The mediating effect of body mass index on the relationship between smoking and hip or knee replacement due to primary osteoarthritis. A population-based cohort study (the HUNT Study)

Abstract

To investigate the total effect of smoking on total hip or knee replacement (THR/TKR) due to primary osteoarthritis (OA) and to quantify the indirect effect of smoking through body mass index (BMI). Participants from the Nord-Trøndelag Health Study (the HUNT Study) were linked to the Norwegian Arthroplasty Register to detect the first THR or TKR due to primary OA. A mediation analysis was used to decompose the total effect of smoking into a direct and indirect effect. BMI was considered a mediator in the analysis. All effects were estimated as hazard ratios (HRs) with 95% confidence intervals (CIs). The indirect effect of smoking mediated through BMI was expressed as a percentage (proportion*100). In total 55 188 participants were followed up during 17.2 years (median). We identified 1322 THRs and 754 TKRs. For men, the total effect of current vs. never smoking revealed a decreased risk of THR (HR 0.59, 95% CI 0.46–0.76) and TKR (HR 0.47, 95% CI 0.32–0.66). For women, current smoking increased the risk of THR (HR 1.34, 95% CI 1.11–1.60). For men, 6% and 7% of the risk reduction for THR and TKR, respectively, was mediated by BMI. We found a negative association between smoking and THR or TKR for men. On the contrary, smoking was associated with increased risk of THR for women. Most of the effect of smoking on joint replacement risk remained unexplained by BMI.

The association between smoking and knee osteoarthritis in a cohort of Danish patients undergoing knee arthroscopy

“…A second hypothesis is that smoking might affect the risk of knee OA through its effect on BMI [16]. However, one former study showed that the indirect effect of smoking on hip and knee OA was small [19], as was indicated by the sensitivity analysis in the present study.…”

Impact of Smoking on the Incidence and Postoperative Complications of Total Knee Arthroplasty: A Systematic Review and Meta-Analysis of Cohort Studies

“…Smoking cessation is another hot spot that orthopedists focus on. In this study, seven included studies distinguished the former smokers and current smokers, four of them focused on the incidence of TKA [12,14,23,24], one focused on the prosthetic joint infection [20],…”

“…The incidence of TKA was mentioned in six studies with a total of 224 865 patients who were diagnosed with RA (n=1) or OA (n=4). There were two indicators to report the outcome: three studies used HR to report the outcome [14,24,26], and the other two studies reported the number of surgical cases [12,23]. According to the previous statistical methods [31,32], we approximately regarded the HR as similar to the RR and conducted the metaanalysis.…”

“…This challenges the traditional view of the relationship between smoking and TKA. In 2013 Pearce et al conducted a meta-analysis to find that smoking has no protective effect on OA progression [11], but several subsequent clinical studies have suggested that smoking is a protective factor for OA or TKA [12][13][14][15]. Meanwhile, some other studies focused on complications after TKA, but the outcome is not comprehensive enough.…”

Nicotine Dependence and Incident Hip Replacement Surgery in Individuals with Type 2 Diabetes Mellitus, TRINET-X, 2021

“…However, the relationship between smoking and bone mineral density is complex and inconclusive. 8 In one study, the relationship between smoking and bone mineral density became non-significant in adjusted analyses. 9 Similarly, body mass index (BMI), a risk factor for OA which leads to total hip arthroplasty, was not related to smoking.…”