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Objective To analyze the CT signs and the clinical relevant factors of degenerative osteoarthritis of athnto-odontoid joint.Methods The CT signs and the clinical information of 214 patients received CT scans of skull from June 2011 to April 2012 were analyzed retrospectively.Results One hundred and twenty patients were diagnosed with degenerative osteoarthritis of atlanto-odontoid joint,while 67 of them having subaxial degenerative osteoarthritis at the same time.Forty-three patients had a history of chronic cervical and occipital pain.95.83％ (115/120) patients showed osteophytes in CT scans,while 44.17％ (53/1 20) showed calcification around dens and 24.17％ (29/120) showed joint space obliteration.The incidence rate increased with age.Seventy-seven patients [64.17％(77/120)] appeared cervical and occipital pain.Conclusions Degenerative osteoarthritis of atlanto-odontoid joint shows hyperostosis,osteophytes at the edge of joint,joint space obliteration and calcification around dens in the CT scans.The incidence rate is increased with age and correlated with cervical and occipital pain.
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Objective To investigate the stress characteristics of atlanto-axial bony structure under conditions of anteflexion,posterior extension,lateral flexion,and rotation after artificial atlanto-odontoid joint arthroplasty using three-dimensional finite element method and to improve the orientation of artificial atlantoodontoid joint from perspective of stress.Methods A three-dimensional finite element model of prosthetic atlanto-odontoid joint arthroplasty was created from CT images of the artificial atlantoodontoid joint and cervical vertebrae using software Mimics,Freeform,and Ansys.Stress characteristics of the model dealt with proneness,posterior extension,lateral flexion,or rotation loads were observed.Biomechanical performance of the bony structure of the model was analyzed and the orientation in improving the prosthesis was discussed.Results Anteflexion loading produced a maximum stress of 0.138 ×l08 N/m2 at the junction of lateral mass and posterior arch of the atlas,and 0.201 × 108 N/m2 at axial nail hole,contact point of plates with the axis,and posterior arch of the axis.Posterior extension loading produced a maximum stress of 0.666 × 107 N/m2 at junction of lateral mass and posterior arch of the atlas and 0.254 × 108 N/m2 at arch of the axis.Besides,stress concentration occurred at atlantoaxis nail hole.Right bending produced a maximum stress of 0.124 × 108 N/m2 at nail hole of right mass of atlas and 0.178 × 108 N/m2 at right contact point of the axis with plates.Right rotation produced a maximum stress of 0.847 × 107 N/m2 at junction of lateral mass and posterior arch of the atlas and 0.170 × 109 N/m2 at contact point of the axis with plates.The finite element model comprised 28 620 nodes and 107 441 units and provided good defining of the structural properties of artificial atlanto-odontoid joint arthroplasty.Under different loading conditions,the stress was mainly distributed in contact point of the vertebral body with plates,nail holes,junction of lateral mass and posterior arch of the atlas,and axial pedicle.Conclusions Prosthetic atlanto-odontoid joint scatters a part of the stress and alters the stress distribution of the atlas and axis from the intact condition.Finite element method can obtain complete analysis of the stress distribution of the artificial atlanto-odontoid joint arthroplasty.
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In order to provide anatomical basis for transoral approach (TOA) in dealing with the ventro lesions of craniocervical junction, and the design and application of artificial atlanto-odontoid joint, microsurgical dissecting was performed on 8 fresh craniocervical specimens layer by layer through transoropharyngeal approach. The stratification of posterior pharyngeal wall, course of vertebral artery, adjacent relationship of atlas and axis and correlative anatomical parameters of replacement of artificial atlanto-odontoid joint were observed. Besides, 32 sets of atlanto-axial joint in adults' fresh bony specimens were measured with a digital caliper and a goniometer, including the width of bony window of anterior arch of atlas, the width of bony window of axis vertebra, the distance between superior and inferior two atlas screw inserting points, the distance between two axis screw inserting points etc. It was found that the width of atlas and axis which could be exposed were 40.2±3.5mm and 39.3±3.7mm respectively. The width and height of posterior pharyngeal wall which could be exposed were 40.1±5.2mm and 50.2±4.6mm respectively. The distance between superior and inferior two atlas screw inserting points was 28.0±2.9mm and 24.0±3.5mm respectively, and the distance of bilateral axis screw inserting points was 18.0±1.2mm. The operative exposure position through TOA ranged from inferior part of the clivus to the superior part of the C3 vertebral body. Posterior pharyngeal wall consisted of 5 layers and two interspaces: mucosa, submucosa, superficial muscular layer, anterior fascia of vertebrae, anterior muscular layer of vertebrae and posterior interspace of pharynx, anterior interspace of vertebrae. This study revealed that it had the advantages of short operative distance, good exposure and sufficient decompression in dealing with the ventro lesions from the upper cervical to the lower clivus through the TOA. The replacement of artificial atlanto-odontoid joint is suitable and feasible. The design of artificial atlanto-odontoid joint should be based on the above data.
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[Objective]To determine the initial stability and function of a new artificial joint in a cadaveric cervical spine model by comparing it with a conventional method. [Methods]Twelve fresh human cadaveric cervical spines(C0~3) were randomly divided into 2 groups: group 1,resection of the odontoid with artificial atlanto-odontoid joint(AAOJ),and group 2,resection of the odontoid with Magerl atlas and axis by transarticular screw fixation(Magerl).For each specimen,the intact and resection of the odontoid underwent a flexibility test firstly,followed by the instrumented construct.Rotational angles of the C0~3 segment were measured to study the immediate stability and function of resection of the odontoid and AAOJ,compared with the intact and resection of the odontoid and Magerl.[Results]Compared to the intact state,resection of the odontoid and AAOJ resulted in a significant decrease in the range of motion(ROM) and neutral zone(NZ) during flexion,extension,and lateral bending(P0.05).Compared to the intact state,resection of the odontoid and Magerl resulted in a significant decrease in the range of motion(ROM) and neutral zone(NZ) during all 6 degrees of freedom(P0.05).[Conclusion]A new type of artificial atlanto-odontoid joint has been designed for correcting atlantoaxial instability resulted from C1、2 anterior decompression procedures.It can restore,to a great extent,the C1、2 axial rotation that is lost during current stabilization procedures.