Subaxial Cervical Sagittal Alignment as an Anatomical Correlate of Obstructive Sleep Apnea Severity: A Cephalometric...

Background: Obstructive sleep apnea syndrome (OSA) is a significant disorder characterized by recurrent upper airway obstruction. Cervical vertebral alignment and lordosis angles may influence airway cross-sectional area. This study aimed to investigate the relationship between cervical lordosis angles and disease severity in patients with OSA. Methods: The study included 30 patients with OSA (mild n = 6, moderate n = 11, severe n = 13 based on Apnea-Hypopnea Index [AHI]) and 30 non-OSA controls presenting with mechanical neck pain. C1-C2, C1-C7, and C2-C7 angles were measured using the Cobb method on lateral cervical cephalometric radiographs. Additional soft tissue and airway parameters - prevertebral soft-tissue thickness at C2 (PST-C2) and C4 (PST-C4), posterior airway space (PAS), and mandibular plane-hyoid distance (MP-H)- were measured as anatomical surrogates given the unavailability of BMI data. Multiple linear regression (ANCOVA) models adjusting for age and sex were constructed for each cervical angle. Results: All cervical angles were significantly reduced in patients with OSA compared to controls (C1-C2: 25.51 ± 6.47° vs 33.3 ± 4.44°; C1-C7: 35.0 ± 11.9° vs 51.2 ± 7.34°; C2-C7: 9.19 ± 10.6° vs 19.9 ± 5.05°; all p < 0.001). Within the OSA group, a significant moderate negative correlation was found between AHI and the C2-C7 angle (ρ = - 0.522, p = 0.003), while the C1-C7 angle showed a borderline association (ρ = -0.361, p = 0.050) and C1-C2 did not reach significance (ρ = +0.118, p = 0.534). After adjustment for age and sex, group membership (OSA vs. control) remained a strong, independent predictor of all three cervical angles (all p < 0.001), whereas neither age nor sex was a significant predictor (all p > 0.34). PST-C2 was significantly higher in the OSA group (4.93 ± 1.06 mm vs. 4.30 ± 0.70 mm, p = 0.017), whereas PST-C4, PAS, and MP-H did not differ significantly between groups (all p > 0.05), and none of these parameters correlated significantly with the C2-C7 angle. Conclusions: Significant cervical lordosis loss was observed in patients with OSA compared to non-OSA controls, with the C2-C7 angle showing a significant negative correlation with AHI within the OSA group; this association remained robust after adjustment for age and sex. Supplementary soft tissue and airway measurements showed no significant correlation with cervical alignment or AHI, suggesting the observed association is not simply attributable to regional soft-tissue thickness or airway narrowing; however, without direct BMI data, a confounding role of systemic adiposity cannot be excluded. These findings suggest a potential association between cervical posture and upper airway dynamics; however, larger prospective studies are required to confirm clinical utility.