To answer this question, scientists analysed 2 studies that tested over 150 people with osteoarthritis of the knee (6 had rheumatoid arthritis). These people had total knee replacement surgery with either a mobile or fixed bearing knee implant and were studied 1 or 7 years after the surgery. These studies provide the best evidence we have today.
What is osteoarthritis and rheumatoid arthritis of the knee and what types of knee implants are there?
Osteoarthritis and rheumatoid arthritis are two forms of arthritis that can affect the knees. In some people, damage and pain in the knee from arthritis may be severe enough for surgery. In these people, the whole knee joint can be replaced by an artificial joint or knee implant. In total knee replacement surgery the ends of the long bones of the leg are usually replaced with metal ends and an insert is placed in between them. The insert can either be "fixed" into place on the end of one bone or not as fixed which makes the insert more movable or "mobile". It is thought that people with a mobile bearing may be able to move their knee more and function better than people with a fixed bearing.
What did the studies show?
The two studies show that the range of motion/movement of the knee was about the same in people who had a fixed or mobile bearing knee implant. The year long study shows that slightly more people with a mobile bearing knee implant had less pain and better function than with a fixed bearing knee implant. But the seven year long study showed no differences in pain or function between the mobile or fixed bearing knee implants.
What is the bottom line?
The level of quality of the 2 studies in this review is "silver". It appears that mobile bearing knee implants provide the same amount of range of motion/movement and pain relief as fixed bearing implants in total knee replacement for osteoarthritis and rheumatoid arthritis of the knee. Ability to function with either type of implant is also the same.