Multicentericity as a pitfall for otherwise carefully planned RCT on surgical techniques
Dear Sir
In July 2002 in your journal, Ward and Hilton reported results from a
prospective randomised multicentre study on the efficacy of the tension-
free vaginal tape (TVT) for primary treatment of female stress urinary
incontinence in comparison to abdominal colposuspension (1). Based on
several standardised outcome measures the cure rates at six months were
interpreted as comparable for both procedures with a potential advantage
of the TVT, based on its minimal surgical access and lower postoperative
complications. This study was very well received because it is one of the
few large randomised controlled studies evaluating new surgical
procedures. However, in an editorial three months later these results were
criticised based on underpowerment and selection bias due to the fact that
a number of women withdrew from the study once they were randomised into
the colposuspension group. Furthermore, those women who withdrew had less
severe incontinence (2). The authors of this editorial concluded that a
more correct interpretation of the study results is that TVT "may be
better, worse or the same as colposuspension".
The recent release of a further analysis of the study data emphasises
that the study is even more flawed. Analysis of outcome by trial centre
revealed success rates ranging between 10 to 90 % for TVT and 20 to 92 %
for colposuspension (3). This incoherence of the primary data set prevents
us to gain any knowledge regarding the success rates of the TVT and
colposuspension at all. What it may add, however, is that poor average
cure rates of 66 % for TVT and 57 % for colposuspension reported in this
study are not related to the procedures themselves but rather to poor
performance and technique in some of the study centres.
Randomised controlled surgical trials have their own rules. Before
starting an RCT on surgical techniques the learning curve needs to be
recognized and evaluated using appropriate statistical techniques
otherwise waste of time and ressources is inevitable (4). Furthermore, the
scientific community and hence patients expectations could be misled by
improperly planned studies.
Literature
1. Ward K, Hilton P
Prospective multicentre randomised trial of tension-free vaginal tape and
colposuspension as primary treatment for stress incontinence
BMJ 2002;325:67-70
2. Maddern GJ, Middleton PF, Grant AM
Urinary stress incontinence
BMJ 2002;325:389-90
3. Hilton P
Trials of surgery for stress incontinence - thoughts on the "Humpty Dumpty
principle". Commentary.
BrJObstetGynecol 2002;109:1081-1088
4. McCulloch P, Taylor I, Sasako M, Lovett B, Griffin D
Randomised trials in surgery: problems and possible solutions
BMJ 2002;324:1448-1451
Rapid Response:
Multicentericity as a pitfall for otherwise carefully planned RCT on surgical techniques
Dear Sir
In July 2002 in your journal, Ward and Hilton reported results from a
prospective randomised multicentre study on the efficacy of the tension-
free vaginal tape (TVT) for primary treatment of female stress urinary
incontinence in comparison to abdominal colposuspension (1). Based on
several standardised outcome measures the cure rates at six months were
interpreted as comparable for both procedures with a potential advantage
of the TVT, based on its minimal surgical access and lower postoperative
complications. This study was very well received because it is one of the
few large randomised controlled studies evaluating new surgical
procedures. However, in an editorial three months later these results were
criticised based on underpowerment and selection bias due to the fact that
a number of women withdrew from the study once they were randomised into
the colposuspension group. Furthermore, those women who withdrew had less
severe incontinence (2). The authors of this editorial concluded that a
more correct interpretation of the study results is that TVT "may be
better, worse or the same as colposuspension".
The recent release of a further analysis of the study data emphasises
that the study is even more flawed. Analysis of outcome by trial centre
revealed success rates ranging between 10 to 90 % for TVT and 20 to 92 %
for colposuspension (3). This incoherence of the primary data set prevents
us to gain any knowledge regarding the success rates of the TVT and
colposuspension at all. What it may add, however, is that poor average
cure rates of 66 % for TVT and 57 % for colposuspension reported in this
study are not related to the procedures themselves but rather to poor
performance and technique in some of the study centres.
Randomised controlled surgical trials have their own rules. Before
starting an RCT on surgical techniques the learning curve needs to be
recognized and evaluated using appropriate statistical techniques
otherwise waste of time and ressources is inevitable (4). Furthermore, the
scientific community and hence patients expectations could be misled by
improperly planned studies.
Literature
1. Ward K, Hilton P
Prospective multicentre randomised trial of tension-free vaginal tape and
colposuspension as primary treatment for stress incontinence
BMJ 2002;325:67-70
2. Maddern GJ, Middleton PF, Grant AM
Urinary stress incontinence
BMJ 2002;325:389-90
3. Hilton P
Trials of surgery for stress incontinence - thoughts on the "Humpty Dumpty
principle". Commentary.
BrJObstetGynecol 2002;109:1081-1088
4. McCulloch P, Taylor I, Sasako M, Lovett B, Griffin D
Randomised trials in surgery: problems and possible solutions
BMJ 2002;324:1448-1451
Competing interests:
None declared
Competing interests: No competing interests