Who Needs a Knee Replacement?  National Institutes of Health, Jan 2014:  nihnewsinhealth@od.nih.gov

Knee replacement is an operation that involves removing parts of one’s natural knee joint and replacing them with artificial ones. Knee replacement is the most common joint replacement surgery.  The main reason to have knee replacement surgery is to ease pain and disability caused by arthritis or other joint problems, while preserving movement. Less commonly, it is used to correct some kinds of knee deformity. Several forms of arthritis can damage knees to the point that they need to be replaced. They include
Osteoarthritis, which occurs when the cartilage covering the ends of the bones where they meet to form joints breaks down. This causes the bones of the joint to rub together. Growths of bone, called spurs, may form around the joint. These changes lead to pain and stiffness.
Rheumatoid arthritis, a condition in which the body's immune system attacks the membrane that lines the joint. This can lead to pain, inflammation and destruction of the joint.
Post-traumatic arthritis, a form of osteoarthritis that may occur after a knee injury such as a fracture or ligament tear. These kinds of injuries can cause inflammation and affect the alignment of the knee, leading to cartilage damage over time. Because of this, an injury that you suffered earlier in life can cause you to have arthritis at middle age or later.
Knee damage can also result from a problem called avascular necrosis, or osteonecrosis, in which the bones lose their blood supply, die, and eventually collapse. Although the cause of avascular necrosis is not well understood, in many people it appears to result from trauma to the knee.
Knee deformities -- such as bowed legs or knock knees— occur when the knees are not formed or aligned properly. Over time, this creates stress on the joints that can wear down cartilage and lead to pain and disability. In these cases, knee replacement can restore the normal alignment of the knee and correct disability.
Your doctor may recommend knee replacement if pain and stiffness interfere with your ability to do everyday activities – particularly if other treatments have not helped. Treatments your doctor will likely recommend before knee replacement include
exercises to strengthen the muscles around the knee and improve flexibility
weight loss, if needed, to reduce the load the knee must bear
walking aids such as canes to reduce stress on the joint
shoe inserts to improve the knee’s alignment
medicines to relieve pain.
The surgeon must consider many factors before recommending knee replacement. People who are generally healthy are the best candidates for the surgery, and those who have surgery before advanced joint damage occurs tend to recover more quickly and have better outcomes.
10 Exercises & Stretches After Knee Replacement Surgery

                       For details on the following exercises, go to:  www.healthline.com/health�