Letter to Editor on “Sarcopenia as a Predictor of Mortality Following Vertebral Compression Fractures Treated With Vertebroplasty” by Hung-Kai Liao et al

First, we would like to congratulate Liao et al for their invaluable contribution to the scientific literature. ¹ Sarcopenia is a topic that concerns all of us and is generating considerable interest in the medical field in general and in the field of spine surgery in particular. I believe that the growing attention given to sarcopenia is mainly due to its association with aging, and nowadays, the elderly population represents a considerable proportion of the patients we face in our daily medical practice. However, not all elderly individuals will develop sarcopenia, and it may remain undetected. For this reason, the medical community should be aware of this entity to implement preventive strategies and diagnose it early, thereby avoiding or minimizing its multiple negative effects on health, which ultimately impact both quality of life and the healthcare system.

The authors’ primary outcome shows that sarcopenia is a factor associated with mortality in patients treated with vertebroplasty for osteoporotic fractures. However, in the title and repeatedly throughout the manuscript, it is stated that vertebroplasty is a predictor of mortality. We believe it is worth clarifying that a predictor is not synonymous with an association, as they arise from different statistical approaches and carry different statistical implications. Association factors are analyzed through univariate analyses, whereas predictive factors are identified through multivariate analyses, in which potential confounding variables are controlled. Therefore, other factors may be involved in patient mortality that are not directly related to sarcopenia. In a recent study, mortality in patients undergoing vertebroplasty for osteoporotic fractures was found to be statistically associated with an ASA level of 4 and elevated creatinine levels. ² Although other studies support that sarcopenia may be a risk factor for mortality in patients undergoing vertebroplasty, we believe it is important to consider that sarcopenia may be associated with comorbidities that themselves increase the risk of mortality. ³

The diagnosis of sarcopenia warrants further discussion. The cutoff value of 0.84 for the Psoas Lumbar Vertebral Index (PLVI) was obtained from a previous study in which this threshold was not associated with patient mortality. ⁴ Furthermore, the isolated measurement of the psoas muscle area is not representative of generalized sarcopenia. ⁵ Another important aspect is that the diagnosis of sarcopenia requires the evaluation of skeletal muscle strength and physical performance, which were not assessed in the study, although they were mentioned as a limitation.

Another point we observed was the high rate of loss to follow-up or missing data. Since the primary outcome was mortality, we believe it would have been useful to employ a statistical strategy such as cumulative incidence to avoid losing patients with complete information. In addition, the number of patients in the sarcopenia group was smaller. Although no statistically significant differences were found in baseline variables, we believe that the small sample size may limit the validity of the analysis.

Despite our constructive criticisms, we once again congratulate the authors and encourage further studies evaluating the impact of sarcopenia on the pathophysiology and surgical outcomes of spinal disorders.