The Utility of Magnetic Resonance Imaging-based Vertebral Bone Quality Scores as a Predictor of Cage Subsidence Following Transforaminal and Posterior Lumbar Interbody Fusion.

Study Design: Retrospective study.

Objectives: The objectives were to determine whether vertebral bone quality (VBQ) scores are associated with interbody cage subsidence following transforaminal (TLIF) and posterior (PLIF) lumbar interbody fusions and whether there is a clinically sensitive threshold for subsidence.

Background: Interbody cage subsidence following lumbar fusion is a complication that can generate poor surgical outcomes. Prior research has correlated cage subsidence with bone mineral density. VBQ scores derived from magnetic resonance imaging (MRI) have been proposed as a tool for measuring bone mineral density, offering a potential new and convenient preoperative risk assessment tool for subsidence.

Methods: The study involved patients undergoing single-level PLIF or TLIF between 2007 and 2022. Exclusions were for nondegenerative diagnoses, multilevel/revision surgeries, inadequate radiographs, missing immediate postoperative radiographs, and preoperative MRI studies older than 1 year. VBQ was calculated at L1-L4 from preoperative T1-weighted MRI images. Subsidence was assessed by changes in disc height (DH; >2 mm difference) and segmental lordosis (SL; >5 degrees difference) between immediate weight-bearing postoperative and latest postoperative lateral radiographs. Statistical analysis included descriptive and inferential statistics.

Results: Subsidence was observed in 27% (SL parameter) and 47% (DH parameter) of 51 total patients. VBQ scores were significantly associated with cage subsidence based on both SL (odds ratio = 7.750, P = 0.012; correlation coefficient = 0.382, P = 0.006) and DH (odds ratio = 4.074, P = 0.026; correlation coefficient = 0.258, P = 0.057) in the combined TLIF/PLIF cohorts. In the cohort of 36 patients undergoing TLIF, a VBQ of 2.70 yielded 100.0% sensitivity and 46.2% specificity in detecting subsidence with SL measurement (area under the curve = 0.812, P < 0.001) and 86.7% sensitivity and 47.6% specificity with the DH measurement (area under the curve = 0.692, P = 0.033).

Conclusions: We found that MRI-based VBQ scores are effective predictors of cage subsidence following TLIF surgery. A VBQ score of 2.70 demonstrated a reliable model and high sensitivity for doing so, identifying a potential clinical threshold for preoperative subsidence risk assessment.

Level Of Evidence: Level III.