Patellar kinematics, Part II

Research Report
Patellar Kinematics, Part II:
The Influence of the Depth of the
Trochlear Groove in Subjects With
and Without Patellofemoral Pain
Background and Purpose. A shallow intercondylar groove has been
implicated as being contributory to abnormal patellar alignment. The
purpose of this study was to assess the influence of the depth of the
intercondylar groove on patellar kinematics. Subjects. Twenty-three
women (mean age 26.8 years, SD 8.5, range 14 – 46) with a diagno-
sis of patellofemoral pain and 12 women (mean age 29.1 years,
SD 5.0, range 24 –38) without patellofemoral pain participated.
Only female subjects were studied because of potential biomechanical
differences between sexes. Methods. Patellar kinematics were assessed
during resisted knee extension using kinematic magnetic resonance
imaging. Measurements of medial and lateral patellar displacement
and tilt were correlated with the depth of the trochlear groove (sulcus
angle) at 45, 36, 27, 18, 9, and 0 degrees of knee flexion using
regression analysis. Results. The depth of the trochlear groove was
found to be correlated with patellar kinematics, with increased shal-
lowness being predictive of lateral patellar tilt at 27, 18, 9, and 0
degrees of flexion and of lateral patellar displacement at 9 and 0
degrees of flexion (r .51–.76). Conclusions and Discussion. The
results of this study indicate that bony structure is an important
determinant of patellar kinematics at end-range knee extension
(0°–30°). [Powers CM. Patellar kinematics, part II: the influence of the
depth of the trochlear groove in subjects with and without patello-
femoral pain. Phys Ther. 2000;80:965–973.]

Key Words: Magnetic resonance imaging, Patellar kinematics, Patellofemoral joint.

Christopher M Powers

Physical Therapy . Volume 80 . Number 10 . October 2000 965

P
atellar malalignment is thought to be among depth of the intercondylar groove on patellar kinemat-
the etiological factors contributing to patello- ics. I hypothesized that subjects with PFP would exhibit
femoral pain (PFP).1 The cause of PFP appears greater amounts of lateral patellar displacement and
to be multifaceted, with components being lateral patellar tilt compared with subjects without PFP
defined by 2 distinct categories: structural and dynamic. and that the magnitude of lateral patellar displacement
Structural considerations include abnormal bony config- and lateral patellar tilt would be associated with the
uration1– 6 or tightness of noncontractile elements.7–9 depth of the trochlear groove. For results and discussion
Dynamic components have been hypothesized as involv- concerning the influence of vastus muscle activity in
ing unequal activity of the different heads of the quad- patellar kinematics, the reader is referred to the article
riceps femoris muscle10,11; however, evidence to support by Powers titled “Patellar Kinematics, Part I: The Influ-
this premise has not been consistent.12,13 ence of Vastus Muscle Activity in Subjects With and
Without Patellofemoral Pain” in this issue.
Brattstrom2 reported that dysplasia of the femoral troch-
lea is the most important etiological factor in recurrent Method
patellar subluxation. Because the lateral femoral condyle
is larger and projects farther anteriorly than the medial Subjects
condyle, the trochlear groove is thought to provide bony Twenty-three women with a diagnosis of PFP and 12
stability resisting laterally directed forces.7 Although women without PFP participated in this study. Only
some authors2,14 have reported that the decreased depth female subjects were studied because of potential biome-
of the intercondylar sulcus is a primary cause of lateral- chanical differences between sexes. Both groups were
ization of the patella, other authors15–18 have hypothe- similar in age, height, and weight (Tab. 1). Age, height,
sized that abnormal patellar kinematics are the result of and weight were found to be normally distributed within
the patella resting above the trochlear groove. Recent each group and when data from both groups were
work by Farahmand and colleagues,19,20 however, sug- combined. No attempt was made to match each subject
gests that stability of the patella is more a function of the specifically for age, height, and weight, as there is no
increased tension of the patellar tendon and quadriceps evidence in the literature to suggest that individuals of
tendon as the knee flexes, and not necessarily a function different ages, heights, and weights will demonstrate
of the depth of the trochlear groove. differences in patellar kinematics.

Although bony abnormalities have been implicated as The subjects with PFP were patients of the Southern
being contributory to abnormal patellar alignment, the California Orthopaedic Institute who were deemed to be
relationship of these factors to patellar tracking patterns appropriate candidates by the treating physician. Prior
has not been established. With the advent of kinematic to participation, all subjects with PFP were screened to
magnetic resonance imaging (KMRI) and cine phase rule out ligamentous instability, internal derangement,
contrast imaging techniques,21 quantification of patellar and patellar tendinitis. Each subject’s pain originated
movement throughout an arc of resisted knee extension from the patellofemoral joint, and only patients with
is possible.22–24 These diagnostic techniques have a dis- histories relating to nontraumatic events were accepted.
tinct advantage over imaging procedures used without In addition, pain had to be readily reproducible with at
allowing for knee movement because contributions of least 2 of the following activities: stair ascent or descent,
the extensor mechanism to patellofemoral joint kine- squatting, kneeling, prolonged sitting, or isometric
matics can be assessed.25 quadriceps femoris muscle contraction.1,19 Subjects were
excluded from the study if they reported previous knee
The purposes of this investigation were to compare surgery or a history compatible with acute traumatic
patellar tracking patterns between subjects with PFP and patellar dislocation.
subjects without PFP and to assess the influence of the

CM Powers, PT, PhD, is Director, Musculoskeletal Biomechanics Research Laboratory, and Assistant Professor, Department of Biokinesiology and
Physical Therapy, University of Southern California, 1540 E Alcazar St, CHP-155, Los Angeles, CA 90033 (USA) (powers@hsc.usc.edu).

Dr Powers provided concept/research design, writing, data collection and analysis, subjects, project management, and fund procurement.

This study was approved for human subjects by the Los Amigos Research and Education Institute Inc of Rancho Los Amigos Medical Center
(Downey, Calif).

This study was partially funded by a grant from the Foundation for Physical Therapy.

This article was submitted December 28, 1999, and was accepted May 29, 2000.

966 . Powers Physical Therapy . Volume 80 . Number 10 . October 2000

Table 1.
Subject Characteristics

Subjects With Patellofemoral Pain Subjects Without Patellofemoral Pain
(n 23) (n 12)
X SD Range X SD Range Pa

Age (y) 26.8 8.5 14–46 29.1 5.0 24–38 .38
Height (cm) 165.6 7.2 151.3–177.1 168.4 8.0 153.6–183.5 .29
Weight (kg) 62.2 9.1 42.0–82.7 61.2 8.0 48.7–74.1 .76
a
Probability values based on independent t tests.

Individuals comprising the comparison group were device was such that the application of the force was
recruited by word of mouth and were either employees always perpendicular to the tibia to ensure a constant
of Rancho Los Amigos Medical Center (Downey, Calif) (isotonic) torque throughout the entire range of
or students from the University of Southern California. motion.23 Weights constructed of nonmagnetic, 316L
Subjects had to have no history or diagnosis of knee series stainless steel‡ supplied the resistive force for this
pathology or trauma and they had to be free of knee maneuver. These plates were placed on a movable
pain at the time of the study. In addition, these subjects carriage that was attached to the pulley apparatus (see
did not report pain with any of the activities listed Fig. 1 in the companion article by Powers in this issue).
earlier. The kinematic data from the comparison group
were previously described in an article discussing the use Procedure
of magnetic resonance imaging (MRI) for assessing Prior to testing, all procedures were explained to each
patellar tracking.23 subject and written informed consent was obtained. All
imaging was performed at Tower Imaging Center in west
Instrumentation Los Angeles, Calif. Subjects were placed prone on the
Kinematic magnetic resonance imaging of the patello- positioning device in a position designed to allow for
femoral joint was assessed with the transmit and receive natural lower-extremity rotation. After this position was
quadrature body coil of a 1.5T magnetic resonance achieved, Velcro straps§ were used to secure the subjects’
system* using a pulse sequence that allowed fast imaging thigh and tibia to the positioning device. Resistance on
times with the best possible temporal resolution (fast- the device was then set at 15% of body weight.
spoiled gradient recall acquisition in the steady state).
Axial-plane imaging was performed using the following After familiarization with the knee extension apparatus,
parameters: time to repeat 6.5 milliseconds, time to subjects were instructed to practice extending their
echo 2.1 milliseconds, number of excitations 1.0, knees at a rate of approximately 9°/s. This rate ensured
matrix size 256 128, field of view 38 cm, flip 6 evenly spaced images throughout the 45-degree arc of
angle 30 degrees, and a 7-mm section thickness with an motion (including the 45° position) and permitted
interslice spacing of 0.5 mm.23 Acquisition time was 6 imaging at 45, 36, 27, 18, 9, and 0 degrees of knee
seconds to obtain 6 images (ie, 1 image per second). flexion. Approximation of this rate was made by the
principal investigator (CMP) with the use of a stopwatch.
All imaging was performed using a specially constructed,
nonferromagnetic positioning device† that permitted Once the subject, in the opinion of the principal inves-
bilateral knee extension against resistance (in the prone tigator, was able to reproduce the desired rate of motion
position) from 45 degrees of flexion to full extension in a smooth and even manner, imaging commenced.
(see Fig. 1 in the companion article by Powers in this Subjects were instructed to initiate extension upon ver-
issue). The device was designed to allow uninhibited bal command and continue until full extension had
movement of the patellofemoral joint and normal rota- been reached. Imaging was done at 3 different image
tion of the lower extremities. I believe that these design planes to assess the entire excursion of the patella in
features are important because patellar tracking may be relation to the trochlear groove (ie, 3 slices were
influenced by tibial rotation.26 obtained for each angle of knee flexion). These proce-
dures were repeated if I thought the rate of knee
Resistance was accomplished through a pulley system extension was too fast or too slow, or not performed in a
with a constant 30.5-cm lever arm. The design of the smooth manner. In addition, the procedure was

‡
* General Electric Medical Systems, 3200 N Grandview Ave, Waukesha, WI 54601. Esco Corp, 6415 E Corvette St, Los Angeles, CA 90242.
† §
Captain Plastic, PO Box 27493, Seattle, WA 98125. Velcro USA Inc, PO Box 5218, 406 Brown Ave, Manchester, NH 03108.

Physical Therapy . Volume 80 . Number 10 . October 2000 Powers . 967

repeated if 6 adequate images were not obtained. An
adequate image was one in which the medial and lateral
borders of the midsection of the patella, the trochlear
groove, and the posterior femoral condyles were well
defined. Visualization of these landmarks was necessary
for subsequent analysis.

Data Management
Prior to analysis, all images were screened by the princi-
pal investigator to ascertain the midsection of the patella
(maximum patellar width) at each angle of knee flexion.
Once the midsection of the patella was determined,
measurements for these images were obtained. Only
images containing a midpatella slice were analyzed.
Figure 1.
To examine patellofemoral joint relationships at the Method used to measure the sulcus angle. This angle was defined by
various degrees of knee flexion, measures that were lines joining the highest points of the medial and lateral condyles and
the lowest point of the intercondylar sulcus (AB and CB) (left). In order to
independent of the shape of the patella and the anterior obtain data when the trochlear groove lacked discernible depth, the
femoral condyles were used.23 This was done in an effort center of the sulcus angle was defined by a perpendicular line that was
to avoid measurement variability resulting from the projected anteriorly from the bisection of the posterior condylar line
continually changing contour of these structures when (right). All sulcus angle measurements were reported in degrees.
viewed at different angles of knee flexion and to allow Reprinted by permission of Lippincott Williams & Wilkins from Powers
CM, Shellock FG, Beering TV, et al. Effect of bracing on patellar
assessment of patellar orientation when the intercondy- kinematics in patients with patellofemoral joint pain. Med Sci Sports
lar groove was not well visualized. All measurements Exerc. 1999;31:1714 –1720.
were made with a computer-assisted program and
included assessment of medial and lateral patellar dis-
placement, medial and lateral patellar tilt, and the sulcus
The sulcus angle was described by Brattstrom2 as the
angle.
angle formed by the highest points of the medial and
lateral femoral condyles and the lowest point of the
Medial and lateral patellar displacement were deter-
intercondylar sulcus (Fig. 1).23 To obtain data when the
mined by the “bisect offset” measurement as described
trochlear groove lacked discernable depth, the center of
by Stanford et al27 and modified by Brossmann et al.22
the sulcus angle was defined by a perpendicular line that
The bisect offset was measured by drawing a line con-
was drawn anteriorly from the bisection of the posterior
necting the posterior femoral condyles and then project-
condylar line (Fig. 1). The estimation of the center of
ing a perpendicular line anteriorly through the deepest
the sulcus angle was based on the evaluation of normal
point (apex) of the trochlear groove. This line inter-
images that showed that the deepest portion of the
sected with the patellar width line, which connected the
intercondylar groove typically overlies the midpoint of
widest points of the patella (see Fig. 2 in the companion
the posterior condyle interval. All sulcus angles were
article by Powers in this issue).23 The perpendicular line
reported in degrees.
was projected anteriorly from the bisection of the poste-
rior condylar line to obtain data when the trochlear
The day-to-day reliability for obtaining the KMRI data
groove was flattened (see Fig. 2 in the companion article
using the procedures and measurements described was
by Powers in this issue). All bisect offset data represented
determined in a previous study to have intraclass corre-
the extent of the patella lying lateral to the projected
lation coefficients ranging from .66 to .82).23 Based on
perpendicular line and were expressed as a percentage
repeated testing, intraobserver measurement error
of total patellar width.
(standard error of measurement) was determined to be
3.4% for the bisect offset measurement, 2.9 degrees for
Medial and lateral patellar tilt were measured using a
patellar tilt, and 2.0 degrees for the sulcus angle.
modification of the technique described by Sasaki and
Although anatomical landmarks were identified manu-
Yagi.28 The patellar tilt angle was the angle formed by
ally, all lines used for angle and displacement measure-
the lines joining the maximum width of the patella and
ments were drawn by the computer software. Quantifi-
the line joining the posterior femoral condyles (see
cation of all angles and distances was performed by this
Fig. 3 in the companion article by Powers in this issue).
same program. This procedure assisted in minimizing
All tilt measurements were reported in degrees.
measurement error.


Figure 2. Figure 3.
Comparison of patellar tilt between the subjects with patellofemoral pain Comparison of patellar displacement (bisect offset) between the subjects
(PFP) and the subjects without PFP from 45 to 0 degrees of knee flexion. with patellofemoral pain (PFP) and the subjects without PFP from 45 to 0
Positive values indicate lateral tilt. Lateral patellar tilt was greater for the degrees of knee flexion. Error bars indicate one standard deviation.
subjects with PFP than for the subjects without PFP (P .05). Error bars Data for subjects with PFP previously reported by Powers et al.23
indicate one standard deviation. Data for subjects without PFP previ-
ously reported by Powers et al.23
subjects without PFP), which occurred at 27 degrees of
Data Analysis knee flexion.
All statistical procedures were performed with BMDP
statistical software. Prior to analysis, descriptive statistics In contrast, there was no difference in bisect offset
were calculated for all variables, and normality of distri- between the 2 groups (no group effect or interaction)
bution was assessed using the Wilk-Shapiro test. Based (Fig. 3). When the data were averaged across all knee
on the analysis of distribution, all data were analyzed flexion angles, the average bisect offset measurement for
using parametric tests. Significance levels were set at the subjects with PFP was 57.9% of the patella lateral to
P .05. midline, as compared with 53.8% of the patella lateral to
midline in the subjects without PFP.
To determine whether patellar indexes varied between
groups or angles of knee flexion, a 2 6 (group Similarly, there was no difference in the sulcus angle
angle) analysis of variance for repeated measures on one between the subjects with PFP and the subjects without PFP
variable (angle) was performed. This analysis was per- (no group effect or interaction) (Fig. 4). When averaged
formed for each kinematic variable. A regression analysis across all angles of knee flexion, the mean sulcus angle was
was performed to determine whether the sulcus angle 149.4 degrees for the subjects with PFP, as compared with
(independent variable) was predictive of patellar tilt or 144.6 degrees for the subjects without PFP.
patellar displacement (dependent variables). This anal-
ysis was repeated for both dependent variables at each Relationship Between Sulcus Angle and Patellar
angle of knee flexion. To control for differences Kinematics
between the 2 groups of subjects, the grouping variable The Pearson correlation coefficients obtained when
was included in all regression equations. assessing the relationship between the sulcus angle and
patellar displacement at the various knee flexion angles
Results ranged from .15 to .74 (Tab. 2). Similarly, the correla-
tion coefficients obtained when assessing the relation-
Patellar Kinematics ship between the sulcus angle and patellar tilt at the
A difference was found in patellar tilt between the 2 various knee flexion angles ranged from .26 to .76
groups. Compared with the comparison group, the (Tab. 2).
subjects with PFP demonstrated a greater degree of
lateral patellar tilt when the data were averaged across all The sulcus angle was a predictor of patellar displace-
angles of knee flexion (10.7° versus 5.5°, P .02) (Fig. 2). ment at 9 degrees of knee flexion (r .46, R2 .21);
The largest difference between the 2 groups was 7 however, it was a stronger predictor of patellar displace-
degrees (11.7° in the subjects with PFP versus 4.7° in the ment at 0 degrees (r .74, R2 .55; Fig. 5). In general, as
the sulcus angle increased (ie, became more shallow),
the amount of lateral patellar displacement also
SPSS Inc, 444 N Michigan Ave, Chicago, IL 60611. increased.


Table 2.
Pearson Correlation Coefficients for Sulcus Angle and Kinematic
Variables

Knee Flexion Angle (°)
Dependent
Variable 45 36 27 18 9 0

Patellar displacement .15 .23 .16 .35 .46a .74a
Patellar tilt .26 .34 .51a .54a .63a .76a
a
Significant at P .05.

The sulcus angle also was a predictor of patellar tilt at
27 degrees (r .51, R2 .26), 18 degrees (r .54,
R2 .29), 9 degrees (r .63, R2 .40), and 0 degrees of
Figure 4. knee flexion (r .76, R2 .58; Fig. 6). As with patellar
Comparison of sulcus angle between the subjects with patellofemoral displacement, an increase in the sulcus angle resulted in
pain (PFP) and the subjects without PFP from 45 to 0 degrees of knee greater amounts of lateral patellar tilt.
flexion. Error bars indicate one standard deviation. Data for subjects
with PFP previously reported by Powers et al.23
Discussion
The sulcus angle, as measured in this study, was repre-
sentative of the depth of the femoral trochlea at the
midsection of the patella. In general, there was a trend
toward a more shallow groove in the subjects with PFP
when the data were averaged across all knee flexion
angles. It is evident from these data, however, that
although the 2 groups had similar sulcus angles at 45, 36,
and 27 degrees of flexion, a substantial increase (loss of
depth) was observed in the subjects with PFP as the knee
extended beyond 27 degrees. This increase in the sulcus
angle is similar to the increases reported by Schutzer
et al29 and Kujala et al30 and suggests that bony stability
at the end-range of extension may be compromised in
people with PFP.
Figure 5.
Relationship between the sulcus angle (in degrees) and bisect offset The sulcus angle was found to be a predictor of lateral
(percentage of the patella width lateral to midline) for the subjects with
patellar tilt at 27, 18, 9, and, 0 degrees, as well as a
patellofemoral pain (PFP) and the subjects without PFP at 0 degrees of
knee flexion (r .74; F 19.3; df 2,33; P .05). predictor of lateral patellar displacement at 9 and 0
degrees. This finding underscores the importance of the
bony anatomy in contributing to patellar stability and
could theoretically explain the clinical manifestation of
lateral patellar subluxation during terminal knee exten-
sion. The association between bony anatomy and patel-
lar stability was evident in the PFP data, where it was
observed that the point at which the sulcus angle began
to deviate from the data obtained for the comparison
group (approximately 27°) was at the same point at
which the lateral displacement became more pro-
nounced (Figs. 3 and 4). The finding that more than half
of the variability in patellar tilt and displacement could be
explained by the sulcus angle at 0 degrees supports the
argument of Brattstrom2 that a shallow femoral sulcus is a
predisposing factor with regard to abnormal patellar kine-
Figure 6. matics at terminal knee extension.
Relationship between the sulcus angle (in degrees) and patellar tilt (in
degrees) for the subjects with patellofemoral pain (PFP) and the subjects
without PFP at 0 degrees of knee flexion (r .76; F 20.6; df 2,33; During knee extension, the sulcus angle of the subjects
P .05). Positive values of patellar tilt indicate lateral tilting. without PFP increased an average of 10 degrees, indicat-


changed very little. Their findings, how-
ever, were based on their analysis of
cadaver specimens under low-level,
static loading conditions. I contend it is
likely that the conditions used in my
investigation (active quadriceps femoris
muscle contraction/shortening) pulled
the patella farther superiorly in the
trochlear groove, thereby accounting for
the differences in the sulcus angles.

Although not significant, the average
increase (flattening) of the sulcus angle
during extension in the subjects with
PFP (19°) was almost twice that of the
subjects without PFP (10°). Although
this increase in the sulcus angle is indic-
ative of compromised patellar stability,
the etiological factor underlying this
finding is not entirely evident. For
example, there are 2 possible explana-
tions for the increase in the sulcus
angle: (1) dysplasia of the cranial
portion of the femoral trochlea and
(2) patella alta (excessive superior
migration of the patella with respect to
the trochlear groove). Although both
of these alternatives are possible, it is
difficult to separate the effects of each
with regard to patellar tracking. Hvid
and colleagues33 reported data that
Figure 7. suggest that both findings are typically
Axial-plane images obtained from a subject without patellofemoral pain (PFP) and 3 subjects
with PFP (patients 1–3). The subject without PFP and patient 1 demonstrate a centered patella
found in conjunction with each other.
within the trochlear groove. Patient 2 demonstrates a moderate degree of lateral displacement Without knowing the vertical position
(lateral border of patella lateral to the anterior femoral condyle) and lateral tilting as well as a of the patella within the femoral troch-
relatively shallow trochlear groove. In patient 3, the patella is positioned well above the lea, however, it would be difficult to
trochlear groove, and there is extreme lateral displacement and lateral tilting of the patella. ascertain whether an increased sulcus
angle was the result of dysplasia or of
patella alta, or a combination of both.
ing that the patella was moving to a more shallow portion This determination would require further radiological
of the femoral trochlea. Because the patella migrates evaluation, using lateral-view techniques that have been
superiorly as the knee extends,31,32 this observation, in my described for assessing trochlear dysplasia14,34 and patella
opinion, suggests that the bony stability afforded by the alta35–37 or serial axial views to determine the exact position
cranial portion of the trochlear groove is less than that of the patella within the trochlear groove.38
provided by the caudal portion. This hypothesis is sup-
ported by the findings of Malghem and Maldague,14 who Despite the fact that the KMRI data collected in this
reported that the depth of the proximal trochlear groove study were limited for assessing the exact vertical posi-
(as determined by lateral radiographs) was less than the tion of the patella, I contend that some qualitative
depth of the middle portion in subjects who were pain-free. information was gained. For example, in 22% of the
subjects with PFP, it appeared that the patella was
In contrast, the finding of an increasing sulcus angle superior to the femoral trochlea, which would be sug-
with knee extension in my investigation appears to gestive of patella alta. As shown in Figure 7, the patella of
contradict the data of Farahmand and colleagues,20 who patient 3 is situated on the shaft of the femur, well above
reported that the geometry of the trochlear groove (as the level of the femoral condyles. In contrast, patient 2
encountered by the sliding patella during knee flexion) demonstrates a relatively shallow trochlear groove,


although the posterior femoral condyles are still visible, ple size (including male subjects), however, would be
suggesting that this image section was not above the level necessary to confirm this observation.
of the femoral trochlea. Therefore, an argument could
be made that the diminished sulcus depth in this subject The subjects without PFP demonstrated an overall pat-
was more likely the result of trochlear dysplasia. tern of decreasing lateral tilt as the knee extended, which is
consistent with findings obtained with cadaver speci-
The bisect offset data obtained for both groups indi- mens41,42 and cine phase contrast imaging techniques.21
cated that the patella was lateral to the midline through- The average tilt values for the subjects, with PFP, however,
out the range of motion. On the average, the subjects remained fairly consistent across all knee flexion angles.
with PFP demonstrated greater patellar lateralization at This finding is in contrast to the data of Brossmann and
all angles of flexion. This finding, however, was not colleagues,22 which showed an overall tendency toward
statistically significant. The normal kinematic pattern for progressive lateral tilt as the knee extended. This pattern of
patellar displacement was characterized by slight medial movement was evident in only 27% of the subjects with PFP
displacement from 45 to 18 degrees of knee flexion, in my investigation, which suggests that this should not be
followed by subtle lateral displacement as the knee considered the dominant motion pattern. This discrepancy
extended from 18 to 0 degrees (Fig. 3). This pattern of could have been the result of the difference in subjects in
movement is consistent with that previously described as the 2 studies, as well as the different measurement tech-
a frontal-plane “C” curve.39 Although, the average patel- niques used to determine patellar tilt.
lar displacement pattern of the subjects with PFP was
similar to that of the subjects without PFP from 45 to 27 The results of my study may have clinical implications for
degrees of flexion, there was a reversal to a progressively the treatment of people with patellar malalignment. For
more lateral alignment as the knee continued to extend. example, if patellar tracking is primarily dictated by bony
The largest difference between groups was evident at 0 structure, then treatment procedures that address only
degrees (62% versus 54% of the patella lateral to the soft-tissue components (such quadriceps femoris muscle
midline), which coincides with the contention of Fulk- strengthening or a lateral retinacular release) may have
erson and Hungerford1 that patellar subluxation typi- limited success. Likewise, the long-term success of a
cally occurs during terminal knee extension. procedure such as a distal realignment may depend on
whether the patella can be relocated within the bony
The bisect offset data of the subjects with PFP demon- confines of the trochlea.
strated large variability at 18, 9, and 0 degrees of flexion.
At these angles, the standard deviations were approxi- A limitation of my study was the fact that a relatively
mately 2 to 3 times those of the subjects without PFP, small comparison group was used to provide comparison
indicating that these subjects exhibited a wide range of data. Although differences were found with respect to
horizontal patellar displacement (Fig. 3). At 0 degrees, patellar tilt, a larger sample size might have increased
for example, 22% of the subjects with PFP had a bisect the ability to find group differences in the bisect offset
offset value greater than 2 standard deviations of the and sulcus angle measurements. Additional study in this
comparison group, whereas 61% had a bisect offset value area should consider larger sample sizes, particularly
within 1 standard deviation of the control group. These given the large variability among individuals with PFP. A
findings support the work of Shellock et al,40 who post hoc power analysis revealed that approximately 80
reported that only 26% of their subjects demonstrated and 110 subjects would be required to find group effects
lateral subluxation of the patella. Although the data of (10% differences) for the sulcus angle and bisect offset,
Shellock and colleagues40 were based on qualitative MRI respectively.
assessment, the results of these previous studies, as well as
the data of my investigation, indicate that excessive lateral As a result of the limitations imposed by the size of the
displacement of the patella is not a universal finding in this MRI bore, the loading condition used in this study (non–
population. The role of abnormal patellar kinematics as a weight bearing) was not consistent with the loading condi-
primary cause of PFP, in my view, may be questioned. tion that would be evident with weight-bearing activities.
Therefore, care should be taken in interpreting the results
The patellar tilt data showed that the patella was laterally of this study until differences in patellar kinematics can be
tilted throughout the range of motion in both groups, established between various loading conditions.
with the subjects with PFP demonstrating greater mag-
nitudes compared with the subjects without PFP when Conclusions
the data were averaged across all knee flexion angles. The results of this study indicate that the sulcus angle is
These results suggest that excessive lateral tilt may be a a predictor of both lateral patellar tilt and lateral patellar
more frequent radiological finding in PFP compared displacement during terminal knee extension. This finding
with lateral displacement or subluxation. A larger sam- suggests that bony structure is an important determinate of


patellar kinematics during this particular activity in young 20 Farahmand F, Tahmasbi MN, Amis AA. Lateral force-displacement
women. Further research should be directed toward iden- behavior of the human patella and its variation with knee flexion: a
biomechanical study in vitro. J Biomech. 1998;31:1147–1152.
tifying additional factors that can improve the predictability
of patellar kinematics as well investigating the influence of 21 Sheehan FT, Zajac FE, Drace JE. Using cine phase contrast mag-
netic resonance imaging to non-invasively study in vivo knee dynamics.
lower-extremity function on patellar alignment.
J Biomech. 1998;31:21–26.
22 Brossmann J, Muhle C, Schroder C, et al. Patellar tracking patterns
References
during active and passive knee extension: evaluation with motion-
1 Fulkerson JP, Hungerford DS. Disorders of the Patellofemoral Joint. 2nd
triggered cine MR imaging. Radiology. 1993;187:205–212.
ed. Baltimore, Md: Williams & Wilkins; 1990.
23 Powers CM, Shellock FG, Pfaff M. Quantification of patellar track-
2 Brattstrom H. Shape of the intercondylar groove normally and in
ing using kinematic magnetic resonance imaging. J Magn Reson Imag-
recurrent dislocation of the patella. Acta Orthop Scand. 1964;68:85–138.
ing. 1998;8:724 –732.
3 Hvid I, Andersen LI, Schmidt H. Chondromalacia patellae: the 24 Shellock FG, Mink JH, Deutsch A, Pressman BD. Kinematic mag-
relation to abnormal patellofemoral joint mechanics. Acta Orthop netic resonance imaging of the joints: techniques and clinical applica-
Scand. 1981;52:661– 666. tions. J Magn Reson Imaging. 1991;7:104 –135.
4 Paulos L, Rusche K, Johnson C, Noyes FR. Patellar malalignment: a 25 Shellock FG, Mink JH, Deutsch AL, Foo TK. Kinematic MR imaging
treatment rationale. Phys Ther. 1980;60:1624 –1632. of the patellofemoral joint: comparison of passive positioning and
5 Vainionpaa S, Laasonen E, Patiala H, et al. Acute dislocation of the active movement techniques. Radiology. 1992;184:574 –577.
patella: clinical, radiographic and operative findings in 64 consecutive 26 van Kampen A, Huiskes R. The three-dimensional tracking pattern
cases. Acta Orthop Scand. 1986;57:331–333. of the human patella. J Orthop Res. 1990;8:372–382.
6 Wiberg G. Roentgenographic and anatomic studies on the femoro- 27 Stanford W, Phelan J, Kathol MH. Patellofemoral joint motion: evalu-
patellar joint. Acta Orthop Scand. 1941;12:319 – 410. ation by ultrafast computed tomography. Skeletal Radiol. 1988;17:487– 492.
7 Fox TA. Dysplasia of the quadriceps mechanism: hypoplasia of the 28 Sasaki T, Yagi T. Subluxation of the patella: investigation by
vastus medialis muscle as related to the hypermobile patella syndrome. computerized tomography. Int Orthop. 1986;10:115–120.
Surg Clin North Am. 1975;55:199 –226. 29 Schutzer SF, Ramsby GR, Fulkerson JP. The evaluation of patello-
8 Jeffreys TE. Recurrent dislocation of the patella due to abnormal femoral pain using computerized tomography: a preliminary study.
attachment of the ilio-tibial tract. J Bone Joint Surg Br. 1963;45:740 –743. Clin Orthop. 1986;204:286 –293.

9 Puniello MS. Iliotibial band tightness and medial patellar glide in 30 Kujala UM, Osterman K, Kormano M, et al. Patellofemoral relation-
patients with patellofemoral dysfunction. J Orthop Sports Phys Ther. ships in recurrent patellar dislocation. J Bone Joint Surg Br. 1989;71:
1993;17:144 –148. 788 –792.

10 Mariani PP, Caruso I. An electromyographic investigation of sub- 31 Goodfellow J, Hungerford DS, Woods C. Patello-femoral joint
luxation of the patella. J Bone Joint Surg Br. 1979;61:169 –171. mechanics and pathology, 2: chondromalacia patellae. J Bone Joint Surg
Br. 1976;58:291–299.
11 Souza DR, Gross MT. Comparison of vastus medialis obliquus:vastus
32 Seedhom BB, Takeda T, Tsubuku M, Wright V. Mechanical factors
lateralis muscle integrated electromyographic ratios between healthy
and patellofemoral osteoarthritis. Ann Rheum Dis. 1979;38:307–316.
subjects and patients with patellofemoral pain. Phys Ther. 1991;71:
310 –316. 33 Hvid I, Andersen LI, Schmidt H. Patellar height and femoral
trochlear development. Acta Orthop Scand. 1983;54:91–93.
12 Boucher JP, King MA, Levebvre R, Pepin A. Quadriceps femoris
muscle activity in patellofemoral pain syndrome. Am J Sports Med. 34 Grelsamer RP, Tedder JL. The lateral trochlear sign: femoral
1992;20:527–532. trochlear dysplasia as seen on a lateral view roentgenograph. Clin
Orthop. 1992;281:159 –162.
13 Powers CM, Landel R, Perry J. Timing and intensity of vastus muscle
activity during functional activities in subjects with and without patel- 35 Blackburne JS, Peel TE. A new method of measuring patellar
lofemoral pain. Phys Ther. 1996;76:946 –955. height. J Bone Joint Surg Br. 1977;59:241–242.

14 Malghem J, Maldague B. Depth insufficiency of the proximal 36 de Carvalho A, Andersen AH, Topp S, Jurik AG. A method for
trochlear groove on lateral radiographs of the knee: relation to patellar assessing the height of the patella. Int Orthop. 1985;9:195–197.
dislocation. Radiology. 1989;170:507–510. 37 Insall J, Salvati E. Patella position in the normal knee joint.
Radiology. 1971;101:101–104.
15 Geenen E, Molenaers G, Martens M. Patella alta in patellofemoral
instability. Acta Orthop Belg. 1989;55:387–393. 38 Shellock FG, Kim S, Mink JH, et al. “Functional” patella alta
determined with axial-plane imaging of the patellofemoral joint:
16 Insall J, Goldberg V, Salvati E. Recurrent dislocation and the
association with abnormal patellar alignment and tracking. [abstract].
high-riding patella. Clin Orthop. 1972;88:67– 69.
J Magn Reson Imaging. 1992;2:93.
17 Insall J, Falvo KA, Wise DW. Chondromalacia patellae: a prospective 39 Hungerford DS, Barry M. Biomechanics of the patellofemoral joint.
study. J Bone Joint Surg Am. 1976;58:1– 8. Clin Orthop. 1979;144:9 –15.
18 Moller BN, Krebs B, Jurik AG. Patellar height and patellofemoral 40 Shellock FG, Mink JH, Deutsch AL, Fox JM. Patellar tracking
congruence. Arch Orthop Trauma Surg. 1986;104:380 –381. abnormalities: clinical experience with kinematic MR imaging in 130
19 Farahmand F, Senavongse W, Amis AA. Quantitative study of patients. Radiology. 1989;172:799 – 804.
quadriceps muscles and trochlear groove geometry related to instabil- 41 Nagamine R, Otani T, White SE, et al. Patellar tracking measure-
ity of the patellofemoral joint. J Orthop Res. 1998;16:136 –143. ments in the normal knee. J Orthop Res. 1995;13:115–122.
42 Reider B, Marshall JL, Ring B. Patellar tracking. Clin Orthop.
1981;157:143–148.


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