Degenerative joint disease (usually termed osteoarthritis [OA]) of the knee is a condition characterized by the progressive destruction of the articular cartilage that lines the knee joints, the subchondral bone surfaces, and synovium, accompanied by pain, immobility, and reduction in function and the ability to complete activities of daily living (ADL).
In 2005, the estimated prevalence of osteoarthritis among adults in the United States (US), the number of individuals who had ever been told by a doctor that they had the condition, was approximately 27 million cases. Prevalence rates vary by the joint involved and the method of ascertainment (clinical vs. radiographic): symptomatically, the knee is the most frequently affected joint. The prevalence of osteoarthritis of the knee is increasing rapidly because of shifting population demographics: The primary risk factors for osteoarthritis of the knee are aging, obesity, prior injury, repetitive use, and female gender. The US Centers for Disease Control have estimated that the prevalence of symptomatic knee osteoarthritis may reach 50 percent by the age of 85. From 2002 to 2012, the number of individuals in the US with a total knee replacement (TKR) doubled from some 2 million to approximately 4 million). The increase in obesity has translated not only into an increase in incidence of osteoarthritis of the knee but also into a younger age of onset and need for treatment; as a result, by the time individuals with osteoarthritis of the knee reach the age of Medicare eligibility, the length of time they have had the condition has grown, their cases are more advanced, and the risk that surgery will be needed has increased. Thus, the aging of the baby boomer population, along with the increased incidence and prevalence of obesity have increased the risk for this condition, all representing an increasing strain on Medicare resources.