This was a retrospective and single-center study with data collected from postmenopausal women (study group and control group) treated at Chinese PLA General Hospital from June 2017 to July 2019. The study group consisted of osteoporotic patients with vertebral compression fractures at the thoracolumbar junction (T11–L2) and vertebroplasty. The inclusion criteria were (i) vertebral compression fracture of low energy (fall from standing height or a lower position and sneeze), (ii) first and only one vertebral body fracture in T11–L2, and (iii) treatment with vertebroplasty. The exclusion criteria were as follows: a tumor, high-energy fracture, spinal scoliosis (Cobb angle > 10°), and lack of information on standing and erect lumbar hyperflexion X-ray. The control group was age-matched (unpaired t-test, p > 0.05) patients with lumbar instability or spondylolisthesis (Meyerding I) verified by lumbar hyperflexion X-ray, excluding patients with spinal tumors, ankylosing spondylitis, inflammatory spondylitis, congenital spinal deformity, spinal scoliosis (Cobb angle > 10°), and a previous history of fracture in T11–L2. The study was approved by the Human Ethics Committee of Chinese PLA General Hospital. All participants were informed about the study and they signed a written consent for inclusion.
Age, weight, body mass index (BMI; kg/m2), and other information of the two groups were recorded on admission. Radiographs of hyperflexion, neutral lateral, and neutral anteroposterior lumbar vertebrae were collected. Data on fracture site, Cobb angle, and disc height in T11–L2 were recorded and calculated.
The TLHCobb was drawn by two lines parallel to the superior endplate of T11 and the inferior endplate of L2 on a hyperflexion lumbar radiograph. Accordingly, the thoracolumbar Cobb angle was measured on a neutral lateral radiograph. The Cobb angle formed on the ventral side was classified as positive, and on the dorsal side as negative. The TLHCobb before fracture was retrospectively assessed by calculating the difference between the post-operation TLHCobb and the Cobb angle change of the fractured vertebra . The pre-fractured Cobb angle of the vertebrae was calculated on the average Cobb angle of the non-fractured vertebrae at the same position in the same group. The postoperative difference in the thoracolumbar Cobb angle between the hyperflexion and neutral postures (DTLCobb) was collected (Fig. 2).
Fig. 2 DTLCobb is the difference between neutral spine posture in A and hyperflexion spine posture in B: DTLCobb = TLHCobb.p - TLCobb.p
The maximal region of the cancellous bone was manually drawn in the middle cross-section of the vertebral body (Fig. 3). The mean of two intact vertebrae in T12–L3 was selected to represent the density of the cancellous bone . The density of the fractured vertebra before fracture was calculated by the mean density of the adjacent vertebrae (the upper and the lower of fractured vertebra) . BMD was classified as normal (BMD > 120 mg/cm3), osteopenia (80–120 mg/cm3), and osteoporosis (BMD > 80 mg/cm3) according to the criteria of the World Health Organization and the American College of Radiology (ACR) . BMD was measured using a QCTPRO2.0 workstation (Mindways Software Inc., Austin, TX, USA) and quantitative computed tomography (QCT) scans in a 16-slice spiral CT scanner (GE Discovery CT750 HD) with the following parameters: 120 kV, 125 mA, pitch 0.985, SFOV 500 mm, aperture 1.25mm, and table height 780 mm.
Fig. 3 The region of interest (ROI) was defined as the largest ellipse in vertebral cancellous bone in the axial position. It has been found that taking the largest ellipse can make the value of the vertebral body BMD more stable and reduce the influence of local hyperplasia and sclerosis in the vertebral body on the BMD value.
Data were analyzed using SPSS version 26 (IBM, Chicago, IL, USA). Descriptive statistics for continuous variables were expressed as means and standard deviations). Differences in age, BMI, QCT findings, and Cobb angles between the two groups were assessed using chi-squared and unpaired t-tests. The association between vertebral compression fracture and TLHCobb was examined using logistic regression analysis. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated using multivariate logistic regression analysis of age, BMI, and QCT findings. The cut-off of the TLHCobb was determined by a receiver operating characteristic (ROC) curve and Youden’s index.