The corresponding author of this article has been invited to respond to the letter by Dr. Kaper and to date, has not done so.

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.