Male Smokers Have Lower Risk for Joint Replacement Surgery

Laurie Barclay, MD

July 13, 2011

July 13, 2011 — Men who smoke have less risk of undergoing total joint replacement (TJR) surgery of the hip or knee than those who have never smoked, according to the results of an Australian cohort study reported online July 8 in Arthritis & Rheumatism.

"Our study is the first to demonstrate a strong inverse correlation between smoking duration and risk of total joint replacement," said lead author George Mnatzaganian, PhD, from the University of Adelaide in Adelaide, Australia, in a news release. "The independent inverse associations of smoking with risk of total joint replacement were evident also after adjusting for major confounders and after accounting for the competing mortality risk in this elderly cohort of men. Further investigation is needed to determine how smoking impacts the development of [osteoarthritis]."

In developed countries, total hip and knee replacements are among the most widely performed elective surgeries, with 230,000 people in the United States estimated to have had hip arthroplasty and 543,000 to have had knee arthroplasty in 2007, based on the National Hospital Discharge Survey.

Severe osteoarthritis (OA) is the most common cause for arthroplasty, with known risk factors including older age, female sex, and obesity.

Using a cohort from the Health in Men Study of 11,388 men for whom clinical data, hospital morbidity data, and mortality records were available, the investigators aimed to examine the associations of smoking, body weight, and physical activity with the risk of undergoing TJR. During the initial health screening from 1996 to 1999, participants from the Health in Men Study provided information regarding smoking history and physical activity. Cox proportional hazards regressions and competing risk regressions allowed modeling of TJR risk in 3 separate age groups based on weight and height at baseline, comorbidity, injury, socioeconomic status, years of smoking, and exercise.

Clinical data were analyzed from baseline through March 2007. Of 857 men who had joint replacement surgery, 59.5% had total knee replacement, and 40.5% had total hip replacement.

Overweight was independently associated with an increased risk for TJR, whereas smoking was independently associated with a reduced risk, and there was a dose-response relationship for both associations. Cox and competing risk regressions models both showed reduced risk among smokers, which was evident after 23 years of smoking. Compared with never-smokers, men who were in the highest quartile (48-plus years of smoking) were 42% to 51% less likely to undergo TJR than never-smokers. Across smoking as well as across weight quantiles, tests for trend in the log hazard-ratios were significant (P < .05).

Vigorous exercise was associated with a greater risk for TJR, but this was statistically significant only in those aged 70 to 74 years (adjusted hazard ratio [HR], 1.64; 95% confidence interval [CI], 1.19 - 2.24). The observed associations were not abolished by adjustment for the Deyo-Charlson Index or Elixhauser's comorbidities.

Limitations of this study include failure to directly determine OA status; self-reported information on the physical activity of the participants; failure to account for changes in patient characteristics with time; and observational design, precluding determination of a causal relationship between smoking and OA.

"This population-based cohort study has shown an increased risk for TJR with body weight and vigorous exercise, and an inverse association with smoking," the study authors write. "More research is needed to better understand the role of smoking in the pathogenesis of OA, but also into the selection pathways for patients for whom TJR is indicated. Notwithstanding the findings, this study reinforces the overwhelming excess risk of premature mortality associated with smoking."

The study authors have disclosed no relevant financial relationships.

Arthritis Rheum. Published online July 8, 2011.

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