Response to Letter to the Editor: “Individuals Over 75-Year-Old Experience Greater Revisions Following Transforaminal Lumbar Interbody Fusion (TLIF): A Propensity Matched Study”

Dear Editor,

We thank the authors for their insightful letter regarding our recently published study, “Individuals Over 75 Year Old Experience Greater Revisions Following Transforaminal Lumbar Interbody Fusion (TLIF): A Propensity Matched Study” in the Global Spine Journal. We appreciate their interest and the opportunity to clarify and expand upon the points they raised.

This observed radiographic equivalence despite higher revision rates in the ≥75 cohort raises important questions. The suggestion that surgeons may be implicitly adopting age-adjusted or “functional alignment” targets is compelling; however, our data do not demonstrate statistically significant undercorrection. In our propensity-matched cohorts, both absolute postoperative alignment and the magnitude of correction were similar between age groups, and loss of correction did not appear to drive the higher revision burden. We agree that a growing body of literature supports the concept of age-adjusted alignment goals, with several studies suggesting that older adults may tolerate greater PI-LL mismatch and sagittal malalignment at comparable HRQOL levels, and that deviations from proposed age-adjusted thresholds may be associated with worse outcomes.^1,2 That said, these findings are not entirely uniform across studies, and consensus regarding optimal alignment targets remains evolving.

We also appreciate the emphasis on the higher revision burden in the elderly despite similar perioperative complication rates. The predominant modes of failure, pseudoarthrosis, adjacent segment disease, and instrumentation failure, point toward intrinsic factors rather than technical shortcomings.

Although matching was performed on BMI and major comorbidities, propensity score matching balances measured variables at the group level rather than eliminating heterogeneity within cohorts. ³ The elderly cohort therefore reflects patients selected for surgery in real-world practice, which itself represents a clinically relevant subset of individuals ≥75 years. Accordingly, both cohorts likely included patients with varying comorbidity burdens. Nonetheless, the observation that factors such frailty (eg, modified Frailty Index), sarcopenia (eg, psoas muscle indexing), cognitive status (eg, MoCA), and functional reserve (eg, 6-minute walk test) may more accurately reflect biological age and postoperative resilience is well taken, and their incorporation into future studies would meaningfully enhance risk stratification models.

Importantly, mortality represents a competing risk in a ≥75 cohort; despite this, revision rates remained higher in the elderly, suggesting that the underlying mechanical and biological vulnerability in this population may be substantial. Because binary revision endpoints do not capture timing, future time-to-event or competing risk analyses could provide a more nuanced understanding of revision dynamics in older patients.

We fully agree that radiographic success alone does not fully capture the patient experience, and the relationship between alignment parameters and quality of life may differ substantially with age. Ongoing work from our group aims to incorporate patient-reported metrics to better correlate alignment maintenance with functional outcomes in the elderly population.

We are grateful for the authors’ recognition of the clinical implications of our work. As they note, the question is no longer simply whether surgery can be performed safely in carefully selected patients ≥75, but how to optimize durability and improve shared decision-making. We hope our study contributes to that ongoing evolution in the care of elderly patients undergoing deformity correction.