European Spine Journal - 2026-04-07 - Journal Article
The HBA-3 score: a simple bedside tool to predict cage subsidence after TLIF.
Najjar E, Khan S, Quraishi NA, Salem KM
Topics
Key Takeaway
The HBA-3 score (HU <131, BMI >30, age ≥60) stratifies cage subsidence risk from 12.5% to 50.0% after single-level TLIF, but subsidence did not correlate with ODI, EQ-5D, or satisfaction at 12 months.
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Summary
This study asked whether a simple CT-based bedside score could predict cage subsidence after single-level TLIF and whether subsidence affected functional outcomes. Seventy-six patients underwent preoperative HU measurement; logistic regression, Random Forest, and XGBoost models identified HU, BMI, and age as dominant predictors, yielding the HBA-3 score with cross-validated AUC 0.73. Subsidence occurred in 31.6% of patients but was not associated with ODI (p=0.66), EQ-5D VAS (p=0.87), or satisfaction (p=0.29) at 12 months, despite a mean ODI improvement of 12.0 points (p<0.0001) across the cohort.
Key Limitation
Twelve-month follow-up is insufficient to capture late subsidence-related complications such as pseudarthrosis, adjacent segment disease, or delayed neurological deterioration that may ultimately affect PROMs.
Original Abstract
BACKGROUND
Cage subsidence is a common radiographic finding following transforaminal lumbar interbody fusion (TLIF), but its clinical relevance remains uncertain. Hounsfield Unit (HU) values from preoperative CT scans have emerged as surrogates for local bone quality, yet few studies have validated simple, clinically applicable prediction models or examined the relationship between subsidence and functional outcomes.
METHODS
Retrospective analysis of 76 patients who underwent single-level TLIF (2019-2023) with preoperative CT imaging and 12-month follow-up. HU was measured at the fused vertebral bodies. Cage subsidence was defined as ≥ 2 mm vertical migration or disc height loss on CT at 6-12 months. Logistic regression, Random Forest, and XGBoost models were applied to identify key predictors. A three-point bedside score (HBA-3) was derived using ROC/Youden thresholds for HU (< 131), BMI (> 30), and age (≥ 60). Outcomes included Oswestry Disability Index (ODI), EQ-5D VAS, and patient satisfaction.
RESULTS
The overall subsidence rate was 31.6% (24/76). HU, BMI, and age consistently emerged as the strongest predictors across all models, while sex, smoking, alcohol, and cage type contributed minimal signal. The HBA-3 score stratified subsidence risk stepwise from 12.5% (0 points) to 50.0% (3 points), with good discrimination (cross-validated AUC = 0.73; logistic 0.70, RF 0.73, XGBoost 0.72). Inter-rater reliability of HU was excellent (ICC = 0.98). Despite these radiographic findings, subsidence was not associated with worse PROMs at 12 months (satisfaction p = 0.29; ODI p = 0.66; EQ-5D VAS p = 0.87). Higher HBA-3 scores were not associated with ODI at 12 months (p = 0.45) or ODI MCID attainment (p = 0.25). ODI improved significantly at 12 months (- 12.0, p < 0.0001), while EQ-5D showed no significant change.
CONCLUSION
The HBA-3 score (HU, BMI, age) provides a simple, reproducible tool for estimating subsidence risk after TLIF, with stepwise increases in risk across strata. However, radiographic subsidence did not predict functional recovery in this single-level degenerative cohort, underscoring the need to distinguish between radiographic and patient-centred outcomes.