We read with great interest the letter from Dr. Mason and colleagues. Since
they raised substantial concerns about the validity of our findings, we
carefully reviewed the data set that formed the basis for all analyses and
figures presented in The Journal.
We reviewed the references cited by Mason et al.1-4 and found no
data shift between the conventional and navigated-surgery groups. Such a shift
was unlikely since the forest plots consistently showed an advantage for the
navigated-surgery cohort.
Mason et al. also claimed that they found additional errors of data
extraction from four other studies that we reviewed5-8, but unless
they are more specific in their criticisms, we cannot respond properly.
We would refer Mason et al. to the Materials and Methods section of our
paper, where we stressed that the numbers of patients were extracted from
histograms whenever possible. This may explain most of the differences that
they noted between their and our data sets. Additional differences might be
related to different handling of the unit of interest—that is, the
patient or the knee. Bolognesi and Hofmann9 did indeed report the
alignment of the femoral and the tibial component rather than the mechanical
axis. However, if navigation improves both femoral and tibial component
alignment, it is very likely that the resulting mechanical axis will be
optimized as well. Since the observed effects were consistent with others, we
decided to include that study in our analysis. We definitely identified and
excluded some kinship studies, but we could not retrieve a dual publication by
Mielke et al.10.
When posing a null hypothesis, it is important to define the accepted
standard of care. Risk ratios and other relative measures are asymmetric. This
was the reason why we also provided risk differences, which can be used for
calculating the number needed to treat. Currently, navigation is an
experimental add-on and may either decrease the risk of malalignment or
increase the chance of alignment. It is, however, not justified to argue that
conventional surgery would increase the relative risk of malalignment over
that associated with navigated component placement. With regard to
health-policy decisions, this is a dangerous statement since it would imply
that all patients who are not operated on with computer assistance but undergo
conventional total knee arthroplasty by an experienced surgeon are at a higher
risk of having malalignment when compared with those who undergo total knee
arthroplasty with navigated component placement.
Importantly, our analyses and plots showed a significant advantage of
navigated over conventional knee replacement in terms of radiographic
surrogates, so we are in complete agreement with Mason et al. Yet, unless
these advantages are consistent with improved outcomes, we think that our
conclusion "Navigated knee replacement provides few advantages over
conventional surgery on the basis of radiographic end points" is
valid.
Finally, we regret that Mason et al., after receiving our data set (the
sending of which shows our openness and willingness to engage in scientific
debate), did not contact us again to compare both data sets and to discuss,
explore, and resolve any possible differences jointly before submitting a
Letter to the Editor challenging our scientific reputation. We are sorry that
Dr. Mason's group could not publish their paper, but we are deeply
disappointed in their behavior.