Death is a possible complication with any surgery. It's certainly the most serious one. Death rates after knee replacement (one or both) are very low. Reports do show an increased number of deaths when both knees are replaced at the same time compared to doing one knee at a time.
Data from a large study of 339,152 total knee replacements shows the death rate to be less than one percent (0.99 percent). This figure shows deaths in the first month after the operation when both knees were done at the same time. The death rate for patients having the second knee done three to six months later was lower (0.30 percent).
In either type of surgery, the risk of death is higher if the patient has a history of heart or lung disease. Older age (over 70 years) is also a risk factor.