SYMPOSIUM: PAPERS PRESENTED AT THE ANNUAL MEETINGS OF THE KNEE SOCIETY
Measuring Tools for Functional Outcomes in Total Knee
Robert B. Bourne MD, FRCSC
Published online: 9 September 2008
? The Association of Bone and Joint Surgeons 2008
increasing scrutiny attributable to the fact that it is a high-
volume, high-cost medical intervention in an era of
increasingly scarce medical resources. Health-related
quality-of-life outcomes have been developed such that
healthcare providers might determine how good an inter-
vention is and whether it is cost-effective. Total knee
arthroplasty has been subjected to disease-specific, patient-
specific, global health, functional capacity, and cost-to-
utility outcome measures. Patient satisfaction is high (90%)
after total knee arthroplasty and 93% of patients would
have this operative procedure again. Large improvements
in preoperative to postoperative WOMAC scores occurred
(over 39 of 100 points in 82% of patients). Cost-to-quality
outcomes demonstrated total knee arthroplasties are ex-
tremely cost-effective. This analysis documents total knee
arthroplasty is a highly efficacious procedure that competes
favorably with all medical and surgical interventions.
We all hope to lead healthy, productive lives with ready
access to an effective healthcare system ; however, an
aging population, new technologies, and competition for
resources have led to a worldwide crisis in health care. As
such, healthcare interventions have come under increasing
scrutiny [12, 14]. Healthcare providers need to know how
good an intervention is and whether it is cost-effective
. The outcomes movement has evolved to answer many
of these questions in a scientifically valid manner [6, 24].
Because TKA is a high-volume, high-cost medical inter-
vention, it is not surprising health-related quality-of-life
outcomes have been developed to allow investigators to
quantify preoperative to postoperative improvements in
TKA patient health status [7, 8, 11, 14, 16]. This research
has been valuable to patients, surgeons, and healthcare
providers. Patients go to orthopaedic surgeons anticipating
the best possible outcomes. For surgeons, outcome studies
aid continuous quality assurance, and improve surgical
techniques and implant selection. For healthcare providers,
outcome studies provide assurance of high-quality, cost-
effective care. Unfortunately, however, there are no gold
standards in terms of TKA outcome tools.
Ideally, outcome measures used to assess an intervention
such as TKA should be valid (measures the proper out-
come), reproducible (same value should be obtained on
repeated assessments of a stable patient), and responsive to
changes in a patient’s condition [17, 18].
For assessing TKA, validated outcomes tools include
those that are disease-specific (ie, WOMAC, Oxford-12)
[3, 11, 12], patient-specific (ie, MACTAR) , global
health (ie, SF-36, SF-12, Nottingham Health Profile,
Sickness Impact Profile, and EuroQol) [8, 20, 25, 28, 29],
functional capacity (ie, 6-minute walk, 30-second stair
The author certifies that he has no commercial associations (eg,
consultancies, stock ownership, equity interest, patent/licensing
arrangements, etc) that might pose a conflict of interest in connection
with the submitted article.
The author certifies that his institution has approved the human
protocol for this investigation, that all investigations were conducted
in conformity with ethical principles of research, and that informed
consent for participation in the study was obtained.
R. B. Bourne (&)
London Health Sciences Centre, University of Western Ontario,
University Campus, 339 Windermere Road, London, ON,
Canada N6A 5A5
Clin Orthop Relat Res (2008) 466:2634–2638
climb, knee injury and osteoarthritis outcome score
[KOOS], pedometry studies, and gait analyses) [8, 10, 15,
23, 30], and cost-to-utility (ie, cost-to-quality adjusted life-
years) [21, 22, 26]. For the most part, patient-generated
data have been preferred to that which is physician-based.
An important addition to TKA outcomes has been the
addition of patient satisfaction data .
The purpose of this study is to provide a sense of how
each of these measures applies to TKA.
Materials and Methods
To illustrate the various validated outcome tools available
to assess patients undergoing TKA, we draw from data
submitted by surgeons in the province of Ontario and
contributed to the Ontario Joint Replacement Registry
(OJRR) and the Canadian Joint Replacement Registry
(CJRR) . The original intent of this data collection was
to allow continuous quality improvement, to help predict
the future need for THAs and TKAs, to determine the
effect of prolonged waiting times on patient outcomes, and
to determine the change score in health-related quality-of-
life outcomes that might be necessary for a patient to be
satisfied with the procedure. Where examples of knee
outcome data were unavailable in the OJRR or CJRR
databases, we have relied on published TKA outcomes,
either our own or those of others, to provide the necessary
information. Much of the data we report has been previ-
ously published as noted. All participating patients signed
an informed consent for their data to be assessed. The data
collection was approved by the Ethics Review Board at the
University of Western Ontario.
For patient satisfaction, we used the validated patient
satisfaction score developed by Jaeschke et al. . In this
satisfaction scale, a patient who was uncertain as to their
outcome was classified as 0, whereas those who were
dissatisfied were scored from -1 to -7 depending on their
degree of dissatisfaction. If they were satisfied, they were
graded +1 to +7 depending on their degree of satisfaction.
For disease-specific TKA outcomes, we most commonly
used WOMAC scoring as developed by Bellamy et al. 
to measure pain, stiffness, and physical function. Other
disease-specific outcome measures used elsewhere are
discussed, particularly in comparison studies to the WO-
MAC score (ie, Oxford-12) [12, 13].
For patient-specific scores, the MACTAR outcome tool
is often used . The MACTAR outcome tool, originally
described for patients with rheumatoid arthritis, provides
an individualized functional priority approach for assessing
improvement in physical disability in clinical trials. For
this outcome, each patient is given prompts such that they
can select the top five most disabling physical or social
activities for which they underwent total joint arthroplasty.
The measure is scored from a 10-cm visual analog scale
with 10 being the most disabling. The instrument therefore
can document improvement in level of function of each of
these activities postoperatively. We have not applied this
approach to TKAs but illustrate the scale for THAs.
Many global health scores are available. Dunbar et al.
 reported the Nottingham Health Profile and the SF-12
 gave the best ‘‘test-retest’’ reliability, but that the SF-
36  and the Sickness Impact Profile demonstrated the
best internal consistency reliability. In their analysis, the
disease site-specific Lequesne, Oxford-12, and WOMAC
outcomes also performed well. Recently, we performed a
study to determine the effect of patient factors such as
gender on TKA outcomes , exploring WOMAC and SF-
12 mental component scores (MCS) and physical compo-
nent scores (PCS) in 436 female and 292 male patients in
whom 843 TKAs were performed and followed for a mean
of 9.5 years (Table 1).
For global health assessment, we commonly used the
SF-36 or SF-12 outcomes tool as developed by Ware et al.
[28, 29]. More recently, the EuroQol global health outcome
tool has been popularized, particularly in Europe, and
several authors believe this five-item tool could replace the
SF-36 as a result of its higher response rate, accepting its
lower responsiveness [9, 13].
A number of tests are available to assess functional
outcomes after TKA. For functional capacity, we have
commonly used the 6-minute walk  and 30-second stair
climb  to assess patients undergoing TKA. Other
functional capacity tools include the KOOS, which is based
on the WOMAC score but has been expanded to include
the outcomes of pain, activities of daily living, sport and
recreation function, and knee-related quality of life .
Other functional outcomes of interest include the Interna-
tional Knee Documentation , the Lower Extremity
Functional Scale , and the UCLA activity-level rating
For cost-to-utility data, the cost-to-quality adjusted life-
year is often used. This is a difficult test to perform because
it requires accurate costing data that can be combined with
a perceived change in outcomes [17, 24].
Table 1. Gender comparisons: preoperative to postoperative change
Scoring method FemaleMale p value
WOMAC26 ± 2324 ± 220.28
SF-12 (MCS) 0.49 ± 12-1.27 ± 110.51
SF-12 (PCS)7 ± 118 ± 110.12
MCS = mental component score; PCS = physical component score.
Volume 466, Number 11, November 2008 Measuring Tools for TKA Functional Outcomes2635
Chesworth et al.  assessed 3003 patients undergoing
total joint arthroplasty whose data were captured in the
OJRR and reported the majority of patients (82%) had
increases in WOMAC scores of over 39 (of 100 total
points) and were satisfied with their procedure (Fig. 1).
Overall, 93% would have their TKA again (n = 2788), 5%
were uncertain (n = 138), and 3% would not have the
procedure again (n = 77). The WOMAC scores document
the remarkable improvement afforded by TKA (Figs. 2, 3).
WOMAC scores document TKA outcomes are superior if
surgery is performed less than 100 days from the decision
date (Fig. 4).
The patient-specific MACTAR scale identifies the top
five most disabling physical or social activities for which
they underwent arthroplasty [8, 27]. Patients undergoing
THA are substantially improved by the first postoperative
year and retain that improvement over 5 years (Fig. 5) .
Fig. 1 These Ontario Joint Replacement Registry data demonstrate
the preoperative to postoperative WOMAC change scores with patient
satisfaction/transition change scores as outlined by Jaeschke et al.
 (n = 3003).
Fig. 2 Patient severity at decision date as measured by WOMAC
scores for TKA (n = 4437) is demonstrated .
Fig. 3 Patient severity 1 year postoperatively after TKA (n = 4437)
is shown .
Fig. 4 The use of preoperative WOMAC scores to predict postop-
erative TKA patient outcomes based on the length of time patients
waited for their surgery. Note that mild (WOMAC, 60), moderate
(WOMAC, 40), and severe (WOMAC, 20) patients all did well if
their surgery was performed within 100 days from the decision date
Fig. 5 An example of outcomes using the patient-specific MACTAR
patient preference disability questionnaire in patients undergoing
THA is shown . When stating the top five reasons for undergoing
THA on a 10-centimeter visual analogue scale, the mean preoperative
to postoperative substantially improved and remained improved up to
four years postoperatively.
2636 Bourne Clinical Orthopaedics and Related Research
We found no differences in pre- to postoperative scores
between genders using the validated WOMAC, SF-12
(MCS), and SF-12 (PCS) outcome tools .
Using a functional outcome, we reported patients with
resurfaced patellae could climb more stairs in 30 seconds
than patients with unresurfaced patellae at 10 or more
years’ followup (Table 2) . The KOOS and UCLA
activity-level ratings have also been valuable in these
assessments [23, 30].
Cost-to-quality adjusted life-year (QALY) is less for
THA and TKA than for other common interventions such
as heart transplants and coronary artery bypass (Fig. 6) [8,
19, 21]. Although controversial, some investigators have
indicated interventions with a cost-to-QALY of less than
$20,000 are so cost-effective that there should be no
question about their use in clinical practice from a cost-
benefit perspective . The same researchers suggest
those interventions with a cost-to-QALY between $20,000
and $100,000 are moderately cost-effective and probably
should be used. These researchers have questioned the
funding of interventions with a cost-to-QALY of more than
$100,000. Obviously, there are substantial ethical and
patient concerns about such an approach.
The ability to measure the performance of medical devices
such as TKA has led to greater acceptance of this inter-
vention based on solid evidence that demonstrates the
efficacy, safety, and cost-effectiveness of this surgical
intervention as compared with other medical interventions
. The application of outcomes data to TKA has fostered
continuous quality improvement not only in surgical
techniques, but also in implant selection. Using high-level
methodology, researchers have and will be able to plan
randomized clinical trials to provide high-quality data on
TKA designs and techniques, perform the trial, analyze the
results, and change clinical practice based on these out-
comes [6, 20].
To date, no single best outcome tool has emerged for
TKA studies. There are considerable agreement-validated
outcomes tools that are responsive, reliable, and repro-
ducible that should be used [11, 20, 22]. Unfortunately, the
widely used Knee Society clinical rating has not been
validated. Work is underway to develop a new validated
Knee Society scoring system and it is hoped this would be
given high priority. As a consequence, the WOMAC and
Oxford-12 disease-specific scores are the most frequently
used outcomes tools. When comparisons to other medical
interventions are needed, the global health outcomes such
as the SF-12, SF-36, or EuroQol are useful. Cost-to-utility
outcomes are of great interest to healthcare providers, but
must be based on very accurate costing data and validated
outcome measures. The use of real costing data rather than
charges must be used if cost-to-utility studies are to be used
and provide meaningful comparative information. Histori-
cally, precise costs have been combined with clinical
improvement on a validated outcome tool such as time
trade-off or standard gamble.
Patient satisfaction data are assuming greater impor-
tance in outcome studies. A link between patient
expectations and postoperative satisfaction has been
established; hence, it seems wise to collect and analyze
both preoperative expectation and postoperative satisfac-
tion data (Fig. 1). In many ways, satisfaction data are good
proxies for a substantially improved validated disease-
specific outcome measure. Using the Jaeschke et al. 
Table 2. Results of functional tests performed at 10 years
of stairs climbed
in 30 seconds
Extension torque63.68 55.670.359
Flexion torque36.92 29.790.627
Deep flexion test
Patellar glide test
Patellar grind test
ROM = range of motion.
Fig. 6 A comparison of cost-to-utility adjusted life years (cost-to-
QALY) of various medical and surgical interventions. Treat-
ments\$20,000 are considered extremely cost-effective, those
between $20,000 - $100,000 moderately so and those[$100,000
expensive. (HT = medical treatment of moderate hypertension,
CAB = coronary bypass, Hemodial = hemodialysis, L. Transp =
liver transplantation, HIV = medical treatment of human immune
virus infections). HT = medical treatment of moderate hypertension;
CAB = coronaryartery bypass;
Transp = liver transplantation; HIV = medical treatment of human
immune virus infections .
Hemodial = hemodialysis;L
Volume 466, Number 11, November 2008Measuring Tools for TKA Functional Outcomes2637
scale, patients who rank +5 to +7 usually have TKA
change scores in excess of 25 of 100 WOMAC points.
The use of outcome tools in TKA will continue to
evolve. There remains a need for the development of a
single, patient-generated outcomes tool that combines at
least some disease-specific, global health, and functional
capacity outcomes. Furthermore, postmarket surveillance
of TKA procedures will continue to grow. Already, there
are national joint arthroplasty registries in Sweden, Nor-
way, Finland, the United Kingdom, Australia, New
Zealand, Canada, and many other countries [2, 5, 13]. This
trend should be encouraged to continuously improve the
field of TKA. The addition of validated outcomes to these
national registries will enhance their already enormous
value (Figs. 1–4).
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2638 Bourne Clinical Orthopaedics and Related Research