Changes and clinical significance of occipito-C2 angle after occipitocervical fusion in patients with basilar invagination

English Keywords:Basilar invagination  Occipitocervical fusion  Occipito-cervical angle  Subaxial cervical curvature

English Abstract:

  【Abstract】 Objectives: To observe the changes of the occipito-C2 angle(OC2A) in basilar invagination(BI) patients after occipito-cervical fusion(OCF). The correlation between postoperative OC2A change value and intraoperative OC2A correction value and its influence on postoperative curvature of subaxial cervical was analyzed. Methods: The clinical data of 30 primary BI patients who underwent OCF surgery in our hospital from September 2013 to April 2019 were retrospectively analyzed. There were 11 males and 19 females, aged 49.0±12.2 years(29-71 years), including C0-C2 fixation in 20 cases, C0-C3 fixation in 8 cases, and C0-C4 fixation in 2 cases. The OC2A of BI patients were measured on standard lateral cervical X-rays before operation and 7 days, 3 months, 6 months, 1 year and 2 years postoperatively. Meanwhile, the heightratio of subaxial cervical disc to vertebral body(S value), the subaxial cervical angle(C2-C7 angle), the occipto-C4 distance(OC4D), atlas-dens interval(ADI) and clivus-canal angle(CCA) were measured at 7 days and 2 years after surgery. The difference of OC2A between 7 days postoperatively and pre-operation was calculated and recorded as OC2A interoperative corrected value, and the differences of OC2A, S value, C2-C7 angle, OC4D, ADI, CCA of patients between 7 days and 2 years after operation were denoted as CO2A postoperative loss value, ΔS value, ΔC2-C7 angle, ΔOC4D, ΔADI, ΔCCA, respectively. Results: The preoperative OC2A of 30 patients was 5.4°±7.2° and the OC2A values 7 days, 3 months, 6 months, 1 year, 2 years postoperatively were 15.8°±5.6°, 13.5°±4.5°, 12.4°±4.7°, 11.6°±4.6°, and 11.2°±5.1° respectively. There was no statistical difference in OC2A between 1 year and 2 years after operation(P>0.05) while the differences of OC2A between other follow-up time points were statistically significant(P<0.05). The S-values of 7 days and 2 years after operation were 0.469±0.034, 0.436±0.042, C2-C7 angle was 16.5°±8.4°, 10.9°±6.7°, OC4D was 6.14±0.63cm, 5.31±0.55cm, ADI was 2.37±0.85mm, 3.18±0.92mm, CCA was 141.4°±21.1°, 132.6°±17.5°. All of this were decrease at 2 years postoperatively compared to 7 days postoperatively, the differences was statistically significant(P<0.05). The OC2A interoperative correction value was 10.4°±9.9° and the OC2A postoperative loss value, ΔS value, ΔC2-C7 angle, ΔOC4D, ΔADI, ΔCCA were 4.6°±4.2°, 0.033±0.018, 5.6°±5.2°, -0.83±0.48cm, -0.81±0.67mm, -8.8°±18.4° respectively. Pearson correlation analysis indicated that the loss value and correction value of OC2A were strongly negatively correlated(r=-0.699, P<0.001). The postoperative OC2A loss value was positively correlated with ΔC2-C7 angle, ΔS value, ΔOC4D, ΔADI, ΔCCA respectively(r=0.429, r=0.413, r=0.347, r=0.296, r=0.675; P＜0.05). Conclusions: The greater of the correction value of OC2A in BI patients, the more OC2A loss after surgery, and the loss of OC2A tended to be stable in 1 year after surgery; and excessive loss of OC2A can easily lead to significant changes in the curvature of the subaxical cervical spine.