The Influence Of Atlanto-axial Pedicle Screw Fixation Fusion On Lower Cervical Spine Sagittal Alignment

ObjectiveTo explore the relationship between the C1-C2 angel and the C2-C7 sagittal alignment after receiving C1-C2 Pedicle Screw Fixation through clinical observation in a long-term follow-up and measurement of the angle and the variations between pre-operation and post-operation at upper cervical spine and lower cervical spine.Methods34 patients who underwent the C1-C2 Pedicle Screw Fixation in Yinchuan Guolong hospital with atlantoaxial instability from 2009 to 2017 were retrospectively analyzed.Before,after the operation and in 2 years after the operation,angles at C1-C2 and C2-C7 in sagittal images were measured,the variations between pre-operation and post-operation were calculated.The analysis was concluded on how fix influence the lower cervical spine sagittal alignment through the determination of the relationship between two angles.ResultsAll the patients obtained bone fusion.Decreased C2-C7 angle was observed in 30 patients.Cervical kyphosis was observed in 1 patients before surgery and deteriorated during follow-up.No patient was received the second surgery.The mean C1-C2 angle before operation was 13.63±12.13°(-13.10 °~40.5°),after operation was 23.04±3.72°(18.2°~34.4°)and in 2 years after operation was 22.81±3.64°(17.8°~33.1°).Respectively,the mean C2-C7 angle were 14.37±6.15°(-4.1°~25.4°),14.68 ±6.31°(-6.2°~26.1°)and 9.62±5.46°(-10.1°~21.3°).There was a statistically significant difference in C1–C2 angle before surgery and in 2 years after operation(P < 0.001),so did in C2-C7 angle(P=0.001).There was a negative correlation betweenpreoperative C1–C2 angle and C2–C7 angle(r=-0.487).This result indicates that C1–C2 angle decrease leads to the increase of C2–C7 angle in the patients who have atlantoaxial instability.But the negative correlation between postoperative C1–C2 angle and C2–C7 angle was not so significant(r=-0.344).The mean C1–C2 angle changes and C2–C7 angle changes were8.82±9.94°(-14.3°~31.8°)and-4.75±4.64°(-12.7°~6.0°),There are negative linear correlation about C1–C2 angle changes and C2–C7 angle changes between preoperative and follow-up(r=-0.849).This result indicates that the patients who have lordotic fixation at C1–C2decrease lordosis at C2–C7 after surgery.This result indicates that the patients who have lordotic fixation at C1–C2 decrease lordosis at C2–C7 after surgery.ConclusionThe change of angle after fusion in atlanto-axial vertebral after atlanto-axial fusion will lead to the change of lower cervical spine curvature for compensation.The increase of angle leads to the decrease of the lower cervical spine curvature and the happening of subaxial kyphotic change.With the increase of atlantoaxial angle before and after surgery,the change of curvature of lower cervical spine also increased.Surgeons should be extremely cautious about the choice of C1-C2 fixation angle and make it personalized when resting the angle of atlanto-axial vertebral,to attain the best curative effect and clinical outcome.