In-Vivo Study Of Three-Dimensional,Cervical Segmental Motion Characteristics And Clinical Relevance Research Following Anterior Cervical Fusion With Different Numbers Of Fusion Levels

Objective:The pathogenesis of adjacent segment degeneration(ASD)and the influence on the range of motion(ROM)of the entire cervical spine following anterior cervical fusion(ACF)surgery with different numbers of fusion levels remains controversial.Kinematics of adjacent segments,and the entire cervical spine,after ACF at different cervical levels was determined by using cone beam computed tomography(CBCT)images combined with 3 dimensions to 3 dimensions(3D-3D)registration technology.The preoperative and postoperative cervical spine stiffness,Visual Analogue Scale(VAS)and the Japanese Orthopaedic Association Scores(JOA)were compared to accurately analyze the biomechanical effects of cervical fusion.Methods:Thirty-six inpatients who underwent ACF were enrolled in the study and categorized into one of three groups based on fusion level: one-level,two-levels,and three-levels.All subjects underwent pre and postoperative(a average follow-up time of 5.9 months)cervical spine cone beam computed tomography(CBCT)scans at 7functional positions.The ranges of motion of the superior and inferior adjacent segments,and the entire cervical spine,were measured using 3D-3D registrations.Changes in the pre-and post-operative ROMs were calculated for each patient.Clinical outcomes were assessed using the cervical spine stiffness scale,VAS and the JOA Scores.Results:Changes in the pre-and post-operative primary ROMs of adjacent segment: The left-right bending ROMs at the superior adjacent segment in the three-level group were significantly greater than in the one-level group(4.9±4.2°vs.1.6±1.4°,p=0.038);At the inferior adjacent segment,the ROMs for left–right twisting and bending in the two-level group were significantly greater than in the one-level group(1.7±1.3°vs.0.6±0.6°,p =0.032 and 3.7±2.9°vs.1.3±1.2°,p = 0.042).Changes in the pre-and post-operative primary ROMs of the overall cervical spine(C1-C7): A significant difference was found in flexion-extension between the one and three-level groups(10.6±0.3° vs.15.5±2.5°,p =0.048).For left–right twisting and bending,the primary ROMs in the one-,two-,and three-level groups were similar to each other(19.4 ±13.6° vs.17.6 ±14.5° vs.16.2 ±9.8°,respectively;p>0.05 and 11.2 ±5.7° vs.10.8 ±6.6° vs.9.6 ±5.4°,respectively;p>0.05).The pre-and post-operative clinical outcomes: The pre-operative cervical spine stiffness scores,VAS and JOA scores were not significantly different among the 3groups.Post-operatively,the VAS and JOA scores showed no significant differences between the three patient groups.However,the mean stiffness score for the three-level group was 1.6±1.3,which was significantly greater than that of the one-level group(0.4 ±0.7,p=0.046).Conclusions:Patients who underwent multilevel ACFs had increased compensatory motion at the unfused adjacent segments and are more likely to develop adjacent disc degeneration.As the number of fusion levels increased,the overall cervical ROMs showed no significant differences during twisting and bending,but three-level fusion reduced the ROM for the cervical flexion-extension.Multilevel fusion leads to a stiffer cervical spine.