| Background:(1)The atlantoaxial dislocation (AAD) caused by congenital ordevelopmental anomalies is the most common reason of spontaneous AAD amongChinese people, and its exact pathogenesis remains unclear.(2) The lateral atlantoaxialarticulation (LAA) assumes the responsibility of both movement and weight bearing ofC1-C2, and the structural variation of LAA will influence the motor pattern andweight-bearing mode and thus leading to the change of C1-C2stability. It possessesimportant fundamental and clinical significance to expore the change of C1-C2stabilityand the pathologic mechanism of congenital AAD from the view of structuremorphology of LAA and biomechanics.(3)Plane radiographs and normal CT scanscan't clearly demonstrate the configuration of LAA because of its deep location, thehindrance of circumambient bony structures and bony deformity of this region. Thedetailed morphology of LAA is underreported.Objectives:(1)To perform three dimensional structure description, functional analysisand clinical classification of LAA both in the healthy people and patients of congenitalanomalies of the craniovertebral junction (CVJ);(2) To explore the relationship betweenthe structural variation of LAA and C1-C2stability and its role in the occurrence ofcongenital AAD;(3) To analyse the relationship between clinical typing of LAA and thereducibility of AAD;(4)To establish deformed model of the occiput-C1-C2finiteelement, and stimulate and analyse the characteristics of its motion and biomechanics ofthis region.Methods:(1)The clinical data and the neutral position of the occiout-cervical CT datawas analysed both in47cases of heathy adult and141cases of congenital ordevelopmental anomalies of the CVJ;(2) The Mimics software was used to performethe multiplanar reconstruction. Frankfort horizontal plane was chosen as the basal plane of the axial plane and then images were resliced. Three dimensional fine structure of theCVJ was set;(3) Measurements of the obliquity of atlantoaxial articular facet wasperformed between the facet and the new horizontal line, with the obliquity ofanteversion/retroversion in sagittal plane and the obliquity of extraversion in coronalplane;(4) The morphological variation of the LAA was studied and the feature wassummarized;(5) The occiput-C1-C2finite element model was established and validated.Then deformed model was set by adjusting the model condition and the degrees of theobliquity of the atlantoaxial articular facets, and then related biomechanical researchwas performed.Results:(1) The normal articular facet of LAA was flat without obvious obliquity. Thedeformed configuration of LAA was defined to four types. Type I, characterized byslight anteversion of LAA without olisthy of the inferior and superior facets; Type II,characterized by partial olisthy of the two facets and evident anteversion of LAA; TypeIII, defined by the separation or complete olisthy of the two facets; Type IV, wherein thearticular facets sloped dorsally.(2)Eighty-seven of91cases in the former three typeswherein articular facet sloped ventrally had AAD. All45type IV cases wherein articularfacet sloped dorsally had no AAD.(3) The degree of the anteversion of LAA hasnegative correlation with the age of initial presence of the clinical manifestation.(4)Theincremental obliquity of the anteversion of the articular facet has close relationship withthe change of C1-C2stability and the progression of the basilar invagination, which wasvalidated in the method of the finite element.Conclusion: Instability at the C1-C2junction in congenital and developmental anomalyof CVJ is likely a direct result of the anteversion and structural variation of LAA, and itaggratates with the increasing obliquity of anteversion of the articular facet.Demonstrating the structural variation and clinical typing of LAA provides a new meansto diagnosis instability in congenital anomaly at CVJ and provide insight into thepathogenesis of AAD and a basis for rational surgical treatment. |
PDF Full Text Request