Effect of coronal balance and kyphosis severity on apical spinal cord morphology in patients with thoracolumbar kyphotic deformity secondary to ankylosing spondylitis

English Keywords:Ankylosing spondylitis  Thoracolumbar kyphosis  Coronal balance  Apical region  Spinal cord morphology  Osteotomy

English Abstract:

  【Abstract】 Objectives: To investigate the effect of coronal imbalance and kyphosis severity on the morphological characteristics of the spinal cord at apical vertebra in patients with thoracolumbar kyphotic deformity secondary to ankylosing spondylitis(AS). Methods: A retrospective analysis was performed on the T2-weighted MRIs of 76 AS patients with thoracolumbar kyphosis who underwent three-column osteotomy(3CO) between January 2002 and January 2022. There were 64 males and 12 females, aged 21-67(37.1±10.9) years old. Patients with a coronal balanced distance(CBD)≤3.0cm were assigned to the coronal balance(CB) group(n=42), while those with a CBD>3.0cm were assigned to the coronal imbalance(CIB) group(n=34). Patients were further categorized based on global kyphosis angle(GK) into: GK≥80° group(n=23) and GK<80° group(n=53). Coronal plane parameters including the coronal Cobb angle and coronal balanced distance(CBD), sagittal parameters such as GK, thoracic kyphosis(TK), thoracolumbar kyphosis(TLK), lumbar lordosis(LL), sagittal vertical axis(SVA), and spinal cord parameters consisting of dural distance(DD), spinal cord sagittal diameter(SDcord), transverse diameter(TDcord), compression ratio(CRcord), and transverse area(TAcord) were measured and compared between groups. The correlations between spinal cord parameters and sagittal spinal parameters were analyzed. Results: No significant differences were observed between CB and CIB groups in age, sex, DD, SDcord, TDcord, CRcord, TAcord, GK, TK, LL, SVA, spinal cord morphological classification, osteotomy level distribution, or apex location(P>0.05). The Cobb angle in the coronal plane was significantly greater in the　CIB group(6.9°±0.7°) than in the CB group(3.2°±0.4°) (P=0.000); The CBD was significantly greater in the CIB group(5.5±0.5cm) than in the CB group(1.2±0.8cm) (P=0.000). In the GK≥80° group, DD, SDcord, CRcord, and TAcord were significantly smaller than those in the GK<80° group(P<0.05), while TDcord was considerably larger(P<0.05). Correlation analysis revealed no significant associations between spinal cord parameters(DD, SDcord, TDcord, CRcord, TAcord) and sagittal parameters in the GK≥80° group(P>0.05). The DD and CRcord in the GK<80° group exhibited a significant negative correlation with GK(P<0.01), while TDcord showed a significant positive correlation with GK(P<0.05). None of the spinal cord morphological parameters demonstrated any correlation with TLK(P>0.05). Conclusions: Coronal imbalance has no significant impact on the spinal cord morphology in the apical vertebral region of AS patients with thoracolumbar kyphosis. In patients with mild-to-moderate kyphosis(GK<80°), spinal cord morphology was correlated with the kyphotic angle, suggesting that kyphosis progression may dynamically affect spinal cord morphology; In patients with severe kyphosis(GK≥80°), spinal cord morphology tended to be stable.