Changes and related factors of cervical sagittal parameters after posterior atlantoaxial fusion

English Keywords:Atlantoaxial fusion  Subaxial lordosis  Cervical sagittal balance  Factor analysis

English Abstract:

  【Abstract】 Objectives: To measure the changes of cervical sagittal parameters and evaluate the related factors after posterior atlantoaxial fusion. Methods: Eighteen patients (aged 25-72 years with mean age of 49.6±13.7 years) with atlantoaxial dislocation in Fuzhou Second Hospital Affiliated to Xiamen University between January 2015 and December 2017 were retrospectively analyzed. There were 8 males and 10 females patients. All patients with atlantoaxial dislocation underwent simple posterior reduction and C1-2 fixation. They were followed up for 5 to 17 months, with an average of 7.4±3.7 months. Cervical sagittal parameters including C0-C2 angle, C2-C7 angle, C0-C7 angle, C1-C2 angle, C2-C7 SVA, T1S, NT and TIA were measured before surgery and at the last follow-up. Chi-square test was used to analyze the relationship of lower cervical curvature lordosis and gender, age (bounded by 60 years old), preoperative T1S (bounded by 25°), preoperative C2-C7 SVA (bounded by 15mm), preoperative TIA (bounded by 70°), preoperative C2-C7 angle (bounded by 20°), preoperative C0-C2 angle (bounded by 20°), preoperative C0-C7 angle (bounded by 45°) and postoperative C1-2 angle (bounded by 20°). At the last follow-up, the subaxial lordosis loss group (5 cases) included the patients whose postoperative C2-C7 angle was reduced, and the subaxial lordosis increase group (13 cases) included the patients whose postoperative C2-C7 angle was increase. Logistic regression analysis was applied to analyze the factors related to the postoperative loss of subaxial lordosis after posterior atlantoaxial fusion. Results: The cervical sagittal parameters of preoperation and last follow-up were as follows respectively: C0-C2 angle 21.6°±16.4° and 28.3°±8.6°, C2-C7 angle 15.3°±12.9° and 16.4°±11.1°, C0-C7 angle 36.8°±19.7° and 44.9°±13.2°, C1-C2 angle 12.4°±17.6° and 17.5°±7.3°, C2-C7 SVA 13.4±14.7mm and 15.1±11.7mm, T1S 22.8°±8.2° and 23.5°±7.3°, NT 50.8°±9.5° and 51.9°±8.9°, TIA 73.6°±11.1° and 75.4°±10.0°. There was no significant difference between the preoperative and last follow-up cervical sagittal parameters(P>0.05). The cervical sagittal parameters of preoperative and final follow-up between two groups were compared, the preoperative C2-C7 angle of the subaxial lordosis loss group was bigger than the subaxial lordosis increase group(27.6°±10.5° vs 10.5°±10.5°, P<0.05), but there was no statistical difference in other parameters. Univariate chi-square analysis showed that reduction of subaxial lordosis after posterior atlantoaxial fusion was associated with preoperative C2-C7 angle ≥20° (χ2=4.923，P=0.026). However, Logistic regression analysis showed that the preoperative C2-C7 angle ≥20° was not an independent risk factor (OR=0.147，P=0.225). Conclusions: Loss of subaxial lordosis can occur after posterior atlantoaxial fusion, and preoperative C2-C7 angle ≥20° is a risk factor of postoperative loss of subaxial lordosis.