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The Forgotten Joint as the Ultimate Goal in Joint Arthroplasty

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The “Forgotten Joint” a
Joint Arth
Validation of a New Patient-R
Henrik Behrend, MD,* Karlme
Johannes M. Giesinger, MSc, PhD,y
arthroplasty, hip joint arthroplasty.
' 2012 Elsevier Inc. All rights reserved.
in everyday life can be regarded as the ultimate goal
in joint arthroplasty resulting in the greatest possible
patient satisfaction.
for an
r into
oint in
OA at
From th
Gallen, S
The Co
found at
' 2012
The Journal of Arthroplasty Vol. 27 No. 3 2012
Based on this consideration and taking the need
instrument with increased discriminatory powe
account, we introduce a new concept in PRO
ment: the patients' ability to forget the artificial j
everyday life.
Materials and Methods
All patients undergoing cemented total hip a
plasty (THA) or total knee arthroplasty (TKA) for
e *Department of Orthopaedic Surgery, Kantonsspital St Gallen, St
witzerland; and yDepartment of Psychiatry and Psychotherapy,
Medical University, Innsbruck, Austria.
tted August 9, 2010; accepted June 15, 2011.
mentary material available at www.arthroplastyjournal.org.
nflict of Interest statement associated with this article can be
gation was performed at the Department of Orthopaedic
Kantonsspital St Gallen, 9007 St Gallen, Switzerland.
t requests: Henrik Behrend, MD, Department of Orthopaedic
Kantonsspital St Gallen, 9007 St Gallen, Switzerland.
Elsevier Inc. All rights reserved.
Joint arthroplasty surgery has proven to be successful in
relieving pain and improving function in patients with
osteoarthritis (OA) [1-3]. Traditional rating systems
assessing the outcome after joint arthroplasty frequently
focus on “objective” surgeons' ratings and often neglect
patients' needs and views. However, patients' concerns
after arthroplasty may differ significantly from those of
their surgeons [4,5]. Consequently, there has been a
growing recognition that postoperative evaluation
should use patient-reported outcome (PRO) tools to
provide a more patient-centered view on treatment
outcome [6].
The first widely used PRO scores emerged in the 1980s,
assessing various aspects of treatment outcome after
joint arthroplasty [7,8].
Over the last decades, joint arthroplasty has evolved
and patient outcome has improved considerably. This
resulted in ceiling effects in commonly applied PRO tools
[9]. These tools show weakness in discriminating
between patients with a good outcome and patients
with an excellent outcome. Many PRO tools are unable
to detect subtle differences in patient satisfaction
between different designs or implantation techniques.
In our opinion, the ability to forget the artificial joint
Abstract: With improving patient outcome aft
increased discriminatory power especially in w
the present study was to develop and validate
introducing a new aspect of patient-reported ou
joint in everyday life. After a pilot study, th
consistency (Cronbach α = .95). Ceiling effec
compared with the Western Ontario and M
Known-group comparisons proved the FJS to b
243 patients. The FJS not only reflects differen
“good,”“very good,” and “excellent” outcome
adequate measurement range and because it
“forgotten joint.” Keywords: forgotten join
s the Ultimate Goal in
eported Outcome Measure
inrad Giesinger, MD, MSc,*
and Markus S. Kuster, MD, PhD*
joint arthroplasty, new assessment tools with
-performing patients are desirable. The goal of
new score (“Forgotten Joint Score,” or FJS)
ome: the patient's ability to forget the artificial
FJS was validated and showed high internal
were considerably lower for the FJS (9.2%)
aster Universities subscales (16.7%-46.7%).
highly discriminative in a validation sample of
s between “good” and “bad” but also between
This concise score is appealing for its more
easures the new, promising concept of the
score, patient-reported outcome, knee joint

The “Forgotten Joint” in Joint Arthroplasty

Behrend et al 431
our institution between January 2003 and June 2007
were considered for enrollment in the study.
Inclusion criteria were as follows:
1. Unilateral THA (cemented Stuehmer-Weber hip
stem, uncemented Fitmore cup; Zimmer, Switzer-
land) or unilateral TKA (cemented LCS complete;
DePuy, Johnson and Johnson, Switzerland)
2. Primary arthroplasty surgery
3. No previous THA or TKA surgery at a different
4. Written informed consent
Sociodemographic and clinical data including sex, age,
education, type and location of implant, and time since
surgery were collected.
Patients received the questionnaires and an informed
consent form via mail. A reminder call was made to
those patients who did not return the questionnaires
within 8 weeks. If there was no response for another
4 weeks, they were excluded. Reasons for not partici-
pating in the study were recorded.
Before the collection of the above validation sample, a
pilot sample for item selection for the final version of
the “Forgotten Joint Score” (FJS) was recruited using
the above-mentioned inclusion criteria. Furthermore,
a group of healthy controls of the same age with no
history of any previous joint surgery was recruited to
obtain reference values for the FJS.
Ethical approval for this study was obtained from the
ethics committee of the canton of St Gallen, Switzerland.
Forgotten Joint Score
A 20-item pool was developed based on literature
research and expert opinion choosing items relevant to
the average population undergoing joint arthroplasty.
The team of experts included clinicians and a method-
ologist and statistician. In addition, we assessed patients'
opinion to identify the activities of daily living that are
important to a population undergoing arthroplasty. All
items were referring to the awareness of the artificial
joint (hip or knee) during various activities of daily
living. The initial item pool was administered to a pilot
sample for item selection. The final version of the FJS
(FJS-12) was subsequently used for data collection in a
larger sample for validating the new score.
Western Ontario and McMaster Universities
The Western Ontario and McMaster Universities
(WOMAC) OA Index is a widely used outcome mea-
sure in patients with lower limb OA and was intro-
duced by Bellamy and Buchanan [10] in 1986. It consists
of 24 questions covering 3 dimensions: pain (5 ques-
tions), stiffness (2 questions), and function (17 ques-
tions). The WOMAC OA Index has been extensively
tested for validity, reliability, feasibility, and responsive-
ness for measuring changes after different OA inter-
ventions [7,11,12].
Statistical Analysis
Sample characteristics are presented as numbers,
percentages, means, standard deviations, and ranges.
For item selection in the pilot study, we calculated
Cronbach α, percentage of missing items, and frequency
of response categories. Ceiling or floor effects of the
scales are described as percentages of patients showing
the best or worst possible score on a scale.
To determine construct validity, group comparisons
were done with regard to the type (hip/knee) and
location (side) of implant, sex, and a reference sample of
healthy controls. For normally distributed data, we
performed t tests for independent samples and 1-way
analyses of variance.
Correlations with WOMAC subscales were calculated
to determine convergent validity of the FJS.
The final version of the FJS was scored by adding up
the item responses and transforming the raw score to a
scale ranging from 0 to 100. In the FJS, high scores
indicate good outcome, that is, a high degree of
“forgetting” the joint. This means that the FJS has an
opposite direction compared with the WOMAC score
where high scores indicate bad outcome.
For ease of interpretation, we use the terms ceiling effect
in reference to good outcome and floor effect in reference
to bad outcome.
Sample Characteristics
For scale development, 46 patients were recruited as a
pilot sample for item selection before the validation
sample. In the pilot sample, the mean (SD) patient age
was 71.7 (10.3) years (range, 50-90 years), and 24
(52.2%) were female. Twenty-three (50%) patients had
undergone THA, and the same number had undergone
TKA. Time since surgery was, on average (SD), 31.2
(12.3) months (range, 15-58 months).
For recruitment of the validation sample, 356 patients
were contacted in our mail survey in August 2008.
Two hundred forty-three (68.3%) completed and sent
back the questionnaires and provided written informed
consent. Reasons for not participating in the study were
as follows: refusal of participation (42 patients; 11.8%),
wrong address (29 patients; 8.1%), death (22 patients;
6.2%), severe cognitive impairment (3 patients; 0.8%),
moving abroad (1 patient; 0.3%), and unknown reasons
(16 patients; 4.5%).
Mean (SD) patient age was 70.6 (11.3) years (range,
32-91 years). One hundred twenty (49.4%) patients
were female. One hundred fifty-seven (64.6%) patients
had undergone THA, and 86 (35.4%) had undergone
TKA. Age was not significantly related to sex or to
type of arthroplasty (THA/TKA). For further details, see
Table 1.
Men were found to have higher educational levels
than women (χ
= 28.7; P b .001).

Frequency of THA and TKA was different in men
compared with women (χ
= 5.2; P = .022), with women
having less THA and more TKA than men.
No other significant differences were found among the
included sociodemographic and clinical variables.
The healthy control sample consisted of 57 individuals
(mean ± SD age, 65.0 ± 8.4 years; range, 45-91 years; 32
women [56.1%]). Twenty-eight individuals were rating
6 items (items 15-20). They were excluded before
analysis of internal consistency. The remaining 14
items proved to show high internal consistency (Cron-
bach α = .96), with no item reducing Cronbach α
significantly. Hence, no item was deleted because of this
selection criterion but with regard to content. For the
final version, item 12 was adjusted to group different
sports activities.
Furthermore, the response format of the definitive
scale was adjusted because the highest response category
(“always”) was rarely used in the pilot study (mean
frequency, 5.9%).
The pilot wording of the 5-point Likert response format
“(never–almost never–sometimes–mostly–always) was
changed to (never–almost never–seldom–sometimes–
mostly) to reduce ceiling effects.”
The final version of the FJS comprised 12 items, the
FJS-12. For further details see Table 2.
Psychometric Properties of the FJS-12
In the larger validation sample, the final 12-item
version of the FJS showed high internal consistency
(Cronbach α = .95), with no item significantly lowering
internal consistency. Correlations between FJS-12 and
Table 1. Sample Characteristics for the Validation Sample
(n = 243)
Sex Male 123/243 (50.6%)
Female 120/243 (49.4%)
Age (y) Mean (SD) 70.6 (11.3)
Range 32-91
Education Compulsory school 54/243 (22.2%)
Apprenticeship 104/243 (42.8%)
A level/professional school 39/243 (16.0%)
University 13/243 (5.3%)
Missing 33/243 (13.5%)
Location THA 157/243 (64.6%)
TKA 86/243 (35.4%)
Side Left 116/243 (47.7%)
Right 127/243 (52.3%)
Time since
surgery (mo)
Mean (SD) 31.1 (12.3)
Range 15-58
432 The Journal of Arthroplasty Vol. 27 No. 3 March 2012
their knee (49.1%), and 29 individuals were rating their
hip (50.9%).
Pilot Study
Data collected from the pilot sample with the initial
item pool showed a high percentage of missing items for
Table 2. Item and Scale Statistics for Pilot Sample
Item Missin
1. Awareness in bed at night? 0
2. Awareness standing for 5 min? 0
3. Awareness standing up from sitting? 2
4. Awareness sitting on a chair for more than 1 h? 2.2%
5. Awareness when you are walking for more
than 15 min?
6. Awareness when you are walking for more
than 1 h?
7. Awareness bathing? 8.7%
8. Awareness doing foot care? 4.3%
9. Awareness driving a car? 2.2%
10. Awareness stair climbing? 0.0%
11. Awareness doing household work? 2.2%
12. Awareness walking on uneven ground? 4.3%
13. Awareness when standing up from
a low-sitting position?
14. Awareness carrying heavy objects? 8.7%
15. Awareness during gardening? 28.3%
16. Awareness riding a bicycle? 37.0%
17. Awareness swimming? 19.6%
18. Awareness mountain hiking? 26.1%
19. Awareness skiing? 80.4%
20. Awareness playing golf? 78.3%
WOMAC scales were as follows: r = −0.75 for WOMAC-
Pain, r = −0.69 for WOMAC-Stiffness, r = −0.78 for
WOMAC-Function, and r = −0.79 for WOMAC-Total.
For further details, see Table 3.
The proportion of missing item responses was 3.8% for
the FJS-12 and 1.9% to 4.8% for the WOMAC
subscales. Ceiling effect was lower for the FJS-12
Frequency of
Highest Response
Category (Always)
Cronbach α
(If the Item
Was Deleted)
2.2% .96 0.78
4.3% .96 0.83
4.4% .96 0.88
4.4% .96 0.75
6.8% .96 0.79
11.1% .96 0.82
4.8% .96 0.75
15.9% .96 0.67
4.4% .96 0.70
6.5% .96 0.79
4.4% .96 0.87
9.1% .96 0.84
16.3% .96 0.83
9.5% .96 0.82

Table 3. Validation Sample: Item and Scale Statistics for FJS-12 and Statistics for WOMAC Scales
Mean SD Range
FJS-12 56.3 30.5 0-100
1. Awareness in bed at night? 2.43 1.41 1-5
2. Awareness sitting on a chair for more than 1 h? 2.56 1.47 1-5
3. Awareness when you are walking for more than 15 min? 2.68 1.53 1-5
4. Awareness taking a bath/shower? 2.04 1.38 1-5
5. Awareness traveling in a car? 2.23 1.40 1-5
6. Awareness climbing stairs? 2.92 1.59 1-5
7. Awareness walking on uneven ground? 2.92 1.55 1-5
8. Awareness when standing up from a low-sitting position? 3.08 1.55 1-5
The “Forgotten Joint” in Joint Arthroplasty

Behrend et al 433
(9.2%) compared with the WOMAC subscales (16.7%-
46.7%). For further details, see Table 4.
Sociodemographic and Clinical Variables and
the FJS-12
Analyses of the impact of sociodemographic and
clinical variables on the FJS-12 score showed that men
scored higher than did women (61.7 vs 50.8; t = 2.82,
P = .005). For further details, see Table 5.
Furthermore, education had a significant impact on
the FJS-12 score (compulsory school 49.7 vs university
78.3; F = 3.85, P = .010). No significant association was
found for side (P = .621), age (P = .170), and time since
surgery (P = .622).
Patients scored significantly lower (56.3 vs 82.5;
t = −7.72, P b .001) compared with the reference
sample from the healthy general population. For further
9. Awareness\ standing for long periods of time?
10. Awareness doing housework or gardening?
11. Awareness taking a walk/hiking?
12. Awareness doing your favorite sport?
WOMAC scales
details, see Fig. 1.
FJS-12 Scores in THA and TKA
Patients who had undergone THA scored significantly
higher on the FJS-12 than did patients who had
undergone TKA (59.8 vs 50.0; t = 2.41, P = .017). This
was also found in the healthy control sample. For
further details, see Table 5. Individuals who were asked
about their hips reported this joint to be more
Table 4. Ceiling Effects and Missing Item Responses for FJS-
12 and WOMAC Scales
Ceiling Effect Floor Effect Missing Items
FJS-12 9.2% 3.3% 3.8%
WOMAC-Pain 38.4% 0.4% 2.7%
WOMAC-Stiffness 46.7% 0.8% 1.9%
WOMAC-Function 19.6% 0.8% 4.8%
WOMAC-Total 16.7% 0.4% 4.1%
“forgotten” compared with the group of individuals
rating their knees (93.0 vs 71.7; t = 4.40, P b .001).
No interaction effect of THA/TKA and sex on FJS-12
was found (F = 0.06, P = .813); that is, the impact of
THA/TKA on the FJS-12 was not different in men and
women, and the impact of sex was not different in
patients after THA or TKA.
To date, no criterion standard for assessing outcome
after THA or TKA has been established. Instead, a wide
range of outcome measures assessing various aspects of
physical functioning and pain are in common use. These
outcome measures are available as self-report instru-
ments or proxy rating scales for health professionals as
well as in the form of clinical tests.
2.85 1.52 1-5
2.96 1.44 1-5
3.12 1.53 1-5
2.94 1.49 1-5
3.0 4.0 0-20
1.5 1.8 0-8
12.9 14.6 0-68
17.4 19.8 0-96
Our study introduces a new concept of evaluating
outcome beyond the traditional measures: the patients'
ability to forget the artificial joint in everyday life. In our
opinion, this is the ultimate goal to ensure maximum
patients' satisfaction. This new concept integrates a
variety of variables such as pain, stiffness, function in
activities of daily living, patients' expectations, patients'
activity levels, and psychosocial factors.
Content validity of the FJS-12 was accomplished by a
team of experts including clinicians, a methodologist,
Table 5. Sex- and Joint-Specific Results for the FJS-12
Location Sex n Mean SD
THA Male FJS 87 63.8 29.2
Female FJS 68 54.7 32.1
TKA Male FJS 35 56.5 30.1
Female FJS 50 45.4 28.0
Healthy controls Male FJS 25 86.6 17.0
Female FJS 32 79.3 23.2

434 The Journal of Arthroplasty Vol. 27 No. 3 March 2012
and patients. By involving the patients as “experts” and
including their opinion during the development phase of
the instrument, we generated questions with content
that is important to the specific population of arthro-
plasty patients.
The newly developed PRO scale, the FJS-12, showed
good results not only with regard to psychometric
properties but also when used for known-group
comparisons. Internal consistency of the scale was very
high as expected for this type of measures. The
measurement range of the scale proved to be adequate
for patients 1 to 3 years after THA/TKA, but also to assess
“joint awareness” of healthy controls.
Compared with the WOMAC OA Index, the FJS-12
showed considerably less ceiling effect. Naturally, ceiling
effects are also related to the number of items in a scale.
Themore items a scale has, the less likely it is that a patient
chooses the highest or lowest response category in every
single item. Despite the fact that the WOMAC total score
Fig. 1. Mean ± 1SD for the FJS-12 in patients and reference
sample (A) and in male and female patients (B) separately for
knee (blue) and hip (green).
comprises twice as many items as the FJS-12, only half as
many patients had the best possible score in the FJS-12.
This indicates that the FJS-12 outperforms the
WOMAC subscales in terms of discriminatory power.
Strong ceiling effects impair a scale's sensitivity to
changes over time and its ability to discriminate well
between different groups. Even in a healthy control
sample of comparable age, mean values were well
below the maximum score of 100; this finding suggests
that the FJS-12 differentiates very well in a highly
functioning group.
Patients who had undergone arthroplasty rated their
knees significantly lower than their hips. This was also
found in the healthy control group and can, therefore,
not be considered only an arthroplasty-specific effect.
Consequently, it is unlikely that this natural difference
can be overcome by arthroplasty.
Convergent validity of the FJS-12 was very good as
indicated by high correlations with the WOMAC scales.
It also performed well in known-group comparisons;
that is, it was highly discriminative for THA and TKA,
showing differences in outcome between men and
women and patients who had undergone arthroplasty
vs healthy individuals of the same age.
Previous studies showed consistently better outcome
after THA compared with TKA [13-17]. This could be
attributed to the fact that patients who had under-
gone THA show greater postoperative improvement
compared with preoperative status than patients who
had undergone TKA [11]. Various authors also
showed better outcome in men compared with women
[18-21]. It has been shown that women of that age group
are more likely to live alone. Patients who live alone
delay joint arthroplasty surgery until they reach an older
age and have greater joint pain and dysfunction than
those who live with another person, leading to a poorer
1-year outcome [22]. Noble et al [18] found patients who
had undergone arthroplasty to have a lower functional
level than age- and sex-matched healthy controls. In
their study, 52% of patients after TKA reported remain-
ing knee problems during various activities vs 22% of
subjects with no previous knee disorders. The authors
concluded that it seemed elusive to think that we could
restore normal healthy joint function with an artificial
joint in the near future. Consistently, other authors
[23-25] found that TKA did not restore the ease asso-
ciated with normal knee function.
Our data also showed a high impact of education on
outcome after arthroplasty. Patients with a university
degree scored significantly higher than did patients who
had just completed compulsory school. However, to
investigate this finding more, thorough studies with
larger sample sizes are necessary.
We found no significant correlation for time since
surgery. This may be attributed to the fact that time since
surgery was more than 12 months for all joints. As

The “Forgotten Joint” in Joint Arthroplasty

Behrend et al 435
Fitzgerald et al [26] have shown in 2004, the patients'
improvement after joint arthroplasty reaches an end
point at the 12-month mark.
Patient age did not significantly influence the FJS-12
in our study. However, this finding may be related to
the rather narrow age distribution in our sample
(mean ± SD age, 70.6 ± 11.3 years; range, 32-91 years).
A favorable feature of this new PRO score may well be
that it is less susceptible to deteriorating general health.
As patients' activity levels naturally decrease with age,
the awareness of the joint during the remaining
activities of everyday life may also alter. Furthermore,
in an older population, health problems unrelated to the
artificial joint often overshadow minor joint-related
impairments; that is, the target-performance compari-
son in the aging patient adjusts itself to some extent.
This could be especially important for long-term
follow-up studies with a longitudinal study design
where other scores tend to get worse by interference
with general health problems [27-29].
Limitations of our study are the lack of clinical,
objective tests as an additional outcome measure to
further investigate convergent validity. We may well
have picked up changes over time by including patients
at an earlier postoperative stage. Furthermore, the cross-
sectional design of our study did not allow us to assess
time-dependent parameters. Currently, we are recruit-
ing patients to determine retest reliability, sensitivity to
change over time, and response shift over time in a
separate study with a longitudinal design. The new
instrument should further be tested by other authors
and in different patient populations.
Regarding a normal healthy joint as the benchmark
to evaluate postoperative results, the lack of “aware-
ness” of the normal healthy joint should be intro-
duced as a new aspect in PRO assessment. In general,
one is not aware of a healthy joint during the usual
activities of daily living. The joint can therefore be
regarded as forgotten.
Because this state of a “forgotten joint” rules out any
significant subjective impairments like pain, instability,
or disabling range of motion, we believe that the
patients' ability to forget about their joint is a valuable
parameter to evaluate subjective joint function.
This concise, disease-specific score reduces patients'
burden andmay be useful in future outcome studies that
include patients' perspective (see Appendix at www.
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436 The Journal of Arthroplasty Vol. 27 No. 3 March 2012

Conditions of use: the FJS-12 is free of charge and may be used in academic as well as commercial settings.
The “Forgotten Joint” in Joint Arthroplasty

Behrend et al 436.e1
FJS-12 score
The following 12 questions refer to how aware you are of your artificial hip/knee joint in everyday life. Please tick
one answer from each question.
Are you aware of your artificial joint…
1. … in bed at night?
○ never ○ almost never ○ seldom ○ sometimes ○ mostly
2. … when you are sitting on a chair for more than 1 hour?
○ never ○ almost never ○ seldom ○ sometimes ○ mostly
3. … when you are walking for more than 15 minutes?
○ never ○ almost never ○ seldom ○ sometimes ○ mostly
4. … when you are taking a bath/shower?
○ never ○ almost never ○ seldom ○ sometimes ○ mostly
5. … when you are traveling in a car?
○ never ○ almost never ○ seldom ○ sometimes ○ mostly
6. … when you are climbing stairs?
○ never ○ almost never ○ seldom ○ sometimes ○ mostly
7. … when you are walking on uneven ground?
○ never ○ almost never ○ seldom ○ sometimes ○ mostly
8. … when you are standing up from a low-sitting position?
○ never ○ almost never ○ seldom ○ sometimes ○ mostly
9. … when you are standing for long periods of time?
○ never ○ almost never ○ seldom ○ sometimes ○ mostly
10. … when you are doing housework or gardening?
○ never ○ almost never ○ seldom ○ sometimes ○ mostly
11. … when you are taking a walk/hiking?
○ never ○ almost never ○ seldom ○ sometimes ○ mostly
12. … when you are doing your favorite sport?
○ never ○ almost never ○ seldom ○ sometimes ○ mostly
Scoring: For scoring the FJS-12, all responses are summed (never, 0 points; almost never, 1 point; seldom, 2 points;
sometimes, 3 points; mostly, 4 points) and then divided by the number of completed items. This mean value is
subsequently multiplied by 25 to obtain a total score range of 0 to 100. Finally, the score is subtracted from 100, to
change the direction of the final score in a way that high scores indicate a high degree of “forgetting” the artificial
joint, that is, a low degree of awareness.
If more than 4 responses are missing, the total score should not be used.