Relationship between occiptocervical angle and subaxial cervical alignment in patients with basilar invagination and atlantoaxial dislocation

English Keywords:Basilar invagination  Atlantoaxial dislocation  O-C2 angle  Subaxial angle

English Abstract:

  【Abstract】 Objectives: To measure the occipitoaxial angle and subaxial alignment in the patients with basilar invagination(BI) and atlantoaxial dislocation(AAD), and to elucidate the relationship between occipitoaxial angle and subaxial cervical alignment. Methods: From January 2009 to June 2013, the clinical data of 21 patients who had BI with AAD undergoing surgery at our institution were retrospectively analyzed. The patients consisted of 12 men and 9 women, and ages ranged from 21 to 65 years(mean, 41.6±10.7 years). The duration of symptoms ranged from 4 months to 18 years(mean, 4.3±3.9 years). O-C2 angle and C2-7 Cobb angle(C2-7 angle) were measured before surgery and at the last follow-up in plain lateral cervical X-ray, and the changes of O-C2(dO-C2) angle and C2-7(dC2-7) angle were also calculated. A plus angle indicated lordosis between occiput and C2, and a minus angle indicated the kyphosis between occiput and C2. According to the value of O-C2 angle, all the 21 patients were divided into 10°≤O-C2≤20° group, ＜10° group and ＞20° group. The difference of C2-7 angle among these three groups, the associations between O-C2 angle and C2-7 angle before surgery and at the last follow-up were studied. Results: Among these 21 patients, C0-C3 fixation was performed in 12 patients, and C0-V4 fixation was performed in 9 patients. The mean follow-up in these 21 patients was 18.3 months with a range of 10 to 32 months. Before and after surgery, the mean change of O-C2 angle was 6.3°, and the mean change of C2-7 angle was -6°. There were significant differences between preoperative and postoperative O-C2 angle and C2-7 angle(P＜0.05). Before surgery, 6(28.6%) patients were in 10°≤O-C2 angle≤20° group, and 12(57.1%) patients in ＜10° group, and 3(14.3%) patients in ＞20° group. Among these groups, C2-7 angle in O-C2 angle ＜10° group was significantly larger than that in 10°≤O-C2 angle≤20° group and O-C2 angle ＞20° group(P＜0.05). There was no difference of preoperative C2-7 angle between 10°≤O-C2 angle≤20° group and O-C2 angle ＞20° group(P＞0.05). At the last follow-up, 10(47.6%) patients were in 10°≤O-C2 angle≤20° group, and 4(19.0%) patients in ＞20° group, and 7(33.4%) patients in ＜10° group. Among these groups, C2-7 angle in O-C2 angle ＞20° group was significantly smaller than that in 10°≤O-C2 angle≤20° group and ＜10° group(P＜0.05). There was no significant difference between the 10°≤O-C2 angle≤20° group and ＜10° group(P＞0.05). There was a significant negative correlation between O-C2 angle and C2-7 angle before and after surgery(r=-0.732 and r=-0.603, P＜0.05). The dO-C2 angle was also negatively associated with the dC2-7 angle(r=-0.721, P＜0.05). Conclusions: There is significantly correlation between O-C2 angle and C2-7 angle in patients with BI and AD. During occiptocervical fusion surgery, attention should be paid to the fixed O-C2 angle. Subaxial alignment will show compensatory decrease if O-C2 angle is too large.