A new study, published in Arthritis & Rheumatism in April, may help determine which arthritis patients benefit most from joint replacement surgery, also called total joint arthroplasty (TJA). It could also help doctors and patients best determine at what point in disease progression is the ideal time to have the surgery in order to get the best outcome.

Among the factors that made a difference: high levels of pre-surgical pain, only one “troublesome” hip or knee, better overall health (no other health conditions), and joint damage caused by osteoarthritis (OA) as opposed to inflammatory types of arthritis.

With an aging population of baby boomers, the number of joint replacement surgeries is surging. According to the Centers for Disease Control and Prevention (CDC) in Atlanta, between 1996 and 2006, total hip replacement in the United States increased more than 30 percent; total knee replacement surgery increased 70 percent. In Canada, where this study was done, the authors say there are already “unacceptably long” wait times for TJA in some situations.

With so many more people deciding to have these procedures, “We want to make sure that people have a good understanding of what this procedure is for and what it is likely to deliver, and that we’re not actually doing [these surgeries] in people that won’t get the benefit they want,” says lead author Gillian A. Hawker, MD, the physician-in-chief of the department of medicine at Women’s College Hospital in Ontario, Canada.

Additionally, the researchers write that they want to help define the criteria for exactly when surgery is appropriate: “This uncertainty leaves many patients, and possibly physicians, at a loss as to know how long and to what level of pain and other symptoms should be tolerated before TJA is considered.”

The researchers followed 202 patients in Canada who had difficulty with such tasks as climbing stairs and rising from chairs, and also had “troublesome” hip or knee joints. They provided assessments of their pain and mobility before and after undergoing a primary TJA (133 knee and 69 hip replacements).

The majority of patients, 93 percent, had osteoarthritis (OA) and 7 percent had inflammatory arthritis, such as rheumatoid arthritis (RA). About 83 percent had at least two “troublesome” joints (and a third reported three or more); nearly 57 percent said they had persistent back pain; more than a third were obese. Only 30 percent reported having no other health problems.

More than half (53.5 percent) of the participants reported “good” outcomes – defined as a clinically important improvement in pain and disability – following surgery. That number is far less than the 80 to 90 percent often touted, the researchers say.

The relatively low percentage of patients who experienced good results makes sense, Dr. Hawker says. In people with other health problems, especially additional troublesome joints, "when you replace one joint it doesn’t result in resolution of all of your problems.” 

There may be two other reasons that the numbers were low. First, Dr. Hawker says the criteria for “good” outcome was strict. Second, the study excluded patients who had a TJA in a second joint – who were more likely to have been satisfied with the first surgery (the “happy campers” as Dr. Hawker calls them).

The study also provided useful insight about the timing for the surgery. For example, the researchers found that patients with the most pain and mobility limitations prior to surgery reported the greatest overall improvement. 

“There probably is a sweet spot, but nobody yet has figured out exactly what that is, and that’s what we need to get to,” Dr. Hawker explained. “Where is the point where you’ve got the greatest likelihood of benefit but you haven’t gone so far that in fact your outcomes are not as optimal? Don’t want to be too early; don’t want to be too late.”

The researcher also found that weight and body mass index (BMI) did not appear to play a significant role in post-surgery outcomes. Dr. Hawker explains, “Weight has consistently not been shown to affect results of joint replacement with respect to pain and disability. It is true that people who are heavier, more obese, have a higher likelihood of peri-operative complication, so they have a greater risk related to the surgery itself. But once they get through the procedure and go home, their benefits in terms of pain and disability appears to be the same as people who are not obese.”

Wael K. Barsoum, MD, chairman of Surgical Operations and vice chairman of the Department of Orthopaedic Surgery at the Cleveland Clinic in Ohio, says the findings have value. “The study is giving us information that I think most physicians will tell you makes a lot of sense and it’s kind of obvious to most of us, but it’s good to put science behind it, and to clearly document what we believe is actually true,” he says.

“My sense is that this study is going to need to be collaborated by larger studies to confirm it,” he adds.