Effects Of Cervical Rotatory Manipulation On The Stress,Strain And Displacement Of The Cervical Spinal Cord And Medulla Oblongata

Objective:The study is to analyze the mechanism of cervical rotatory manipulation on cervical spinal canal contents such as cervical spinal cord and cranial contents of medulla oblongata from morphological,kinematic and biomechanical perspectives,and to provide morphological basis and scientific basis for the clinical application of cervical rotatory manipulation.Methods:1.Fresh and embalmed cadaveric specimens were used to observe the morphological and kinematic characteristics of the cervical spinal cord,medulla oblongata,nerve roots and other structures during craniocervical flexion,extension and rotation.2.Mimics,Geomagic,Solidworks and ABAQUS softwares were used to construct and validate an intact craniocervical model based on a normal Chinese male individual.3.Based on the normal craniocervical model,the CRM was simulated in the 15°flexion position,15° extension position and neutral position.The stress,strain,sagittal diameter,cross-sectional area and anterior-posterior eccentricity of the cervical spinal cord were quantified in real time.The changes in medullary stress,strain and distance from the foramen magnum were analysed.4.Three different models were developed and validated by adding mild,moderate,and severe OPLL to the normal model in C5 and C6 segments.The occupying ratios of mild,moderate,and severe OPLL in the vertebral canal were considered to be 20%,40%and 60%.We simulated the CRM in the 15° flexion position on the OPLL models and quantified the stress of cervical spinal cord and dura matter in different phases of CRM.The stress of the nerve roots in different segments was also analysed.Results:1.(1)The posterior surface of the cervical spinal cord elongated during craniocervical flexion,with a mean strain of 8.55%;the posterior surface of the cervical spinal cord shortened during craniocervical extension,with a mean strain of 7.16%.(2)The cervical spinal cord is displaced cephalad relative to the two sides of the pedicle in craniocervical flexion position and caudally in craniocervical extension position.(3)During flexion and extension,there was no significant displacement of the medulla oblongata relative to the foramen magnum and no change in the position of the conus medullaris.(4)In the flexion position,the nerve root tension increased and the suprashoulder angle between the nerve root sleeve and the dura matter became larger;In the extension position,the nerve root tension decreased and the supra-shoulder angle between the nerve root sleeve and the dura matter became smaller;in the axial rotation,the nerve root tension increased on the rotating side.2.A complete three-dimensional craniocervical finite element model based on a normal male individual containing cervical canal contents such as the cervical spinal cord and cranial contents such as the medulla oblongata was successfully constructed and validated.3.We have studied CRM in the direction to the right:(1)the peak spinal cord stress and strain were smaller in the flexion position of CRM.The peak stress and strain in the flexion and neutral position of CRM were located on the white matter,while the extension position of CRM was on the grey matter.The peak spinal cord stress and strain in the CRM in all three positions were located in the C1 and C2 segments.(2)The sagittal diameter and cross-sectional area of the spinal cord were smaller in the flexion position of CRM and larger in the extension position of CRM(P<0.05).(3)The spinal cord was closer to the anterior wall of the spinal canal in the flexion position of CRM and closer to the posterior wall in the extension position of CRM.(4)The peak stress and strain in the medulla oblongata were smaller than those in the spinal cord in CRM,and the peak stress and strain in the medulla oblongata were concentrated in the right posterior lateral sulcus of the medulla oblongata and at the junction with the pons.The distance between the medulla oblongata and the foramen magnum of the occipital bone did not change significantly during CRM.4.The models of mild,moderate and severe segmental OPLL in C5 and C6 segments were successfully constructed and validated.We have studied the right-sided CRM in flexion position.(1)The stress of dura matter and nerve roots was significantly higher in the mild OPLL group compared to the normal model(P<0.05).(2)In addition to a significant increase in the stress of dura matter and nerve roots,the stress of the spinal cord was also significantly higher in the moderate or severe OPLL group(P<0.05).Conclusions:Intraspinal structures such as the cervical spinal cord exhibit different morphological,kinematic and biomechanical characteristics in different body positions of the CRM.CRM in the flexion position is relatively safe compared to the other two positions and CRM has little effect on the normal medulla oblongata.Caution should be applied when performing CRM on OPLL patients.