Thoracolumbar burst fractures are common unstable spinal injuries often treated with posterior fixation when neurological deficit or marked instability is present. Despite advances in pedicle screw systems enabling strong intraoperative reduction, postoperative correction loss and kyphotic recurrence still occur. Therefore, identifying preoperative risk factors for correction loss is clinically important.

The Load Sharing Classification (LSC) has been widely used to predict implant failure; however, fracture morphology alone may not sufficiently explain postoperative stability. Hounsfield unit (HU) values obtained from computed tomography images serve as a convenient marker of bone quality, but their role in maintaining postoperative correction after thoracolumbar burst fracture surgery remains unclear. The purpose of this study was to evaluate the impact of preoperative vertebral HU values on postoperative correction loss after posterior fixation.

We retrospectively reviewed 42 consecutive patients (mean age 42.6 years; 83.3% male) who underwent posterior fixation between 2014 and 2025 using the USS fracture system with a consistent surgical technique. Only two-level fixation constructs were included, and all patients were followed for at least six months. HU values were measured at L1 and at the instrumented vertebrae using the mean of three axial CT slices. Kyphotic angle and vertebral body height were assessed at 1 and 6 months postoperatively.

Although satisfactory reduction was achieved immediately after surgery, gradual correction loss occurred over time. Correction loss was associated with patient age and magnitude of reduction, but low vertebral HU values—particularly at the instrumented vertebrae—showed the strongest association with vertebral height loss and progression of kyphosis. Multivariate analysis identified decreased HU at the screw-inserted vertebra as an independent predictor of correction loss, whereas LSC showed no significant association. Preoperative vertebral HU values significantly influence maintenance of postoperative alignment. Patients with low HU values may require modified surgical strategies or closer follow-up.