) was measured between the long axis

All the radiographic

Radiographic

(ii)

and to

displacement

patellofemoral

ble angular

findings.

of the patella

ratio

prior to this study had lasted 2-72 months (mean duration, 16 months). The right knee was affected in 26 patients; the left knee, in 19 patients. Seventeen patients were competitive athletes; 28 patients, recretropatellar

position

Insall-Salvati index (13) is the to the LP. The Blackburne-Peel

patible

were

stored

microcomputer

microprocessor

in an IBM-com-

that used

to perform

analysis

the 80386 with

the 1990 version of the statistical program library of Biomedical Data Processing (University

of California,

comparison

between

Berkeley)

the affected

(i8).

and un-

RESULTS The results of the comparison between the affected and unaffected knees are listed in the Table. Compared with the patellar tendons in the healthy knee, the patellar tendons in the affected knees were significantly longer while the lengths of the patellas were equal. The other two indexes of patellar height (LT/LP and A/B) also indicated that the position of the patella in the affected knees was significantly higher than that in the healthy knees (Fig 3). The 95%

In

confidence

of the LT, LT/LP, most completely

limits

for

and A/B separated

the

means

were albetween

December

1992

I

Figure

2.

Methods

of determining

shape

of the intercondylar

lateral

position

of the patella

sulcus

the

and

medio-

to demonstrate

possible pateblofemoral incongruence and lateral patellar tilt. In a-d, L = lateral side of the knee, M = medial. (a) The SA (15). 0’) The LPA (11). According to Laurin et al (11) and Laurin (16), in normal knees the LPA always opens laterally; in chondromabacia, 10% of the patients show parallel lines (0#{176}); and in recurrent dislocation of the patella, 60% of the patients show parallel lines and in the other 40% the LPA opens medially in evidence of a lateral patellar tilt. (c) The LPD (expressed in millimeters) (11). According to Laurin et al (11) and Laurin

(16), in normal

knees

the LPD is always

0 or

negative (negative indicates medial displacement). Thirty percent of patients with chondromalacia and 53% of patients with recur-

rent

dislocation

of the patella

have

positive

LPD values. (d) The PFI (11). This index is defined as the relationship between the relalive thickness of the medial (M) and lateral (L) patelbofemoral compartments (M/L). Measurement M is the shortest distance between

the medial femoral groove and the junction of the medial and lateral patellar facettes. Measurement L corresponds to the shortest distance between the lateral patellar facette and lateral femoral condyle. According to Laurin et al (ii), in all normal knees the PFI is 1.6 or less, but in 93% of patients with chondromalacia and all patients with recurrent dislocation of the patella the PFI is greater than 1.6. Laurin et al regard the PFI as a good indicator of the lateral “mini-tilt” of the patella.

d.

the affected and the healthy knees, showing minimal overlap. The Levene F test for variability indicated no significant differences in the data distributions around the means. The four indexes analyzed from the tangential views (SA, LPA, LPD, and PFI) showed no significant differences between the affected and healthy knees. The 95% confidence limits for the means were almost the same. Furthermore, the Levene F test for variability showed that the data distributions around the means were not significantly different. The knee angles analyzed from the anteroposterior radiographs were also similar in the affected knees and the healthy knees, and no significant differences could be found. DISCUSSION The cause of the patellofemoral pain syndrome is still unknown. However, many predisposing factors Volume

185

Number

#{149}

3

have been proposed, including overuse, immobilization, acute trauma, obesity, genetic predisposition (a family history), congenital patellar abnormalities (bipartite or hypoplastic small patella), and malalignment of the knee extensor mechanism (a valgus knee; external tibial torsion; increased Q angle; and patella alta, instability, or subluxation) (2,12,19-27). In many confusing cases, however, no obvious reasons for the pain exist (21,28-30). Even arthroscopy of the knee has been a source of confusion. On one hand, involvement of the patellar articular cartilage has been demonstrated by means of arthroscopic examination in patients without symptoms (31-33); on the other hand, normal cartilage has been observed by means of arthroscopy in many patients with abnormal radiographs and clinically clearly manifest symptoms (5-8). In addition, in those patients with both cartilaginous lesions and symptoms, no correlation appears to

exist between the severity of the lesions and symptoms (9,10,21,24-26). Therefore, arthroscopy is not recommended as a sensitive or specific method to verify the clinical diagnosis of the patellofemoral pain syndrome. This study showed conclusively that in patients with unilateral patellofemoral pain syndrome, the affected

patella than

is riding

significantly

higher

that

in the healthy knee, and that the reason for higher riding is the longer patellar tendon (Table). These findings were clear and consistent when three standard methods for evaluation were used. Thus, this prospective study confirmed the previous statements that patella alta is related to idiopathic patellofemoral pain (13,34). Patella alta can well be a causal factor, too, because it is known to alter the contact area of the patellofemoral joint, with resultant increase in the contact stress and cartilaginous breakdown (35). In previous studies that compared patients with healthy subjects, a similar trend in favor of patella alta existed among patients, but the differences were not significant, most likely because a small number of subjects were studied (12,36,37). In our study group (in which persistent retropatellar pain and crepitation during activity without symptoms or signs of patellar instability was the reason to visit the physician), no signs of patellofemoral incongruence or lateral patellar tilt were seen at analysis of SA, LPA, LPD, and PFI (Table). These results are in accordance with previous findings of Laurin et al (ii), Dowd and Bentley (36), and Kujala et al (12), all of whom compared patients with healthy subjects instead of performing side-toside comparison, which is more informative and precise (3). Laurin et al (11) and Laurin (16) concluded that LPA or LPD cannot be considered reliable radiographic signs of chondromalacia patellae but that the PFI can enable distinction between patients and healthy subjects. The resuits of my study are in complete agreement with the conclusion of Laurin et al (ii) but not in agreement with that of Laurin (16); in my patient population, FF1 was the same in affected and healthy knees. It is likely that in the study by Laurin et al (11) the group labeled “chondromalacia” included some patients with mild instability problems; as pointed out by Minkoff and Fein (3), Laurin et al did not define criteria to establish the diagnosis of chondromalacia patellae. When comparing the mean values Radiology

861

#{149}

of the

indexes

used in other

in this studies

study

with

Indexes of Patellar Syndrome

and socalled normodative limits, one must be careful because differences in radiographic techniques and indexical measurements may exist despite seeming similarity. Furthermore, the study groups are likely to vary with regard to many background variables, such as to age, sex, height, and weight. Despite these confounding factors, it is interesting to notice that in the healthy knee the mean LT/LP (1.17) was under, and in the affected knee, the mean LT/LP (1.30) was over, the given upper limit of normal (1.2) (19,34). On average, the LT/LP values in this study were high. In Dowd and Bentley’s study (36), the LT/LP of healthy subjects averaged 1.03; in the study by Kujala et al (12), 1.04; in the study by Sjoberg et al (37), 1.02; and in the study by Velluti et al (38), 1.04. The average A/B values in this study (healthy knees, 0.97; affected knees, 1.17) were higher than those in healthy knees reported by Kujala et al (0.92) (12) and Velluti et al those

used

(0.88)

Position

Healthy (n

Index LT

(cm)

and the mediolateral patella were similar

(4.6 4.7 (4.4

LP (cm)

Radiology

#{149}

±

0.7

-

5.9)

LTILP

± -

5.0)