ELSEVIER
Journal of
Ort hopaed ic
Research
Journal of Orthopaedic Research 23 (2005) 1083-1090
www.elsevier.com/locate/orthres
Altered loading during walking and sit-to-stand is affected
by quadriceps weakness after total knee arthroplasty
Ryan L. Mizner, Lynn Snyder-Mackler *
Department of Physical Therapy. University of Delaware, 301 McKinly Laboratory, Newark, DE 19716, United States
Accepted 28 January 2005
Abstract
Purpose: Total knee arthroplasty (TKA) successfully reduces pain, but has not achieved comparable improvements in function.
We hypothesized that quadriceps strength affects performance by altering loading and movement patterns during functional tasks.
Methods: Fourteen subjects with isolated, unilateral TKA were tested three months after surgery. Quadriceps strength was
assessed isometrically and kinematics, kinetics, and EMG were collected during level walking and sit-to-stand (STS). Function
was assessed using the timed up and go test (TUG), stair climbing test (SCT), and the 6 min walk test (6MW).
Results: Functional performance was significantly related to the quadriceps strength of both legs, but was more strongly related
to the uninvolved strength (involved rho = -0.43 with TUG; -0.65 with SCT; 0.64 with 6MW) (uninvolved rho = -0.63 with TUG;
-0.68 with SCT; 0.77 with 6MW). During STS, subjects shifted weight away from the operated limb (p < 0.01). Quadriceps muscle
activity and the extension moments at the knee and hip were smaller in the involved compared to the uninvolved (p < 0.05). The
amount of asymmetry in knee excursion during weight acceptance in gait, the asymmetry in weight bearing from sit-to-stand,
and the uninvolved hip extension moment during STS were related to the amount of asymmetry in quadriceps strength
(rho > 0.56, p < 0.05).
Conclusions: Quadriceps weakness in patients with TKA has a substantial impact on the movement patterns and performance of
the knee during functionally important tasks.
0 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.
Keywords: Total knee replacement; Muscle; Compensation; Strength; Function
Introduction
Total knee arthroplasty (TKA) is one of the most
common knee surgeries performed in the United States
with an incidence (300,000 per year) greater than twice
the incidence of anterior cruciate ligament reconstruction [I]. TKA reliably reduces knee pain [10,16], but
has not been shown to lead to comparable improvements
in functional performance. Reductions of about 20% in
walking speed and 50% in stair climbing speed com-
Correspondingauthor. Tel.: +1 302 831 3613; fax: + I 302 831 4234.
E-mail address: smack@udel.edu(L. Snyder-Mackler).
pared to age-matched groups without knee pathology
have been reported a year after surgery [32].
Patients with TKA exhibit qualitative and quantitative deficits in functional tasks. Shortened stride length
and limited knee excursion during weight acceptance is
a common finding after TKA [3,4,6,7,11,17,33].Patients
with TKA rise from a chair more slowly than control
groups and use higher hip and knee moments in the
uninvolved leg compared to the involved leg to stand
[31]. The involved knee and hip joints also perform proportionally less work than the uninvolved while negotiating a curb [5]. Even patients considered to be fully
rehabilitated with excellent self-assessment scores have
smaller sagittal plane knee ranges of motion, angular
0736-0266/%- see front matter 0 2005 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.orthres.2005.OI.O21
1084
R. L. Mizner. L. Snyder-Muckler I Journal of' Ortliopaedic Research 23 (2005) 1083-1090
velocities, and maximum knee moments in the operated
limb during loaded knee extension than control subjects
during stair climbing and chair transfers [14,33].
The cause of persistent disability and aberrant movement patterns in individuals who have undergone TKA
is unclear, but quadriceps weakness is a likely contributor. Quadriceps weakness is a common and persistent
impairment after TKA and has been correlated with
poor functional performance in older adults [8,23].
Weakness is often pronounced even years after knee
replacement surgery with deficits ranging from 30% to
40%0when compared to age-matched comparison groups
[3,11,20,25,32]. Impaired quadriceps strength would appear to be a prime factor to consider when examining
disability after TKA.
The impact of strength on function and movement
patterns has gone unexamined in patients with TKA.
Several investigations have suggested that movement
strategies used during functional tasks are due to quadriceps weakness, but they stop short of measuring this
impairment [5,14,31]. To date, only three studies have
included quadriceps strength assessment in conjunction
with a motion analysis assessment for patients with
TKA [4,29,33], but they did not report the relationship
between quadriceps weakness and altered movement
patterns.
The purpose of this investigation was to determine the
relationship between quadriceps weakness and function
after TKA when patients are discharged from outpatient
rehabilitation. We hypothesized that ( 1) quadriceps muscle strength (peak torque) will show a (high) positive correlation with functional outcomes measures, (2) knee
flexion at heel strike in gait would be higher and knee
excursion during weight acceptance would be less in
the involved leg compared to the uninvolved, (3) knee
moments will be lower in the involved compared to the
uninvolved leg during the weight acceptance phase of
gait and sit-to-stand (STS) and hip moments will be lower in the involved lower extremity compared to the uninvolved during sit-to-stand, and (4) the amount of
symmetry between legs in quadriceps strength will be
strongly and positively correlated with the amount of
symmetry in knee flexion during weight acceptance in
gait, symmetry in vertical ground reaction force in standing, and the distribution of lower extremity extension
moments in standing.
Methods
Subjects
The study included fourteen subjects (9 men, 5 women) who had
undergone TKA for osteoarthritis three months prior to testing (Table
I). Patients were referred by a group of local orthopedic surgeons who
performed tricompartmental, cemented total knee arthropkasty with a
medial parapatellar surgical appmach. Subjects were excluded from
the study if they had uncontrolled blood pressure, diabetes mellitus,
neoplasms, neurological disorders, or a body mass index (weight in
kg/(height in m)') of greater than 40 (morbidly obese). In addition,
subjects were excluded if they required an assistive device to walk or
if they could not stand from a chair independently without the use
of arm rests. The uninvolved leg was required to be asymptomatic
and the operated leg could have no more than a 5" flexion contracture
and an active flexion range of motion greater than 100".
All subjects underwent three days of inpatient physical therapy followed by two to three weeks of home physical therapy visits. Subjects
received six weeks (2-3 tirneslweek, mean = 17 visits) of outpatient
physical therapy. Physical therapy included interventions designed
to control pain and swelling, and improve knee range of motion,
muscle strength and functional ability [19]. Motion analysis testing
Table 1
Subiect descriDtions
~
X
~~
SD
7
11.7
Ranee
53-74
7 1.7- 109.8
1.57-1.85
22.4-37.5
Age (Y)
Weight (kg)
Height (m)
BMI (kg/m2)
62
89.6
1.74
29.7
Time to stand (s)
Gait speed ( d s )
TUG (s)
SCT (s)
6MW (m)
1.94
1.34
7.31
11.34
590
I .30
3.04
I13
I .55-2.53
1.15-1.57
5.32-9.32
7.20-15.43
40 1-8 18
Ext ROM (deg) Involved
Flex ROM (deg) Involved
Ext ROM (deg) Uninvolved
Flex ROM (deg) Uninvolved
Involved quadriceps NMVIC ( N d B M I )
Uninvolved quadriceps NMVIC ( N d B M I )
Quadriceps index (QI)
0.8
117
0.4 hyper
130
5.73
8.83
65%
2.2
10.2
4.2
8.47
2.55
3.12
14'X)
2 hyper-5
105-132
7 hyper-I0
114-147
2.65-1 1.56
3.94-1 6.92
40- 89'%1
0.10
3.6
0.24
0.1 1
BMI = body mass index, ROM = range of motion, NMVIC = normalized maximal voluntary isometric contraction, Quadriceps Index (QI) = peak
torque of involved quadricepdpeak torque of uninvolved quadriceps, N = newtons, m = meters, deg = degrees, s = seconds. Gait speed refers to the
speed during the motion analysis collection.
R. L. Mizner, L. Snyder-Muckler 1 Journul i ~ Orthopuedic
f
Research 23 (2005) 1083-1090
was performed within a week of strength testing. The Human Subjects
Review Board of the University of Delaware approved the study and
all subjects gave written informed consent.
Functionul testing
Measures of functional performance included the timed up and go
(TUG) test, a stair climbing test (SCT), and the 6-min walk (6MW)
test. The TUG measures the time it takes a patient to rise from an
armed chair (seat height of 46 cm), walk 3 m, turn and return to sitting
in the same chair [28]. Subjects were asked to walk as quickly as they
felt safe and comfortable. The subject was allowed to use the arms of
the chair to stand up and sit down. The SCT measures the time it takes
a subject to ascend and descend a flight of twelve, seven inch high steps
with a depth of eleven inches. Subjects were asked to complete the test
as quickly as they felt safe and comfortable and one handrail was allowed if required. For both the TUG and SCT, one practice test was
performed and the average of two subsequent tests was used for analysis. For the 6MW test, subjects were asked to cover as much distance
as possible in 6 min while walking laps 516 ft long in a 10 ft wide tiled
hallway. Feedback on the time remaining for the test was given at two,
four and five in minutes into the 6 min test. Assistive devices were not
used to complete all tests and all subjects used a foot over foot technique to go up and down the stairs.
Quudriceps strength testing
Maximal voluntary isometric contraction (MVIC) of the quadriceps femoris was assessed with a burst superimposition technique
[30]. In brief, subjects were seated in an electromechanical dynamometer (Kin-Com 500 H, Kin Com, Chattecx Corporation, Harrison,
Tennessee) with the hip flexed to 90" and the knee flexed to 75". Subjects performed two submaximal contractions and one maximal isometric contraction of 2-3 s in duration to familiarize the patient with
the testing method.
After 5 min of rest, subjects were instructed to maximally contract
the quadriceps for a contraction lasting approximately 3 s. Verbal
encouragement and visual output of their force was used to provide
feedback to help facilitate the highest force possible. Approximately
2 s into the contraction, the stimulator (Grass S8800 stimulator with
a Grass model SIU8T stimulus isolation unit, Grass Instruments,
Braintree, Massachusetts), delivered a supramaximal electrical stimulus to the quadriceps muscle. If maximum volitional force output
was achieved and no augmentation of force was observed due to the
stimulation (i.e. optimal recruitment) then the testing session was concluded for that limb. If augmentation was present during the application of the electrical stimulus, the test was repeated. Five minutes of
rest was provided between test contractions. A maximum of three trials
were recorded. The highest volitional torque achieved during the three
attempts was used for analysis. Burst superimposition testing was performed on uninvolved limb first and then the operated leg. The burst
superimposition technique has been shown to be highly reliable in subjects without knee pathology, with repeated testing that demonstrated
an intraclass correlation coefficient of 0.98 [27].
1085
version 3.7 build 074, Oxford Metrics, London, England). Two force
plates (Bertec Corp, Worthington, OH) were positioned in the floor
to capture two successive steps during walking and to assess the
ground reaction forces for each leg during sit-to-stand transfers. Force
plate data were acquired at 1080 Hz and kinematic data were sampled
at 120 Hz. Retro reflective anatomical markers (25 mm in diameter)
were placed bilaterally on the head of the fifth metatarsal, lateral malleolus, lateral femoral condyle, greater trochanter, iliac crest, acromioclavicular joints, and centrally on the 7th cervical vertebrae. Rigid,
thermoplastic shells with four markers a f i e d to their surfaces were attached bilaterally to the lower leg and thigh using elastic wraps (SuperWrapTM,Fabrifoam, Inc. Exton, PA) to minimize movement artifact.
Another four-marker shell used to track the trunk was affixed to the
skin midline at approximately the level of the 8th thoracic vertebrae
through the use of double sided tape. A shell with a triad of markers
was placed over the sacrum to track the motion of the pelvis. Two
markers were placed on the heel counter of the shoe and with the marker on the 5th metatarsal provide a triad of markers to track the three
dimensional movement of the foot. Each body segment was assumed
to be rigid.
A standing calibration was performed prior to the walking trials
and the sit-to-stand trials to identify joint centers with respect to each
segments coordinate system. Prior to STS collections, subjects were
positioned in the center of the calibrated volume on an armless and
backless chair with their trunk oriented vertically. The height of the
chair was set to the height of the subject's knee joint line. The subjects
were asked to hold the arms across the chest to standardize arm position and prevent the upper extremities from blocking markers during
the collection. The subject was positioned on the chair so that the feet
were shoulder width apart and a long-arm goniometer was used to
place the knees in 90" of flexion. The subject's position on the seat
and floor was marked with chalk to allow for consistent reproduction
for each trial. The subjects stood from the chair at a self-selected pace.
One practice trial was used to confirm understanding of verbal instructions and the mean of five trials were used for analysis.
Upon the completion of the STS collections, the subjects practiced
walking trials until they walked at a consistent self-selected walking
pace. Gait trials were continuously collected until the subject had 10
trials with only one foot on each force plate and speed was maintained
within 5% of practice speed.
Electromyography
Electromyography (EMG) was recorded at 1080Hz with a 16channel system (Motion Lab Systems, Baton Rouge, LA) interfaced
with the VICON 512 workstation (Vicon, Oxford Metrics, London,
UK) for simultaneous recording. Active surface electrodes were taped
over the mid-muscle belly of the vastus lateralis, biceps femoris, the
anterior tibialis, the medial head of the gastrocnemius, the soleus. Elastic bands (SuperWrapTM,Fabrifoam, Inc., Exton, PA) were wrapped
over the electrodes to minimize movement on the skin. The subject
was positioned on a padded plinth in order to isometrically test the
quadriceps, hamstrings, gastrocnemius, anterior tibialis [I 51 for verification of electrode placement and for normalization. Maximal soleus
activity was tested in a seated position with the knees flexed.
Pain measurement
Data management and analysis
A numeric rating scale was used to quantify knee pain during the
MVIC and the motion analysis collection. Subjects were asked to verbally rate knee pain during the contraction on a scale from zero to ten
where zero represented no pain and ten represented the worst pain
imaginable. Numeric rating scales were appropriate for repetitive knee
pain assessments in this study as they can be completed quickly and
easily and have demonstrated good reliability in arthritic populations
[91.
The torque produced during strength assessment was normalized to
body mass index. A quadriceps index (QI) was determined to give a relative measure of strength and as a measure of symmetry in quadriceps
force production between limbs (quadriceps index (QI) = involved torqueluninvolved torque * loo'%).
Marker trajectories from the motion analysis collection were low
pass filtered at 6 Hz and force plate data was low passed filtered at
40 Hz [2] with a recursive fourth order Butterworth digital filter. Sagittal plane hip, knee and ankle joint angles were calculated using rigid
body analysis (Visual3D, Version 2.84, C-Motion, Inc., Rockville,
MD). Joint kinetics were calculated using inverse dynamics, and are
expressed as net internal moments normalized to body mass and
height. In walking, each trial's stance time was normalized to loo%,
of weight acceptance defined as the time from heel strike to peak knee
flexion. In STS, each trial's standing time was normalized from the
Motion analysis
Motion analysis testing of walking and a sit-to-stand (STS) task
was performed using a three dimensional, six camera motion analysis
system (VICON 512, MCam cameras, Workstation 512 with software
1086
R L . M i x e r , L. Snyder-Muckler I Journal of Orthopaedic Research 23 (2005) 1083-1090
start of standing (defined as the initiation of hip flexion) to the end of
stand (defined as when hip angular velocity reached zero). Trials within
a testing session were averaged to obtain a mean for each subject.
The signal for the EMG data was pre-amplified at the skin and then
band pass filtered from 20 to 1000 Hz with mechanical filters prior to
sampling at 1080 Hz. Visual 3D software was used to digitally filter the
signals with a low pass filter at 350 Hz. Following full wave rectification, a linear envelope of the signal was created using a phase corrected
filter with a low pass cutoff frequency of 20 Hz. This linear envelope
was normalized to the maximum signal obtained during the MVIC trials or during dynamic contractions during the walking or STS trials.
The integral of the quadriceps activity during the loading response during walking and during sit-to-stand was used for analysis.
Nonparametric tests were used for analysis to reduce the threat of
outliers inaccurately skewing the findings of the investigation. Differences in means between limbs in strength, peak joint moments, peak
flexion angles, peak vertical ground reaction force during STS, and
normalized, integrated EMG activity were analyzed with Wilcoxon
Sign Rank tests. Spearman Correlation Coefficients were used to analyze the strength of relationships between the factors of interest in this
study. The first specific relationship of interest was between peak quadriceps torque during strength testing and functional performance during the TUG, SCT, and 6MW. The relationship between normalized,
integrated quadriceps muscle activity and peak knee flexion during
weight acceptance and the ratio of the involved over the uninvolved
vertical ground reaction force during standing was also analyzed. Finally, the relationship between the degree of symmetry in quadriceps
strength (i.e. quadriceps index) and the symmetry between limbs in
knee excursion in weight acceptance and vertical ground reaction force
during STS was analyzed. An alpha level of 0.05 was chosen for
significance.
Results
The involved quadriceps muscles were weaker (650/0)
than the uninvolved 0, < 0.01) (Table 1). Two subjects
had mild knee pain during quadriceps strength assessment (1/10 and 2/10). One subject reported mild discomfort (2/10) on the lateral aspect of the involved knee
during STS trials. Quadriceps strength in the involved
leg correlated negatively with the time to complete the
SCT (rho = -0.65, p < 0.01), positively with the distance
traveled on the 6MW (rho = 0.64, p < 0.01), but it did
not significantly correlate with the time to complete
the TUG (rho = -0.43, p = 0.12). Quadriceps strength
in the uninvolved leg was correlated negatively with
the time to complete the SCT (rho = -0.68, p < 0.01),
positively with the distance traveled on the 6MW
(rho = 0.77, p < 0.01), and had a significant negative
correlation with the time to complete the T U G (rho =
-0.63, p = 0.02). Functional performance in all tests
was more strongly correlated to the uninvolved quadriceps strength than the involved quadriceps strength for
all tests.
During walking, there was no significant difference
in the knee flexion angle at heel strike between legs
(p = 0.10) (Fig. 1). The average peak knee flexion angle
during weight acceptance was significantly lower in the
involved limb than the uninvolved leg (p = 0.02) (Fig.
1). Correspondingly, knee excursion during weight
acceptance was also significantly lower in the involved
limb (p < 0.01) (Fig. 1). Despite less knee flexion in gait,
Fig. 1. Mean knee flexion angle, internal knee extension moment, and
normalized quadriceps muscle EMG activity during stance (i.e. heel
strike to toe of).
the peak knee extension moment for the involved knee
was not different from the extension moment in the
uninvolved knee (p = 0.43) (Fig. 1). There were no significant differences in the normalized EMG integrals between the quadriceps muscles (p=O.67) (Fig. 1). The
ratio of the involved leg’s knee excursion over the uninvolved leg’s knee excursion in weight acceptance was
correlated to the QI ( r = 0.70, p < 0.01) (Fig. 2).
For the STS assessment, there were no significant differences in the peak flexion angles of the hip (involved =
R.L. Mizner, L. Snyder-Mackler I Journal of Orthopaedic Research 23 (2005) 1083-1090
v
U
C
C
.-
0
2
a
8
0
0
K
W
B
Hip Joint
__^____^
rho = 0.70
p < 0.01
12
0
0.6
0.5
0.4
0.3
0
0.2
4
0.1
Y
C
2
I087
0
-0.1
0
0
-0.2
4
8
12
Rank of Quadriceps Index
Fig. 2. Graph of the relationship between symmetry in quadriceps
strength and symmetry in knee excursion during weight acceptance in
gait. Quadriceps index = involved quadriceps torque/uninvolvedquadriceps torque. Knee excursion index = involved knee excursion in
weight acceptanceluninvolved knee excursion in weight acceptance.
Larger rank is associated with higher score.
The hypotheses that quadriceps strength correlates to
functional performance with altered loading and movement patterns in weight bearing activities were sup-
50
75
Time (% of stand)
25
100
Knee Joint
0.6
0)
-
z
:B
O C
Discussion
I
0
E
96 f 9.3", uninvolved = 96 f 8.1") (p = 0.64), knee
(involved = 83 f 5.4", uninvolved = 85 f 4.3") (p = 0.1 l),
or ankle joints (involved = 11 f 3.3", uninvolved =
13 f 4.0")(p = 0.06) between legs. The average peak vertical ground reaction forces were lower (14% less than
uninvolved) in the involved leg (514 f 81 N) compared
to the uninvolved (599 k 89 N) (p < 0.01). All subjects,
except the subject with the highest peak involved quadriceps muscle torque, had a lower peak vertical ground
reaction force in the involved leg compared to the uninvolved. The ratio of the involved over the uninvolved
vertical ground reaction force was correlated with quadriceps index (r = 0.56, p = 0.04).
The involved leg's average peak hip (p<O.Ol) and
knee moments (p < 0.01) were significantly lower than
the uninvolved leg while the peak ankle moments were
not significantly different between legs (p = 0.98) (Fig.
3). The vastus lateralis (p < 0.01) had significantly smaller integrals of EMG activity in the involved leg compared to the uninvolved during STS (Fig. 4). The
remaining muscles did not have significantly different
integrals between limbs (p > 0.17) (Fig. 4). The peak
knee torque of the involved quadriceps correlated with
the peak involved knee moment (r = 0.60, p < 0.02) during STS. The QI correlated negatively with the uninvolved hip moment (Y = -0.61, p = 0.02) (Fig. 5); the
more symmetrical subjects were in quadriceps strength
the more symmetrical they were in the distribution of
moments between hips.
'
0.5
-
~
~
0.4
0.3
-0
0.2
U
0.1
M
w
0
-0.1
0
25
50
75
100
Time (% of stand)
Ankle Joint
0.6
-
p 0.4
z.o 5B
0.3
ge
0.2
k
0.1
w
0
-0.1
r'
Time (% of stand)
Fig. 3. Lower extremity sagittal moments of both limbs during sit-tostand. BW = body weight (kg), HT = height (m).
ported by the data. At three months after surgery,
patients with TKA exhibited pronounced weakness in
the involved quadriceps muscles typical of the patient
population. Functional performance was significantly
related to the quadriceps strength of both legs, but
was more strongly related to the uninvolved quadriceps
strength. Asymmetry in quadriceps strength was correlated to asymmetry in knee excursion during the weight
acceptance phase of gait. Subject's had lower normalized
quadriceps EMG activity as well as smaller extension
moments at the knee and hip during STS.
R.L. Mizner, L. Snyder-Muckler I Journal of Orthopaedic Research 23 (2005) 1083-1090
1088
QUADRICEPS
HAMSTRINGS
60%
Involved
9)
-8
50%
g
3
40%
W
.-E
J
E
z
30%
30%
20%
20%
10%
10%
0%
I
0%
0
25
50
75
100
0
25
50
75
100
Time (YOof stand)
Time (% of stand)
GASTROCNEMIUS
60%
-8
50%
5
40%
0
P
SOLEUS
60%
,
50% 40%-
30%20%-
0%
10%
1
0
25
I
50
75
Time (% of stand)
100
0%
1
0
25
50
75
Time (% of stand)
100
Tibialis Anterior
60%
50%
40%
0% 4
I
0
25
50
75
Time (% of stand)
100
Fig. 4. Mean muscle activity from the start to end of standing. The level of EMG activity was normalized to peak activity recorded during MVIC or
a dynamic trial.
-
0 1
0
1
I
4
8
I
12
Rank of Quadriceps Index
Fig. 5. Graph of the correlation between symmetry in quadriceps
strength (quadriceps index) and uninvolved peak hip extension
moment during standing. Larger rank is associated with higher score.
Those individuals with weaker quadriceps used the
uninvolved limb as a compensation to complete the
function tasks. Compensations were particularly evident
in the bilateral support task of STS. Increasing the involved leg’s strength should improve loading symmetry
between limbs with a corresponding improvement in
the functional performance of patients with TKA. Reliance on the uninvolved leg to compensate for the involved leg during functional tasks could help to
explain the persistent quadriceps weakness present in
this population. Not only did the involved leg have
lower peak torque production during strength assessment, but the subjects performed the STS task with relatively lower levels of quadriceps muscle recruitment.
Less loading and lower muscle activity in the involved
leg may be limiting the stress to the involved limb’s musculature to the point that the quadriceps are not stressed
enough to provide a stimulus for strength gain [21].
The movement pattern used during STS has potential
ramifications for exercise prescription for patients with
R. L. Mizner, L. Snyder- Muckler I Journal of Orthopurdic Research 23 (2005) 1083-1090
TKA. An exercise prescription that stresses bilateral
activities (e.g. leg press) may not provide an overload
for inducing gains in strength. Any exercise that uses
both legs provides an opportunity for the uninvolved
limb to compensate for weakness in the involved limb.
Incorporating unilateral exercises (e.g. seated knee
extension) in a strengthening program after TKA may
enhance quadriceps strength gains in this population
as it isolates the limb and prevents potential compensations for weakness.
Depending on the uninvolved limb to accomplish
functional tasks may have considerable long-term consequences. Shakoor and colleagues found in patients who
undergo unilateral knee replacement, the contralateral
knee joint was the most common second joint to undergo replacement [24]. In patients with osteoarthritis for
whom the second joint replacement was the hip, the contralateral side was more than twice as likely to be replaced as the ipsilateral side. In contrast, the evolution
of subsequent hip joint replacement in patients with
rheumatoid arthritis was random and no laterality was
observed. The authors remarked that absence of such
laterality in patients with rheumatoid arthritis suggests
that osteoarthritis progression may be mediated by
extrinsic factors such as altered joint loading. The unequal distribution in loading related to involved quadriceps weakness in this study may help explain the
nonrandom nature of subsequent hip and knee joint
replacements after primary unilateral TKA. The impact
of quadriceps weakness on the wear of the prosthesis
and the progression of osteoarthritis in the uninvolved
lower extremity merits further investigation.
While our inclusion criteria were selective, virtually
all other studies of kinetics and kinematics of walking,
rising from a chair and stair climbing have demonstrated similar movement patterns as we are reporting
despite widely varying inclusion and exclusion criteria
[4,11,14,26,29,31,33]. While it is unclear from the present study how the movement patterns and relationships
described in this investigation may change over time,
other studies suggest our findings are quite robust. A
cross-sectional study examining a control population,
people with knee OA awaiting TKA surgery, and people
after TKA would suggest that compensations during sitto-stand were present prior to surgery [3 I]. Prospective
studies also suggest that movement patterns after TKA
are influenced by preoperative patterns [26]. Patients
with TKA continue to make significant improvements
in quadriceps strength after three month assessments
[20,22]. The differences between limbs in this investigation may lessen as quadriceps strength between limbs becomes more symmetrical, but the influence of weakness
on movement patterns would remain as patients have
exhibited significant differences in quadriceps strength
between limbs even years after surgery [12].
1089
Knee pain is another factor common to patients with
knee osteoarthritis that can influence joint loading and
movement patterns of the knee [13]. Preoperative knee
pain could have contributed to habitual movement patterns that persist after knee replacement. The small (21
10) knee pain in only one subject during the testing,
however, suggests that knee pain did not affect performance in this sample at three months after TKA. While
pain reduction after TKA has been shown to relate to
improved walking performance [ 181, simply eliminating
pain and providing good range of motion, as in this
study, was not sufficient to restore normal symmetrical
knee and hip kinetics and kinematics.
Quadriceps weakness is a significant impairment that
plays an important role in functional outcomes after
TKA. Subjects with TKA adopted a strategy of movement which allows the uninvolved limb to compensate
for involved quadriceps weakness during functional
tasks as opposed to a potential alternate strategy of
increasing the recruitment of the involved quadriceps.
Quadriceps strength influenced lower extremity loading
in a way that could alter the wear of the prosthesis
and progression of osteoarthritis in the major weight
bearing joints of the lower extremity. Better outcomes
in the involved quadriceps strength may result in a more
balanced distribution of load between limbs.
Acknowledgments
This work was supported by the National Institute of
Health (ROlHD041055-01 and T32 HD07490) and The
Foundation for Physical Therapy (PODS scholarship).
The authors of this manuscript will receive no financial
benefit from the publication of these findings.
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