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Research Report
Early Postoperative Measures Predict
1- and 2-Year Outcomes After
Unilateral Total Knee Arthroplasty:
Importance of Contralateral Limb
Strength
Joseph A. Zeni Jr, Lynn Snyder-Mackler
Background. Total knee arthroplasty (TKA) has been shown to be an effective
surgical intervention for people with end-stage knee osteoarthritis. However, recovery of function is variable, and not all people have successful outcomes.
Objective. The aim of this study was to discern which early postoperative functional measures could predict functional ability at 1 year and 2 years after surgery.
Design and Methods. One hundred fifty-five people who underwent unilateral TKA participated in the prospective longitudinal study. Functional evaluations
were performed at the initial outpatient physical therapy appointment and at 1 and
2 years after surgery. Evaluations consisted of measurements of height, weight,
quadriceps muscle strength (force-generating capacity), and knee range of motion;
the Timed “Up & Go” Test (TUG); the stair-climbing task (SCT); and the Knee
Outcome Survey (KOS) questionnaire. The ability to predict 1- and 2-year outcomes
on the basis of early postoperative measures was analyzed with a hierarchical
regression. Differences in functional scores were evaluated with a repeated-measures
analysis of variance.
Results. The TUG, SCT, and KOS scores at 1 and 2 years showed significant
improvements over the scores at the initial evaluation (P⬍.001). A weaker quadriceps
muscle in the limb that did not undergo surgery (“nonoperated limb”) was related to
poorer 1- and 2-year outcomes even after the influence of the other early postoperative measures was accounted for in the regression. Older participants with higher
body masses also had poorer outcomes at 1 and 2 years. Postoperative measures were
better predictors of TUG and SCT times than of KOS scores.
J.A. Zeni Jr, PT, PhD, is Research
Assistant Professor, Department of
Physical Therapy, University of
Delaware, 301 McKinly Laboratory, Newark, DE 19716 (USA).
Address all correspondence to Dr
Zeni at: [email protected].
L. Snyder-Mackler, PT, ScD,
FAPTA, is Alumni Distinguished
Professor, Department of Physical
Therapy, and Academic Director,
Graduate Program in Biomechanics and Movement Science, University of Delaware.
[Zeni JA Jr, Snyder-Mackler L. Early
postoperative measures predict 1and 2-year outcomes after unilateral total knee arthroplasty: importance of contralateral limb
strength. Phys Ther. 2010;90:
43–54.]
© 2010 American Physical Therapy
Association
Conclusions. Rehabilitation regimens after TKA should include exercises to improve the strength of the nonoperated limb as well as to treat the deficits imposed
by the surgery. Emphasis on treating age-related impairments and reducing body mass
also might improve long-term outcomes.
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January 2010
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Early Measures After Unilateral Total Knee Arthroplasty
T
otal knee arthroplasty (TKA)
has been proven to be an effective and cost-efficient intervention for end-stage knee osteoarthritis (OA). Most people who
undergo TKA show marked improvements in function and reductions in
pain compared with their preoperative condition.1,2 However, recovery
of functional ability is variable, and
not all patients experience significant improvements.3,4 The ability to
predict which patients will have successful recoveries relies on the ability to identify factors that result in
different functional outcomes.
Preoperative measures that predict
postsurgical functional status were
examined in many previous investigations. Lower levels of preoperative
quadriceps muscle strength (forcegenerating capacity) and selfperceived functional ability and a
larger number of comorbidities have
been shown to predict decreased
functional ability 6 to 24 months after TKA.4 – 6 In the short term, greater
preoperative knee pain and less preoperative range of motion (ROM) are
related to reduced walking ability 2
months after surgery.7 Other factors,
such as a high body mass index
(BMI), female sex, and older age,
have been implicated as factors that
predict poor short-term outcomes,
higher per-patient costs, or higher
postoperative complication rates.8,9
Although preoperative predictors
may aid in the identification of people at risk for postoperative difficulties, it also is important to recognize
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early postoperative factors that may
predict poor long-term outcomes.
Van den Akker-Scheek et al10 found
that early postoperative evaluations
of self-efficacy were better predictors of long-term outcomes than preoperative evaluations. This finding is
important because most people receive outpatient physical therapy
services after TKA, but preoperative
therapeutic interventions are not as
common. Physical therapists, therefore, can tailor rehabilitation regimens to maximize early postoperative self-efficacy, whereas increasing
preoperative self-efficacy is not always feasible.
No studies have evaluated the ability
to predict long-term functional outcomes on the basis of early postoperative measures. The purpose of
this study was to discern whether
age, BMI, pain, knee ROM, and knee
strength measured at an initial physical therapy evaluation could predict
functional ability at 1 year and 2
years after surgery. We hypothesized
that certain factors would best predict long-term outcomes. Identification of these factors will aid in the
creation of targeted therapeutic interventions to maximize postoperative functional ability.
Method
One hundred and fifty-five people
who underwent primary unilateral
TKA for end-stage knee OA participated in the study (Tab. 1). Before
surgery, participants were excluded
if they reported symptomatic OA in
the contralateral limb, as measured
by maximal pain of greater than 4 on
a scale of 1 to 10 in that limb during
daily activities. All participants
signed an informed consent form approved by the Human Subjects Review Board of the University of Delaware. Participants were treated 2 or
3 times per week for 6 weeks in the
same outpatient physical therapy
clinic. Outpatient physical therapy
began shortly after they concluded
Number 1
home-based therapy (under direct
physical therapist supervision) and
had their staples removed. The physical therapy regimen consisted
of
progressive
lower-extremity
strengthening exercises, modalities
to control pain and inflammation,
electrical stimulation to improve
quadriceps muscle function, and
manual therapy to improve ROM
(Appendix).
Quantitative clinical measurements
were obtained at the initial evaluation and at 1 and 2 years after surgery. These measurements included
age, height, weight, bilateral quadriceps muscle strength, knee flexion
and extension ROM, the Timed “Up
& Go” Test (TUG), and a stairclimbing task (SCT). Two subsets of
the Knee Outcome Survey (KOS),
the activities of daily living subset
(KOS-ADLS) and the pain subset
(KOS-Pain), also were used.
Quadriceps Muscle Strength
Quadriceps muscle strength was defined in this study as the volitional
isometric force created by the quadriceps muscle. It was measured with
the participants seated with their
knees flexed to 75 degrees and their
hips flexed to 85 degrees on a KinCom dynamometer.* Knee flexion of
75 degrees was chosen to ensure
consistency between time points
and participants. After surgery, it
was likely that a percentage of the
participants would not be able to
achieve knee flexion of greater than
75 degrees. Seventy-five degrees of
knee flexion during isometric knee
extension also results in the greatest
force output of the quadriceps muscle after TKA.11 Participants were
given verbal encouragement to kick
“as hard as possible” for 3 seconds.
Three trials were completed, and the
average of these trials was recorded.
The raw force measured by the dy* Isokinetic International, 6426 Morning Glory
Dr, Harrison, TN 37341.
January 2010
Early Measures After Unilateral Total Knee Arthroplasty
namometer, in newtons, was normalized to each participant’s BMI (N/
BMI), and this value was used as
quadriceps muscle strength.
Table 1.
Participant Demographics at Initial Evaluation, 1 Year, and 2 Yearsa
Characteristicb
Knee ROM
Active knee flexion ROM was measured with participants in the supine
position. The axis of the goniometer
was aligned over the lateral epicondyle of the femur. The distal arm was
aligned with the lateral malleolus of
the fibula, and the proximal arm was
aligned with the long axis of the
shaft of the femur and directed toward the greater trochanter. Participants were instructed to maximally
bend their knees by flexing their
hips and sliding their heels toward
their buttocks. No overpressure was
applied by the therapist during knee
flexion. Three trials were performed,
and the average knee flexion angle
was recorded. All measurements
were obtained with respect to full
extension of the knee being 0 degrees and increasing knee flexion being recorded as positive values. Goniometric measurements in people
with knee OA have been shown to
be highly reliable.12
TUG
The TUG is a functional test that has
been used extensively to examine
functional outcomes in people with
knee OA and after TKA.5,13,14 The
test begins with a participant seated
in a chair with both feet touching the
floor. When instructed to “go,” the
participant rises from the chair,
walks 3 m, turns around, returns to
the chair, and sits down. Participants
were instructed to complete the task
as quickly as possible. They performed 2 trials, and the average time
to complete the task was recorded.
They were permitted to use the arms
of the chair during standing and returning to a seated position. This test
has excellent interrater and intrarater reliability in older adults and
is responsive to changes after
TKA.15,16
January 2010
Age, y
64.9 (8.7)
Sex, % of men/women
57/43
Height, m
2 Years
(nⴝ125)
1.72 (0.10)
89.1 (17.0)
91.2 (17.5)
94.1 (18.6)
BMI, kg/m2
30.2 (4.9)
31.0 (5.2)
31.8 (5.7)
6.3 (4.1)
0.4 (2.8)
0.3 (2.9)
97.1 (15.0)
120.1 (10.4)
120.2 (11.3)
9.9 (4.1)
20.7 (8.5)
20.6 (8.8)
Nonoperated quadriceps
muscle strength, N/BMI
24.0 (8.7)
22.7 (9.4)
21.0 (9.3)
Days since surgery
27.7 (3.7)
Flexion AROM, °
Operated quadriceps muscle
strength, N/BMI
b
1 Year
(nⴝ155)
Weight, kg
Extension AROM, °
a
Initial
Evaluation
(nⴝ155)
Values are reported as mean (SD) unless otherwise indicated.
BMI⫽body mass index, AROM⫽active range of motion.
SCT
The SCT is a measure of a participant’s ability to ascend and descend
a flight of 12 steps as quickly as possible in a safe manner. Participants
began at the bottom of the stairs and,
at the investigator’s instruction, ascended the steps, turned around,
and descended the steps as quickly
as possible with the use of the handrail only if needed for balance. Participants performed 1 practice trial
and then 2 timed trials, the average
of which was recorded. This test has
been used to successfully measure
recovery after TKA.5,15,17
KOS
For the purpose of this study, we
used 2 subsets of the KOS, the KOSADLS and the KOS-Pain. The KOSADLS consists of 14 questions pertaining to a participant’s ability to
perform activities of daily living. The
KOS-ADLS is represented as a percentage score, with higher scores indicating higher levels of selfperceived functional ability. With
the KOS-Pain, participants rate their
pain on a 6-point scale, in which 0
represents no pain and 5 represents
pain that prevents daily activities.
The KOS has been shown to have
high reliability and validity in people
with knee pathology.18,19
Data Analysis
A hierarchical regression model was
created to predict the TUG, SCT, and
KOS-ADLS scores at 1 and 2 years
after TKA. Baseline test scores and
then participant age, BMI, KOS-Pain
score, flexion ROM, quadriceps muscle strength of the limb that underwent TKA (“operated limb”), and
quadriceps muscle strength of the
limb that did not undergo TKA
(“nonoperated limb”), all obtained at
the initial physical therapy evaluation, were entered into the hierarchical regression model as independent
variables, in that order. The order of
the variables was chosen on the basis
of their clinical relevance, and the
baseline test scores were entered
first to account for changes in each
variable over time. Preoperative
quadriceps muscle strength and
knee ROM are predictors of postoperative outcomes and often are directly addressed during postoperative physical therapy.5,7 For this
reason, the order of the regression
was designed to determine whether
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Early Measures After Unilateral Total Knee Arthroplasty
Figure 1.
Significant improvements in results of the Timed “Up & Go” Test (TUG) and stairclimbing task (SCT) and in scores on the activities of daily living subset of the Knee
Outcome Survey (KOS-ADLS) at 1-year follow-up and 2-year follow-up (asterisk indicates P⬍.001). Error bars represent 95% confidence intervals.
knee strength and ROM would significantly improve the predictive
ability of the model, even when the
influence of age, BMI, knee pain, and
baseline test scores was accounted
for.
A change in the F score from each
step of the model to the next (the
addition of each variable) was analyzed for significance (Pⱕ.05). An
analysis of variance with 1 repeated
measure (time) was used to determine differences in the TUG, SCT,
and KOS-ADLS scores at the initial
evaluation and those at 1 and 2 years
after TKA.
Results
Participants reported to outpatient
physical therapy an average (median) of 28 days after TKA. The median number of physical therapy
treatments was 17, with 90% of the
participants receiving 16 to 18 treatments. No participants reported any
major neurological or cardiovascular
events after surgery. The Mauchley
test of sphericity was significant, suggesting unequal variances between
the time points. When the Green46
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house–Geisser correction was used,
a significant effect of time on all of
the outcome measures was revealed.
The TUG, SCT, and KOS scores at 1
and 2 years showed significant improvements over the scores at the
initial evaluation (P⬍.001) (Fig. 1).
The TUG and SCT showed 34% and
53% reductions in the times needed
to complete the tasks at the initial
evaluation and at 1 year, respectively. The KOS-ADLS score increased by 52% between the initial
evaluation and 1 year. Post hoc testing revealed no significant differences between 1 and 2 years
(P⬎.43). For descriptive purposes,
the TUG, SCT, and KOS-ADLS scores
at 3 months after TKA (near the time
of discharge from physical therapy)
were 8.23 seconds (SD⫽1.87 seconds), 13.63 seconds (SD⫽4.76 seconds), and 78.6% (SD⫽12%),
respectively.
Early postoperative values were predictive of the TUG, SCT, and KOS
scores at 1 year after TKA (Tabs. 2, 3,
and 4). After the other variables in
the regression were accounted for,
Number 1
the quadriceps muscle strength of
the nonoperated limb significantly
improved the predictive ability of
the model with respect to the TUG,
SCT, and KOS-ADLS scores. Increased force production in the nonoperated limb was related to improved scores on the TUG, SCT, and
KOS (Fig. 2). Age also improved the
predictive ability of the model for
the TUG and SCT times, and BMI
improved the predictive ability for
the SCT time. A younger age and a
lower BMI predicted better functional outcomes in terms of faster
times to complete the TUG and SCT.
The KOS-Pain and strength of the
involved limb did not predict scores
for outcomes. The BMI was the most
significant predictor of the KOSADLS score (P⫽.023), with a higher
postoperative BMI predicting a
lower KOS-ADLS score at 1 year after
TKA. A stronger quadriceps muscle
in the nonoperated limb also significantly contributed to the prediction
of an improved KOS-ADLS score,
whereas age, the KOS-Pain, knee
flexion ROM, and quadriceps muscle
strength of the operated limb did
not.
One hundred twenty-five participants returned for the 2-year followup. The remaining 30 participants
either failed to return for the 2-year
follow-up or had undergone TKA
less than 2 years earlier. Similar to
the 1-year results, the quadriceps
muscle strength of the nonoperated
limb significantly improved the ability of the model to predict the TUG
and SCT times at 2 years after TKA,
even when the other variables were
accounted for (Pⱕ.011) (Tabs. 2 and
3). Age also significantly added to the
predictive ability of the model for
the TUG and SCT times, whereas the
BMI, KOS-Pain, knee flexion ROM,
and quadriceps muscle strength of
the operated limb did not. The
trends were the same as those at 1
year, with a stronger quadriceps
muscle and a younger age predicting
January 2010
Early Measures After Unilateral Total Knee Arthroplasty
Table 2.
Timed “Up & Go” Test Results
Modela
Year
1
2
R
R2
R2
Change
F
Change
Significance
of F Changeb
TUG
.587
.345
.345
80.581
<.001
TUG ⫹ age
.657
.432
.087
23.264
<.001
TUG ⫹ age ⫹ BMI
.663
.440
.008
2.126
.147
TUG ⫹ age ⫹ BMI ⫹ KOS-Pain
.664
.441
.001
0.278
.599
TUG ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM
.671
.451
.010
2.720
.101
TUG ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM ⫹ op quad
muscle strength
.672
.451
.000
0.065
.799
TUG ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM ⫹ op quad
muscle strength ⫹ nonop quad muscle strength
.704
.495
.044
12.891
<.001
TUG
.596
.355
.355
64.979
<.001
TUG ⫹ age
.633
.401
.046
8.974
.003
TUG ⫹ age ⫹ BMI
.645
.416
.015
3.061
.083
TUG ⫹ age ⫹ BMI ⫹ KOS-Pain
.648
.419
.003
0.561
.456
TUG ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM
.650
.423
.004
0.735
.393
TUG ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM ⫹ op quad
muscle strength
.654
.428
.005
1.018
.315
TUG ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM ⫹ op quad
muscle strength ⫹ nonop quad muscle strength
.678
.460
.032
6.671
.011
a
TUG⫽Timed “Up & Go” Test, BMI⫽body mass index, KOS-Pain⫽pain subset of the Knee Outcome Survey, ROM⫽range of motion, op quad⫽operated
quadriceps, nonop quad⫽nonoperated quadriceps.
b
Values in bold type were significant at P⬍.05.
Table 3.
Stair-Climbing Task Results
Modela
Year
1
2
R
R2
R2
Change
F
Change
Significance
of F Changeb
SCT
.656
.430
.430
115.510
<.001
SCT ⫹ age
.694
.481
.051
15.008
<.001
SCT ⫹ age ⫹ BMI
.704
.495
.014
4.128
.044
SCT ⫹ age ⫹ BMI ⫹ KOS-Pain
.707
.500
.004
1.327
.251
SCT ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM
.721
.520
.021
6.405
.012
SCT ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM ⫹ op quad
muscle strength
.721
.520
.000
0.000
.996
SCT ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM ⫹ op quad
muscle strength ⫹ nonop quad muscle strength
.758
.574
.054
18.728
<.001
SCT
.647
.419
.419
85.167
<.001
SCT ⫹ age
.675
.455
.036
7.711
.006
SCT ⫹ age ⫹ BMI
.685
.470
.014
3.162
.078
SCT ⫹ age ⫹ BMI ⫹ KOS-Pain
.688
.474
.004
0.928
.337
SCT ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM
.697
.485
.012
2.556
.113
SCT ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM ⫹ op quad
muscle strength
.699
.488
.003
0.650
.422
SCT ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM ⫹ op quad
muscle strength ⫹ nonop quad muscle strength
.743
.552
.064
15.888
<.001
a
SCT⫽stair-climbing task, BMI⫽body mass index, KOS-Pain⫽pain subset of the Knee Outcome Survey, ROM⫽range of motion, op quad⫽operated
quadriceps, nonop quad⫽nonoperated quadriceps.
b
Values in bold type were significant at P⬍.05.
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Early Measures After Unilateral Total Knee Arthroplasty
Table 4.
Knee Outcome Survey Results
R
R2
R2
Change
F
Change
Significance
of F Changeb
KOS-ADLS
.315
.099
.099
15.924
<.001
KOS-ADLS ⫹ age
.316
.100
.001
0.180
.672
Modela
Year
1
2
KOS-ADLS ⫹ age ⫹ BMI
.363
.132
.032
5.248
.023
KOS-ADLS ⫹ age ⫹ BMI ⫹ KOS-Pain
.377
.142
.010
1.655
.200
KOS-ADLS ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM
.377
.142
.001
0.087
.768
KOS-ADLS ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM ⫹ op
quad muscle strength
.397
.158
.015
2.526
.114
KOS-ADLS ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM ⫹ op
quad muscle strength ⫹ nonop quad muscle
strength
.440
.194
.036
6.230
.014
KOS-ADLS
.283
.080
.080
10.381
.002
KOS-ADLS ⫹ age
.289
.083
.003
0.404
.526
KOS-ADLS ⫹ age ⫹ BMI
.380
.144
.061
8.327
.005
KOS-ADLS ⫹ age ⫹ BMI ⫹ KOS-Pain
.394
.155
.011
1.528
.219
KOS-ADLS ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM
.399
.159
.004
0.522
.472
KOS-ADLS ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM ⫹ op
quad muscle strength
.399
.159
.000
0.013
.909
KOS-ADLS ⫹ age ⫹ BMI ⫹ KOS-Pain ⫹ ROM ⫹ op
quad muscle strength ⫹ nonop quad muscle
strength
.409
.167
.008
1.100
.296
a
KOS-DLS⫽activities of daily living subset of the Knee Outcome Survey, BMI⫽body mass index, KOS-Pain⫽pain subset of the Knee Outcome Survey,
ROM⫽range of motion, op quad⫽operated quadriceps, nonop quad⫽nonoperated quadriceps.
b
Values in bold type were significant at P⬍.05.
better functional outcomes at 2 years
(Fig. 3). Similar to the 1-year results,
BMI was the strongest predictor of
the KOS-ADLS score at 2 years after
TKA (P⫽.005) (Tab. 4); a lower BMI
was related to a higher KOS-ADLS
score at 2 years. The KOS-Pain and
strength of the involved limb did not
contribute significantly to any of the
models.
The R2 values for the TUG and SCT
were more than twice the R2 values
for the KOS-ADLS at 1 and 2 years
(Tabs. 2, 3, and 4).
Discussion
The participants showed significant
and clinically meaningful improvements in the first year after TKA. The
recovery of function appeared to be
nearly complete by this time because
no improvements were seen between the 1- and 2-year time points.
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As hypothesized, postoperative variables predicted scores on the TUG,
SCT, and KOS-ADLS. A stronger
quadriceps muscle on the nonoperated side and a younger age were the
main variables related to improved 1and 2-year outcomes for the TUG
and SCT. A lower BMI was important
for maximizing self-reported measures of function at 1 and 2 years.
Interestingly, these variables are not
typically addressed during postoperative physical therapy.
As expected, the participants in the
present study showed dramatic increases in function at 1 year after
TKA. This finding supports the general consensus that TKA is an effective intervention for restoring quantitative and self-perceived functional
abilities.2,17,20,21 No improvements in
the TUG, SCT, or KOS scores were
seen between 1 and 2 years, suggest-
Number 1
ing that the majority of functional
recovery occurs within the first year
after surgery. Other investigators examining multiyear outcomes have reported similar results.4,22
The early postoperative variables
considered in the present study were
better at predicting the scores of the
quantitative functional measures at 1
and 2 years than at predicting the
KOS-ADLS scores. The TUG and SCT
had much higher R2 values than the
KOS-ADLS at 1 and 2 years after TKA
(Tabs. 2, 3, and 4). This inconsistency may be explained by the discrepancy between functional measures and self-reported measures of
function.23,24 Quadriceps muscle
strength and knee ROM are quantitative functional measures. An older
age and a higher BMI also affected
clinical measures and resulted in reduced strength, a lower freely choJanuary 2010
Early Measures After Unilateral Total Knee Arthroplasty
sen walking speed, and impaired
stair-climbing ability.25,26 Because
most of the predictor variables are,
or affect, quantitative measures,
their predictive ability may have
been oriented toward performancebased outcome measures rather than
self-perceived functional ability.
Many investigators have examined
preoperative predictors of postoperative status in people who have undergone TKA; they concluded that
greater preoperative knee flexion
ROM and quadriceps muscle
strength on the operated side or a
higher level of self-perceived functional ability predicted improved
outcomes.4,5,27,28 These variables often are addressed during physical
therapy. The postoperative predictors noted in the present study were
impairments that might not or cannot be addressed during physical
therapy. Maximizing patients’ outcomes in minimal time is often the
emphasis of physical therapy interventions. For this reason, clinicians
focus on the most obvious functional
deficits, such as knee ROM and
strength of the operated limb. People who have undergone TKA show
marked improvements in the quadriceps muscle strength of the operated
limb after a course of physical therapy.17 However, in the present
study, the strength of the nonoperated limb accounted for most of the
variability in functional outcomes,
with reduced strength predicting
poorer outcomes. Rehabilitation regimens should also focus on improving the strength of the nonoperated
limb because quadriceps muscle
strength is strongly correlated with
functional ability.29 If left untreated,
weakness in the nonoperated limb
may continue to impede functional
ability and result in poorer 1- and
2-year functional outcomes. Although the inclusion of these variables may be vital to maximizing outcomes, knee flexion ROM and
January 2010
Figure 2.
Significant relationship between the quadriceps muscle strength of the nonoperated
limb at initial evaluation and quantitative functional measures at 1 year. BMI⫽body
mass index, SCT⫽stair-climbing task, TUG⫽Timed “Up & Go” Test.
strength on the involved side should
not be overlooked.
It also is possible that the quadriceps
muscle strength of the nonoperated
limb represents disease progression
on the nonoperated side.30 –32 People
undergoing unilateral TKA often
have bilateral joint disease.33 The
more involved joint is typically replaced first, with the hope that improved functional ability will reduce
the symptoms on the nonoperated
side. However, the incidence of replacement of the cognate joint is relatively high, at 37%, by 10 years.33 It
has been shown that the status of the
nonoperated limb at 3 years after surgery best predicts the functional ability of the operated limb at that time
point.34 Those data support our finding that reduced quadriceps muscle
strength of the nonoperated limb
predicted poorer long-term functional outcomes. If we can assume
that quadriceps muscle weakness is
related to disease progression, then
people with more advanced OA in
the nonoperated limb after TKA may
expect poorer outcomes at 1 and 2
years after TKA.
Although age is a variable that cannot be addressed by rehabilitation,
age-related impairments, such as
poor balance and strength, can be
treated with rehabilitation.35,36 In addition to treating the deficits imposed by the surgery, physical therapists should focus on improving
balance and generalized lowerextremity strength in older participants. Although further research is
warranted, a rehabilitation regimen
that incorporates training to treat
age-related functional deficits may
lead to improved functional outcomes. The older participants in the
present study may have had a greater
risk for poorer outcomes secondary
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Early Measures After Unilateral Total Knee Arthroplasty
participants tended to have shorter
TUG and SCT times. Although some
participants with a quadriceps muscle strength of less than 30 N/BMI
did have quick TUG and SCT times,
others did not. This finding was clinically meaningful and suggested that
if the quadriceps muscle strength of
the nonoperated limb at the initial
evaluation was greater than 30
N/BMI, then participants would
likely achieve nearly normal TUG
and SCT scores at 1 and 2 years after
surgery. A quadriceps muscle
strength of less than 30 N/BMI might
not result in similar satisfactory
outcomes.
Figure 3.
Significant relationship between the quadriceps muscle strength of the nonoperated
limb at initial evaluation and quantitative functional measures at 2 years. BMI⫽body
mass index, SCT⫽stair-climbing task, TUG⫽Timed “Up & Go” Test.
to delayed recovery of muscle function after surgery; this notion provides support to the suggestion that
undergoing TKA earlier in the course
of OA or earlier in a patient’s life may
improve functional outcomes.3,37
A higher BMI also was found to predict poorer outcomes, particularly
those described by self-reported
measures. This interesting finding
suggests that having a high body
mass or being overweight may skew
how people view their functional capacity, even if there are no quantitative changes in function. Providing
patients with access to nutrition and
weight loss services is essential to
reducing body mass after TKA because TKA alone does not facilitate
weight loss.38 Clinicians and patients
should treat high body mass as a separate concern that will not be resolved merely through improved
50
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functional ability after TKA. Rehabilitation programs should include a
cardiovascular component for patients with a high body mass after
surgery.
Although the TUG and SCT are measures that validly and reliably quantify functional ability, they do have a
ceiling effect. However, these tests
are still sensitive enough to measure
differences between people with
and without knee pathology39 (Figs.
2 and 3). The strength of the relationship between the quadriceps muscle
strength of the nonoperated limb at
the initial evaluation and the functional measures varied depending on
the quadriceps muscle strength.
When the quadriceps muscle
strength was less than 30 N/BMI,
there was much more variability in
the data, whereas above 30 N/BMI,
the relationship was less variable and
Number 1
Despite the ceiling effect and the
fact that the TUG and SCT scores
reached a plateau within 1 year after
surgery,29 we chose to include these
measures to capture dysfunction that
might have been associated with disease progression in the nonoperated
limb. Functional ability, as determined with outcome measures, declines with time since surgery,40 possibly because of complications
related to advanced age or deterioration of the cognate joint. We wanted
to use a consistent set of measurement variables throughout the study,
and although we did not expect to
see much further improvement after
1 year, we wanted to ensure that we
would be able to identify functional
deficits if they occurred.
The present study had a few limitations. First, the KOS-ADLS has been
used to extensively evaluate people
with knee pathology, although the
instrument has not yet been validated for people with TKA. However, it is not likely that this instrument would be any less valid than
similar measures of functional ability. Second, radiographs were not
evaluated for disease progression in
the contralateral limb, although correlations of radiographic disease progression and functional ability are
weak.31,41 Finally, the determination
January 2010
Early Measures After Unilateral Total Knee Arthroplasty
of 30 N/BMI of quadriceps muscle
strength as a cutoff for success with
the TUG and SCT was based on a
qualitative analysis of the data, and
this value did not represent a statistical cutoff value. Traditional statistical methods of determining cutoff
values rely on a dichotomous variable that represents success or failure. With the data and methodology
used in the present study, no such
dichotomous outcome variables
were defined. Future investigations
should be performed to evaluate disease progression on the contralateral
side in relation to long-term functional ability. Additionally, future
studies should be done to determine
clinically and statistically meaningful
cutoff values for variables that predict success or failure after TKA,
such as quadriceps muscle strength.
Because a portion of the variability
was not explained by the variables
selected in the present study, future
work also should incorporate different predictor variables that might account for a portion of the unexplained variability.
Of the variables selected, the
strength of the nonoperated limb,
age, and BMI explained most of the
variability in functional outcomes at
1 and 2 years after TKA. The weakness of the nonoperated limb, older
age, and higher BMI at the initial
evaluation predicted poorer functional outcomes. Treatment regimens after TKA should focus on improving the strength of the
nonoperated limb in addition to
treating the deficits imposed by the
surgery. People with more advanced
disease progression on the nonoperated side may also experience
poorer functional outcomes after
TKA. Future research should focus
on evaluating the effects of tailored
rehabilitation protocols that incorporate bilateral quadriceps muscle
strengthening, cardiovascular and
weight loss regimens, and exercises
January 2010
to reduce age-related impairments
on long-term functional outcomes.
Both authors provided concept/idea/research design, writing, and data analysis. Dr
Snyder-Mackler provided project management, fund procurement, and facilities/
equipment.
This study was approved by the Human Subjects Review Board of the University of
Delaware.
An abstract based on the data was presented
at the 2009 World Congress of the Osteoarthritis Research Society International; September 10 –13, 2009; Montreal, Quebec,
Canada.
Funding for the study was provided by National
Institutes
of
Health
grants
R01HD041055 (NICHD) and P20RR016458
(NCRR). This research also was funded by
the National Center for Research Resources
of the National Institutes of Health.
This article was received March 17, 2009, and
was accepted August 13, 2009.
DOI: 10.2522/ptj.20090089
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Appendix.
Physical Therapy Treatment Regimen–Aggressive Strengthening Protocol
All exercises were incorporated into treatment in the clinic and were advanced as described below. Direct physical
therapist guidance and assistance were provided for all exercises until participants became self-sufficient and
completed the exercises with proper form. Participants also performed stretching and strengthening exercises at
home on days on which they did not receive physical therapy in the clinic.
I. Warm-up exercise
a. Five to 10 minutes of riding an exercise bicycle
II. Range of motion (for participants with less than 120 degrees of knee flexion or with knee flexion contracture)
a. Patellar mobilization (if indicated)
1. Three sets of 10 repetitions with knee in full extension
2. Active superior patellar glides
b. Incision mobility
1. Soft-tissue mobilization of the entire length of the incision
2. Greater emphasis on the distal third
c. Knee extension stretch
1. Manual overpressure on the knee
d. Standing knee flexion stretch
1. The participant stands at the bottom of a flight of stairs with the foot of the operated side placed on the
third step. While holding the rail, the participant leans forward, sits down to bend the knee to the end
range, and holds the position for 30 seconds. The participant repeats the exercise 3 times.
2. Supine active assisted wall slides
e. Manual stretching of hamstring muscle, quadriceps muscle, gastrocnemius muscle, and joint capsule as
needed
III. Strengthening
a. Weight should be 70% of participant’s 1-repetition maximum
b. Three sets of 8 repetitions for all exercises
c. One to 2 minutes of rest between sets
d. Exercises are advanced when the participant can complete the exercises and maintain control through 3 sets
of 8 repetitions
e. Exercises (initial)
1. Straight leg raises (without quadriceps muscle lag)
● The participant lies supine with the hip and knee on the nonoperated side flexed and the foot placed
flat on an exercise table. The participant first isometrically contracts the quadriceps muscle and then
lifts the leg to about 45 degrees of hip flexion while keeping the knee extended. The participant lowers
the leg slowly to the starting position.
2. Hip abduction (side-lying position)
● The participant is in the side-lying position on the nonoperated side. The participant flexes the bottom
leg for balance and then lifts the top leg until 45 degrees of hip abduction is reached. The participant
lowers the abducted leg slowly to the starting position. The participant should not externally rotate the
hip during abduction.
3. Standing terminal knee extension with resistance band
● The participant stands with a rubber band resisting knee extension. The participant flexes the knee to
45 degrees and straightens the leg against the resistance to full extension.
4. Lateral step-ups
● The exercise begins with a 5.08-cm (2-in) block and advances to a 10.16-cm (4-in) block and then a
15.24-cm (6-in) block. The participant should step to the side with slow, controlled movements during
ascent and descent.
5. Hamstring muscle curls
● Standing with hands on a table or counter for support, the participant flexes the knee maximally.
(Continued)
January 2010
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Early Measures After Unilateral Total Knee Arthroplasty
Appendix.
Continued
f. Exercises (additional)
1. Seated knee extension (90°–0°)
● The participant sits on a knee exercise machine with the knee bent to 90 degrees and the tibial pad
placed at a 2-finger width proximal to the lateral malleolus. The participant extends the knee to full
extension and then slowly lowers it to the starting position.
2. Terminal knee extension (45°–0°)
● With the participant in the long sitting position, a bolster is placed under the operated knee to keep
it in a flexed position (45°). The participant extends the knee to full extension and then slowly lowers
it to the starting position.
3. Heel-raises
● In the standing position, the participant raises the heel as far as possible and then slowly lowers it to
the starting position. Bilateral heel-raises are used if the participant is unable to perform 15 repetitions
of the unilateral heel-raise. Unilateral heel-raises are used if the participant is able to perform more than
15 repetitions of the unilateral heel-raise. A weighted backpack is used to increase the challenge once
the participant is able to perform 3 sets of 10 repetitions of unilateral heel-raises.
4. Wall slides
● Standing with the back against the wall, the participant flexes the hips and knees, slides the back down
until reaching 45 degrees of knee flexion, and then slides the back up to return to the starting position.
The exercise is advanced by increasing the degree of knee flexion up to 90 degrees.
5. Front lunges
● Standing with hands on hips, the participant puts the involved leg forward and lunges until the forward
knee reaches 45 to 90 degrees, depending on the level of progression.
IV. Quadriceps femoris neuromuscular electrical stimulation
a. The participant is seated on a Kin-Com dynamometer with the involved knee flexed to 60 degrees, and a
portable stimulator (Empi 300pv)a is used for stimulation. The participant performs 1 submaximal warm-up
and then 2 maximum voluntary isometric contractions (MVICs). The average of the 2 MVICs is considered
to be the participant’s daily MVIC.
b. Parameters
1. On time: 12 seconds; off time: 50 seconds
2. Symmetrical waveform at 50 pulses per second
3. Two-second ramp time
4. Pulse width of 400 microseconds
5. Amplitude to maximum tolerable (at least 30% of the MVIC)
c. Ten contractions per session
d. Three sessions per week until the quadriceps muscle MVIC is 80% of that of the uninvolved limb
V. Management of pain and swelling
a. Ice and elevation after exercises
b. Compression as needed
VI. Functional retraining
a. Gait training with emphasis on heel-strike and push-off at toe-off and on normal knee joint excursions
b. Stair ascending and descending
1. Step-over-step pattern
2. Training should be performed when the unilateral stance is steady and not painful
a
Empi, 599 Cardigan Rd, St Paul, MN 55126-4099.
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