by: Kathleen A. Hogan, MD
Hip and knee replacements first began being performed in the United States in the early 1970’s. They are now considered to be one of the most common and most successful orthopedic operations. Over a million joint replacements are performed each year, and it is estimated that over 7 million people in the United States are currently living with artificial hips or knees. This is approximately two percent of the population of this country! The prevalence of joint replacement increases with age. It is estimated that of people over the age of 80, ten percent have had knee replacements and five percent have had hip replacements.
How many people who have arthritis in one hip or knee will have it in the other joint?
Bilateral arthritis is fairly common. This makes sense as the same factors which increase the risk of arthritis (with the exception of injuries) affect both sides equally. For example, a body mass index greater than 35 increases the risk of developing knee arthritis by four and a half times. This should affect both right and left sides equally. One study of patients undergoing joint replacement found an incidence of radiographic arthritis in bilateral joints in over 80 percent of patients.
And, how common is it to have both hips and both knees replaced?
Patients often ask what the odds are of needing to have a second joint replaced. One recent study found that after a hip replacement, almost 30 percent of patients had their contralateral hip replaced within 20 years. After a knee replacement, 45 percent had the contralateral knee replaced. However, the risk of having a hip replacement following a knee replacement (or vice versa) was much lower, only two to six percent.
Why is having both hip and both knees replaced so much less common?
Most people with arthritis in multiple different joints have a systemic cause of their arthritis, such as rheumatoid arthritis (RA). In the past, patients with RA often had severe, crippling deformities with debilitating arthritis of several joints. Joint replacements miraculously restored mobility to patients who were often wheelchair dependent. Many of these patients required both hip and knee replacements. Today, medications have drastically reduced severity of arthritis in patients with RA. It is now somewhat unusual to see severe, untreated rheumatoid arthritis except in third world countries.
Consequentially, it is now also somewhat rare to see a patient who requires replacement of both hips and both knees. Although it has been estimated that eight and a half percent of patients with joint replacements have had at least one hip and one knee replaced, there is no data on the number of patients having both hips and both knees replaced. For those patients who do require quadruple joint replacements, surgery can restore mobility and function and drastically improve the quality of their life.