Biomechanical Study Of Lower Cervical Spine Disalignment After ACDF With Different Disc Height

Objective:(1)We constructed finite element model of C3-T1 cervical spine with different disc heights,compared and analyzed the ranges of motion of lower cervical spine,von mises of facet joint capsule and intervertebral disc,and tensions of anterior longitudinal ligament,to find the appropriate disc height of ACDF.(2)By simulating C5-C6 single-level ACDF surgery on cervical spine of fresh goat cadavers,we analyzed the von mises of facet joint capsule and ranges of motion of lower cervical spine at different disc heights to find the appropriate disc height of ACDF.(3)By simulating C5-C6 single-level ACDF surgery on cervical spine of human cadavers,we analyzed the von mises of facet joint capsule and ranges of motion of lower cervical spine at different disc heights to find the appropriate disc height of ACDF.Methods:(1)We constructed a normal C3-T1 three-dimensional finite element model from the CT imaging data of a healthy volunteer.The ranges of motions of the model under flexion,extension,lateral flexion and rotation conditions were compared with other references’ data to verify the validity of the finite element model.(2)The plate and screw internal fixation system was loaded on the normal C3-T1 three-dimensional finite element model.And four C3-T1 cervical spine finite element models with different disc heights were constructed respectively.The ranges of motion,von mises of facet joint capsule and intervertebral disc and tensions of anterior longitudinal ligament of 4 models were compared and analyzed.(3)Four kinds of C3-T1 goat cervical spine models with different disc heights(100%、125%、150% and 75% benchmark disc height)were constructed.The ranges of motion and von mises of facet joint capsule were analyzed.(4)Four kinds of C3-T1 human cervical spine models with different disc heights(100%、125%、150% and 75%benchmark disc height)were constructed.The ranges of motion and von mises of facet joint capsule were analyzed.Result:(1)In this study,the number of elements in the C3-T1 three-dimensional finite element model was 140,500 and the number of nodes was 306,076.The difference in the activity of each segment was not large,which could be used for subsequent finite element studies.Comparing with other references,the C3-T1three-dimensional finite element model had been proved good for cervical finite element analysis.(2)Four groups were classified by disc heights: group Ⅰ(disc height was not changed)、groupⅡ(disc height increased 1.4 mm)、groupⅢ(disc height increased 2.8 mm)、groupⅣ(disc height decreased 1.4 mm).The ranges of motion and von mises of facet joint capsule in groupⅢ are greater than that in other groups.The von mises of disc in groupⅡ are smaller than that in other groups.(3)The differences of the von mises of goat facet joint capsule among four groups were statistically significant.The ranges of motion in 125% benchmark disc height model were greater than that in 100%,150% and 75% benchmark disc height models.(4)The differences of the von mises of human facet joint capsule among four groups were statistically significant.The ranges of motion in 125% benchmark disc height model were greater than that in 100%,150% and 75% benchmark disc height models.Conclusion:(1)The model of groupⅠ、groupⅢ and groupⅣ has serious impact on lower cervical spine alignment.In this study,we recommend the optimal increased disc height is 1.4mm(125% original disc height).(2)In this study,125% benchmark disc height was considered to be the best choice for the ACDF.