Some revision surgeries are relatively minor – for instance, when one component of the implant is exchanged for another. But many entail removing and replacing the entire implant device, the ends of which are affixed to the thigh and shin bones. Revisions are long and complex, require special surgical skills and are rarely as successful as the first operation in terms of restoring normal function and range of motion.

And the reason for increased rates among younger patients? It’s not what many people may think, says senior study author David Ayers, MD, chair of the department of orthopaedics and physical rehabilitation at UMMS.

“People assume that most knee replacement patients are young, active baby boomers who have damaged their knees through sports and other activities. But when we look at the representative set of patients age 45 to 64, they aren’t anything like that; they are actually fairly unhealthy, are more obese and have more comorbidities than the over-65 group,” he explains.

That creates a clinical dilemma. “If a patient has debilitating pain and loss of function at age 47, do we ask him to wait as long as possible before undergoing total knee replacement so the need for revision is less likely? Or do we perform the procedure, relieve the pain and get the person back in the workforce, knowing that he may need a revision 20 years down the road?” asks Dr. Drew. (According to the Centers for Disease Control and Prevention, arthritis is the most common cause of disability in the United States.) “That question is very difficult to answer because we don’t know what’s going to happen for a particular patient. That unpredictability hampers us in weighing the short- and long-term risks and benefits.”

William Robb, MD, director of the Illinois Bone and Joint Institute, an orthopaedic practice in the Chicago area, agrees with the study findings but thinks some key information is missing.

“This is [hospital discharge] data and doesn’t provide an in-depth understanding of factors such as comorbidities or implant type” – factors that may influence revision rates, he says. “It appears that revision rates are growing in a younger age group, but the value is to focus on understanding why these patients are at increased risk.”

Understanding why total knee replacements fail is exactly what researchers at the University of California, San Francisco (UCSF) set out to do in a separate effort. Using the same database used in the Massachusetts study, they evaluated the reasons for nearly 302,000 revision procedures performed between 2005 and 2010.