If you are unfortunate enough to require a knee replacement on both legs, occasionally surgeons will offer to do them simultaneously. This is a big decision to make as it is obviously harder to rehabilitate when you don't have a "good" leg to rely upon.
Why would anyone do this?
Well, there are some advantages. The total recovery time is usually much quicker having them done together than the total of two separate occasions. This makes it an attractive proposition for people with a hectic schedule.
You will only have to have one anesthetic, although it will be of significantly longer duration. It is also likely to cost much less than two separate surgical interventions.
The main problem is a more difficult initial phase of the recovery. For this reason surgeons pick their candidates carefully.
Simultaneous total knee replacements will only be offered to low risk patients. They need to be free of upper limb problems due to the increased initial load on the arms when ambulating. Social factors are important also. Living with an able bodied partner in level accommodation is easier than living alone on the 5th floor with no lift. Medical complications and risk factors such as cardiovascular disease, diabetes and obesity will often see a surgeon recommend one knee at a time.
If the possibility of 2 knee replacements is offered to you, discuss it with your family,and consider how much support you will receive in the short term.
There are benefits to be had, but they are best suited for highly motivated, low risk individuals with a good support network.