To The Editor:
In the recent study "Navigated Total Knee Replacement. A
Meta-Analysis" (2007;89: 261-9), Bauwens et al. concluded that
"navigated knee replacement provides few advantages...on the basis of
radiographic end points." However, our analysis of this paper suggests
that this conclusion is invalid.
While meta-analysis of randomized controlled trials represents the gold
standard in validation of interventions, overcoming the reduced statistical
power of small sample sizes, it cannot compensate for poor scientific
methodology in the analyzed papers. The authors included not only randomized
trials but also quasi-randomized controlled trials, nonrandomized cohort
studies, studies with historical cohorts, and studies investigating the
outcome of computed tomography or image-free navigation systems for both
unicompartmental and total knee arthroplasty.
A meta-analysis must use a predefined, documented search strategy that
allows for an assessment of its completeness; however, this was not reported.
The "mean straightness of mechanical axes" is an inappropriate
outcome measure. The mean mechanical axis says nothing about the distribution
of values that it represents without reporting standard deviations and ranges,
although 95% confidence intervals were given. However, two groups may have
significantly different distributions of alignment values centered about
similar mean values.
Navigation reduces the number of implants with a predetermined variance
from the true mechanical axis, commonly defined as ±3°. The authors
estimated risk ratios of 0.79 and 0.76 for deviations of >3° and
>2°, respectively, when navigated knee arthroplasty was compared with
conventional knee arthroplasty. Navigation reduced the relative risk of
>3° malalignment by 25%, thus avoiding one additional patient with
unfavorable component positioning in any five patients managed with
computer-assisted instead of jig-based methods.
The authors conclude that "the benefits of navigation diminished
rapidly with increasing thresholds of proper implant positioning." If we
were to accept a deviation of as much as 6° from the true mechanical axis,
then both conventional jig and navigation-based arthroplasty are almost
equally efficacious; however, this degree of error is greater than most
arthroplasty surgeons would accept.
Navigated total knee arthroplasty improves implant alignment, but
consequent improved implant survival remains unproven. We are concerned that
this metaanalysis will be regarded by many as definitive evidence, although
its methodological shortcomings and interpretation of results do not justify
the conclusions reached.