Abstract
For 3 decades surgeons have vigorously debated whether it is reasonable to offer simultaneous bilateral total knee replacement (TKA) to patients. Even after this substantial period of time there remain no randomised clinical trials that have addressed this issue and thus, it remains difficult to fully evaluate both the relative risks and the absolute risks of bilateral simultaneous versus staged bilateral knee replacement. What has emerged over the past couple of decades, however, is an understanding that there is a subset of patients with substantial comorbidities such as pre-existent cardiac disease and advanced age for whom bilateral simultaneous knee replacement seems unwise. For younger or otherwise healthy patients the debate continues in 2016 and seems to be focused less on the data itself than on how individual surgeons come to reconcile the differences between Relative Risk and Absolute Risk. When data is pooled from multiple retrospective studies of simultaneous versus staged bilateral TKA there are 2 clear trends that appear in the data. First, the relative risk of certain substantial complications (cardiac, thromboembolic, neurologic, gastrointestinal, and death) seems to be higher after simultaneous bilateral TKA than after staged bilateral TKA. Oakes and Hanssen highlighted these differences in Relative Risk noting that for each of those 5 outcomes there was a 2 to 5 times greater incidence of these complications after bilateral versus unilateral TKA. At the same time, however, it is clear that for most medically uncomplicated patients the Absolute Risk of a major complication is still fairly low — it is likely that >93% of such patients can undergo simultaneous bilateral TKA without encountering a major complication. Individual surgeons and individual patients often view those kinds of statistics in markedly disparate ways. One set of surgeons and patients will view the Relative Risk as most important and be decidedly concerned about the 2–5 times higher risk of certain complications. Another set of patients and surgeons will look at the Absolute Risk as most important and determine that it is decidedly most likely (>93%) that an individual healthy patient will make it through bilateral simultaneous TKA without major medical complications. Overall the conclusions of Oakes and Hanssen from a decade ago remain relevant in 2016: the overall risk of a peri-operative complication is higher with simultaneous bilateral TKA … and this is particularly true for the risk of peri-operative death. While some surgeons and some patients will decide that the increases in Relative Risk is offset by the fairly low Absolute Risk of complications and thus, feel comfortable with bilateral simultaneous TKA, other patients and other surgeons will not.
