Limited evidence supports simultaneous bilateral total knee arthroplasty for patients aged 70 or younger or ASA status 1-2, because there are no increased complications.

Rationale
There is one low quality retrospective comparative study (Yoon 2010) evaluating systemic complications in consecutive patients who had bilateral simultaneous total knee arthroplasty that met criteria for inclusion. They found equivalent complications among patients who were not elderly (defined as less than 71 years old) or not high risk (defined as ASA 1 and 2). Analysis showed patients aged 71 and older or ASA 3-4 were at higher risk of having systemic complications.

More data was not available for inclusion because many of the relevant studies included a mixture of patients with osteoarthritis and rheumatoid arthritis and the outcomes data was not split out. 
  1. Yoon,H.S., Han,C.D., Yang,I.H. Comparison of simultaneous bilateral and staged bilateral total knee arthroplasty in terms of perioperative complications. J Arthroplasty 2010/2; 2: 179-185