Study: Smokers at Elevated Risk for Infection After TKA

By: Terry Stanton

A study of patients undergoing total knee arthroplasty (TKA) found that current smokers carried a 92 percent increased risk of surgical site infections (SSIs) than never smokers. For past smokers, the risk of infection was 36 percent higher.

The study, presented Wednesday by Matthew Boylan, a medical student at SUNY Downstate College of Medicine, used the ACS NSQIP database to identify the 54,374 patients who underwent primary TKA and the 4,154 patients who underwent revision TKA over an 8-year period. In addition to smoking status, which was categorized as never, past, or current, patients were categorized according to the number of pack-years smoked.

Current smokers had an increased risk of both superficial and deep SSI, and the risk was significantly higher for primary TKA but not revision TKA. The risk of infection was significantly increased for patients with smoking histories of 20 or more pack-years.

“Cigarette smoking is a known and modifiable risk factor for many adverse medical outcomes,” Mr. Boylan commented. “Prior studies have found an association between cigarette smoking and SSI in orthopaedic trauma and reconstruction surgeries, but these studies had a number of limitations, including lack of data on pack-year smoking history and small sample sizes.”

The study team, led by Michael A. Mont, MD, of the Rubin Institute for Advanced Orthopaedics in Baltimore, Md., saw a dose-response relationship between the duration of smoking and surgical site infection.

“We were also interested to find that the risk of infection was significant among smokers who underwent primary TKA, but not smokers who underwent revision TKA, although this finding may have been a consequence of the smaller sample size of revision procedures,” Dr. Mont said.

Abstract
Introduction:
SSIs are severe complications that can lead to implant failures, increased lengths of hospital stay, and hospital readmissions. Cigarette smoking is a potential risk factor for SSI, although there are limited data on this association with total knee arthroplasty. This study sought to examine the relationship between cigarette smoking and the risk of surgical site infection following total knee arthroplasty.

Methods: The ACS NSQIP database was used to identify patients who underwent primary (n = 54,374) or revision (n = 4,154) total knee arthroplasty between January 2005 and December 2012. Patients were categorized according to smoking status (never, past, current) and pack-years smoked (0, 1–9, 10–19, 20–29, 30–39, ≥ 40). Regression models, adjusted for patient age, body mass index, sex, diabetes mellitus, and chronic corticosteroid use, were used to calculate the risk of SSI within 30 days of surgery.

Results: At the time of surgery, 8.73% of patients were current smokers and 8.37% were past smokers. Compared to never smokers, the adjusted risk of SSI was 92% higher for current smokers (P < 0.001) and 36% higher for past smokers (P = 0.018). Among current smokers, the increased risk was similar for superficial SSI (P < 0.001) and deep SSI (P < 0.001), and was stronger for primary arthroplasty (P < 0.001) compared to revision arthroplasty (P = 0.132). Markedly increased risk was noted among current smokers with pack-year histories of 20–29 years (P < 0.001), 30–39 years (P < 0.001), and ≥ 40 years (P = 0.001), when compared to patients with pack-year histories < 20 years.

Conclusions: For current and past cigarette smokers, there is an increased risk of SSI following total knee arthroplasty. Further studies are needed to assess the role of smoking cessation strategies on the risk of postoperative SSI among patients seeking elective total knee arthroplasty.

Mr. Boylan’s and Dr. Mont’s coauthors are Bhaveen H. Kapadia, MD; Steven Daniels, MD; and Carl B. Paulino, MD.

Details of the authors’ disclosures as submitted to the Orthopaedic Disclosure Program can be found in the Final Program; the most current disclosure information may be accessed electronically at www.aaos.org/disclosure

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