Effect of Different Occipitocervical Angles on Craniocervical Sagittal Alignment After Posterior Occipitocervical Fusion for Basilar Invagination with Atlantoaxial Dislocation

Cao Rui; Sheng Jun; Xun Chuanhui; Zhang Long; Xu Tao; Maierdan·Maimaiti; Cai Xiaoyu; Gao Shutao; Sheng Weibin

Abstract：Objective To investigate the characteristics of craniocervical sagittal alignment in patients with basilar invagination with atlantoaxial dislocation,and to evaluate the effect of occipitocervical fusion on craniocervical sagittal parameters as well as the efficacy of different fixation strategies for the occipitocervical angle.Methods A retrospective analysis was conducted on the clinical data of 4 3 patients(patient group)with basilar invagination with atlantoaxial dislocation who were admitted to the first affiliated hospital of Xinjiang medical university from January 2009 to December 2023,including 28 males and 15 females,aged 18 to 76 years with a mean age of(43.12±15.79)years.Meanwhile,the data of 86 healthy subjects(healthy group)were matched from the outpatient department and physical examination center of the hospital.(1)The chin-brow vertical angle(CBVA),cranial slope(CS),occipital-C2 angle(O-C2a),C2～C7 Cobb angle(C2～7a),C2～C7 sagittal vertical axis(CSVA),C2 slope(C2S),T1 slope(T1S),thoracic inlet angle(TIA),neck tilt(NT),T1 slope minus C2～C7 Cobb angle(T1 S-CL),as well as the visual analogue scale(VAS)score for pain,modified Japanese orthopaedic association(mJOA)score,neck disability index(NDI),physical component summary(PCS)and mental component summary(MCS)of the 36-item short form health survey(SF-36)were evaluated in the patient group before and after surgery.(2)The imaging parameters were compared between the patient group and the healthy group.(3)According to the postoperative O-C2a,the patients were divided into four subgroups:the kyphosis subgroup(O-C2a＞0 °)with 10 cases,the low-angle subgroup(-10 °≤O-C2a≤0 °)with 9 cases,the moderate-angle subgroup(-20 °＜O-C2a＜-10 °)with 9 cases,and the high-angle subgroup(O-C2a≤-20 °)with 15 cases.Results(1)All 43 patients in the patient group successfully underwent surgery,with a postoperative follow-up of 12 to 48 months and a mean follow-up of(15.58±9.53)months.The VAS,mJOA,NDI,PCS and MCS scores at post-operation and the last follow-up were significantly improved compared with those before surgery(P＜0.05).Compared with the preoperative values,the postoperative C2～7a,CSVA and T1S-CL increased significantly(P＜0.05),the C2S changed from retroversion to anteversion(P＜0.05),and the O-C2a decreased significantly(P＜0.05);the CSV A at the last follow-up was significantly lower than that at post-operation(P＜0.05).(2)Before surgery,at post-operation and the last follow-up,there were statistically significant differences in CBVA,CS,O-C2a,C2～7a,C2S and T,S-CL between the patient group and the healthy group(P＜0.05);before surgery and at the last follow-up,there was a statistically significant difference in CSVA between the two groups(P＜0.05).(3)The postoperative parameters in the moderate-angle subgroup were the most optimally improved and were closer to those of the healthy group(P＜0.05);the clinical indicators were significantly improved at post-operation and the last follow-up in all subgroups(P＜0.05),and there were intergroup differences in clinical indicators at the last follow-up(P＜0.05).The clinical efficacy of the moderate-angle subgroup was comparable to that of the low-angle subgroup and was superior to that of the high-angle subgroup(P＜0.05).Conclusion Patients with basilar invagination with atlantoaxial dislocation have obvious abnormalities in craniocervical sagittal alignment.Occipitocervical fusion can promote spontaneous compensatory correction of the lower cervical spine,and the postoperative sagittal alignment in the moderate-angle subgroup is closer to that of healthy subjects with remarkable clinical efficacy.In addition,occipitocervical fusion should avoid insufficient or excessive correction of O-C2a to prevent cervical compensatory imbalance.