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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.




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


Physical Therapy . Volume 80 . Number 10 . October 2000                                                                                      Powers . 969
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-


970 . Powers                                                                              Physical Therapy . Volume 80 . Number 10 . October 2000
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,




Physical Therapy . Volume 80 . Number 10 . October 2000                                                                           Powers . 971
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



972 . Powers                                                             Physical Therapy . Volume 80 . Number 10 . October 2000
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
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Physical Therapy . Volume 80 . Number 10 . October 2000                                                                                   Powers . 973

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Patellar kinematics, Part II

  • 1. 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
  • 2. 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
  • 3. 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
  • 4. 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. 968 . Powers Physical Therapy . Volume 80 . Number 10 . October 2000
  • 5. 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. Physical Therapy . Volume 80 . Number 10 . October 2000 Powers . 969
  • 6. 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- 970 . Powers Physical Therapy . Volume 80 . Number 10 . October 2000
  • 7. 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, Physical Therapy . Volume 80 . Number 10 . October 2000 Powers . 971
  • 8. 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 972 . Powers Physical Therapy . Volume 80 . Number 10 . October 2000
  • 9. 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. Physical Therapy . Volume 80 . Number 10 . October 2000 Powers . 973