Neck posture-dependent variations in cervical central canal stenosis among ossification of the posterior longitudinal ligament patients: Follow-up neutral position magnetic resonance study.

In patients with cervical ossification of the posterior longitudinal ligament (OPLL), posture differences in neutral Magnetic Resonance Imaging (MRI) can affect central canal stenosis evaluation, but their impact on sagittal alignment parameters and central canal stenosis measurements remains unclear. This retrospective cohort study sought to evaluate neck posture-dependent variations in central canal stenosis in patients with OPLL and assess the influence of sagittal alignment parameters. Fifty-seven patients underwent two neutral-position MRI scans within six months. Occipito-C2 (O-C2) angle, C2-C7 Cobb angle, K-line-C7 angle, and C2-C7 sagittal vertical axis (SVA) were measured. Central canal stenosis was assessed using anteroposterior (A-P) diameter, Disc-OPLL thickness, ligamentum flavum thickness, and stenosis grading. The results showed that C2-C7 Cobb angle (p < 0.001), K-line-C7 angle (p < 0.001), and C2-C7 SVA (p < 0.001) showed significant differences, whereas O-C2 angle remained unchanged (p = 0.175). Changes in C2-C7 SVA had the strongest correlation with A-P diameter (p = 0.009). Central canal stenosis grading changed in 35.1% of cases at the level adjacent superior to the most stenotic site, 24.6% at the level adjacent inferior, and 5.3% at the most stenotic level, suggesting that posture differences influence both quantitative and qualitative assessments Variations in neck posture, particularly C2-C7 SVA, significantly influenced central canal measurements. Given its strong positive correlation with A-P diameter, C2-C7 SVA should be carefully considered during MRI acquisition for accurate assessment of cervical OPLL progression.