Thoracic inlet angle is not a constant morphological parameter: A cross-sectional study based on asymptomatic Chinese
Objective:Thoracic inlet angle (TIA) is traditionally considered as a constant morphological parameter and independent of position or movement, but the relationship between TIA and gender, age, and cervical sagittal balance is still controversial. This study aimed to assess the correlation of TIA with sex , age, and cervical sagittal balance in asymptomatic Chinese.Methods:Four hundred asymptomatic Chinese volunteers were recruited, and they had an average age of 49.9±14.4 years (range, 18~85 years). A standing cervical lateral radiograph in a neutral position in all subjects. Thoracic inlet (TI) parameters, including thoracic inlet angle (TIA), neck tilt (NT), and thoracic (T1) slope (T1S), were measured. Cervical lordosis (CL) and sagittal vertical axis (SVA) were also measured to evaluate the sagittal balance of the cervical spine. Pearson correlation analysis of sex, age, CL, SVA, and TI parameters was performed by using SPSS 27.0 software.Results:The mean TIA, T1S, NT, SVA, CL, and T1S-CL were (74.2°±10.1°), (26.4°±7.0°), (47.8°±7.8°), (19.0 mm±9.6 mm), (17.0°±11.4°), and (9.4°±8.6°), respectively. TIA, T1S, NT, and CL in male subjects were significantly larger than those in female subjects (P≤0.001). TIA had a significant correlation with sex (r=-0.420), age (r=0.370), T1S (r=0.636), NT (r=0.722), SVA (r=0.225), and CL (r=0.425). TIA showed a increasing trend with the increase in decade years (ANOVA P<0.001), and TIA in male subjects was larger than that of female subjects in each age group(P<0.001). SVA was strongly positively correlated with T1S-CL (r=0.467). TIA was positively correlated with CL (r=0.425). However, TIA was not significantly correlated with T1S-CL (r=-0.05).Conclusion:Mean TIA is (74.2°±10.1°) in asymptomatic Chinese. TIA is not a constant TI parameter as it increases with age and in males. As a key factor of affecting outcomes after cervical surgery, T1S-CL does not correlate with TIA. Patients with a high TIA can reduce the occurrence of cervical sagittal imbalance by increasing cervical curvature, and TIA is not recommended as an independent factor for predicting sagittal imbalance after cervical spine surgery. These results could serve as baseline data for further studies on the cervicothoracic sagittal balance.
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