Laird Harrison

February 10, 2012

February 10, 2012 (San Francisco, California) — Patients with severe osteoarthritis of the knee who undergo knee replacement have a 7-year mortality rate that is half that of those who don't undergo the procedure, researchers reported here at the American Academy of Orthopaedic Surgeons 2012 Annual Meeting.

"This is more good evidence for the benefits of knee arthroplasty," lead researcher Scott Lovald, PhD, told Medscape Medical News.

Dr. Lovald and his colleagues from Exponent, a private consulting firm in San Francisco, California, were hired by Biomet, which makes products for knee arthroplasty, to analyze the costs and benefits of the procedure.

They looked at a 5% sample of patients insured by Medicare to identify those with osteoarthritis of the knee. They divided these patients into those who did not undergo total knee arthroplasty (n = 80,629) and those who did (n = 53,829) from 1997 to 2009.

They looked at the patients' data for up to 7 years to compare their health statistics and to measure how much they spent on healthcare.

Over the 7 years, they found that the Medicare payments (parts A and B) for patients who did not get knee replacements totaled $63,940; for those who did get knee replacements, they were $83,783 — a difference of $19,843.

What did that money buy? The most dramatic difference between the 2 groups was in mortality.

Those with knee replacements had half the 3.1% 7-year mortality rate of those who did not (hazard ratio [HR], 0.48 to 0.54; P < .001).

Also, those with knee replacements had a slightly lower rate of heart failure at 3 years (21.1%; HR, 0.89; P < .001) and at 7 years (40.9%; HR, 0.93; P < .001).

"Many would consider that a cost-effective treatment," said Dr. Lovald.

However, both groups had roughly the same rate of diabetes (27.5% at 1 year, rising to 43.3% at 7 years).

In addition, those with replaced knees had a higher rate of depression in the first year after the procedure (9.37%; HR, 1.28; P < .0093), although this difference faded in the subsequent years.

The study does not prove that knee replacement reduces mortality or heart failure rates, Dr. Lovald acknowledged. The patients who had knee replacements might have been healthier to begin with than those who did not, he pointed out.

The HRs were calculated after the researchers controlled for age, sex, region of residence, comorbidities (using the Charlson Comorbidity Index), and socioeconomic status (using the Medicare buy-in status, which estimates how much patients spend on healthcare), but it is impossible to control for all variables, Dr. Lovald said.

Marc Dehart, MD, clinical assistant professor of orthopaedic surgery at the University of Texas in Galveston, told Medscape Medical News that it makes sense that knee replacements would lead to longer lives. "You are able walk and exercise more," he said. "That would help with the most common causes of death, which are cardiac."

He cautioned, however, that knee replacement surgery has not been shown to reduce body mass index. This could account for its failure in this study to change the rate of diabetes, he said.

The increased depression in the first year could be related to the long recovery period from the procedure, and perhaps to patients' high expectations. "It could be that they had expectations that the knee replacement would do more than ease the pain," he said.

A limitation of this type of study, which culls information from a database rather than enrolling patients who can be interviewed, is that it's hard to get answers to questions like this, he said.

Still, Dr. Dehart was impressed by the powerful benefits of knee replacement surgery, compared with its cost. In fact, knee replacement could be even more cost-effective because this study did not take into consideration the expense of prescription drugs, which could be higher in people who don't have the procedure because they likely need more pain control.

Dr. Lovald is an employee of Exponent, a private consulting firm hired by medical device companies. Dr. Dehart has disclosed no relevant financial relationships.

American Academy of Orthopaedic Surgeons (AAOS) 2012 Annual Meeting: Abstract P149. Presented February 8, 2012.


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