Previous bariatric surgery before knee arthroplasty: A cautious interpretation.

We read with interest the nationwide register-based study by Aljuboori et al. examining previous bariatric surgery (BAS) and reintervention after knee arthroplasty. The authors appropriately state that their findings do not establish a benefit of BAS or negate the influence of residual obesity. We highlight several interpretive constraints. Matching on body mass index (BMI) at arthroplasty conditions on a post-exposure variable, while restriction to patients who ultimately underwent arthroplasty excludes those who improved sufficiently to avoid surgery. The 95% confidence interval for 2-year reintervention supports the absence of a statistically detectable difference, not equivalence or non-inferiority. Two-year follow-up may miss later mechanical failures, and exclusion of approximately 9% of screened records, including patients with missing BMI, may introduce additional selection bias. Glucagon-like peptide-1 (GLP-1) receptor agonists remain an important future perspective. Overall, the study provides useful short-term conditional observational evidence among selected arthroplasty recipients with comparable BMI, rather than an estimate of the overall causal effect of BAS before knee arthroplasty.