Response to the letter to the editor: Inconsistencies in obesity criteria: implications for systematic reviews on endoscopic spine surgery
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To the Editor,
We sincerely thank the correspondents for their insightful comments and for their interest in our systematic review and meta-analysis entitled “Endoscopic spine surgery for obesity-related surgical challenges: a systematic review and meta-analysis of current evidence [1].” We appreciate the opportunity to clarify the methodological concern raised regarding inconsistencies in the definition of obesity, particularly in Asian populations.
In our systematic review and meta-analysis, obesity was defined a priori as body mass index (BMI) ≥30 kg/m2 according to the World Health Organization (WHO) global classification, which remains the most widely used standard in international research and evidence synthesis [1]. However, we acknowledge that several included studies, particularly from Asian cohorts, adopted lower BMI cutoffs such as >25 kg/m2 or >28 kg/m2 in accordance with population-specific classifications. Notably, the WHO Expert Consultation [2] recognized that Asian populations may develop obesity-related metabolic risk at lower BMI values, and therefore recommended considering lower BMI thresholds in Asian settings. Similarly, national or regional guidelines such as those from the Japan Society for the Study of Obesity support population-adapted criteria for defining obesity [3].
We agree with the correspondents that variability in BMI thresholds may lead to potential exposure misclassification (overweight vs. obesity) and may contribute to heterogeneity in pooled analyses. This issue is particularly relevant in spine surgery research because elevated BMI influences surgical exposure, instrumentation difficulty, complication profiles, and postoperative recovery. Thus, the correspondents’ comments highlight an important methodological point that should be explicitly addressed in future systematic reviews with multi-regional populations. At the same time, we would like to emphasize that the currently available evidence on endoscopic spine surgery (ESS) in patients with elevated BMI remains limited. Most published studies are observational, include relatively small-to-moderate sample sizes, and demonstrate heterogeneity in study design, surgical techniques, and BMI stratification criteria. This restricted the feasibility of conducting robust subgroup analyses stratified by obesity definitions (global vs. Asian-specific cutoffs).
Our study’s limitations, ESS has several conceptual and practical advantages in patients with obesity. In obese individuals, traditional open surgery often requires wider exposure, longer incisions, and extensive soft tissue dissection, which may increase the risk of wound-related complications and infection [1]. ESS provides a minimally invasive approach with smaller incisions and reduced muscle dissection, which may mitigate wound morbidity, facilitate earlier mobilization, and potentially shorten hospital stay [4–8]. These considerations are clinically important because patients with obesity frequently represent a high-risk surgical population. Our synthesis aimed to evaluate the best available evidence regarding whether ESS could help address these obesity-related surgical challenges (Figs. 1, 2). Accordingly, given the limited and heterogeneous evidence base, we adopted a pragmatic approach by including eligible studies that explicitly analyzed higher-BMI cohorts using regionally accepted thresholds, to preserve clinical relevance and avoid excluding potentially informative data. Nevertheless, we acknowledge that clearer reporting and stratification of BMI definitions are essential to enhance transparency and global interpretability. We strongly support future high-quality prospective studies with standardized BMI classifications and uniform outcome reporting, including subgroup analyses based on globally standardized obesity cutoffs versus Asian-specific thresholds.
Operative room setup for full endoscopic spine surgery (Performed by Prof. Wongthawat Liawrungrueang, MD).
Representative intraoperative images of full endoscopic lumbar discectomy in an obese patient. (A) Endoscopic view demonstrates an extruded herniated disc fragment. (B) Removal of the disc material using endoscopic forceps. (C) Final endoscopic view after discectomy and decompression, showing adequate neural decompression with a clear surgical field and no residual tissue compression. (D) Large disc fragment removed during full endoscopic spine surgery.
To further improve clarity for international readers, we also propose that future reviews include a simple conceptual figure summarizing the rationale for lower BMI thresholds in Asian populations and the clinical implications in ESS research. Such a figure may help readers interpret BMI definitions, heterogeneity sources, and the translational value of ESS in obese and overweight cohorts. We sincerely thank the correspondents again for their constructive feedback, which will contribute meaningfully to improving methodological transparency in future evidence synthesis on ESS.
Notes
Conflict of Interest
No potential conflict of interest relevant to this article was reported.
Acknowledgments
Watcharaporn Cholamjiak would like to thank University of Phayao and Thailand Science Research and Innovation Fund (Fundamental Fund 2026, Grant No. 2253/2568).
Author Contributions
Conceptualization: WL. Methodology: WL, PS, WC, KTL. Data curation: WL, WC, PS, KTL. Formal analysis: WL, WC. Visualization: WL, WC, PS, YMS, PHW, MHW, YJL, LCY, ZI, STC, KTL. Project administration: WL. Writing–original draft preparation: WL. Writing–review and editing; WL. Supervision: WL. Final approval of the manuscript: all authors.