To find a satisfactory way of replacing the knee joint has proven difficult. It is not the simple joint it might seem. There is in fact a very complicated sequence of movements of hinge, slide and rotation and it has proven difficult to find mechanical means to cope with this.
The earlier methods were to resurface the joint with biological materials, and they didn’t stand up to wear. Then simple hinged joints were tried, and they broke or worked loose. Progressively the problems were revealed by experience and the currently employed prostheses are so much more satisfactory that the operation is performed in the United States on about 130,000 knees each year and the longest duration available shows 94% satisfaction 15 years after the operation. But there are problems that have occurred and will occur again. Most doctors will agree that surgical replacement of a joint is a last resort, to be undertaken when all other measures have proven insufficient to overcome a real and increasingly severe problem.
In general, the reasons to undergo an orthopaedic operation are: pain and loss of function which significantly interferes with the enjoyment of life, and which cannot be controlled or reversed by non-operative methods such as medication and different forms of therapy. Where the knee is concerned, this is particularly likely to mean restriction of physical activity due to pain, and if more severe, intolerable pain even at rest.