Hounsfield units and vertebral bone quality score for predicting mechanical complications after adult spinal deformity surgery: a systematic review and meta-analysis.

The purpose of this systematic review and meta-analysis is to assess existing literature and determine the association between the Hounsfield unit (HU) value and the vertebral body quality (VBQ) score with mechanical complications (MCs) after adult spinal deformity (ASD) surgery. Although bone quality is considered an increasingly important factor for MCs after ASD surgery, the utility of the HU value assessed by computed tomography and the VBQ score assessed by magnetic resonance imaging remains unknown. A systematic review of PubMed, Embase, and Cochrane Library databases was performed to find studies evaluating the association between the HU value and the VBQ score with MCs after ASD surgery. In the subsequent meta-analysis, MC outcomes were combined using a random-effects model, and the standardized mean difference and 95% confidence interval were calculated. The final analysis included a total of 20 studies. Nineteen studies reported HU values, and two studies reported VBQ scores. Proximal junctional kyphosis/failure (PJK/PJF) was reported as the MC in 16 studies, whereas other MCs were included in 6 studies. Six studies with a pool of 506 patients with ASD revealed that preoperative HU values at the upper instrumented vertebra (UIV) and UIV+1 were significantly lower in patients with PJK/PJF (standardized mean difference, -0.74; 95% confidence interval, -1.09 to -0.40). Three studies suggested an cutoff HU value of approximately ≤120, yielding a pooled sensitivity of 0.77, specificity of 0.67, and diagnostic odds ratio of 7.01. However, two studies reported conflicting results on the relationship between the VBQ score and PJK/PJF. Low HU values predicted the risk of certain MCs, particularly PJK/PJF, after ASD surgery. An HU value of <120 should alert surgeons to be cautious about the postoperative occurrence of PJK/PJF. Future studies are needed to validate the cutoff HU value and evaluate the utility of the VBQ score.