Abstract: Objective   To evaluate the correlation between different occipitocervical angle (C0~C2), C1~C2 angle and postoperative lower cervical curvature (C2~C7 angle) after posterior atlantoaxial fixation fusion, and to explore the best angle of atlantoaxial fixation and assess the reliability of the influence of these two indexes on the lower cervical curvature, so as to provide theoretical basis for clinical treatment.    Methods From January 2016 to June 2018, 78 patients with disorders of the upper cervical spine who underwent posterior atlantoaxial fixation fusion were followed up. C0~C2, C1~C2 and C2~C7 angles on lateral radiographs of cervical spine were measured respectively. Lordosis was "+" value, kyphosis was "-" value, and the correlation between the included angles was observed.   Results   All patients were followed up for 12 to 18 months, with an average of 16 months. The mean C0~C2 angles during preoperative and postoperative follow-up were (11.87±1.36)°and (20.14±5.20)°, respectively, with statistically significant differences (t=-14.635, P<0.001). The mean C1~C2 angles during preoperative and postoperative follow-up were (15.55±1.70)° and (26.67±7.70)°, respectively, the difference was statistically significant (t=-12.748, P<0.001). The mean C2~C7 angle during preoperative and postoperative follow-up were (18.16±2.81)° and (13.05±6.27)°, respectively, with statistical significance (t=7.500, P<0.001). The postoperative follow-up included 37 cases with the fixed angle of C0~C2 <20° (10°~20°) and 41 cases with the fixed angle ≥20°(20°~28°). There were 37 cases of C1~C2 fixation angle <25°(10°~25°), and 41 cases of C1~C2 fixation angle ≥25°(25°~42°). During follow-up, there was no clear correlation between C1~C2 angle <25°, C0~C2 angle <20° and C2~C7 angle (P=0.635 and 0.510, r=0.081 and 0.112). C1~C2 angle ≥25° and C0~C2 angle ≥20° were negatively correlated with C2~C7 angle (P=0.002 and 0.000, r=-0.466 and -0.872, respectively). C0~C2 angle fixing angle ≥20° is strongly correlated with C2~C7 angle (r=-0.872, absolute value > 0.8), while C1~C2 angle fixing angle ≥25° is not closely correlated with C2~C7 angle (r=-0.466, absolute value<0.5).  Conclusion  With posterior atlantoaxial fixation fusion, the fixation angle of C0~C2 ≥20° or the fixation angle of C1~C2 ≥25° may lead to the decrease of the postoperative curvature of the lower cervical spine, while the fixation angle of C1~C210°~25° and the fixation angle of C0~C2 10°~20° may better maintain the physiological curvature of the lower cervical spine. The fixed angle of C0~C2 is more reliable.

Key words: Posterior,  ,  , Atlantoaxial,  ,  , Fixed angle,  ,  , Lower cervical curvature