Knee Surgery Does Not Improve Life Quality for Many Patients

Pam Harrison

March 29, 2017

Total knee replacement provides minimal quality-of-life benefit for patients with less severe disability at baseline, according to new research. Thus, the treatment, as currently practiced in the United States, is not cost-effective.

"Improvements in quality of life with total knee replacement were on average smaller than previously shown," Bart Ferket, MD, from the Icahan School of Medicine at Mount Sinai, New York City, and colleagues write. "Given its limited effectiveness in individuals with less severely affected physical function, performance of total knee replacement in these patients seems to be economically unjustifiable."

"If the procedure were restricted to patients with more severe functional status, however, its effectiveness would rise, with practice becoming economically more attractive."

The study, which was published online March 28 in the BMJ, analyzed data from the Osteoarthritis Initiative (OAI) database, a multicenter cohort of 4498 individuals from the general US population with or at risk for osteoarthritis of the knee. "Study participants were aged 45-79 [years] at enrolment and were tracked with repeated follow-up evaluations for nine years," study authors state. The authors also validated their findings on a separate cohort of 2907 participants with osteoarthritis of the knee involved in the Multicenter Osteoarthritis Study (MOST). Follow-up of the MOST cohort was 2 years.

Dr Ferket and colleagues modeled the effect knee replacement had on quality of life, using the Short Form (SF)-12 physical component summary (PCS) score, the SF-12 mental component summary score, the SF-6D utility index, the Western Ontario and McMaster Universities arthritis index, and the quality-of-life subscale on the knee injury and osteoarthritis outcome score. They also assessed the effect surgery had on pain medication use out to 96 months.

Perhaps not surprisingly, those with osteoarthritis of the knee at baseline in the OAI cohort had more severely affected function, as reflected with worse SF-12 PCS, SF-6D, and osteoarthritis-specific quality-of-life scores than those at high risk for osteoarthritis of the knee (P < .001). Among this particular cohort, investigators documented 382 knee replacements, most of which were done before the last assessment at 96 months. In the MOST cohort, investigators identified 135 total knee replacements before the last visit at 30 months.

After adjusting for confounding variables both at baseline and across time, investigators documented an absolute improvement of 1.70 points on the SF-12 PCS among participants who had undergone knee surgery compared with those who had not undergone surgery. Changes on the SF-12 mental component summary score as well as the SF-6D utility index were both minor, at −0.22 and 0.008 points, respectively, they add.

Osteoarthritis-specific measures of quality of life indicated that knee replacement surgery improved the Western Ontario and McMaster Universities arthritis index score by 10.69 points, whereas the knee injury and osteoarthritis outcome quality-of-life score improved by 9.16 points.

"These improvements became larger with decreasing functional status at baseline," the researchers note. For example, one calculation suggested that "total knee replacement would become more effective if it was restricted to patients with SF-12 PCS scores <50."

Quality-Adjusted Life-Years

Researchers also estimated differences in lifetime costs and quality-adjusted life-years (QALYs) according to the patient's baseline symptom level. "For the base case analysis, we modeled 10 scenarios, ranging from current practice with rates as observed in the OAI, to lower rates of practice in which the procedure was performed only in individuals with lower SF-12 PCS levels (from <55-<20), to a scenario without total knee replacement," Dr Ferket and colleagues explain. They also factored in different cost-effectiveness thresholds from $50,000, $100,000, and $200,000 for each QALY for decision-making.

The only scenario in which the incremental cost effectiveness ratio for knee replacement surgery fell below $100,000/QALY was for individuals with a SF-12 PCS score of less than 20, indicating significant baseline disability. At a cost-effectiveness threshold of $200,000 per QALY, the economically most attractive strategy would be to restrict knee replacement surgery to patients with a baseline SF-12 PCS score of under 35, whereas expanding to include those with a score less than 40 would make the procedure borderline cost-effective.

In contrast, extending knee replacement surgery to patients with a baseline SF-12 PCS of 40 and under would be financially viable if hospital costs dropped below $14,000 per hospital admission. As researchers point out, findings were validated in the MOST cohort as well. "Considerable cost savings could be made by limiting eligibility [of surgery] to patients with more symptomatic knee osteoarthritis," the authors conclude.

Patient Satisfaction

Asked by Medscape Medical News to comment on the study, Daniel Riddle, PT, PhD, from the Department of Orthopaedic Surgery and Rheumatology, Virginia Commonwealth University, Richmond, felt the main limitation to this kind of cost-effectiveness study is that it does not account for patient satisfaction.

"What the OAI does not do is provide information about whether these patients were satisfied with how they were doing after surgery," Dr Riddle said. "Because it could be that people who had minimal improvement on the SF-12 PCS were still satisfied even though they started out in a place where their symptoms were not as severe as those who had more substantial improvement following surgery."

Moreover, 20 years ago, knee replacement surgery was intended to help only those patients who had end-stage osteoarthritis and very poor function. "Over the last 20 years, we've seen not only improvements in the surgery itself, but the implants surgeons use and also the recovery process, so it's a different procedure than it was 20 years ago," Dr Riddle suggested.

Again, it may well be that patients who have less severe pain or less severe functional loss still gain substantially from the surgery, even though it's not the same order of magnitude as those who are more severely affected.

"Let's face it, people who are on the very severe end of the spectrum of pain and functional loss have a lot more gain to make, but we already knew that," Dr Riddle said. "What this study does show us is that the cost associated with these small changes is very high and whether we can afford such minimal benefits for such a great cost is a question that the greater society has to try and answer."

The cost of performing total knee replacement now exceeds 10 billion a year in the US.

The authors and Dr Riddle have disclosed no relevant financial relationships.

BMJ. Published online March 28, 2017. Full text

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