The HBA-3 score: a simple bedside tool to predict cage subsidence after TLIF

Area of Science:

• Spine surgery
• Orthopedic research
• Biomechanical engineering

Background:

• Cage subsidence is a common radiographic finding after transforaminal lumbar interbody fusion (TLIF), but its clinical significance is unclear.
• Preoperative Hounsfield Unit (HU) values assess bone quality, yet prediction models for subsidence and their link to functional outcomes are underexplored.

Purpose of the Study:

• To develop and validate a simple, clinically applicable model predicting cage subsidence risk after TLIF.
• To investigate the relationship between preoperative bone quality metrics, subsidence, and patient-reported outcomes (PROMs).

Main Methods:

• Retrospective analysis of 76 patients undergoing single-level TLIF with preoperative CT scans.
• Cage subsidence defined as ≥2 mm vertical migration or disc height loss on CT at 6-12 months.
• Developed a three-point bedside score (HBA-3) using Hounsfield Unit (HU), Body Mass Index (BMI), and age; analyzed prediction models (Logistic Regression, Random Forest, XGBoost) and correlated with Oswestry Disability Index (ODI), EQ-5D VAS, and patient satisfaction.

Main Results:

• The overall subsidence rate was 31.6%.
• HU, BMI, and age were the strongest predictors of subsidence, forming the HBA-3 score which demonstrated good discrimination (AUC=0.73).
• Radiographic subsidence did not correlate with worse PROMs at 12 months, and higher HBA-3 scores did not impact ODI or MCID attainment, despite significant ODI improvement post-surgery.

Conclusions:

• The HBA-3 score is a simple, reproducible tool for estimating TLIF subsidence risk.
• Radiographic subsidence in this cohort did not predict functional recovery, highlighting the importance of differentiating radiographic findings from patient-centered outcomes.