| ObjectivesTo develop and validate a3-D nolinear finite element model of the upper cervicalspine. To elucidate the effect of head posture and force direction on different types of thetransverse atlantal ligament injuries. A3-D finite element model of anterior atlantoaxialdislocation for transverse atlantal ligament rupture was established according to a clinicalcase. Biomechanical research was carried out to evaluate atlantoaxial joint stability aftertransverse ligament rupture.Materials and MethodsThe upper cervical spine (C0-3) of a healthy volunteer was scanned by64-mutidetector spiral CT. The data of CT were converted into STL format data bySimpleware3.0,and developed a geometric model of upper cervical spine by Geomagic12.0. The ligaments and material properties were added to the upper cervical modelaccording to previous reports. The finite element model of the upper cervical spine wasvalidated against the experimental data and finite element models of previous reports.The finite element model of the upper cervical spine were applied by loads of1.5N·mto simulate flexion, extension, axial rotation and lateral bending. A size of8g impact loadwas applied when the model was on neutral flexion, extension, axial rotation and lateralbending position. The von Misses stresses, changes of stress with time (50ms) and stresscloud of transverse ligament and atlas were showed to predicted the risks of transverseatlantal ligament injuries.Base on clinical case, removal of the transverse atlantal ligament was to simulaterupture on the normal upper cervical spine model. And change of load deformation curvewas to simulate injuries of other ligaments. A finite element model of atlantoaxial anteriordislocation was developed. The range of motion of the atlantoaxial anterior dislocationmodel were measured and analyzed by Abaqus6.12, and compared with the normal model. Results1.The normal model of upper cervical spine was agreement with normal anatomy ofthe upper cervical spine, and consisted of206747elements and72500nodes. The modelwas validated by the Panjabi’s experimental data and finite element models reported byBrolin and Zhang.2. Stresses of transverse atlantal ligament substantive(type I) were large whendownward impact load applied on the model in different head positions. The greatest vonMiss stress was5.55MPa when the head was in rotational position. Stresses of lateral massof the atlas(type II) were also large when downward impact load applied on the model indifferent head positions. The greatest von Misses stress was11.21MPa when the head wasin lateral bending position. Stresses of transverse atlantal ligament substantive and lateralmass of the atlas were relatively small when front impact load applied on the model indifferent head positions.3. The finite element model of atlantoaxial anterior dislocation due to transverseatlantal ligament rupture was established. The results were agreement with clinical case.The ranges of motion was larger in atlantoaxial anterior dislocation model than those of inthe normal upper cervical spine model, especially in flexion increased by17.8°,andextension increased by13.7°.Conclusions1. The3-D nolinear finite element model of the upper cervical spine was validated bythe experimental data and results of previous finite element models.2. The impact load in downward direction most likely to lead to transverse atlantalligament injuries. The transverse atlantal ligament substantive(type I) was prone to injurywhen the head was in rotational position, and lateral mass of the atlas(type II) was prone toinjury when the head in lateral bending position. The transverse atlantal ligament is noteasy to injury when front impact load applied in different head positions.3. The atlantoaxial joint was serious instability after the transverse ligament rupture,especially in the direction of flexion and extension. The finite element model ofatlantoaxial anterior dislocation due to transverse atlantal ligament rupture can be used for biomechanical analysis. |
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