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Knee replacement

Researchers Pinpoint Risk Factors for Knee-Implant Infections

May 28, 2019
Identifying risk factors let doctors choose best treatment for patients.

In the largest study of its kind, researchers from the Musculoskeletal Research Unit at the University of Bristol have identified the most important risk factors for developing severe infection after knee implant surgery. They found that male patient under age 60 with chronic pulmonary disease, diabetes, liver disease, and a higher body mass index are at increased risk of having the joint replacement redone (known as revision) due to infections.

The study looked at the risk of infection following first-time (primary) knee replacement. This study used data from the National Joint Registry (NJR) for England, Wales, Northern Ireland, and the Isle of Man linked to the Hospital Episode Statistics database.

Knee replacement, used mainly to treat pain and disability caused by osteoarthritis, is a common procedure, with around 110,000 operations performed annually in the UK alone. A rare but serious complication affecting about 1% of patients is deep infection. This causes considerable distress and often requires long and protracted treatments, including revision surgery.

This study showed that revision surgery due to infections were influenced by the type of procedure performed, and the type of prosthetic, and how it was attached. For example, surgery performed following trauma, inflammatory arthropathy, or a history of previous infection in the knee were more likely to become infected and need revised. And cemented total knee replacements were more likely to be revised for infection compared to patients with an uncemented total-knee implants. Finally, the risk of revision was increased for patients with a posterior stabilized fixed-bearing implant or a constrained condylar (CC) implant compared to those with an unconstrained (or cruciate retaining) fixed-bearing implant. The experience of the surgeon and the size of the orthopedic center had no or only minor effects on the risk of revision for infection.

Uniquely, the research identified that these important factors have a different effect depending on the postoperative period, with liver diseases and inflammatory arthropathy increasing the risk of revision for infection in the long term. Patients receiving a patellofemoral, unicondylar, or uncemented total knee replacement, however, had lower risks of late revision for infection. This is an important factor to consider when conducting further research in this area as just considering overall risk or short-term risk may mean important effects are missed entirely. Most risk factors identified are generally associated with complex initial knee replacements.

“This work has identified key patient and surgical characteristics which influence the risk of revision for infection following knee replacement, and specifically the risk of further surgery for infection two years or more after the initial operation,” says Michael Whitehouse, a researcher at the Bristol Medical School. “This information provides me with the strong evidence I need to discuss infection risks with my patients undergoing knee replacement and helps identify strategies to minimize those risks.”

This research follows similar work the team did on hip replacements published last year which showed some patients are at higher risk of early infection, while others are more prone to later infections after knee replacement. The study analyzed data from over 670,000 primary hip replacement patients, with 3,659 requiring revision for infection.

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