Abstract
To the editor:
We sincerely thank the authors for their thoughtful review of our manuscript 1 and their constructive insights regarding our study. We appreciate their recognition of the clinical importance of frailty assessment and agree that our hope is to inspire further clinical research on frailty assessment that enables preoperative optimization and improved postoperative outcomes.
We agree with some of the limitations authors point out such as the low severely frail cohort and the potential selection bias in postoperative CT scans obtained for fusion assessment. We were limited by the retrospective nature of the study and do support that future prospective studies would be necessary to truly understand the prognosticating role of the mFI-5. Importantly, the direction and magnitude of the association between frailty and PROMs were consistent across all frailty strata as a “dose response” type relationship, supporting the robustness of the observed relationships.
The authors also provide a handful of thoughtful methodological recommendations, including modeling the mFI-5 as a continuous or spline-based variable, applying time-to-event methods for return-to-activity outcomes, and performing sensitivity analyses that exclude the functional-dependence item to address potential circularity with baseline PROMs. Each of these suggestions represents a valuable extension of our analytic framework and will be considered in future iterations as the dataset expands and more granular variables become available.
We appreciate the authors’ emphasis on additional potential confounders such as bone mineral density, preoperative opioid dose, biologic use, etc. We agree these forms of cofounders are important in the assessment of patients before surgery and multivariate analysis to understand their importance. This however is something that has extensively been done in the literature across spine surgery.2,3 Rather, this study aimed to analyze the mFI-5 index. One point worth highlighting is the central rationale behind frailty assessment. Frailty indices such as the mFI-5 are intentionally designed to use a small number of readily obtainable variables as proxies for broader physiologic vulnerability. Their clinical value lies not in replacing comprehensive comorbidity profiling, but in providing a rapid, validated, and practical method to stratify risk during routine preoperative evaluation. The mFI-5 has been widely adopted precisely because of this feasibility and its strong performance across numerous surgical populations.4,5 As the authors note, other frailty indices such as risk analysis index, Edmonton Frailty Scale have been more recently described and have been shown to be efficacious. 6 The purpose of the present study was to describe how mFI-5 can help prognosticate postoperative outcomes in MIS TLIF patients. Nonetheless, we fully agree that incorporating richer physiologic measures and additional comorbidities would refine risk adjustment.
We appreciate the authors’ engagement and constructive recommendations. Frailty remains a complex and multidimensional construct, and our study aimed to provide an accessible, clinically practical starting point using the widely adopted mFI-5. We agree that future studies incorporating more comprehensive frailty indices, standardized imaging follow-up, and advanced modeling techniques will further clarify the relationship between frailty and outcomes after lumbar fusion. We again thank the authors for their valuable contribution and for helping advance research efforts surrounding frailty assessment in spine surgery.
