In reference to “Association of serum sodium with morbidity and mortality in hospitalized patients undergoing major orthopedic surgery”

McCausland and colleagues have published an excellent study on the association of dysnatremia with morbidity and mortality in patients undergoing major orthopedic surgery, which found that it was associated with greater mortality. However, we have some concerns regarding the article and wish to share them. First, what is the definition of major orthopedic surgery? The authors did not give us a criterion. In our opinion, internal or femoral neck fracture belongs to minor orthopedic surgery, but such fractures usually occurs in patients older than 65 years, who have a higher incidence of perioperative hyponatremia. Therefore, a detailed definition of major orthopedic surgery was needed in this article. Second, the sample in this study included individuals aged 18 years and was not limited to individuals with fractures. However, as we know, young patients are usually healthy and without dysnatremia except for multiple fractures. Those with multiple fractures also have a higher chance of hyponatremia and higher mortality, mainly caused by the trauma itself. We think such confounding factors could affect the validity of this article.