Finite element study of anterior occipital condyle plate and screw in the treatment of upper cervical spine instability / 中华创伤杂志

ABSTRACT

Objective:To explore the difference in properties of anterior occipital condyle plate screws compared with common anterior occipitalcervical fusion internal fixation.Methods:A 28-year-old healthy adult male volunteer's CT data of the occiput and neck was selected to establish finite element models：including the normal model，simple artificial vertebral fixation model（special-shaped titanium cage+clival screws），anterior occipital condyle plate and screw fixation model，and clival plate and screw fixation model，then a 50 N gravity and a torque of 1.5 N m were exerted upon the upper surface of the occipital bone to make the model produce flexion and extension，lateral bending and rotation. The motion range，internal fixation stress distribution and occipital bone stress distribution of each model under varying conditions were compared.Results:Under the conditions of flexion，extension，lateral bending and rotation，the range of motion of the normal model was 18.65°，15.35°，9.82° and 34.68°，respectively；that of the simple artificial vertebral fixation model was 3.20°，3.63°，2.94° and 3.92°，respectively；that of the clival plate and screw fixation model was 0.40°，0.50°，0.35° and 0.89°，respectively；that of the anterior occipital condylar plate and screw fixation model was 0.27°，0.33°，0.13° and 0.30°，respectively. Compared with the simple artificial vertebral fixation model，the range of motion of the clival plate and screw fixation model decreased by 87.5%，86.2%，88.1% and 77.3% in flexion，extension，lateral bending and rotation. The range of motion of the anterior occipital condylar plate and screw fixation model decreased by 91.5%，90.1%，95.6% and 92.3%，respectively. Under the conditions of flexion and extension，lateral bending and rotation，the stress peak of the simple artificial vertebral fixation model was 52.3 MPa，51.9 MPa，52.6 MPa，respectively；that of the clival plate and screw fixation was 100.1 MPa，158.1 MPa，170.6 MPa，respectively；that of the anterior occipital condylar plate and screw fixation was 114.2 MPa，62.9 MPa，132.9 MPa，respectively. Under the condition of flexion and extension，lateral bending and rotation，the stress peak of the occipital bone in the simple artificial vertebral body internal fixation model was 52.9 MPa，50.9 MPa and 62.3 MPa，respectively；that of the clival plate and screw fixation model was 19.7 MPa，55.9 MPa and 38.3 MPa，respectively；that of the anterior occipital condylar plate and screw fixation model was 37.8 MPa，15.0 MPa and 16.3 MPa，respectively. The stress in bone near the hypoglossal canal was close to 0 MPa，much smaller than the stress peak in occipital bone.Conclusion:Anterior occipital condylar plate and screw fixation in front of the special-shaped titanium cage can improve the stability of occipitocervical fusion with little effect on the occipital bone and hypoglossal canal or without obvious stress concentration，and hence is a safe and reliable anterior fixation method for upper cervical spine instability.