The vertebral bone quality (VBQ) score is an influential factor associated with lumbar pedicle screw loosening, and a higher VBQ score is significantly correlated with a higher risk of screw loosening. This is according to a recent study, published in Spine by Linfeng Wang (The Third Hospital of Hebei Medical University, Shijiazhuang, China) et al, and which also indicated that VBQ score is a better predictor of pedicle screw loosening than the Hounsfield Unit (HU) value in patients who underwent pedicle screw fixation for degenerative lumbar disease.
The retrospective study aimed to investigate whether or not the magnetic resonance imaging (MRI)-based VBQ score can predict pedicle screw loosening in patients who underwent pedicle screw fixation, and to compare which measurement, the VBQ score or the HU value, is more predictive of pedicle screw loosening.
The research team reviewed patients who were treated with lumbar pedicle screw fixation. The VBQ score was measured using MRI scans and the HU value for L1-4 lumbar bone mineral density (BMD) was measured with computed tomography scans. Logistic regression analysis was used to identify factors associated with pedicle screw loosening and receiver-operating characteristic curve (ROC) analysis was used to evaluate the value of VBQ scores in predicting pedicle screw loosening.
A total of 156 patients were included in the final analysis and the pedicle screw loosening rate was 35% (55 of 156 patients). The postoperative low-back pain Visual Analogue Scale (VAS) score was higher in the loosening group (3 ± 2 vs. 2.4 ± 1.8, p<0.05). The VBQ score was higher in the loosening group than in the non-loosening group (3.28 ± 0.58 vs. 2.82 ± 0.50; p<0.01).
In multivariable analysis, non-single segment fixation (odds ratio [OR], 3.992; 95% confidence interval [CI] 1.643–9.701; p=0.002), LIV at S1 (OR, 3.378; 95% CI 1.387–8.226; p=0.007), HU value (OR, 0.988; 95% CI 0.976–1; p=0.047), and VBQ score (OR, 3.908; 95% CI 1.624–9.405; p=0.002) were factors associated with screw loosening.
The areas under the curve for using the VBQ score and HU value to predict pedicle screw loosening were 0.72 and 0.702, respectively. The optimal VBQ score threshold was 3.05 for predicting pedicle screw loosening (sensitivity, 0.655; specificity, 0.713).