We thank you for the considerations made to our article through a letter to the editor
presented by colleagues regarding the article “Radiographic Evaluation of Postoperative
Alignment in Total Knee Arthroplasty” – Rev Bras Ortop 2021 (
https://doi.org/10.1055/s-0041-1726061
) (efirst).[1] In our article, we tried to demonstrate the greater accuracy of panoramic radiographs
of the lower limbs (long) in relation to short radiographs of the knee in the measurement
of the mechanical axis of the lower limb after total knee arthroplasty (TKA). We considered
valid the observation about the time of performance of the radiography and the fact
that a possible attitude in flexo and external rotation could lead to a positioning
bias. The fact that long radiographs are performed in bipodal support when patients
are still hospitalized in our hospital occurs at a time when analgesia is adequate,
reducing the intensity of the pain. We routinely perform saphenous nerve block in
the adductor canal with sonographic control, which enables knee analgesia without
motor loss of the quadriceps.[2] Thus, the patients are able to start the support early, which accelerates their
postoperative rehabilitation and decreases the possibility of difficulty being in
the position of orthostasis and, therefore, performing the examination.
It is worth mentioning that all short radiographs used in the evaluation were obtained
directly from the panoramic radiography itself, as stated in the section of materials
and methods of our article, precisely to avoid the influence of possible rotations
in the performance of new radiographs.[3] Thus, the comparative analysis performed decreased the chance of bias in relation
to positioning, even if it did not totally exclude it. In addition, we consider the
suggestion of colleagues to be valid to be investigated in a future study, comparing
the analysis of long radiographs in the immediate postoperative period and six weeks
later, in order to evaluate possible interferences of immediate postoperative situations.
We remember that Abu-Rajab et al.[3] do not recommend x-rays in six weeks, but do perform them as a routine currently.
So, the study proposal is valid.
Although the anatomical axis is the only axis that is actually reproducible on short
radiography, Felson et al.[4] showed that the agreement between the measurement of the anatomical axis on short
knee radiography and the measurement of the mechanical axis on long radiography is
only moderate. In another study, by the Muticenter Osteoarthritis Group,[5] the authors concluded that there are significant limitations to the use of the anatomical
axis to predict the alignment of the lower limbs, especially when an accurate measurement
of the mechanical alignment is necessary. We used as reference other published studies
that applied this methodology to try to predict the measurement points of the mechanical
axis.[3] Thus, it was possible to compare their results with those obtained by our group.
Then, we reproduce a methodology already widely presented in the literature and used
in several studies.
We consider that the suggestion about the postoperative time to perform panoramic
radiography may be the object of a future study, as a way of comparing the results
obtained by different observers in the highlighted period. Regarding the use of the
tibiofemoral anatomical axis in the postoperative period of TKA, we recall that the
literature is conflicting in relation to the use of this measure; therefore, we chose
to follow the methodology of studies previously performed in order to obtain comparative
results.
