Operative risk of staged bilateral knee arthroplasty is underestimated in retrospective studies.

To find a safer surgical option, a number of studies have compared postoperative complications after bilateral total knee arthroplasty vs staged total knee arthroplasty (STKA) by contrasting postoperative complications collected retrospectively. However, we believe that a comparison based on retrospective studies could be biased. The purpose of this study was to demonstrate the misclassification bias associated with a retrospective study in comparing operative outcomes. Our analysis indicates that any conclusions based simply on retrospective analysis of subjects who successfully completed STKA is biased because it includes only cases that recovered after the first operation, rather than all of the patients who had planned STKA. In the absence of a prospective study to date, published studies should be interpreted with caution.