Comment on “Preoperative malnutrition and risk of re-revision and mortality following revision arthroplasty”

We read with great interest the study by Yao et al[1] titled “Preoperative Malnutrition and Risk of Re-revision and Mortality Following Revision Arthroplasty,” which evaluated the prognostic value of the preoperative Prognostic Nutritional Index (PNI) in hip or knee revision arthroplasty. This large retrospective cohort showed a significant association between low PNI and higher risks of infection driven re-revision and long-term mortality, and the authors deserve recognition for their rigorous statistical methods and identification of clinically useful cutoffs. However, despite these contributions, several methodological and interpretive concerns require clarification, and caution is needed when applying these findings to broader clinical practice. First, the conclusion that each 1-point reduction in PNI corresponds to an approximately 15% increase in the risk of re-revision requires clearer specification of its applicable range. It also requires caution to avoid excessive extrapolation. This relationship is derived from statistical modeling of the observed data and assumes a near linear association between PNI and re-revision within the analytic interval. In actual clinical populations, PNI values do not decrease or increase without limit. Extreme values often reflect different pathological states in which the risk pattern may plateau or even reverse. A more rigorous approach would involve restricted cubic spline analysis or stratified evaluation to identify the upper and lower boundaries of the risk range as well as potential inflection points. Without such clarification, readers may mistakenly interpret the reported 15% increment as an absolute and continuously extendable risk coefficient, which would not be clinically accurate. Second, the explanation for dislocation related re-revision does not sufficiently consider key mechanical factors such as prosthesis positioning and limb alignment, which are well-established determinants of postoperative instability. The study did not evaluate essential radiographic parameters including acetabular anteversion, inclination, or femoral stem orientation, even though these are often the primary causes of dislocation. In clinical practice, an initial dislocation without implant loosening is usually managed with closed reduction and immobilization rather than immediate revision. The subsequent reduction in mobility, appetite, and overall physiological reserve may lead to declines in albumin and lymphocyte counts, resulting in a lower PNI. In this context, low PNI may reflect the consequences of instability and postoperative deconditioning instead of a true preexisting risk factor. While chronic malnutrition might theoretically weaken periarticular muscles and increase dislocation risk, it is only one possible mechanism and cannot be considered the main explanation without detailed mechanical and radiographic data. Third, PNI reflects a mixture of immune, inflammatory, and nutritional status rather than a precise measure of caloric or protein intake. Albumin and lymphocyte counts are affected by many non-nutritional factors, including inflammation, infection, liver dysfunction, fluid shifts, kidney related protein loss, and medication use. In revision arthroplasty patients, subclinical infection and systemic inflammation are common and can readily reduce PNI. Therefore, interpreting low PNI as purely malnutrition may overstate the role of nutritional deficiency and underestimate the overall disease burden. It is more appropriate to view PNI as an integrated marker of immune nutritional status and inflammatory load rather than a strict diagnostic indicator of malnutrition. Fourth, the study did not include multidimensional assessments of nutritional status such as body composition, dietary intake, recent weight change, or muscle function. It relied solely on laboratory surrogate markers, which limits the strength of the conclusions. Modern nutrition assessment emphasizes multiple domains including weight loss history, body mass index, skeletal muscle mass, distribution of body fat, handgrip strength, physical performance, and detailed evaluation of protein and energy intake. The absence of these parameters means that the diagnosis of malnutrition cannot be confidently established. Drawing conclusions about nutritional causality based only on a single laboratory index introduces interpretative limitations and reduces the precision of the findings. Fifth, among the 64 patients who underwent re-revision, 43 cases were related to joint infection. This high proportion strongly suggests that infection itself may be the dominant factor driving re revision. In these patients, persistent infection, incomplete eradication of the initial infection, or new postoperative infection could have contributed to surgical failure. A reduced PNI in this setting may simply represent the systemic effects of infection and inflammation rather than an independent causal risk factor. The observed association between low PNI and re-revision may therefore reflect shared upstream influences, particularly infectious and inflammatory processes. It should not be automatically interpreted as evidence that decreasing PNI directly leads to infection and subsequent failure. This study fully follows the 2025 TITAN Guidelines, ensuring appropriate disclosure and responsible application of artificial intelligence[2].