Does smoking cessation increase risk of knee replacement? a general population-based cohort study.

Summary Objective Smoking represents a major issue for global public health. Owing to methodologic challenges, findings of an association between smoking and risk of knee osteoarthritis (OA) are inconsistent. We sought to assess the relation of onset of smoking cessation to the risk of OA sequelae, i.e., knee replacement, and to perform sub-cohort analysis according to weight change after smoking cessation. Design Using The Health Improvement Network, we conducted a cohort study to examine the association between smoking cessation and risk of knee replacement among patients with knee OA. Participants who stopped smoking were further grouped into three sub-cohorts: weight gain (body mass index [BMI] increased>1.14 kg/m2), no substantial weight change (absolute value of BMI change 1.14 kg/m2) after smoking cessation. Results We identified 108 cases of knee replacement among 1,054 recent quitters (26.7/1000 person-years) and 1,108 cases among 15,765 current smokers (17.4/1000 person-years). The rate difference of knee replacement in recent quitter cohort versus current smoker cohort was 10.4 (95% confidence interval [CI]:5.3-15.6)/1000 person-years and the adjusted hazard ratio (HR) was 1.30 (95%CI:1.05-1.59). Compared with current smokers, risk of knee replacement was higher among quitters with weight gain (HR=1.42,95%CI:1.01-1.98), but not among those with no substantial weight change (HR=1.29,95%CI:0.90-1.83) or those with weight loss (HR=1.11,95%CI:0.71-1.75). Conclusions Our large population-based cohort study provides the first evidence that smoking cessation was associated with a higher risk of knee replacement among individuals with knee OA, and such an association was due to weight gain after smoking cessation.