The study examined the influence of patellofemoral pain (PFP) and quadriceps femoris muscle weakness on gait variables. Nineteen females with PFP and 19 controls underwent gait analysis during various activities and isometric knee extension testing. Compared to controls, those with PFP walked slower due to shorter stride length and slower cadence. Increased knee extension torque correlated with improved gait, while PFP was not associated with locomotor function. Weak quadriceps strength, not pain, appeared to influence gait limitations in those with PFP.

1. Are Patellofemoral Pain and
Quadriceps Femoris Muscle Torque
Associated With Locomotor Function?
Background and Purpose. The purpose of this investigation was to
determine the influence of pain and muscle weakness on gait variables
in subjects with patellofemoral pain (PFP). Subjects. Nineteen female
subjects with a diagnosis of PFP and 19 female subjects without PFP
participated in the study. Methods. Subjects underwent gait analysis
(stride characteristics and joint motion) during level walking, ascend-
ing and descending stairs, and ascending and descending ramps, in
addition to isometric torque testing of the knee extensors of the
involved limb. Pain and functional status also were assessed. Results.
Compared with the comparison group, the primary gait compensation
in the PFP group was a reduced walking speed, which was a function of
both a reduced stride length and cadence. Knee extensor torque was
the only predictor of gait function, with increased torque correlating
with improved stride characteristics. In addition, PFP was not associ-
ated with locomotor function. Conclusion and Discussion. These
findings suggest that functional ability in persons with PFP is associated
with increased quadriceps femoris muscle torque. Future research is
needed to determine whether function improves with quadriceps
femoris muscle strengthening. [Powers CM, Perry J, Hsu A, Hislop HJ.
Are patellofemoral pain and quadriceps femoris muscle torque associ-
ated with locomotor function? Phys Ther. 1997;77:1063-1078.1
Key Words: Gait, Patellofemoral pain, Quadriceps femoris muscle torque.
Christopher M Powers I
Jacquelin Pemy
Arthur Hsu
Helen J Hislop
Physical Therapy . Volume 77 . Number 10 . October 1997

2. uring the stance phase of gait, the knee is
D
in inhibition of alpha motoneurons in the anterior horn
believed to be the principal determinant of of the spinal cord.'%lthough in clinical practice pain
limb stability.' The quadriceps femoris mus- and inhibition have been associated,14decreased motor
cles act as the primary stabilizers of the knee, unit recruitment of the quadriceps femoris muscle
especially during loading response, when the knee flex- appears to be linked to knee joint e f f ~ s i o n ~ ~ ~ ' ~ ' " ~ ~
ion moment is the g r e a t e ~ tActivity of these muscles is
.~ and has been reported to be independent of pain.I2,l"
necessary to support the flexed knee posture." Young et all7 reported that afferent block by local
anesthesia was not effective in reducing quadriceps
Reduced knee flexion during loading response is gener- femoris muscle inhibition, despite a complete reduction
ally thought to be an action aimed at limitingjoint forces in pain. Additionally, Stratford12 did not observe a
and may be indicative of knee pathology.' For example, relationship between pain and inhibition that would
pain and weakness are commonly associated with patel- explain reduced electromyographic activity of the quad-
lofemoral joint p a t h ~ l o g y and the avoidance of knee
,~ riceps femoris muscle during a maximal isometric con-
flexion during stance has been found in persons with traction in persons with acutely effused knees. In con-
patellofemoral joint pathology.~erchuck a16 used the
et trast, deAndrade and colleagues15 presented evidence
term "quadriceps avoidance pattern" for persons with that pain reduction through lidocaine injection reduced
anterior cruciate ligament (ACL) deficiency to describe quadriceps femoris muscle inhibition in knees that were
a gait pattern that minimizes the knee flexion moment artificially distended. These observations, however, were
during the loading response and therefore the demand made on only four subjects.
of the knee extensors. Persons with PFP also may adopt
a similar strategy to reduce the patellofemoral joint Despite the current state of knowledge regarding the
reaction forces associated with increased knee flexion cause of quadriceps femoris muscle inhibition, many
and quadriceps femoris muscle activity. A quadriceps functionally related questions remain. For example, are
femoris muscle avoidance pattern could be deleterious compensatory gait patterns a result of pain, weakness, or
to the patient with PFP, however, if further quadriceps both? Do gait adaptations associated with patellofemoral
femoris muscle atrophy results from disuse. This avoid- joint pathology differ among persons with varying
ance pattern may contribute to patellar instability, which degrees of pain? What is the relationship between PFP
is commonly believed to be at least partly the result of and quadriceps femoris muscle weakness? The purpose
weakened dynamic stabilizer^.^.^.^ of our investigation was to determine the influence of
PFP and quadriceps femoris muscle weakness on stride
Although gait patterns have been described for various characteristics and the amount of knee flexion during
knee pathologies such as degenerative joint di~ease,''.~~'the loading response in different gait conditions (level
rheumatoid arthritis,"-l1 and ACL insufficiency,~ittle is walking, ascending and descending stairs, ascending and
known about subjects with PFP and the relationship descending ramps). Functional assessment scores were
between pain and weakness. The relationship between also correlated with actual gait characteristics. We
knee pain and quadriceps femoris muscle inhibition, hypothesized that there would be a correlation between
however, has been discussed previously in the literature. either pain or quadriceps femoris muscle weakness and
Reflex inhibition has been demonstrated in subjects with the limitations in gait function associated with PFP. This
knee pathology12and is reported to occur when afferent information could assist in identifying variables associ-
stimuli from receptors in or around the knee joint result ated with gait limitations in this population and could
CM Powers, PhD, PT, is Assistant Professor, Department of Biokinesiology and Physical Therapy, University of Southern California, 1.540 E Alcazar
St, CHP 135, Los Angeles, CA 90033 (USA) (powers@hsc.usc.ed~~). Address all correspondence to Dr Powers.
J Perry, MD, is Chief, Pathokinesiology Service, Rancho Los Amigos Medical Center. Downey, Calif. and Professor, Departrnent of Biokinesiolog
and Physical Therapy, University of Southern California, Los Angeles.
A Hsu, PhD, PT, is Assistant Professor, Departrnent of Biokinesiology and Physical Therapy, University of Southern California, 1.0s i2ngeles.
HJ Hislop, PhD, PT, FAPTA, is Professor and Chair, Department of Biokinesiology and Physical Therapy, University of Southern California, L.os
Angeles.
This study was approved for human subjects by the Los Amigos Research and Education Institute Inc of Rancho 1.0s Amigos Medical Center.
This study was supported in part by a grant from the Foundatiori f i ~ Physical Therapy IIIC.
r
nrtic.1~ submittpd August 8, 1996, nnd runs occc?t(.cl April 25, 199%
Thi~ ruas
1064 . Powers et al Physical Therapy . Volume 77 . Number 1 0 . October 1997

3. Table 1. with PFP, and they had no other limitations that would
Subiect Characteristics
alter their gait.
PFPa Group Comparison Group
(n= 1 9) (n= 19) P
Isometric knee extensor torque was recorded using a
Age (YI Lido d y n a ~ ~ ~ o m e tPrior to testing, compensation for
er.*
X 25.4 27.5 limb weight and the effects of gravity was made automat-
SD 8.2 4.7 .35 ically by the dynamometer's computer software program
Range 14-46 23-3 8 (Version 3.8, 1989). Reliability of the data used for
H c g h t (cm) correction was not assessed. Torque data were recorded
X 165.1 165.3 by a DEC 11/23 computert at a rate of 2,500 Hz. The
SD 7.6 7.7 .94
Range 151 .l-177.2 149.9-183.5 DEC computer was interfaced with the dynamometer.
W e i g h t (kg)
X 62.4 59.2 Knee pain was recorded using a visual analog pain scale
SD 9.3 7.5 .25 (VAS). The VAS consisted of a 10-cm horizontal line, the
Range 42.0-82.7 46.8-74.1 ends of which defined the minimum ("no pain") and
maximum ("extreme pain") of perceived pain. Each s u b
ject placed a mark on the line to indicate the intensity of
pain. The amount of pain indicated on the line was
aitl in guiding treatment programs aimed at improving converted to a numerical value based on the distance (in
function. centimeters) from the minimal possible pain to the mark
on the line. The VL4S been shown by Chesworth et allx
has
Method to be a valid indicator of pain changes in patients with PFP.
Subjects To evaluate symptoins and functional limitations in the
Nineteen female sul~jects between the ages of 14 and 46 subjects with PFP, a functional assessment questionnaire
years with a diagnosis of PFP participated in this study (FAQ developed by Kujala et all'' was used. The validity
(Tall. 1). Subjects were recruited fi-om the Southern and reliability of measurelnents obtained with the FAQ
Califorr~iaOrthopaedic Institute (Van Nuys, Calif) and have not been reported. This questionnaire contained
were scl-eened to rule out ligamentous instability, inter- 13 multiple-choice questions relating to patellofemoral
nal der;angement, and patellar tendinitis. In addition, joint symptoms. Scoring was based on a numerical scale
sul~jects not have any other orthopedic or neurologic
did depending on question response, with some items being
impairments, as determined by physical examination weighted more than others. The maximum possible
and questionnaire, that would adversely affect gait. Each score was 100, which represented no pain aild no
sut!ject':s pain originated from the patellofemoral joint functional deficits. This scoring system has been demon-
(as determined through their complaints and a physical strated to differentiate between different classifications
exatnination), and only patients with histories relating to of patellofemoral disorders.l0
overuse (ie, symptoms related to repetitive activity) or
insidious onset were accepted. The physical examination Stride characteristics were recorded with a micro-
consisted of passive range of motion, active range of processor-based Footswitch Stride Analyzer system.:
motion, palpation of the patella and related structures, This system consisted of compression-closing foot-
and a patellar grind test. In addition, each subject's pain switches taped to the soles of the subjects' bare feet. The
was readily reproducible with at least two of the follow- footswitches contained sensors at the heel, the first and
ing acthities: stair ascent or descent, squatting, kneeling, fifth metatarsal heads, and the great toe that responded
prolonged sitting, or isometric quadriceps femoris mus- to compressive loads equal to o r greater than 3 psi.
cle contraction. The subjects with PFP were varied with Stride characteristics calculated from this system includ-
respect to the severity and duration of symptoms. Sub- ed: speed, stride length, cadence, single- and double-
jects were excluded from the study if they reported limb support times, and stance and swing durations.
ha~ing either knee surgery or acute traumatic patellar
dislocation. Sagittal-plane motion of the ankle, knee, and hip joints
was measured with a Vicon motion analysis system.s Six
Nineteen female subjects between the ages of 23 and 38
years served as a comparison group (Tab. 1). These
subjects had no history or diagnosis of knee pathology or
trauma, and they were free of any current knee pain. In ' 1.oredan Biomedical Ill,-, 16.12 Ua 'lnci (:t, PO Box 1154, Davis. (:A 95617.
adtlitior~,
these subjects did not report discomfort with
' Digiral 'quipment C o ~ p 146 Main St, Maynalrl, MA 01754.
,
B&1. E:ngincer-~ng,8807 Pioneel Blvd, Suitr (:. Snt~ta Springs. (1% 90670.
Fc
any of the activities described as criteria for the subjects ' Oxli~rd Mctrica L.td Unit 14, '7 Weat Way, Botlry. O x h ~ l d ,
Etlgla~ldOX:! OUR.
Physical Therapy . Volume 77 . N u m b e r 10 . O c t o b e r 1997 Powers et al . 1065

4. infrared cameras operating at a 50-HT sampling rate walking, subjects were instructed to walk at their normal
were used. speed. For fast walking, subjects were instructed to walk
at a speed as if they were in a hurry. Joint motion and
A 10-m walkway was used for free- and fast-walking trials, stride characteristics were then assessed simultaneously
with data being collected over the middle 6 m. Analysis during free and fast level walking, ascending and
of stair use was done with a four-step staircase with a descending stairs, and ascending and descending ramps.
slope of 33.7 degrees, a step height of 20.3 cm, and a
tread depth of 30.5 cm. Ramp walking was assessed with Data Analysis
a 12-degree incline that was 6.1 nl in length. Sagittal-joint motion of the ankle, knee, and hip was
calculated for all conditions tested. Raw motion data
Procedure were filtered at 6 HL using a fourth-order, Butterworth
All data collection was performed at the Pathokinesiol- recursive filter." The data were then digitized and
ogy Laboratory, Rancho Los Amigos Medical Center, linearly interpolated to 0.01-second intervals. The stance
Downey, Calif. Before testing, all procedures were phase of each stride of motion collected Ivas normalized
explained to each subject and informed consent was LO 6'2% of the gait cycle in order to average data from
obtained. Subjects were then asked to complete the FAQ m ~ ~ l t i p strides and different subjects. We believe this
le
based on their current symptoms and limitations. value to be representative of normal walking,[ and it was
consistent with the average stance phase deinonstrated
Prior to gait analysis, maximal isometric knee extensor by our subjects for all conditions. Maxirnuni and rnini-
torque and knee pain were measured. Subjects were mum motion for each joint were analyzed for each phase
seated on the Lido dynamometer chair with the hips of the gait cycle. Analog signals obtained from the
flcxed to 90 degrees and the knee flexed to 60 degrees. individual footswitch sensors were synchronized with the
The axis of rotation of the dynamometer was then motion data and were used as event markers to deter-
positioned in line with the axis of rotation of the knce, mine the different phases of the gait cycle.
with the resistance arm cuff placed just proximal to the
malleoli. A Velcro@strap1was placed across the pelvis to Torque data were integrated at 0.1-second intervals. The
e n w r e proper stabilization. Sixty degrees of knee flexion torque produced by the limb weight (as determined by
was used because this position has been found to result the gravity cornpcnsation test) was added to the raw
in the greatest torque output in female subjects without torque to account for the effects of gravity. The greatest
inlpairment~.'~) value over the 5-second trial was recorded for each
subject. T o control for the cffkcts of subject size, a11
Isometric torque during a 5-second maximal contraction torque data were normalized by body weight and
was then recorded. Verbal encol~ragement was given to expressed in newton-meters per kilogram.
all sub.jects during the trial. After torque was measured,
the subjects with PFP were asked to rate, using the VAS, The BMDP statistical software' was used for all data
their knee pain during the maximal contraction. Our analyses. The data were tested for normality of distribu-
rationale for assessing pain during contraction rather tion using the Wilks-Shapiro W statistic. All significance
than during the locomotor tasks was that we expected levels were set at P<.05.
that pain scores obtained during ambulation would not
reflect true symptoms. We believed that the subjects Subject characteristics (age, height, and weight) were
would most likely adopt gait strategies to reduce or compared between groups using two-sample t tests.
eliminate pain. Comparison of isometric torque values between groups
also was made using a two-sample 1 tcst.
Following the torque and pain assessment, subjects were
prepared for gait analysis. Footswitches were taped to T o determine whether w i d e charactcristics differed
both of the subjects' bare feet, and the reflective rnarkers between groups and conditions, a 2 X 6 (group X
that were used to determine sagittal-plane motion were condition) two-way analysis of variance (ANOVA) for
placed at the designated landmarks (posterior heel, fifth repeated measures on one variable (condition) was
metatarsal head, dorsum of the foot, medial and lateral performed. This analysis was repeated for each stride
malleoli, anterior tibia, medial and lateral fe~noralepi- characteristic. Data for stride length and cadence during
condyles, anterior thigh, greater trochanter, bilateral stair amhulation were omitted from thc analysis due to
anterior superior iliac spines, and sacrum). One practice the limitation imposed o n these variables as :i result of
trial of both free and fast walking allowed the subjects to the fixed ctair height and depth. Peak motion at each
beconle familiar with the instrumentation. For free
' r l c ~ - oL'S4 Inc, P C ) Box 5218, 406 BI.OM.II v r , M d ~ l c h r ~ r lN11 0::lOX
h -,
1066 . Powers et a1 Physical Therapy . Volume 77 . Number 1 0 . October 1 9 9 7

5. Table 2. Table 3.
Moximurr Knee Extension Torque (Normalized by Body Weight) Individual Volues for Knee Extension Torque, Visuol Analog Poin
Scale (VAS), ond Functional Assessment Q ~ e s t i o n n o i r e '(FAQ) for
~
Subiects With Patellofemorol Pain
PFPa Group Camparison Group
Tocque (N.m/kg) Knee Extension VAS (1 0= FAQ ( 1 00=
Subject Torque Maximum Maximum
0.78 0.69 .03 No. (Nem/kg) Pain) Function)
Range 1.28-3.92 1.96-4.02
1 2.54 8.6 53
" pain.
PFP=~x~tc~llofe~~~o~~~il 2 2.09 7.6 35
3 1.45 9.6 37
4 3.90 6.5 70
joint also was compared between groups and conditions 5 1.43 3.4 85
using a 2 x 6 (group x condition) two-way ANOVA for 6 2.14 0 73
repeated measures. This analysis was repeated for each 7 2.74 4.1 84
8 1.78 4.8 73
phase of the gait cycle. 9 2.2 1 0.2 73
10 1.23 6.8 38
To assess the association among PFP, quadriceps femoris 11 2.73 0.8 73
muscle torque, and FAQ score, we used the Pearson 12 1.79 1.1 75
product-moment correlation coefficient. We used sepa- 13 1.23 3.2 62
14 3.16 5.1 68
rate analyses to assess the linear relationship between 15 2.42 0 100
PFP and torque, PFP and FAQ score, and torque and 16 2.21 8.6 45
FAQ score. 17 2.92 6.4 83
18 3.64 3.8 74
Stepwise regression analyses were performed to deter- 19 3.48 3.0 82
-
mine whether any of the independent variables (pain, X 2.35 4.4 67.5
quadriceps femoris muscle torque, or FAQ score) were SD 0.78 3.1 18.1
.
.
predictive of any of the stride characteristics or the
alnount of knee flexion during loading response
... .
(dependent variables). This analysis was performed for
100 8
the subjects with PFP only and was repeated for all six
walking conditions.
Results
.
Relationship Among Knee Extensor Torque, Pain, and
Functional Assessment Score
After normalizing by body weight, the maximum knee
extensol- torque of the PFP group was less than that of
the cornparison group (2.35 N-m/kg versus 3.04
OI
40 -- . .
20 I
N.m/kg, P c . 0 5 ) (Tab. 2). During the maximal isomet- 0 2 4 6 8 10
ric test, the PFP group reported an average pain level of
4.4 out of 10 on the VAS (Tab. 3 ) . The mean score o n
VISUAL ANALOG PAIN SCORE
the FAQ for the PFP group was 67.5 out of a possible 100 Figure 1.
(Tab. 3 ) . Correlation behveen functional assessment questionnaire (FAQ) score
and visual analog pain score for subiects with patellofemoral poin
(n=19, r =.72, P<.001).
The VAS pain score was not correlated with knee exten-
sor torque in the PFP group ( r =.03). In addition, knee
extensor torque was not correlated with the FAQ score cadeilce and in stride length when the data were aver-
( r = .25). The VAS pain score, however, demonstrated a aged across all conditions (except data for ascending
correlation with the FAQscore in the PFP group ( r = . 7 2 , and descending stairs, which were omitted from the
P<.001:1 (Fig. 1). analysis) (Figs. 3, 4). In general, the PFP group demon-
strated decreased values for these stride characteristics
Stride Characteristics cornpared with the other group.
There was a difference between the PFP and comparison
groups for walking speed when the data were averaged The average walking speed of the PFP group (for all
across all conditions (significant group effect, no inter- conditions) was 81% of the average walking speed of the
action) (Fig. 2). Similarly, there was a difference in cornparison group (56.5 m/rnin versus 69.7 m/min,
Physical Therapy . Volume 7 7 . Number 10 . October 1997 Powers et al . 1067

6. FR FT AS DS AR DR
Condition
, Comparison
Group
,,
- PFP Group
Figure 2.
Mean walking speed for subiects with patellofemoral pain [PFP group, n= 19) and subjects without patellofemoral pain (comparison group, n= 19)
for all conditions tested. Mean walking speed was lower for the PFP group than for the comparison group when averaged across all conditions
(P<.001). FR=free walking, FT=fast walking, AS=ascending stairs, DS=descending stairs, AR=ascending ramps, DR=descending ramps.
P<.001) (Fig. 2). The average stride length of the PFP Joint Motion
group across all conditions was 88% of the average stride There was a significant group effect and a significant
length of the comparison group (1.22 m versus 1.38 m, interaction for ankle joint motion during the terminal
P<.001) (Fig. 3). Cadence of the PFP group was 91% of stance phase of gait. When conditions were analyzed
that of the comparison group when averaged across all separately between the two groups, the PFP group
conditions (114.1 steps/min versus 125.2 steps/min, demonstrated greater ankle dorsiflexion compared with
P<.001) (Fig. 4). There were n o differences between the other group for fast walking (9.9" versus 7.0".
groups for time spent in single-limb support, double- P<.05), descending stairs (27.6" versus 18.g0,P<.001),
limb support, swing, and stance. and descending ramps (15.8" versus 1l.gO,P<.01) (Fig.
5 ) . No other differences for ankle motion were found.
Of the three variables measured (pain, torque, and FAQ There were n o differences in knee motion between
score), knee extensor torque was the only predictor of groups for any phase of the gait cycle, regardless of the
speed, with higher torque values being associated with condition (Fig. 6 ) . Similarly, hip joint motion was not
higher walking speeds. This association was evident for different between groups, regardless of the condition,
five of the six conditions (free walking: r=.59, P<.05; for any phase of the gait cycle (Fig. 7).
fast walking: r =.59, P<.05; ascending stairs: r z.50,
P<.05; ascending ramps: r = .62, P<.05; descending Pain, quadriceps femoris muscle torque, and FAQ score
ramps: r=.67, P<.05) (Tab. 4). Knee extensor torque were not predictors of the amount of knee flexion
also was the only predictor of stride length for four of during loading response. This finding was consistent for
the six conditions (free walking: r=.73, PC.05; fast all conditions tested.
walking: r = .61, P<.05; ascending ramps: r = .62, P< .05;
descending ramps: r =.76, P < . 0 5 ) (Tab. 4). No other Discussion
associations were found between any of the three vari- We found a decrease in knee extensor torque in the PFP
ables and the remaining stride characteristics. group (77% of the knee extension torque of the com-
1068 . Powers et al Physical Therapy. Volume 77 . Number 10 . October 1997

7. 1.8
1.6
1.4
.
g 1.2
5
P
a
1.0
$ 0.8
.-
'L
0.6
0.
84
0.2
0.0
FR FT AR DR
Condition
Comparison PFP Group
Group
Figure 3.
Mean stride length for subiects with patellofemoral pain (PFP group, n= 19) and subiects without patellofemoral pain (comparison group, n= 19) for
level walk.ing and ramp walking conditions (stairclimbing data omitted due to the limitations imposed as a result of the fixed stair height and depth).
Mean stride length was lower for the PFP group than for the comparison group when averaged across all conditions (P<.001). FR=free walking,
FT=fast walking, AR=ascending ramps, DR=descending ramps.
parison group), as well as an average pain score of 4.4 we did not assess swelling, we cannot determine whether
out of a possible 10 during testing. These associated this really occurred. None of the subjects with PEP,
findings suggest that pain may have played a role in however, demonstrated gross joint effusion.
reducing quadriceps femoris muscle torque. When pain
was correlated with knee extensor torque, however, this An alternative explanation for the lack of a correlation
inference did not hold true. These two variables between pain and quadriceps femoris muscle torque
appeared to be completely independent of one another could be related to the testing position used to elicit
(r=.03). This finding would imply that knee extensor knee pain. Our procedure assessed the maximum iso-
torque was not affected by pain, which is consistent with metric knee extension torque at 60 degrees of flexion,
the observations of Stratford" and Young et al." which placed the quadriceps femoris muscle at its great-
est length-tension advantage2" but may have been inad-
The lack of an association between knee extensor torque equate in reproducing the amount of patellar pain that
and pain may have been related to numerous factors. would inhibit normal function. Although the high quad-
For example, patients dealing with persistent pain might riceps femoris muscle forces produced at this knee
tend to protect themselves during an activity in which flexion angle also would have resulted in substantial
they would expect to experience pain. Possibly, in order patellofemoral joint reaction forces,'"he modest pain
to avoid pain, patients would not produce a maximum scores reported by our subjects suggest that this com-
torque value that truly reflects their strength. This pression was reasonably tolerated. These relatively low
concept is supported by the fact that 5 of the 19 subjects hain scores may have bken the result of the increase in
with PEP reported little or no pain during the maximal contact surface area between the patella and femur,
isometric quadriceps femoris muscle test. Furthermore, which has been reported by Mathews and colleagues" to
inhibition of quadriceps femoris muscle activity as a be approximately 40% more at 60 degrees of knee
result c~feffusion also could have contributed to the flexion as compared with 15 degrees of flexion.
reduction in quadriceps femoris muscle torque. Because Increased contact area would have reduced the joint
Physical Therapy . Volume 77 . Number 10 . October 1997 Powers et al . 1069

8. 160.0
140.0
120.0
h
.-
c
<
V)
P
100.0
a,
+
80.0
a,
0
C
a, 60.0
3
0
40.0
20.0
0.0
FR FT AR DR
Condition
pFp Group
Group
Figure 4.
Mean cadence for subjects with patellofemoral pain (PFP group, n= 19) and subiects without patellofemoral pain (comparison group, n= 19) for level
walking and ramp walking conditions (stair-climbingdata omitted due to the limitations imposed as a result of the fixed stair height and depth). Mean
cadence was lower for the P P group than for the comparison group when averaged across all conditions (P<.001). FR=free walking, FT=fast
F
walking, AR=ascending ramps, DR=descending ramps.
contact pressure, as the joint forces would have been Table 4-
Stepwise Regression Results for Predicting Walking Speed, Stride
distributed over a greater area. In addition, because PFP Length, and Cadence
has been linked to patellar s ~ b l u x a t i o n * ~ because
and
patellar subluxation has been shown radiographically to
Stride Independent Variable
occur at angles of less than S degrees of knee flexion,?"
O Conditiona Characteristic (Predictor) r"
it is possible that testing the subjects with the knee less
flexed (ie, 0"-SO0) would have yielded greater pain FR Walking speed Knee extension torque .59
FT Walking speed Knee extension torque .59
scores. This position, however, would have placed the
AS Walking speed Knee extension torque .50
quadriceps femoris muscle at a mechanical disadvan- DS Walking speed None
tage" and therefore would have resulted in lower torque AR Walking speed Knee extension torque .62
values. Given this paradox between testing position and DR Walking speed Knee extension torque .67
the pain-torque relationship, as well as the need to assess FR Stride length Knee extension torque .73
FT Stride length Knee extension torque .6 1
both variables simultaneously for correlation purposes, AR Stride length Knee extension torque .62
we believe that it is not surprising that no relationship AR Stride length Knee extension torque .76
was found. FR Cadence None
FT Cadence None
An inverse linear association was found between pain AR Cadence None
DR Cadence None
and the FAQ score, indicating that the FAQ may be
sensitive to individual pain levels. The fact that many of " FR=t~ee walk~ng,FT=fayt ~ a l k l n g AS=asrendrng talrs, DS=descendlng
,
stairs, AR=ascending ramps, DK=descrnding ramps. Stride lerlgth and
the FAQ questions related to the reproduction of symp-
cadrnre for ascending and descending staira omitted due to the linritations
toms may explain the correlation between these two the fixed stair u
and deDth,
scores. Care must be taken in interpreting these results, "AH rzalues significant at the P<.05 level. Ellipsis ind~catesnot applicable.
however, as we did not assess pain during functional
activities. Whether the pain associated with the maximal
isometric quadriceps femoris muscle contraction has a
1070 . Powers et a1 Physical Therapy . Volume 7 7 . Number 10 . October 1997

9. 30-
I -30-
I
20-
I I
-ao--
I I
-C
10- I
.-
-a~-- a~--
I
I .
-30- I 30 I I I : I : ; : ; ; 1
o 10 ao 30 40 so eo 70 ao eo loo o 10 ao so ro so so 70 no ao loo
%GaitCycle %GaitCycle
FR FT*
+
30- I I
I
-
- 10--
I
I
5
.-
+
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-w
10.-
0.-
I
I
c
C
+
.-
0
r"
1
l I
I
I
l i
w
-
Y
2 -10.-
I
I <
Y
-10.-
I
I
I -ao- I
-ao--
I I
-
o
3 0
10
7
ao
:
so
:
ro
II
so
I :
eo
:
70
I
ao
I I
eo
I
loo
-307
o
I
10
;
ao
;
so
: I :
ro ao ao 70
I
eo
;
oo
,
loo
%GaitCycle %GaitCycle
AS DS*
30- 30-
I I
I I
ao--
I 20.- I
-
A
C C
0
.- 0
.- lo--
+
r"
w
-
< -10-
-ao--
- a O ? I :
I ,I
I ,
; ,
, ,
,
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o 10 ao so ro so so 70 ao a0 loo o 10 ao so ro so so 70 ao ao loo
%GaitCycle %GaitCycle
AR DR*
Fi ure 5.
A J l e motion for subiects with patellofemoral pain (light line, n= 191 and subjects without patellofemoral pain (dark line, n= 191 for all conditions
tested. Dotted vertical line delineates the division between stance and swing . phases (62% of the gait cycle). Dashed vertical line indicates terminal
-
stance. Asterisk (*] indicates the mean ankle dorsiflexion during terminal stance was greater in thebatellofemoral pain group than in the comparison
group ( P <.05). FR=free walking, FT=fast walking, AS=ascending stairs, DS=descending stairs, ARbascending ramps, DR=descending ramps.
Physical Therapy . Volume 77 . Number 10 . October 1997 Powers et al . 107 1

10. 80- so-
8.
0- 8.
0.
-
-
70--
- 70-
C
80-
- 8.
0-
0 so-- g
.- so--
30-
-107 I
o 10 ao no 40 so eo 70 so so loo o 10 ao 30 40 so eo 70 ao eo loo
%Gait
Cycle %GaitCycle
FR FT
so-
8.
0-
7.
0-
-
- 60-
07
o 10 ao ao ro no eo 70 so eo loo o 10 ao ao 40 so eo 70 eo so loo
%GaitCycle %GaitCycle
AS DS
807 so-
8.
0.
80-
-
"
-
70-
6.
0-
-
o
7.
0-
80-
C
O
.- 60--
3-'
0
2 4w-
a,
a, 30--
5
-107 I
o 10 ao 30 ro so eo 70 eo so loo o 10 ao ao ro so eo 70 ao eo loo
%GaitCycle %GaitCycle
AR DR
Figure 6.
Knee motion for subjects with patellofemoral pain (light line, n= 191 and subjects without patellofemoral pain (dark line, n= 19) for all conditions
tested. Dotted vertical line delineates the division between stance and swing phases (62% of the gait cycle). Dashed vertical line indicates terminal
stance. FR=free walking, FT=fast walking, AS=ascending stairs, DS=descending stairs, AR=ascending ramps, DR=descending ramps.
1072 . Powers et al Physical Therapy . Volume 77 . Number 10 . October 1997

11. 80
eO1
601-
-
-
60
40
6
+
30
5 ao
p 10
0
-10
-ao
o 10 ao 30 40 so so 70 eo eo loo o 10 ao 30 40 60 so 70 80 90 100
% Gaitcycle %GaitCycle
FR FT
10-
Ot I I
o 10 ao 30 40 so eo 70 so eo loo o
% Gait Cycle %GaitCycle
AS DS
60-
-
-
8.
0-
40.-
C
: : : : 1
$
a
I lo-
0-
.
-107
o 10 ao 30 40 so eo 70 so eo loo o 10 ao 30 40 so eo 70 eo eo loo
%GaitCycle %Gait
Cycle
7
AR DR
Figure 7.
Hip motion for subiects with patellofemoral pain (light line, n= 19) and subiects without patellofemoral pain (dark line, n= 19) for all conditions tested.
Dotted vertical line delineates the division between stance and swing .phases (62% of the gait cycle). Dashed vertical line indicates terminal stance.
- - .
FR=free -walking, FT=fast walking, AS=ascending stairs, DS=descending stairs, AR=ascending ramps, DR=descending ramps
Physical 'Therapy . Volume 77 . Number 10. October 1997 Powers et al . 1073

12. relationship to the pain that may be present during gait be related to the higher quadriceps femoris muscle
is not known at this time and is a limitation that should demand associated with accelerated speed.
be addressed in f~iturestudies. The lack of an association
between quadriceps femoris muscle torque and the FAQ The reduction in gait speed in the PFP group was a
score was not surprising t->ecausemost of the possible function of reduced stride length and cadence, both of
responses to items in the questionnaire pertained pri- which were less in the PFP group than in the comparison
marily to pain during functional activities. group in all conditions. The tendency toward decreased
terminal swing hip flexion in the PFP group contributed
We did not find a reduction in knee flexion during the to this decreased stride length by limiting the forward
loading response in the PFP group, indicating that these position of the limb at initial contact. As with walking
subjects [lid not alter the normal knee joint kinematics speed, quadriceps femoris muscle torque was the only
during early stance. This finding is contrary to the predictor of stride length in four of the six conditions
collcl~~sions Dillon and colleagues,who reported that
of tested. further supporting the relationship between
subjects with PFP reduce knee flexion during the stance qriadriceps femoris muscle torque and stride variables.
phase to minimile the patellofemoral joint reaction
force. Our kinematic data indicate that this gait adapta- Conclusion
tion cannot be grneralized to persons with PFP. Our The results of our study have potential clinical implica-
findings also suggest that quadriceps femoris muscle tions. Conservative care for individuals with PFP typically
.-
torque in the PFP group, although reduced, was capable involves both pain management and strengthening of
of providing stability during this phase of the gait cycle. the extensor rnechai~ism.~~~J"he fact that greater iso-
metric quadriceps femoris muscle torque was associated
The primary gait adaptation in the PFP group was a with increased walking speed and stride length suggests
reduction in walking speed, which was consistent across that strength of this muscle group may be an important
all conditions. The greatest differences between groups factor in deterrnini~rgthe gait characteristics of persons
occurred during the more vigorous tasks of fast walking with PFP. Quadriceps femoris muscle strengthening,
and ascending ramps, which suggests that the higher- therefore, lnay be useful for improving functional ability,
demand activities required greater speed attenuation. a clinical practice already used for persons with PFP.
Winter"' has demonstrated that a slower gait speed Qiiadriceps femoris muscle strengthening may be par-
reducrs the demand of the quadriceps fenloris muscle ticularly important for individuals who want to return to
during initial stance by decreasing the flexion moment. higher-demand activities such as running o r other ath-
The reduction of the knee flexion Inornent during letic activities.
slower walking is most likely the result of the reduced
vertical component of the ground reaction force, which References
is the predominant external force contributing to the Thclrofarr, Nl:
1 Perry J. Gail Anoly.ci.5: Normol and Pol/~olo~irc~lFunt.lion.
Slack Inc; 1992.
knee flexion moment. T h r influence of walking speed
on the magnitude of the vertical ground reaction force 2 Kadaha hlP. Kamakrislinan HK. Wootrn ME. et al. Repeatability (11'
has been demonstrated by Powers e t who found a hincm;ltic, kinetic, a n d elcctromyog~.aphicdata ill normal adult p i t .
linear relationship between these two variables. There-
,I Orll~opRrc.1989;7:8414-860.
fore, a decrease in walking speed could allow for a 3 Hsu A, Perry J , (;ronley JK, Hislop HJ. Q~ladl.iceps force and
mvoelectric activity during flexed k n r e stance. Clir~Ortho/). 1993;288:
reduction of muscular demand, without a compromise
254-262.
in knee kinematics, and is concordant with previous
findings of decreased electroinyographic activity of the 4 Fox TA. Dvsplasia of ttie quadriceps ~liechanism:hvpoplasia of the
vastus ~nedialis muscle as related to llle hypernlobile patella syndrome.
vastus muscles of subjects with PFP.2n
Surg Clin .Vorlh Am. 1975;55:199-226.
5 Dillon PZ, Updyke U'F, Allen WC. Gait analvsis w i ~ hI-efcrence to
Althongh it would appear that persons with PFP inay
patellae. J Orthop Sporl.s I>hy.s Thpr. 1983;5:127-131.
cho~itiromalacia
adopt a slower gait speed as a possible way of reducing
the patellofemoral joint reaction force, there was no 6 Herchuck M, A~ildriacchi Bach RR, Rcider B. Gait adaptations hy
TP,
paticrits who have a deficient antel-ior crnciate ligament. J Bor~~,Jcrinl
relationship hetuleen the amount of knee pain and S11rg A M . 1990;72:871-877.
walking speed for any of the conditions. There was a
7 Fulkrrson ,JP. I-Iuligerford DS. I l i ~ o r d m f the Pnt~llofrrnorol
o Joint. 2nd
relationship, however, between quadriceps femoris mris-
Mtl: Willhms & UTilkills; 1990.
c d . Bal~iniore,
cle torque and walking speed for five of the six condi-
tions (descending stairs excepted), with increased quad- 8 Halhrecht,1L..Jackso11DW. Acute dislocation OF the patella. In: Fox
JM, Dcl Pizzo W, cds. 7'hr Polellofumorrrl,/ojnl. Nrw York, NY: MrGraw-
riceps femoris muscle torques resulting in faster walking l-lill luc; 1093:123-134.
speeds. This association suggests that persons with
,9 (;yo17 AN, C:liac~Em, Staulfer RN. Functional evaluatiori of normal
greater levels of quadriceps femoris muscle torque tend
a n d pa~hologicalknees during gait. Arrh P11ysiZf~d
Kuliobil. 197&57:571-
to demorlstrate greater ainbrllation speeds, which may 577.
1074 . Powers et a1 Physical Therapy . Volume 7 7 . Number 1 0 . October 1997

13. 10 Stal~ttcl-KN, C:hao ETi, C;yory AN. Biornechar~iralg a i ~ analysis of 20 Licb KJ, Perry,]. Q~ladricrps Iltnrtion: a n elrrtron~yographic study
the tliseased k n r r ,joint. Clin Orllroj~.1977; 1 2fi:24fi-2i5. under isonretric rontlitions.,] U o n ~ j o i r t SIITXAni. 197l;.i3:749-7.511.
t
11 Kettlek~mp DB, Lravei-ton PE, Misol S. Ciait rhar;tcteristics of thc 21 Winter DA. Hiorn,rchnnic.r rrnd ~LJolur New
(;wn/lol f f H u m n n .Llo7~rrn~nl.
rheumatoial knee. A~.rliStrrg. 1972;104:~ZO-34. Kirk, NY John Wiley & Sons Inc; 1990.
12 Stratford PW. Electromyography of the qu;tdriccps finloris muscle 22 Maquet PC;. Biome~;/trrni[.r thr Knrt. 2nd ed. Ncw York, NY
uj'
in sut?jects with rlornmal knees iultl acutely effi~sedknees. P11ys 7%rr: Springer-Vrrlag New %I-k lnc; 1984.
1981;ti?:27<)-2113.
23 Mathews LS, Sonstrgard DA, Henke JA. Load-braring characteris-
13 Stokes M, Young A. Investigations of quadricrps inhihition: impli- tics of the patellofcnloral j o i ~ ~Actcr Orlhop .Sr.nnd. 1977;48:511-516.
t.
cations for rlinical pl-artice. Plrysiothcrclpy. 1984;70:425-428.
24 Heyvood WB. Rerurrcnt tlisloratiot~ the patella.,] Llonrjoit~l.Surg
of
14 hlcCor~nell,J. T h e management of chorrcl~~on~alacia patellae: a Rr. 19(il;43:50H-5 17.
long-term sl~lution.
Austrtllianjo~~rrrnl I'l~y,io/hrrcrpy.1986;32:2 1.5-223.
of
25 Brossmann J, Muhle C:, Schrotler C. e t al. Patellal- trarking pattcl-ns
15 dr.4ndr;rtlc JR, Grant (;, Dixon '4. Joint diste~lsiorl
and reflex muscle during active and passibe kner extension: cvaluatior~ with motion-
inhibition in the kner. J Ronpjoinl S u ~ g Am. 19fi5;47:313-322. triggered cine MR inlaging. Kndiolo~g.19!)3;1 X7:20.5-212.
16 Spencer JI); Hayes KC, ..lexander 1J. I 1 c . r ,joint cffrlsion and 26 Wintel- DA. Kinematic and kinetic patterns in human gait: variabil-
q11ac11-ireps
I-eflcx inl~ibition man. Arth P1~y.r,/lrd Kr~hfibil.l!lX4;f;.5:
in ity a n d roinpensatiug effrcts. Hrtmcirt Mo71ernrlrl Sciunct. 1984;3:51-76.
171-1 77.
27 Powers CM, Rao S, Pel-ryJ. Loading charactrristics ill s~~t?jects
with
17 Young A, Stokes M, Shakrspeal-e DT, Sherman Kt'. T h r effect of patellofcmol-al pain. (;nit nrtd IJo.rturr. 1905;3:84. Abstrart.
intl-a-artic1.1lar bupivicaine orr quadriceps inhihition after rnerliscec-
28 Powel-s CM. Landel R, Perry J. Tirning ant1 ~ntrnsity v;latus ln~rsclr
of
tomy. ,Vfr~o' Sport.r Exrrr. 1983;1.5:1.54. Abstract.
Sri
activity during functional activities irr subjerts with aud witho~ltpatcl-
18 (:hesworth BM, C u l h a ~ n EG, Tala GE, Peat M. Valiclatio~~ of lofemoral pain. 1'hy.r 7 7 1 ~ 19!9fi;76:946-955.
~.
outcome measures in patier~ts with patcllofrmoral syndi-ome.,/ Or.thol,
S/~mt.r h y 7%rr. 1989; 10:30?-308.
P
19 Krljala IJM, Jaakkola LH, Koskiner~ SK, et nl. Sroring of pitccl-
lofmmral disorders. ,]o~rrr~nl Artl~ro.m~py Rr.lntr(l .Xurqrry. 1993:9:
oj' find
1.59-163.
Invited Commentary
I appreciate having the opportunity to comment on this motion in response to PFP. Bioniechanical models also
interesting and clinically relevant article. Understanding predict increased patellofemoral contact forces, with
the manner in which patients alter their mechanics as a increasing knee flexion and quadriceps femoris muscle
result of either pain or weakness is important for both force.':-' Therefore, as noted by Powers e t al, decreased
researchers and clinicians. Clinicians gain insight into knee flexion during the loading phase of gait activities
potential problenis that could develop as a result of the appears to be a logical compensatory mechanism for
compensatory pattern and can then integrate preventa- persons with PFP and was the premise of this study.
tive strategies into their treatment regimens. Research-
ers gain a greater understanding about the mechanisxns The purpose of the investigation was to determine the
behind these altered movement patterns. influence of the quadriceps femoris muscle torqne and
PFP on the amount of knee flexion during the loading
I conlrrlend the authors for undertaking a study of this response during a variety of locomotor activities. The
nature, because the manner in which pa~ientscompen- authors hypothesized that pain and weakness would be
sate for injuries is still not vely well understood. In associated with decreased gait function. What they
addition, patellofemoral pain (PFP) is enigmatic and found, however, was that neither measure predicted the
difficult to study, presenting an even greater challenge. amount of knee flexion during the loading response of
Patellofemoral joint ~llotion does not lend itself well to the locornotor activities tested. Although the authors
standard motion analysis techniques, necessitating more offered some explanation for these findings, other fac-
invasive p r ~ c e d u r e s . ~ It is a logical assumption, how-
.' tors might also be considered.
ever, that PFP will indirectly lead to abnormalities in
tibiofeinoral joint motion, which is easier to measure. A critical component of the study of compensatory
This assumption is supported by the fact that many of us, patterns is the reproduction of the conditions that are
as clinicians, have seen patients alter their knee joint hypothesized to lead to the alterations. Among the
Physical Therapy. Volume 77 . Number 10 . October 1997 McClay . 1075