[Vertebral bone density distribution in different coronal imbalance classifications of degenerative lumbar scoliosis]

Objective: To investigate the distribution patterns of vertebral bone density in degenerative lumbar scoliosis (DLS) patients with different coronal imbalance classifications. Methods: A retrospective study was conducted on 154 patients with DLS who underwent long-segment spinal fusion surgery at Nanjing Drum Tower Hospital between January 2017 and December 2022. The patients were classified according to the Nanjing Drum Tower coronal imbalance classification of DLS: Type A, coronal balance distance (CBD) <3 cm; Type B, CBD ≥3 cm and C₇ plumb line (C₇PL) located on the concave side; Type C, CBD ≥3 cm and C₇PL located on the convex side. The major curve Cobb angle and CBD were measured on preoperative standing full-spine radiographs. Preoperative assessments also included L_1-4 T-scores and femoral neck T-scores obtained from dual-energy X-ray absorptiometry (DXA). Additionally, overall vertebral body bone density and Hounsfield unit (HU) values on the concave and convex sides were measured using preoperative CT scans. The patients with L_{1 HU} value <110 were diagnosed with osteoporosis (OP). Comparative analyses included OP prevalence and coronal plane bone mass distribution patterns among the different coronal classifications. Results: A total of 154 patients were included in this study, comprising 21 males and 133 females, with an average age of (62.9±6.6) years. Among them, 99 patients were classified as Type A, 30 as Type B, and 25 as Type C. The prevalence of OP was 48.7% (75/154), with the prevalence in Type C (72.0%, 18/25) patients being higher than that in Types A (44.4%, 44/99) and B (43.3%, 13/30) (both P<0.05). The mean HU value of the S₁ vertebra for all patients was 140.8±63.1, it was the lowest in Type C patients (108.2±53.4), which was statistically significantly lower than that in Types A and B patients (150.2±66.0 and 137.1±52.0, respectively, both P<0.05). For all the patients, the HU values on the concave side of the main curve were all greater than those on the convex side (all P<0.005), with the greatest asymmetry observed at the apex vertebra. The asymmetry ratios of the concave to convex sides of the S₁ vertebra in Type B and Type C patients were higher than those in Type A patients (1.25±0.24, 1.23±0.24, and 1.11±0.22, respectively; P<0.01). Conclusions: Patients with DLS exhibit a high prevalence of OP, with Type C patients showing the highest OP prevalence and the lowest bone density at the S₁ vertebral body. Based on these findings, it is recommended that, for type C patients, distal internal fixation be performed using iliac screws or S₂ sacroiliac screws to reduce the risk of internal fixation failure.