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N Engl J Med, Vol. 347, No. 2
·
July 11, 2002
·
www.nejm.org
·
81
The New England
Journal
of
Medicine
Copyright © 2002 by the Massachusetts Medical Society
VOLUME 347
J
ULY
11, 2002
NUMBER 2
A CONTROLLED TRIAL OF ARTHROSCOPIC SURGERY
FOR OSTEOARTHRITIS OF THE KNEE
J. B
RUCE
M
OSELEY
, M.D., K
IMBERLY
O’M
ALLEY
, P
H
.D., N
ANCY
J. P
ETERSEN
, P
H
.D., T
ERRI
J. M
ENKE
, P
H
.D.,
B
ARUCH
A. B
RODY
, P
H
.D., D
AVID
H. K
UYKENDALL
, P
H
.D., J
OHN
C. H
OLLINGSWORTH
, D
R
.P.H.,
C
AROL
M. A
SHTON
, M.D., M.P.H.,
AND
N
ELDA
P. W
RAY
, M.D., M.P.H.
A
BSTRACT
Background
Many patients report symptomatic re-
lief after undergoing arthroscopy of the knee for os-
teoarthritis, but it is unclear how the procedure
achieves this result. We conducted a randomized,
placebo-controlled trial to evaluate the efficacy of ar-
throscopy for osteoarthritis of the knee.
Methods
A total of 180 patients with osteoarthritis of
the knee were randomly assigned to receive arthro-
scopic débridement, arthroscopic lavage, or placebo
surgery. Patients in the placebo group received skin
incisions and underwent a simulated débridement
without insertion of the arthroscope. Patients and
assessors of outcome were blinded to the treatment-
group assignment. Outcomes were assessed at mul-
tiple points over a 24-month period with the use of
five self-reported scores — three on scales for pain
and two on scales for function — and one objective
test of walking and stair climbing. A total of 165 pa-
tients completed the trial.
Results
At no point did either of the intervention
groups report less pain or better function than the pla-
cebo group. For example, mean (±SD) scores on the
Knee-Specific Pain Scale (range, 0 to 100, with higher
scores indicating more severe pain) were similar in the
placebo, lavage, and débridement groups: 48.9±21.9,
54.8±19.8, and 51.7±22.4, respectively, at one year
(P=0.14 for the comparison between placebo and la-
vage; P=0.51 for the comparison between placebo
and débridement) and 51.6±23.7, 53.7±23.7, and 51.4±
23.2, respectively, at two years (P=0.64 and P=0.96,
respectively). Furthermore, the 95 percent confidence
intervals for the differences between the placebo
group and the intervention groups exclude any clin-
ically meaningful difference.
Conclusions
In this controlled trial involving pa-
tients with osteoarthritis of the knee, the outcomes
after arthroscopic lavage or arthroscopic débridement
were no better than those after a placebo procedure.
(N Engl J Med 2002;347:81-8.)
Copyright © 2002 Massachusetts Medical Society.
From the Houston Veterans Affairs Medical Center (J.B.M., K.O., N.J.P.,
T.J.M., D.H.K., C.M.A., N.P.W.); the Department of Orthopedic Surgery
(J.B.M.), the Department of Medicine, Section of Health Services Research
(K.O., N.J.P., T.J.M., C.M.A., N.P.W.), and the Center for Medical Ethics
and Health Policy (B.A.B.), Baylor College of Medicine; and International
Survey Research (D.H.K.) — all in Houston; and the Laguna Honda Hos-
pital, San Francisco (J.C.H.). Address reprint requests to Dr. Wray at the
Section of Health Services Research, Baylor College of Medicine, 2002
Holcombe Blvd. (M.R. 152), Houston, TX 77030, or at nwray@bcm.
tmc.edu.
HEN medical therapy fails to relieve
the pain of osteoarthritis of the knee,
arthroscopic lavage or débridement
is often recommended. More than
650,000 such procedures are performed each year
1
at a cost of roughly $5,000 each. In uncontrolled
studies of knee arthroscopy for osteoarthritis, about
half the patients report relief from pain.
2-16
However,
the physiological basis for the pain relief is unclear.
There is no evidence that arthroscopy cures or arrests
the osteoarthritis. Therefore, we conducted a random-
ized, placebo-controlled trial to assess the efficacy of
arthroscopic surgery of the knee in relieving pain
and improving function in patients with osteoarthri-
tis. Both patients and assessors of outcome were blind-
ed to the treatment assignments.
METHODS
The college and hospital institutional review board approved
the protocol. A data and safety monitoring board monitored the
study.
Study Participants
Participants were recruited from the Houston Veterans Affairs
Medical Center from October 1995 through September 1998.
Patients were eligible if they were 75 years old or younger, had os-
teoarthritis of the knee as defined by the American College of
Rheumatology,
17
reported at least moderate knee pain on average
(»4 on a visual-analogue scale ranging from 0 to 10) despite max-
imal medical treatment for at least six months, and had not un-
dergone arthroscopy of the knee during the previous two years.
W
The New England
Journal
of
Medicine
Copyright © 2002 by the Massachusetts Medical Society
VOLUME 347
J
ULY
11, 2002
NUMBER 2
82
·
N Engl J Med, Vol. 347, No. 2
·
July 11, 2002
·
www.nejm.org
The New England Journal of Medicine
The severity of osteoarthritis in the study knee (that with the
greatest pain-induced limitation of function) was assessed radio-
graphically and graded on a scale of zero to four.
18
The scores for
the three compartments were added together to generate a sever-
ity grade of 0 to 12. Criteria for exclusion were a severity grade
of 9 or higher, severe deformity, and serious medical problems.
All patients provided informed consent, which included writing
in their chart, “On entering this study, I realize that I may receive
only placebo surgery. I further realize that this means that I will
not have surgery on my knee joint. This placebo surgery will not
benefit my knee arthritis.” Of the 324 consecutive patients who
met the criteria for inclusion, 144 (44 percent) declined to par-
ticipate. Participants were younger than those who declined to
participate (52.3±11.3 years vs. 55.3±12.4 years, P=0.002), were
more likely to be white (62.2 percent vs. 50.7 percent, P=0.03),
and had more severe arthritis (25.0 percent vs. 12.5 percent with
grade 7 or 8 arthritis, P<0.001).
Randomization Process and Treatment Groups
Participants were stratified into three groups according to the
severity of osteoarthritis (grade 1, 2, or 3; grade 4, 5, or 6; and
grade 7 or 8). A stratified randomization process with fixed blocks
of six was used. Sealed, sequentially numbered, stratum-specific
envelopes containing treatment assignments were prepared and
given to the research assistant. After the patient was in the oper-
ating suite, the surgeon was handed the envelope. The treatment
assignment was not revealed to the patient.
Participants were randomly assigned to arthroscopic débridement,
arthroscopic lavage alone, or the placebo procedure. One orthope-
dist performed all the operations. Patients in the débridement group
or the lavage group received standard general anesthesia with endo-
tracheal intubation. Patients in the placebo group received a short-
acting intravenous tranquilizer and an opioid and spontaneously
breathed oxygen-enriched air.
Lavage
After diagnostic arthroscopy in patients in the lavage group, the
joint was lavaged with at least 10 liters of fluid. Anything that could
be flushed out through arthroscopic cannulas was removed. Nor-
mally, no instruments were used to mechanically débride or remove
tissue. However, if a mechanically important, unstable tear in the
meniscus (e.g., a displaced “bucket-handle” tear) was encountered,
the torn portion was removed and the remaining meniscus was
smoothed to a firm, stable rim. (There is general agreement that
it is inappropriate to leave this type of meniscal tear untreat-
ed.
11,13,19, 20
) No other débridement was performed.
Débridement
After diagnostic arthroscopy in patients in the débridement group,
the joint was lavaged with at least 10 liters of fluid, rough articular
cartilage was shaved (chondroplasty was performed), loose debris
was removed, all torn or degenerated meniscal fragments were
trimmed, and the remaining meniscus was smoothed to a firm and
stable rim. No abrasion arthroplasty or microfracture was performed.
Typically, bone spurs were not removed, but any spurs from the
tibial spine area that blocked full extension were shaved smooth.
Placebo Procedure
To preserve blinding in the event that patients in the placebo
group did not have total amnesia, a standard arthroscopic débride-
ment procedure was simulated. After the knee was prepped and
draped, three 1-cm incisions were made in the skin. The surgeon
asked for all instruments and manipulated the knee as if arthros-
copy were being performed. Saline was splashed to simulate the
sounds of lavage. No instrument entered the portals for arthros-
copy. The patient was kept in the operating room for the amount
of time required for a débridement. Patients spent the night after
the procedure in the hospital and were cared for by nurses who
were unaware of the treatment-group assignment.
Postoperatively, there were two minor complications and no
deaths. Incisional erythema developed in one patient, who was giv-
en antibiotics. In a second patient, calf swelling developed in the leg
that had undergone surgery; venography was negative for thrombo-
sis. In no case did a complication necessitate the breaking of the
randomization code.
Postoperative care was delivered according to a protocol spec-
ifying that all patients should receive the same walking aids, grad-
uated exercise program, and analgesics. The use of analgesics after
surgery was monitored; during the two-year follow-up period,
the amount used was similar in the three groups.
End Points
Study personnel who were unaware of the treatment-group as-
signments performed all postoperative outcome assessments; the
operating surgeon did not participate in any way. Data on end points
were collected 2 weeks, 6 weeks, 3 months, 6 months, 12 months,
18 months, and 24 months after the procedure. To assess whether
patients remained unaware of their treatment-group assignment,
they were asked at each follow-up visit to guess which procedure
they had undergone. Patients in the placebo group were no more
likely than patients in the other two groups to guess that they had
undergone a placebo procedure. For example, at two weeks, 13.8
percent of the patients in the placebo group guessed that they had
undergone a placebo procedure, and 13.2 percent of the patients
in the lavage and débridement groups guessed that they had under-
gone a placebo procedure.
The primary end point was pain in the study knee 24 months
after the intervention, as assessed by a 12-item self-reported Knee-
Specific Pain Scale (KSPS) created for this study (see Supplemen-
tary Appendix 1, available with the full text of this article at http://
www.nejm.org). Scores on this scale range from 0 to 100, with
higher scores indicating more severe pain. In addition, to ensure
our ability to detect any benefit, we also used five secondary efficacy
end points: two additional assessments of pain and three assessments
of function at all time points. Arthritis pain in general (i.e., not spe-
cifically in the study knee) was assessed by means of the four-item
pain subscale of the Arthritis Impact Measurement Scales (AIMS2-
P).
21,22
Higher scores on this subscale indicate more severe pain.
Body pain (i.e., not necessarily from arthritis and not necessarily in
the knee) was assessed with the 2-item pain subscale of the Medical
Outcomes Study 36-item Short-Form General Health Survey (SF-
36-P).
23,24
Higher scores on this subscale indicate less severe pain.
The AIMS2-P and the SF-36-P scores were transformed into scores
on a scale from 0 to 100.
Two self-reported measures of physical function were used: the
5-item walking–bending subscale from the AIMS2 (AIMS2-WB,
transformed into scores on a scale from 0 to 100, with higher
scores indicating more limited function
21,22
) and the 10-item phys-
ical-function subscale from the SF-36 (SF-36-PF, transformed into
scores on a scale from 0 to 100, with higher scores indicating better
function
23,24
). As an objective measure, we devised the Physical
Functioning Scale (PFS) to record the amount of time in seconds
that a patient required to walk 30 m (100 ft) and to climb up and
down a flight of stairs as quickly as possible. Longer times indicate
poorer functioning.
All six outcome scales had good reliability. The median Cron-
bach’s alpha (according to analyses of data from eight time points
for all scales) exceeded 0.80. Results for all the outcome measures
at all the time points that are not reported here are summarized
in Supplementary Appendix 2, available with the full text of this
article at http://www.nejm.org.
Statistical Analysis
Our pilot study indicated that it would be feasible to recruit 60
patients per year. The trial was designed to have 90 percent power,
A RANDOMIZED TRIAL OF KNEE ARTHROSCOPY
N Engl J Med, Vol. 347, No. 2
·
July 11, 2002
·
www.nejm.org
·
83
with a two-sided type I error of 0.04, to detect a moderate effect
size (0.55) between the placebo group and the combined arthro-
scopic-treatment groups in terms of body pain as measured by the
SF-36-P at two years, with an enrollment of 180 patients and 16
or fewer lost to follow-up (i.e., 164 or more completing the two-
year follow-up). The primary hypothesis was that the patients in
two arthroscopic-intervention groups combined would report the
same amount of knee pain at two years as the patients assigned
to the placebo group. All statistical tests compared the treatment
groups in terms of the values at each visit rather than analyzing
the changes from base line. (Scores for these changes [“change
scores”] were analyzed, with results that did not differ from the
results presented here.) The data and safety monitoring board re-
viewed interim data 15 months and 24 months after enrollment
began, using the Haybittle–Peto group-sequential method, with
stopping boundaries of P=0.001 for the two interim analy-
ses.
25,26
All reported P values are two-sided and have not been ad-
justed for multiple comparisons.
Our prespecified analytic strategy was to test, at all time points,
for the superiority of the arthroscopic procedures over the place-
bo procedure. Lacking evidence of superiority, we tested for ev-
idence that the arthroscopic procedures were equivalent
27-29
to the
placebo procedure by determining the extent to which the study
was powered to reject the hypothesis that the arthroscopic treat-
ments caused a small but clinically important improvement (the
“minimal important difference”). The minimal important differ-
ence for a scale is the smallest change score associated with a pa-
tient’s perception of a change in health status,
30
but it can vary
somewhat according to the method of calculation and the study
sample.
31,32
Minimal important differences for each of the six study
scales were calculated on the basis of the trial data by two differ-
ent methods: the change ratings of patients (their scores on a sin-
gle-item scale that asked patients if their condition was the same,
somewhat better [or worse], or much better [or worse] than be-
fore surgery) and the standard error of measurement (the SD of
the instrument multiplied by the square root of one minus its re-
liability coefficient).
30-32
Estimates were also obtained from the lit-
erature.
31-33
For each scale, we tested the hypothesis that the place-
bo procedure was equivalent to the arthroscopic procedures, using
as the minimal important difference the midpoint of the range of
the minimal important differences reported in the literature or
calculated on the basis of our data. If the 95 percent confidence
interval around the estimated size of the effect does not include
the minimal important difference, one can reject the hypothesis that
*There were no significant differences among the three groups. Plus–minus values are means ±SD.
†Severity of osteoarthritis was assessed by radiography.
‡Percentages are based on the number of patients who participated in the trial.
§Scores on the Knee Society Clinical Rating Scale range from 0 to 100, with higher scores indi-
cating fewer knee-related symptoms.
¶Scores for all psychological attributes, except expectations for benefit, range from 0 to 100, with
higher scores indicating more of the variable (e.g., more anxiety, depression, or optimism).
¿Expectations were retrospectively assessed two weeks after the procedure. Scores range from 1 to 5,
with higher scores indicating higher expectations.
T
ABLE
1.
B
ASE
-L
INE
C
HARACTERISTICS
OF
THE
R
ANDOMIZED
P
ATIENTS
.*
C
HARACTERISTIC
P
LACEBO
G
ROUP
(N=60)
L
AVAGE
G
ROUP
(N=61)
D
ÉBRIDEMENT
G
ROUP
(N=59)
Age (yr) 52.0±11.1 51.2±10.5 53.6±12.2
Male sex (%) 93.3 88.5 96.6
Race (%)
White 60.0 59.0 61.0
Black 31.7 31.2 22.0
Other 8.3 9.9 17.0
Severity of osteoarthritis in knee (%)†
Mild 28.3 27.9 30.5
Moderate 46.7 45.9 45.8
Severe 25.0 26.2 23.7
Analgesic use (%)‡
Nonprescription 70.0 67.2 64.4
Prescription 21.7 21.3 15.3
Mean score on Knee Society Clinical Rating Scale‡§
Knee symptoms 49.4 50.2 51.4
Function 62.2 62.4 57.6
Psychological attributes¶
Anxiety 27.0±21.0 30.2±19.9 28.4±22.4
Depression 20.0±32.0 28.1±37.2 22.0±35.3
Expectations for benefit¿ 3.5±1.0 3.5±0.9 3.6±1.1
Optimism 72.6±21.0 74.5±19.4 73.7±17.1
Satisfaction with general health 39.3±25.1 43.7±22.4 46.5±24.8
Social functioning 65.5±25.6 60.3±23.9 67.6±25.2
Somatization 11.3±12.7 9.6±12.4 10.0±10.7
Stress 28.4±19.7 26.1±18.2 27.9±18.8
Vitality 54.8±21.0 52.7±19.7 57.7±19.3
84
·
N Engl J Med, Vol. 347, No. 2
·
July 11, 2002
·
www.nejm.org
The New England Journal of Medicine
the arthroscopic procedures have a small but clinically important
benefit.
27
RESULTS
A total of 180 patients underwent randomization;
60 were assigned to the placebo group, 61 to the la-
vage group, and 59 to the débridement group. Base-
line characteristics were similar in the three study
groups (Table 1).
At no point did either arthroscopic-intervention
group have greater pain relief than the placebo group
(Fig. 1, Table 2, and Supplementary Appendix 2). For
example, there was no difference in knee pain between
the placebo group and either the lavage group or the
débridement group at one year (mean [±SD] KSPS
scores, 48.9±21.9, 54.8±19.8, and 51.7±22.4, re-
spectively; P=0.14 for the comparison with the la-
vage group, and P=0.51 for the comparison with
the débridement group) or at two years (mean KSPS
scores, 51.6±23.7, 53.7±23.7, and 51.4±23.2, re-
spectively; P=0.64 and P=0.96, respectively). Sim-
ilarly, there was no significant difference in arthritis
pain between the placebo group and the lavage
group or the débridement group at one or two years
(Table 2).
Furthermore, at no time point did either arthro-
scopic-intervention group have significantly greater
improvement in function than the placebo group
(Fig. 2, Table 3, and Supplementary Appendix 2). For
example, there was no significant difference between
the placebo group and either the lavage group or the
débridement group in the self-reported ability to
walk and bend at one year (mean AIMS2-WB scores,
49.4±25.5, 49.6±29.1, and 56.4±28.4, respectively;
P=0.98 for the comparison with the lavage group,
and P=0.19 for the comparison with the débride-
ment group) or at two years (mean AIMS2-WB score,
53.8±27.5, 51.1±28.3, and 56.4±29.4, respectively;
P=0.61 and P=0.64, respectively). Indeed, objective-
ly measured walking and stair climbing were poorer in
the débridement group than in the placebo group at
two weeks (mean PFS score, 56.0±21.8 vs. 48.3±
13.4; P=0.02) and one year (mean PFS score, 52.5±
20.3 vs. 45.6±10.2; P=0.04) and showed a trend to-
ward worse functioning at two years (mean PFS score,
52.6±16.4 vs. 47.7±12.0; P=0.11) (Table 3).
Lacking evidence of the superiority of the arthro-
scopic treatments over the placebo procedure in re-
lieving pain or improving function, we considered
whether the 95 percent confidence intervals for the
Figure 1.
Mean Values (and 95 Percent Confidence Intervals) on the Knee-Specific Pain Scale.
Assessments were made before the procedure and 2 weeks, 6 weeks, 3 months, 6 months, 12 months, 18 months, and
24 months after the procedure. Higher scores indicate more severe pain.
0
Before
Procedure
100
90
80
70
60
50
40
30
20
10
2 yr2 wk 6 wk 3 mo 6 mo 1 yr 18 mo
After Procedure
NO. AT RISK
Placebo
Lavage
Débridement
60
61
58
57
57
59
59
59
59
56
59
58
57
59
56
53
57
50
52
56
51
55
55
53
Mean Knee-Specific Pain Scale Score
Débridement
Lavage
Placebo
A RANDOMIZED TRIAL OF KNEE ARTHROSCOPY
N Engl J Med, Vol. 347, No. 2
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July 11, 2002
·
www.nejm.org
·
85
differences in outcome between each arthroscopic
procedure and the placebo procedure included clin-
ically important differences. The minimal important
differences used for this evaluation were as follows:
a difference of 13.5 points on the KSPS, 10.0 on the
AIMS2-P, 11.8 on the SF-36-P, 12.8 on the AIMS2-
WB, 11.3 on the SF-36-PF, and 4.5 on the PFS. At
almost all time points during follow-up (72 of 84
comparisons), the confidence intervals excluded these
minimal important differences.
DISCUSSION
This study provides strong evidence that arthro-
scopic lavage with or without débridement is not
better than and appears to be equivalent to a place-
bo procedure in improving knee pain and self-report-
ed function. Indeed, at some points during follow-up,
objective function was significantly worse in the dé-
bridement group than in the placebo group.
Arthroscopy is the most commonly performed type
of orthopedic surgery, and the knee is by far the most
common joint on which it is performed.
1
Numerous
uncontrolled, retrospective case series have reported
substantial pain relief after arthroscopic lavage or ar-
throscopic débridement for osteoarthritis of the
knee.
2-16
In the only previous double-blind, random-
ized, controlled trial of knee arthroscopy of which we
are aware,
34
patients with minimal osteoarthritis as
assessed by radiography were assigned to undergo
arthroscopic lavage with either 3000 ml of fluid (treat-
ment) or 250 ml of fluid (control) and were followed
for one year. Both the treatment and the control
groups reported improvement in function at 12
months, and although the report interprets the study
as having proved the efficacy of lavage, there was no
statistically significant difference between the groups
in terms of the primary outcome at any point during
follow-up.
To explain the improvement that has been report-
ed after these procedures, some have proposed that
the fluid that is flushed through the knee during ar-
throscopy cleanses the knee of painful debris and in-
flammatory enzymes.
4,6,9,15,16,34
Others have suggest-
ed that the improvement is due to the removal of
flaps of articular cartilage, torn meniscal fragments,
hypertrophied synovium, and loose debris.
2-14
How-
ever, our study found that outcomes after arthro-
scopic treatment are no better than those after a pla-
cebo procedure. This lack of difference suggests that
the improvement is not due to any intrinsic efficacy
of the procedures. Although patients in the placebo
groups of randomized trials frequently have improve-
ment, it may be attributable to either the natural his-
tory of the condition or some independent effect of
the placebo.
Because we found no evidence that lavage or dé-
*Plus–minus values are means ±SD. CI denotes confidence interval. Scores were transformed into scores on a scale ranging from 0 to 100, with higher scores indicating more severe pain.
†This 95 percent confidence interval includes the minimal important difference.
T
ABLE
2.
S
CORES
ON
THE
P
AIN
S
UBSCALE
OF
THE
A
RTHRITIS
I
MPACT
M
EASUREMENT SCALES.*
VARIABLE BEFORE PROCEDURE AFTER PROCEDURE
2 WK 6 WK 3 MO 6 MO 1 YR 18 MO 2 YR
Placebo group
No. with data 59 5957565754 52 55
Score 59.5±18.5 47.9±23.9 50.8±23.2 50.1±21.3 50.0±20.7 53.6±22.1 55.6±23.6 52.5±25.1
Lavage group
No. with data 61 5957595957 57 56
Score 59.3±16.7 51.9±20.3 52.4±22.1 53.7±23.1 54.8±21.6 57.8±23.5 55.4±24.6 56.7±24.1
Débridement group
No. with data 58 5859585551 51 53
Score 59.3±22.2 53.2±21.7 49.9±23.3 49.9±21.7 52.0±20.8 53.3±25.4 50.7±24.4 54.0±23.3
Placebo group vs. lavage group
Difference between mean scores (95% CI) 0.2
(¡6.2 to 6.6)
¡4.0
(¡12.1 to 4.1)
¡1.6
(¡10.1 to 6.8)
¡3.6
(¡11.8 to 4.6)
¡4.8
(¡12.5 to 3.0)
¡4.2
(¡12.8 to 4.4)
0.3
(¡8.9 to 9.4)
¡4.2
(¡13.5 to 5.1)
P value 0.95 0.33 0.70 0.39 0.23 0.34 0.95 0.37
Placebo group vs. débridement group
Difference between mean scores (95% CI) 0.3
(¡7.2 to 7.7)
¡5.2
(¡13.6 to 3.1)
0.9
(¡7.7 to 9.4)
0.3
(¡7.7 to 8.2)
¡2.0
(¡9.8 to 5.7)
0.3
(¡8.9 to 9.5)
4.9
(¡4.5 to 14.3)†
¡1.5
(¡10.8 to 7.7)
P value 0.94 0.22 0.84 0.95 0.60 0.95 0.30 0.75
86 · N Engl J Med, Vol. 347, No. 2 · July 11, 2002 · www.nejm.org
The New England Journal of Medicine
bridement is superior to a placebo procedure, the
question arises whether these arthroscopic procedures
could have small but clinically important benefits that
we missed because of our limited sample size. To eval-
uate this possibility, we determined the size of the
clinical benefit that the trial was able to rule out, us-
ing the minimal important difference for each of our
scales. Because estimates of minimal important dif-
ferences based on different samples and different
methods do not yield the same values, we used the
midpoint of the range of available minimal impor-
tant differences in order to test our hypothesis about
the equivalence of the three procedures. For the great
majority of comparisons, the 95 percent confidence
intervals did not contain the minimal important dif-
ference, indicating that there was not a clinically im-
portant improvement that the study had simply failed
to detect.
One surgeon performed all the procedures in this
study. Consequently, his technical proficiency is crit-
ical to the generalizability of our findings. Our study
surgeon is board-certified, is fellowship-trained in
arthroscopy and sports medicine, and has been in
practice for 10 years in an academic medical center.
He is currently the orthopedic surgeon for a Nation-
al Basketball Association team and was the physician
for the men’s and women’s U.S. Olympic basketball
teams in 1996.
The principal limitation of this study is that our
participants may not be representative of all candi-
dates for arthroscopic treatment of osteoarthritis of
the knee. Almost all participants were men, because
the study was conducted at a Veterans Affairs medical
center. We do not know whether our findings may
be generalized to women, although uncontrolled
studies do not indicate that there are differences be-
tween the sexes in responses to arthroscopic proce-
dures.
8,10,13
A selection bias might have been intro-
duced by the fact that 44 percent of the eligible
patients declined to participate in the study. We be-
lieve this high rate of refusal to participate resulted
from the fact that all patients knew they had a one-
in-three chance of undergoing a placebo procedure.
Patients who agreed to participate might have been
so sure that an arthroscopic procedure would help
that they were willing to take a one-in-three chance
of undergoing the placebo procedure. Such patients
might have had higher expectations of benefit or
been more susceptible to a placebo effect than those
who chose not to participate.
Figure 2. Mean Values (and 95 Percent Confidence Intervals) on the Walking–Bending Subscale of the Arthritis Impact
Measurement Scales (AIMS2).
Assessments were made before the procedure and 2 weeks, 6 weeks, 3 months, 6 months, 12 months, 18 months, and
24 months after the procedure. Higher scores indicate poorer functioning.
0
Before
Procedure
100
90
80
70
60
50
40
30
20
10
2 yr2 wk 6 wk 3 mo 6 mo 1 yr 18 mo
After Procedure
NO. AT RISK
Placebo
Lavage
Débridement
60
61
58
57
57
59
59
59
58
56
59
58
57
59
55
54
57
51
52
57
51
55
56
53
AIMS2 Walking–Bending Subscale
Débridement
Lavage
Placebo
A RANDOMIZED TRIAL OF KNEE ARTHROSCOPY
N Engl J Med, Vol. 347, No. 2 · July 11, 2002 · www.nejm.org · 87
If the efficacy of arthroscopic lavage or débride-
ment in patients with osteoarthritis of the knee is no
greater than that of placebo surgery, the billions of
dollars spent on such procedures annually might be
put to better use. This study has also shown the great
potential for a placebo effect with surgery, although
it is unclear whether this effect is due solely to the
natural history of the condition or whether there is
some independent effect. Researchers should recon-
sider the best ways of testing the efficacy of surgical
procedures performed purely for the improvement
of symptoms. In the debate about placebo-controlled
trials of surgery, the critical ethical considerations
surround the choice of the placebo. Finally, health
care researchers should not underestimate the place-
bo effect, regardless of its mechanism.
35
Supported by a grant from the Department of Veterans Affairs.
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*Scores indicate the number of seconds the patient required to walk 30 m (100 ft) and to climb up and down a flight of stairs as quickly as possible; longer times indicate poorer functioning. Plus–minus
values are means ±SD. CI denotes confidence interval.
†This 95 percent confidence interval includes the minimal important difference.
TABLE 3. SCORES ON THE PHYSICAL FUNCTIONING SCALE.*
VARIABLE BEFORE PROCEDURE AFTER PROCEDURE
Placebo group
2
WK 6 WK 3 MO 6 MO 1 YR 18 MO 2 YR
No. with data 59 59565454494644
Score 48.5±14.5 48.3±13.4 45.9±12.0 47.3±16.0 47.0±13.0 45.6±10.2 48.5±12.4 47.7±12.0
Lavage group
No. with data 59 57545552544950
Score 50.0±14.3 53.0±25.3 49.5±19.4 48.8±21.0 49.4±20.4 50.4±17.6 51.2±18.8 53.2±21.6
Débridement group
No. with data 58 57585654474444
Score 52.1±20.2 56.0±21.8 51.7±24.7 49.5±17.4 49.8±17.4 52.5±20.3 52.8±20.9 52.6±16.4
Placebo group vs. lavage group
Difference between mean scores (95% CI) ¡1.6
(¡6.8 to 3.7)
¡4.6
(¡12.0 to 2.8)
¡3.6
(¡9.7 to 2.5)
¡1.4
(¡8.5 to 5.6)†
¡2.4
(¡9.0 to 4.1)
¡4.9
(¡10.6 to 0.9)
¡2.7
(¡9.2 to 3.8)
¡5.5
(¡12.8 to 1.8)
P value 0.56 0.22 0.25 0.69 0.47 0.09 0.41 0.13
Placebo group vs. débridement group
Difference between mean scores (95% CI) ¡3.6
(¡10.0 to 2.8)
¡7.7
(¡14.3 to ¡1.1)
¡5.8
(¡13.1 to 1.4)
¡2.2
(¡8.5 to 4.1)
¡2.8
(¡8.7 to 3.1)
¡6.9
(¡13.3 to ¡0.4)
¡4.3
(¡11.5 to 2.8)
¡4.9
(¡11.0 to 1.2)
P value 0.27 0.02 0.11 0.49 0.34 0.04 0.23 0.11
88 · N Engl J Med, Vol. 347, No. 2 · July 11, 2002 · www.nejm.org
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