To the Editor:
I read with interest the article "Staggered Bilateral Total Knee
Arthroplasty Performed Four to Seven Days Apart During a Single
Hospitalization", by Sliva et al. The best and safest surgical "timing"
for patients presenting with bilateral degenerative joint disease, of
essentially equal severity, is and remains a quandry.
The methodology applied in this study, however, calls into question
the validity of the results and conclusions set forth in the article. As
was appropriately pointed out, this study represented a retrospective
review with "retrospective assignment" of patients to one of the three
study groups. First, the large numbers assigned to the "staggered" group,
compared to the other two groups(241 vs 65+26), suggests an initial
selection bias on the part of the primary surgeons.
The pre-operative assessment of patients being considered for
bilateral TKA's is, as noted, essential. The fact that patients with
"substantial cardiac, pulmonary, or other serious" medical comorbidities
were deferred to the "staged" group is also a very strong selection bias.
Similarly, it is identified that if a patient initially slated for a
"staggered" approach developed a problem intra- or post-operatively, that
the second TKA was deferred to a later date. No mention is made as to how
many patients fell into such a category, nor is it stated whether or not
these patients were thereby subsequently included in the "staged" group.
If this were to be the case, this would introduce yet another selection
bias. If, for example, a patient developed a post-operative cardiac
arrhythmia after their first TKA, thereby postponing their scheduled,
"staggered", contralateral TKA to a later "staged" date, this would
naturally shift a complication out of the "staggered" group and into the
"staged" group.
Furthermore, I was concerned about the length of time elapsed between
the first and second TKA in the "staged" group. The average "staging" was
70.5 weeks, with a very wide range from 1.6 weeks to 270.9 weeks. In
order to answer the question of the safest and most reliable outcomes for
patients needing bilateral TKA's, I am not sure that including patients
whose second TKA was done more than one year later (certainly not five
years later) allows for accurate comparison. We are all well aware that
in our older patients (especially since the "staged" group was noted to be
significantly older), their medical circumstance can dramatically
change/worsen over a relatively short time span. With such a long time
interval between the first and second TKA, it would almost seem that an
entirely new assessment of their medical circumstances and co-morbidities
would be in order. This was not addressed in this study.
Finally, the authors conclude that the overall rate of complications
in the "sequential" and "staged" groups were 2.5x higher than in the
"staggered" group (a statistic quoted directly in the JBJS CME test).
Given the relatively small number of major complications, little
statistically inference can be made in regard major complications
(although the only death and MI occurred in the "staggered" group). The
main determinant of the authors' conclusion seems to come from the rate of
minor complications. A review of the assigned ASA score may have allowed
further insight into exactly the cummulatively differences in overall
patient health. The authors did analyze the reimbursement figures-
however, what would have been worth further review would have been an
analysis of the total cost of each procedure/hospitalization to assess the
effect of the reported higher complication rate. Given the fact that the
overall length of stay data was not noted to be significantly different in
the "staggered" and "staged" (when the two hospitalizations were added
together) groups, leads me to believe that the higher reported
complication rate did not translate into a more expensive hospitalization
or a longer length of stay. The overall clinical outcomes of the patients
with regard Knee Society Score, range of motion, or rate of revision was
similarly not assessed.
In summary, the authors are to be commended on their attempts to shed
further light onto this difficult question of how bilateral TKA's are best
scheduled. I am not sure, however, that their conclusions are based on
sound enough methodology to allow clinicians to suggest to patients that
"staggering" their TKA's is truly the best and safest approach for this
challenge.
Bertrand P. Kaper, M.D.
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