Knee Replacement Data Scarce for Long-Term Safety, Effectiveness

March 05, 2012

March 5, 2012 — Knee replacement surgery is a success story of modern medicine, yet not enough is known about patient outcomes or the effectiveness of various implants, and consensus is lacking about the precise indications for the procedure, according to a study published online March 6 in the Lancet.

The authors, based in the United Kingdom, Sweden, and Australia, write that surgeons need improved decision-making as more and more possible candidates for new knees fall are younger than 55 years — a group that has a higher rate of revision or follow-up surgery. On another problematic note, some patients undergo the operation despite having good functional ability and only mild pain beforehand.

The article, based on a literature review going back to 1970, is the second in less than a week raising doubts about the evidence on orthopaedic joint implant safety and effectiveness. On February 28, the British Medical Journal published an article charging that hundreds of thousands of patients with metal-on-metal hip replacements were kept in the dark about possible exposure to toxic substances.

Andrew Carr, FRCS FmedSci, lead author of the Lancet article, and coauthors write that the number of total knee replacements (TKRs) in the United States increased from 31.2 per 100,000 person-years in the period from 1971 to 1976 to 220.9 per 100,000 person-years in 2008, for a total that year of more than 650,000 procedures. The authors predict that the demand for knee replacement will continue to grow in developed countries, in light of aging populations and rising obesity rates, which both portend higher rates of osteoarthritis, the main clinical indication for the operation.

Although more and more people are getting new hardware for their knees, fuzzy thinking prevails as to who really needs it.

"No clear consensus exists within the surgical community about exact indications, particularly severity of preoperative symptoms, obesity, and age," Dr. Carr and coauthors write. They point to a task force organized by the Osteoarthritis Research Society International and a rheumatology organization that found that "pain, function, and radiographic severity are not associated with a surgeon's recommendation for knee replacement."

Improve Treatment of Early-Stage Osteoarthritis to Avoid Surgery

Outcomes data on the safety and effectiveness of knee-replacement surgery also are fuzzy, according to the authors. Most published reports of outcomes, they write, are single-surgeon or single-center case series. Many of these reports chronicle the practice of a surgeon who invented the implant, "which introduces bias and a potential conflict of interest."

The key outcome studied was the rate of revision surgery to deal with complications. Aseptic loosening, usually caused by implant wear, is the most common reason for revision surgery, and "is mainly a concern in young and active patients." The second most common reason is infection. Other major causes are postoperative pain, instability, and stiffness.

The authors write that an implant's design can make a big difference in minimizing or maximizing the risk for adverse events that require revision surgery, hence the need to monitor implants through national registries. However, revision surgery also can be blamed on preoperative diagnosis; surgical technique, experience, and skill; patient factors; operating room conditions; and postoperative care.

Outcomes data break down into those for TKRs vs those for partial-knee replacements (PKRs). Surgeons and their patients sometimes will choose a PKR for the sake of a more normal-feeling knee, less extensive surgery, and a lower risk for infection, knowing that they have the option of converting to a TKR if need be. However, partial replacement has a higher risk for revision surgery than total replacement, and a conversion TKR is more likely to require more follow-up than a primary TKR, according to registry data.

The authors urge the continued development of national registries to monitor the long-term outcomes of knee replacement surgery, as well as the use of electronic health record systems to facilitate this. They note that registries tend to report less glowing outcomes for knee replacement than published clinical trials. "Without high quality, unbiased, and reliable information, surgeons cannot make informed decisions about how to achieve the best outcome in each clinical situation," the authors write.

In addition to recommending better patient selection and better reporting of outcomes, particularly as it relates to individual implant devices, the authors also call for new strategies to treat early-stage osteoarthritis in younger patients that will "avoid the need for major surgery altogether."

Despite the misgivings they express about the state of knee replacement, the authors also render praise.

"Joint-replacement surgery," they write, "is one of the most successful examples of innovative surgery, and has resulted in substantial quality-of-life gains for people with end-stage arthritis."

One coauthor is paid by the Australian Orthopaedic Association as director of the National Joint Registry. One coauthor has received honoraria and support for travel from Biomet. One coauthor has received consultancy fees from Stryker and institutional research grants from Genzyme. The 4 remaining authors have disclosed no relevant financial relationships.

Lancet. Published online March 6, 2012. Abstract


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