Artificial Atlanto-odontoid Joint Research Articles

Atlantoaxial Non-Fusion Using Biomimetic Artificial Atlanto-Odontoid Joint: Technical Innovation and Initial Biomechanical Study.

A biomechanical in vitro investigation. To evaluate the function and stability of self-designed biomimetic artificial atlanto-odontoid joint (BAAOJ) replacement on the atlantoaxial joint. Upper cervical fusion surgery is a common treatment for various atlantoaxial disorders, and favorable clinical outcome has been achieved. However, the fusion surgery results in loss of atlantoaxial motion as well as adjacent segments degeneration, reducing the quality of life of patients and might produce severe neurological symptoms. Non-fusion technology is expected to solve the above problems, but various designed devices have certain defects and are still in the exploratory phase. Biomechanical tests were conducted on 10 fresh human cadaveric craniocervical specimens in the following sequence: 1) intact condition, 2) after the BAAOJ arthroplasty, 3) after BAAOJ fatigue test, 4) after odontoidect-omy, and 5) after anterior rigid plate fixation. Three-dimensional movements of the C1-C2 segment were evaluated to investigate the function and stability of BAAOJ arthroplasty compared with the intact condition after the BAAOJ fatigue test, odontoidect-omy, and rigid plate fixation. Comparing the BAAOJ implantation to the intact state, the range of motion and neutral zone were slightly reduced in all directions (P > 0.05). Compared with the rigid plate fixation, the BAAOJ implantation significantly increased the range of motion and neutral zone in all directions, especially in the axial rotation (P < 0.05). We designed a BAAOJ for correcting atlantoaxial disorders arising from atlantoaxial instability. As a non-fusion device, the most critical feature of BAAOJ replacement is the retention of flexion-extension, lateral bending, and axial rotation range of motion similar to the normal state. It can also stabilize the atlantoaxial complex, and the BAAOJ itself has a good initial stability.Level of Evidence: 4.

Novel posterior artificial atlanto-odontoid joint for atlantoaxial instability: a biomechanical study.

OBJECTIVE Atlantoaxial instability is usually corrected by anterior and/or posterior C1-2 fusion. However, fusion can lead to considerable loss of movement at the C1-2 level, which can adversely impact a patient's quality of life. In this study, the authors investigated the stability and function of a novel posterior artificial atlanto-odontoid joint (NPAAJ) by using cadaveric cervical spines. METHODS The Oc-C7 regions from 10 cadaveric spines were used for anteroposterior (AP) translation and range of motion (ROM) tests while intact and after destabilization, NPAAJ implantation, and double-rod fixation. RESULTS The mean AP C1-2 translational distances in the intact, destabilization, and double-rod groups were 6.53 ± 1.07 mm, 11.54 ± 1.59 mm, and 3.24 ± 0.99 mm, respectively, and the AP translational distance in the NPAAJ group was significantly different from that in the intact group (p < 0.05). The AP translational distance in the NPAAJ group was not significantly different from that in the double-rod group (p = 0.24). The mean flexion, extension, and axial rotation ROM values of the NPAAJ group were 9.87° ± 0.91°, 8.75° ± 0.99°, and 61.93° ± 2.93°, respectively, and these were lower than the corresponding values in the intact group (p < 0.05). The mean lateral bending ROM in the NPAAJ group (9.26° ± 0.86°) was not significantly different from that in the intact group (p = 0.23), and the flexion, extension, and rotation ranges in the NPAAJ group were 79.5%, 85.2%, and 82.3%, respectively, of those in the intact group. CONCLUSIONS Use of NPAAJ for correction of atlantoaxial instability disorders caused by congenital odontoid dysplasia, odontoid fracture nonunion, and C-1 transverse ligament disruption (IA, IB, and IIB) may restore the stability and preserve most of the ROM of C1-2. Additionally, the NPAAJ may prevent soft tissue from embedding within the joint. However, additional studies should be performed before the NPAAJ is used clinically.

An Experimental Biomechanical Study on Artificial Atlantoodontoid Joint Replacement in Dogs.

This study tested the biomechanics of artificial atlantoodontoid joint replacement (AAOJR) in a dog model. Dogs were divided into the artificial AAOJR group (n=10), the decompression group (n=10), and the healthy control group (n=10) using a random number table. To evaluate whether the use of AAOJR for repair of atlantoaxial instability retains rotation and restores stability. Atlantoaxial instability is characterized by excessive movement or laxity at the junction between the atlas (C1) and axis (C2). Pure decompression can lead to considerable loss of head and neck rotation and postoperative impairment. A series of biomechanical tests on cadavers found that the artificial AAOJR might rebuild the stability and retain the rotation function. We designed the AAOJ based on the radiologic and anatomic data of the dog atlas and axis, and established an animal model by resecting the odontoid and implanting the AAOJ into dogs. The biomechanical experiments measured the range of motion (ROM), neutral zone (NZ), and stiffness of flexion, extension, lateral bending, and axial rotation in the intact state, the decompressed state, after AAOJR, and after a fatigue test. Compared with the intact state, after decompression operation, ROM and NZ in all directions, and stiffness during flexion were increased, and stiffness in all other directions was decreased. Compared with the after decompression state, AAOJR before and after the fatigue test resulted in decreased ROM in all directions (all P<0.05), decreased NZ during flexion/extension and lateral bending (all P<0.05), an increased NZ during axial rotation (both P<0.05), and increased stiffness in all directions (all P<0.05). These results indicate that AAOJR could reconstruct the vertebral stability of the C1-C2 segment and retain some axial rotation function.

Biomechanical study of the atlantoaxial joint after artificial atlanto-odontoid joint arthroplasty

ObjectiveTo investigate the stability and three-dimensional movements of the atlantoaxial joint after artificial atlanto-odontoid joint (AAOJ) arthroplasty by comparing with a conventional method. MethodsAfter anterior decompression, 24 human cadaveric spinal specimens of C0-C3 were randomly divided into two groups: Group A receiving artificial AAOJ arthroplasty; Group B experiencing anterior transarticular screw (ATAS) fixation. Two groups underwent flexibility test in intact and instrumented states. Rotational angle of the C0-C3 segments was measured to study the immediate stability and function of anterior decompression with AAOJ arthroplasty compared with the intact state and ATAS fixation. ResultsCompared with the intact state, anterior decompression with AAOJ arthroplasty resulted in a significant decrease in the range of motion (ROM) and neutral zone (NZ) during flexion, extension and lateral bending (P<0.05); however, with regard to axial rotation, there was no significant difference in ROM and NZ (P>0.05). Compared with anterior decompression with ATAS fixation, anterior decompression with AAOJ arthroplasty during flexion, extension and lateral bending, significant difference was found in ROM and NZ (P>0.05); however, as for axial rotation, there was a significant increase in ROM and NZ (P<0.05). ConclusionThe self-designed AAOJ has an excellent biomechanical performance, which can restore excellent instant stability and preserve the movement of the atlanto-axialjoint.

Construction of Finite Element Model for an Artificial Atlanto-Odontoid Joint Replacement and Analysis of Its Biomechanical Properties.

To investigate the stress distribution on artificial atlantoaxial-odontoid joint (AAOJ) components during flexion, extension, lateral bending and rotation of AAOJ model constructed with the finite element (FE) method. Human cadaver specimens of normal AAOJ were CT scanned with 1 mm -thickness and transferred into Mimics software to reconstruct the three-dimensional models of AAOJ. These data were imported into Freeform software to place a AAOJ into a atlantoaxial model. With Ansys software, a geometric model of AAOJ was built. Perpendicular downward pressure of 40 N was applied to simulate gravity of a skull, then 1.53 N• m torque was exerted separately to simulate the range of motion of the model. An FE model of atlantoaxial joint after AAOJ replacement was constructed with a total of 103 053 units and 26 324 nodes. In flexion, extension, right lateral bending and right rotation, the AAOJ displacement was 1.109 mm, 3.31 mm, 0.528 mm, and 9.678 mm, respectively, and the range of motion was 1.6°, 5.1°, 4.6° and 22°. During all ROM, stress distribution of atlas-axis changed after AAOJ replacement indicating that AAOJ can offload stress. The stress distribution in the AAOJ can be successfully analyzed with the FE method.

Finite element analysis of biomechanical performance of atlanto-axial bony structure following artificial atlanto-odontoid joint arthroplasty

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. Key words: Cervical vertebrae; Biomechanics; Finite element method ; Atlanto-odontoid joint

Construction and validation of a finite element model of atlanto-axial joint following artificial atlanto-odontoid joint arthroplasty

Objective To develop and validate an anatomic detailed finite element model of atlanto-axial joint following artificial atlanto-odontoid joint arthroplasty.Methods The normal fresh human specimens of atlas and axial and artificial atlanto-odontoid joint were subjected to CT scan.Three-dimensional model was established by Mimics software.According to clinical practice,dealing with atlas and axial and assembling artificial atlanto-odontoid joint by Freeform.After constructing the geometric model and meshing the solid model using tetrahedral solid elements,adding the relevant ligament structure,the meshed model was acqujred and finished by Ansys at last.The ligaments were modeled with tension-only spring elements with bilinear modulus of elasticity data according to neutral and elastic zones.The ligaments of model includes:atlantoaxial joint capsule and ligaments,facet joint capsular ligament,interspinous ligament,supraspinous ligament.Sliding contact definitions with friction were used for all the facet joints.In the analysis,the weight of the skull was simulated by applying vertical load of 40 N on the fixed handle,and the inferior surface of the C2 venebral body was fully constrained but the upper part of the atlas without any constraints.Pure moment loading of 1.53 N.m was applied to the fixed handle to simulate various movements of the atlanto-axial joint under flexion,extension,lateral bending and axial rotation configurations.The the range of motion (ROM) of model under different direction were evaluated biomechanically.To validate the finite element model in term of ROM compared against the experimental data by Yong Hu at al.Results The model consists of 26324 nodes and 103053 elements,In the conditions of flexion,extension,righe flexion and right rotatio,the ROM of the artificial atlanto-odontoid joint are 1.6°,5.1 °,4.6 ° and 22.0°,that is correlated well with the results by Yong Hu at al.Conclusion The anatomic detailed finite element model realistically simulates atlanto-axial joint following artificial atlanto-odontoid joint arthroplasty and facilitate the further biomechanical research,and for further optimization of artificial atlanto-odontoid joint. Key words: Biomechanics; Atlanto-odontoid joint; Atlanto-axial joint; Arthroplasty

Three-dimensional finite element analysis on three-dimensional stability of improved artificial atlanto-odontoid joint

Objective To evaluate three-dimensional stability of improved artificial atlanto-odontoid joint by finite element method.Methods The finite element model was constructed by the software Mimics with CT images.According to the clinical practice,atlas was dealt with and artificial atlanto-odontoid joint was assembled.The meshed model was acquired and imported to software Ansys to analyze three-dimensional stability of the model.Results The displacement of artificial atlanto-odontoid joint under flexion,extension,lateral flexion load was 1.109,3.310,0.528 mm respectively.The displacement was 9.678 mm under rotation load.The range of motion was 1.6°,5.1°,4.6° and 22.0° respectively by further calculation.Conclusion Improved artificial atlanto-odontoid joint arthroplasty can basically restore excellent stability and reserve the movement of atlanto-axial joint instantly after operation. Key words: Biomechanics ; Atlanto-odontoid joint; Arthroplasty

The analysis of imageology for screw tunnel of atlas-axis components of artificial atlanto-odontoid joint

Objective To investigate feasibility and safety for screw tunnel of atlas-axis components of artificial atlanto-odontoid joint (AAOJ) arthroplasty in bony specimens of atlanto-axial joint.Methods The thin-slice CT scannning and the three-dimension reconstruction were performed through 32 sets of artificial atlanto-odontoid joint arthroplasty in adults' bony specimens.The indicators related to AAOJ internal fixation were measured and applied to observe the safe space among screw tunnel of atlas-axis components and important anatomy structures such as transverse foramen,groove for vertebral artery,vertebral canal,etc.Results The length of screw tunnel of atlas components (L) was (21.5 ±3.7) mm,the extraversion angle of screw tunnel of atlas components (α) was ( 12.9 ± 4.8) °,the length of screw tunnel of axis components (S) was (28.6± 3.7) mm,the extraversion angle of screw tunnel of axis components (β) was (22.6 ±4.3)°,and the downslope angle of screw tunnel of axis components (θ) was ( 15.8 ±2.6) °.Conclusion There is a comparatively large safe space between screw tunnel of atlas-axis components of AAOJ arthroplasty and transverse foramen,groove for vertebral artery,vertebral canal,etc. Key words: Atlanto-odontoid joint; Artificial joint; Atlanto-axial joint; Screw; Placement

Biomechanical evaluation of stability and three-dimensional movements of the atlantoaxial joint after artificial atlanto-odontoid joint arthroplasty

To investigate the stability and three-dimensional movements of the atlantoaxial joint after artificial atlanto-odontoid joint (AAOJ) arthroplasty. Ten sets of AAOJ implanted in bony specimens from 10 adults were used to test the pull-out strength of the atlas-axis components with a MTS858 Mini Bionix machine. Another twelve human cadaveric specimens including C(0)-C(4) were used to evaluate the three-dimensional movements of C(1)-C(2) under five different conditions in sequence, that is, the complete specimen, anterior decompression, posterior transarticular screws fixation, AAOJ arthroplasty and fatigue test. There were significant differences between atlas and axis components in the maximum pull-out strength and trajectory length, however the yield length was not significantly different. The maximum pull-out strength of the atlas and axis was positively correlated with trajectory length (r(1)= 0.880, P < 0.05) and yield length (r(2)= 0.606, P < 0.05), respectively. After AAOJ arthroplasty, the range of movement (ROM) with respect to rotation and the neutral zone of the atlantoaxial joint were close to normal (P > 0.05), but the ROM in flexion-extension and lateral bending was significantly smaller compared with the specimens which underwent anterior decompression (P < 0.05). No abrasion and abnormal mobilization were observed after 2000 cycles of flexion, extension, lateral bending and axial rotation in the fatigue test. The self-designed AAOJ has excellent biomechanical performance, and AAOJ arthroplasty can restore excellent instant stability and preserve the movement of the atlantoaxial joint.

Biomechanical Study of Artificial Atlanto-Odontoid Joint

An in vitro biomechanical study. 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. Resection of the odontoid and anterior arch of the atlas results in atlantoaxial instability, which if left uncorrected may lead to severe neurologic complications. Currently, such atlantoaxial instability is corrected by anterior and/or posterior C1-C2 fusion. There were 24 fresh human cadaveric cervical spines (C0-C3) 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 Harms anterior atlantoaxial plate (Harms). For each specimen, the intact and resection of the odontoid underwent a flexibility test first, followed by the instrumented construct. Rotational angles of the C0-C3 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 Harms. Compared with the intact state, resection of the odontoid and AAOJ resulted in a significant decrease in the range of motion (ROM) and neutral zone during flexion, extension, and lateral bending (P < 0.05); however, with regard to axial rotation, there was no significant difference in ROM (P > 0.05). Compared with resection of the odontoid and Harms, resection of the odontoid and AAOJ during flexion, extension, and lateral bending, there was no significant difference in ROM (P > 0.05). We have designed a new type of AAOJ for correcting atlantoaxial instability arising from C1 to C2 anterior decompression procedures. The unique aspect of this joint is that it restores, to a great extent, the C1-C2 axial rotation that is lost during current stabilization procedures.

The biomechanical evaluation of stability and three-dimensional movements for atlanto-axial joint following artificial atlanto-odontoid joint arthroplasty

Objective To investigate the biomechanical performance of stability and three-dimensional movements for athmto-axial ioint following artificial atlanto-odontoid ioint arthroplasty.Methods Twelve human cadaveric specimens CO-C4 were loaded nondestructively with 1.53 Nm in the unconstrained testing apparatus.The tested states were intact specimen,after odontoidectomy,posterior transarticular screws,after artificial atlanto-odontoid ioint arthroplasty,and after fatigue test in order.After each state,the range of motion(ROM)at the level of C1,2 Was measured in flexion-extension,lateral bending,and axial rotation direction.Results The angular range of motion and neutral zone during axial rotation at C1-C2 after artificial atlanto-odontoid ioint arthroplasty were proven to get close normal ROM.But there was significant difierence in flexion,extension,lateral bending at C1-C2 as compared with odontoidectomy and intact spine.There were smaller ROM during flexion.extension and lateral bending at C1-C2 after artificial atlanto-odontoid ioint arthroplasty and transarticular screws,but there was significant difference in axial rotation after artificial atlanto-odontoid ioint arthroplasty and transarticular screws.No abrasion and bnormal mobilization were observed after 2000 cycles of flexion,extension,lateral bending and axial rotation in flatigue test.Conclusion The serf-designed artificial atlanto-odontoid ioint arthroplasty Call basically restore excellent stability,and reserve the movement of atlanto-axial ioint instantly after operation. Key words: Biomechanics; Atlanto-odontoid joint; Atlanto-axial joint; Arthroplasty

Biomechanical study of arlas-axis components pull-out strength following artificial atlanto-odontoid joint arthroplasty

Objective To investigate the arias-axis components pull-out strength following artifi-cial atlanto-odontoid joint arthroplasty and evaluate its biomechanical performance. Methods Ten sets of artificial atlanto-odontoid joint used in adults' bony specimens were selected for biomechanical test in MTS858 Mini Bionix machine including the arias-axis components pull-out strength. Results F-maxs were (894.36±102.30) N in the atlas components, and (1227.59±143.35) N in axis components respec-tively. The screw length of atlas components was (20.69±1.43) mm, and that of axis components was (24.03±1.31) mm. The yield length of atlas and axis components was (1.51±0.11) and (1.0.12) mm respectively. There was statistically significant difference between pull-out strength of the atlas-axis components and the screw length of the atlas-axis components (P 0.05). A statistically sig-nificant positive correlation was observed between pull-out strength of the arias-axis components and the screw length of the atlas-axis components (r1=0.880). There was statistically significant positive correla-tion between pull-out strength of the atlas-axis components and the yield length of the atlas-axis compo-nents (r2=0.606). Conclusion The atlas-axis components had excellent biomechanical performance of pull-out strength. The screws of atlas components should be implanted unicortically. The screws of axis components should be implanted bicortically. Screw path length is one of the important factors influencing the arias-axis components pull-out strength. Key words: Biomechanics; Atlanto-edontoid joint; Artificial joint; Atlanto-axial joint; Replacement

Artificial atlanto-odontoid joint replacement through a transoral approach

Resection of the odontoid process and anterior arch of the atlas results in atlantoaxial instability, which if left uncorrected may lead to severe neurological complications. Currently, such atlantoaxial instability is corrected by anterior and/or posterior C1-C2 fusion. However, this results in considerable loss of rotation function of the atlantoaxial complex. From the viewpoint of retaining the rotation function and providing stability, we designed an artificial atlanto-odontoid joint based on anatomical measurements of 50 pairs of dry atlantoaxial specimens by digital calipers and 10 fresh cadaveric specimens by microsurgical techniques. The metal-on-metal titanium alloy joint has an arc-shaped atlas component, and a hollow cylindrical bushing into which fits a rotation axle of an inverted v-shaped axis component and is implanted through a transoral approach. After the joint was implanted onto specimens with anterior decompression, biomechanical tests were performed to compare the stability parameters in the intact state, after decompression, after artificial joint replacement, and after fatigue test. Compared to the intact state, artificial joint replacement resulted in a significant decrease in the range of motion (ROM) and neutral zone (NZ) during flexion, extension, and lateral bending (P < 0.001); however, with regard to axial rotation, there was no significant difference in ROM (P = 0.405), a significant increase in NZ (P = 0.008), and a significant decrease in stiffness (P = 0.003). Compared to the decompressed state, artificial joint replacement resulted in a significantly decreased ROM (P B 0.021) and NZ (P B 0.002) and a significantly increased stiffness (P \ 0.001) in all directions. Following artificial joint replacement, there was no significant difference in ROM (P C 0.719), NZ (P C 0.580), and stiffness (P C 0.602) in all directions before and after the fatigue test. The artificial joint showed no signs of wear and tear after the fatigue test. This artificial atlanto-odontoid joint may be useful in cases of odontoid resection due to malunion or nonunion of odontoid fracture, atraumatic odontoid fracture, irreducible atlas dislocation, posterior atlantoaxial subluxation, or congenital skull base abnormalities.

The anatomic study on replacement of artificial atlanto-odontoid joint through transoral approach

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+/-3.5 mm and 39.3+/-3.7 mm respectively. The width and height of posterior pharyngeal wall which could be exposed were 40.1+/-5.2 mm and 50.2+/-4.6 mm respectively. The distance between superior and inferior two atlas screw inserting points was 28.0+/-2.9 mm and 24.0+/-3.5 mm respectively, and the distance of bilateral axis screw inserting points was 18.0+/-1.2 mm. 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.