| Background:Stability of the occipitocervical region is maintained by bony structures (the occipital, atlas and axis) and surrounding ligaments, muscles and joint capsules, fascias. In this region, various causes result in structural damage or dysfunction, and incur clinical symptoms of the occipitocervical instability. The etiology of occipitocervical instability is complex, and is calssified as following:1 congenital causes, such as odontoid dysplasia or absent, odontoideum, occipitalization of the atlas, Klippel-Fei short-necked deformity, basilar invagination and chromosomal abnormalities; 2 traumatic causes, including the occipital condyle fractures, atlantoaxial fracture, atlantooccipital dislocation or atlantoaxial dislocation and transverse ligament injury; 3 pathological causes, such as structural damage by the inflammation, tuberculosis or cancer; 4 iatrogenic causes, such as the instability resulted from the absent of the posterior arch of the atlas or occipital bone flap removed after posterior decompression. Currently, early surgical intervention is advocated to remove comppression or stimulation over the spinal cord or never, restoring normal alignment and stability of the occipitocervical region with a rigid fixation. However, anatomy of this region is complex, surrounded by important nerves and blood vessels, resulting in great difficulty and risks for any surgical procedures.Posterior occipitocervical fixations are main surgical treatment. However, the posterior fixations are not suitable for some patients, as congenital or iatrogenic absent of the bony structure. In addition, the posterior instrumentation is not appropriate for some revision cases as the local bony damage of the original screw trajectory and screw loosening without sufficient screw pull-out strength. Anterior occipitocervical fixations are alternative to the aforementioned cases. In clinic, ventral spinal cord compression may be caused by severe basilar invagination with occipitalization of the atlas, atlantoaxial dislocation, or shift-up of dens into the foramen magnum. The current strategy is to release the decompression firstly by anterior cervical or transoral approach, then apply a posterior occipitocervical fixation via a posterior approach. Recently, the anterior occipitocervical fixation with a titanium cage anchored at clivus or screws inserted into the occipital condyles has been used for the aforementioned cases, being a one-stage operation for releasing, reduction, decompression and fixation. Those techniques greatly decrease the risk of surgery, shorten the operation time and improve clinical outcome. However, due to insufficient stability of current anterior occipitocervical fixations, it is needed to find a new way to enhance the stability and use a minimal invasive surgery techniques in anterior occipitocervical fixations.Our previous anatomic and imaging studies showed the clival screw insertion safe. In the present study, we designed and develop a clival reconstruction plate system for patients with a ventral defect in the occipitocervical region, and a clival plate for patients with deformity and instability in this region. Furthermore, the present study establish three anterior occipitocervical techniques, including a clival reconstruction plate system fixation for ventral defect in the occipitocervical region, a clival plate for instability of the occipitocervical region, and the anterior atlanto-occipital transarticular screw fixation. This study analyzed the applied anatomy of this three fixation methods, and evaluate spinal stability, which provided the experimental data for clinical application of these anterior occipitocervical fixations.Objective:1. Develop a clival reconstruction plate system to reconstruct the ventral defect of the occipitocervical region, and perform a biomechanical evaluation.2. Develop a clival fixation plate to correct the deformity and restore the stability of the occipitocervical region, and perform a biomechanical evaluation.3. Analysis the applied anatomy of the trans-clivus occipitocervical fixation by each step of the transoral approach, quantified the exposure arear of the clivus and analysis the feasibility of the clival screw placement, in order to provide a reliable anatomical data for the anterior occipitocervical fixation methods.4. Analysis the applied anatomy of anterior atlanto-occipital transarticular screw fixation, and perform a biomechanical evaluation, in order to provide an anterior minimal invasive fixation method to restore the stability of the atlanto-occipital joint.Methods:1. Development and biomechanical test of the clival reconstruction plate system1) Development of the clival reconstruction plate systemDimensions relevant to the clival reconstruction plate were measured on 40 adult dry bones and CT images of 30 healthy volunteers, based on it the clival reconstruction plate system was designed and produced.2) Stability evaluation of the clival reconstruction plate systemIn this part of the experiment, we carried out the in-vitro biomechanical testing on 7 fresh adult cervical spines (Oc-C4). The testing status including: ①the intact status;②) fashioned mesh cage+posterior occipitocervical fixation;③ clival reconstruction plate system+posterior occipitocervical fixation;④clival reconstruction plate system fixation alone. The anterior fixation was applied between the clivus and C3 body, and the posterior fixation was applied to each specimen anchored at the occiput, C1 pedicle, C3 and C4 lateral mass. The repeated measurement design was used in test. Under the intact, injury and different fixed state, each specimen was applied a pure moment of 1.5Nm in directions of flexion/extension, left/right lateral bending and left/right axial rotation, respectively, by the spinal testing machine. Optotrak Certus 3D motion measurement system was used to collect the motion data of the infrared marking points which placed on the occipital bone, C3 and C4 vertebra connected by K-wire, analysing and calculating the range of motion (ROM) and the neutral zone (NZ) of the Oc-C3 segments.2. Development and biomechanical test of the clival fixation plate1) Development of the clival fixation plateDimensions relevant to the clival fixation plate were as the same as the above parameters measured on the clival reconstruction plate system, and then the clival fixation plate was designed and produced.2) Stability evaluation of the clival fixation plateIn this part of the experiment, we carried out the in-vitro biomechanical testing on 8 fresh adult cervical spines (Oc-C3). The testing status including: ① the intact status; ②the intact status+clival fixation plate;③ the injury status:the type II odontoid process fracture companion with the resection of the apical and alar ligments and tectorial membrane;④ the injury status+clival fixation plate; ⑤ the injury status+posterior occipitocervical fixation. The anterior fixation was applied between the clivus and C2 body, and the posterior fixation was applied to each specimen anchored at the occiput, C1 and C2 pedicle. The repeated measurement design was used in test. Under the intact, injury and different fixed state, each specimen was applied a pure moment of 1.5Nm in directions of flexion/extension, left/right lateral bending and left/right axial rotation, respectively, by the spinal testing machine. Optotrak Certus 3D motion measurement system was used to collect the motion data of the infrared marking points which placed on the occipital bone, C1 and C2 vertebra connected by K-wire, analysing and calculating the ROM and the NZ of the Oc-C2 segments. The effect of different fixation methods on the arrangement of the occipitocervical region was compared.3. The applied anatomical study of the anterior occipitocervical fixationsThe transoral approach was performed on 7 fresh cadaveric heads. There were five surgical approaches to the cranniocervical region:simple transoral approach (TO), transoral with soft palate split (TOP), transoral with hard plate split (TOHP), mandibulotomy (MO) and mandibuloglossotomy (MLO). After each approach complete, observing the distribution of the pharyngeal soft tissue and the shape of the vertebral artery, measuring the thickness of the soft tissue, the distance between the vertebral artery and the middle line, the exposed area of the clivus and the clival screw entry angles (between the tangent line of the extracranial clivus and the line from the bottom of the lower incisors or mandibular to the exposed area of the clivus), recording the exposed area of the cervical spine.4. The anatomical and biomechanical study of the anterior atlantooccipital transarticular screw fixation1) The anatomical study of the anterior atlantooccipital transarticular screw fixationThirty normal cervical spines had computed tomography scans with reformates reviewed to determine screw entry points, entry angles and proposed screw lengths. Following screw (4 mm in diameter) insertion in eight fresh frozen human cadaver spine specimens, radiographs and dissection verified screw location relative the vertebral artery, spinal cord and hypoglossal canal.2) Stability evaluation of the anterior atlantooccipital transarticular screw fixationIn this part of the experiment, we carried out the in-vitro biomechanical testing on 6 fresh adult cervical spines (Oc-C3). The testing status including: ① the intact status;② the injury status:resect the apical and alar ligments and tectorial membrane; ③the injury status+anterior atlantooccipital transarticular screw fixation; ④ the injury status+posterior atlantooccipital fixation. The posterior fixation was applied to each specimen with the occiput plate-screw system and C1 pedicle screws. The repeated measurement design was used in test. Under the intact, injury and different fixed state, each specimen was applied a pure moment of 1.5Nm in directions of flexion/extension, left/right lateral bending and left/right axial rotation, respectively, by the spinal testing machine. Optotrak Certus 3D motion measurement system was used to collect the motion data of the infrared marking points which placed on the occipital bone and C1 vertebra connected by K-wire, analysing and calculating the ROM and NZ of the Oc-C1 segments.5. Statistical analysis of the data was performed using the SPSS 13.0 software. Anatomical data were measured three times, and the data were expressed as mean± standard deviation (x±s), a paired t test was used for the comparisons between the left and right sides measured data. For the biomechanical test, repeated measures analysis of variance was performed to determine whether significant differences existed, the method of SNK (Student-Newman-Keuls) was used to compare between different groups.Results:1. Development and biomechanical test of the clival reconstruction plate system1) Development of the clival reconstruction plate systemThe mean clival length, the clival widest and narrowest diameter were 25.8±2.6 mm,32.6±2.1 mm and 18.9±1.5 mm, respectively. The height and width of the C1 lateral mass were 15.7±2.9 mm and 26.4 ±2.9 mm, and the diverge angle of the lateral mass screw was 10.4°±2.5°. The distances between the clivus and the C` anterior arch and C3 body were 16.1±1.7mm and 59.1±3.2mm, respectively. The clival-cervical angle was 130.2°±8.0±. The clivus screw length was ranged from 4.3 mm to 16.0 mm.The clivus reconstruction plate (China patent:201420441488.7), shaped as cruciform structure, was consists of the oblique clivus component, the horizontal vertebrae component and the bilateral flank component. The clivus component was an inverted v-shaped arm and anatomically fitted to the clival morphology with three 3.5-mm screws. There was an appropriate front lean angle (clival-cervical angle) between the clivus component and the vertebrae component, anatomically fitting to the ventral curve of the craniovertebral juncion. The vertebrae component included two sliding grooves (a pair of oval holes), allowing two sliding groove screws (4.0 mm in diameter) connected to the posterior titanium mesh cage. The lower part of the vertebrae component was fixed to the C3 body with two 3.5-mm screws. The bilateral flank component was inwardly arc shaped, for fitting snugly into the atlas. It had two holes at both ends for two 3.5-mm screws fixed to the Cllateral mass. The clivus reconstruction plate was made of titanium alloy (Ti6A14V) with a 1.6-mm thickness. The clivus plate reconstruction fixation system was composed of a clivus plate, a titanium mesh cage and connecting screws on the sliding grooves.2) Stability evaluation of the clival reconstruction plate system.ROMs of the intact were 22.4°,19.5°,10.5° and 47.3° in flexion, extension, lateral bending and axial rotation, respectively. Compared with the intact state, the fashioned mesh cage status, the clival reconstruction plate system fixation status and the clival reconstruction plate system fixation alone all significantly decrease the ROM or NZ in all the directions (P<0.05). The clival reconstruction plate system reduced ROMs to 0.1° in flexion,0.2° in extension,0.3° in lateral bending and 0.6° in axial rotation. Compared with the fashioned mesh cage status, the clival reconstruction plate system fixation status significantly decrease the ROM in flexion, lateral bending and axial rotation (P<0.05), the trend was also found in extension but there was no significantly difference (P>0.05). There was no significantly difference in NZs in all directions between the above two fixation statuses (P>0.05). The fashioned mesh cage status or the clival reconstruction plate system fixation status significantly decrease the ROM or NZ in all directions compared to the clival reconstruction plate system fixation alone (P<0.05).2. Development and biomechanical evaluaiton of the clival fixation plate1) Development of the clival fixation plateDimensions relevant to the clival fixation plate were as the same as the above parameters measured on the clival reconstruction plate system. The clival fixation plate (China patent:201520753712.0) consists of three components:the upper, middle and lower components. The upper clivus component, in where three clival screw holes designed as a triangular layout, which can fixed the upper clivus component onto the extracranial clivus, and there was an oblique angel between the upper clivus component and the body of the plate. The middle atlas component can be divided into two segments:the neck segment extending from the clivus component; the shoulder segment inverted T-shaped and extending from the neck segment, expanding bilaterally and formed an open slot at the bottom. There was a screw hole on the left or right side of the shoulder segment, enabling the screws fixed the atlas component into the C1 lateral mass. The lower axis component, extending downwardly from both sides of the shoulder segment of the atlas, and formed a transitional ladder at the intersection of the atlas and axis component with a posterior-inferior angle, there were two screw holes on the left or right side of the axis component, enabling the screws fixed the axis component into the C2 body. The detail dimensions of the clival fixation plate based on individual. Screw was designed as a locked screw with a diameter of 3.5 mm, preventing the screw exit effectively. The clivus fixation plate was made of titanium alloy (Ti6Al4V) with a 1.6-mm thickness.2) Stability evaluation of the clival fixation plateCompared with the intact state, the injury status increased the ROM or NZ significantly in flexion, extension, lateral bending and rotation (P<0.05). Compared with the intact state, the three fixation status all significantly decrease the ROM or NZ in all the directions (P<0.05). The injury+the clival fixation plate status reduced ROMs to 1.7° in flexion,1.2° in extension,2.8° in lateral bending and 4.3° in axial rotation, which were smaller than the ROMs in all direction compared to the intact+ the clival fixation plate status (P<0.05). The injury+posterior occipitocervical fixation status constrained motion to 1.0°,1.3°,1.4° and 1.1° in flexion, extension, lateral bending and axial rotation, respectively, which indicate the same ROMs in all directions except in axial rotation as the injury+the clival fixation plate status (P>0.05). There was no difference in NZs among this three fixation status in all directions (P>0.05). The impact of different fixation methods on the arranged motion for the occipitocervical region:in rotation, the clival fixation plate status and posterior occipitocervical fixation status both increase the percentage of the ROM in Oc-C1, and the three fixation methods have the same ratio of the ROM in Oc-C1 and C1-C2; In flexion, extension and lateral bending, the clival fixation plate status increase the percentage of the ROM in Oc-C1, and the injury status and the posterior occipitocervical fixation status both increase the ratio of the ROM in C1-C2.3. The applied anatomical study of the anterior occipitocervical fixationClival screw fixation for the occipitocervical region was technique possible in up to 0% of specimens by TO approach,71% by TOP approach,86% by TOHP approach and 100% by MO approach. The minimum thickness of the soft tissue of the posterior pharyngeal wall above the pharyngeal tubercle was 3.5mm, and the value ranged from 4 mm to 5 mm above the cervical spine. The distance between the vertebral artery and the middle line of the vertebrae was 20 mm at the C1/2 level, and about 14 mm at the C2/3-C4/5 level. With the TO approach, the longitudinal diameter of the exposed clivus was 8 mm, and the distance between the lower incisor and the upper and lower part of the clivus, C1 anterior arch, C2 and C3 vertebral body were 105 mm,99 mm,81 mm,75 mm and 69 mm, respectively, and the clival screw entry angle ranged from 98° to 100°, six specimens exposed down to C3 vertebral body and one specimen to C2 vertebral body. With the TOP approach, the longitudinal diameter of the exposed clivus was 19 mm, and the distance between the lower incisor and the upper part of the exposed clivus, the pharyngeal tubercle were 108 mm and 105 mm, respectively, and the clival screw entry angle ranged from 88° to 100°. With the TOHP approach, the longitudinal diameter of the clivus was 26 mm, and the distance between the lower incisor and the upper part of the exposed clivus was 112 mm, and the clival screw entry angle ranged from 80° to 100°. With the MO or MLO approach, it can exposed all the clivus, and the distance between the bottom of the mandible and the apex and lowest points of the clivus, the pharyngeal tubercle were 142 mm,131 mm and 121 mm, respectively, and the clival screw entry angle ranged from 63° to 83°, the cervical vertebrae can be exposed down to C5/6 level.4. The anatomical and biomechanical study of the anterior atlantooccipital transarticular screw fixation method1) The anatomical study of the anterior atlantooccipital transarticular screw fixationThirty patients with CT measurements show the ideal posterior inclination angle of the screw on the sagittal plane was 41.7°± 8.5°, ideal diverge angle on the coronal plane was 11.6°± 3.5°, and the ideal screw length was 30.4±4.0 mm; 3 cases were impossible to perform the anterior atlantooccipital transarticular screw fixation due to the block by the mandible; In 2 patients, hypoglossal canal was located in the middle and posterior part of the occipital condyle, who would suffered a high risk of the hypoglossal nerve injury. After the screw inserted in eight fresh frozen human cadaver spine specimens, radiographs and dissection verified the screw had no penetration into the brain or the spinal canal, no violation to the artery and the hypoglossal nerve.2) Stability evaluation of the anterior atlantooccipital transarticular screw fixation methodROMs of the intact were 12.0°,10.1°,6.5° and 7.8° in flexion, extension, lateral bending and axial rotation, respectively. Compared with the intact state, the injury status increased the ROMs and NZs in all directions (P<0.05). The anterior atlantooccipital transarticular screw fixation status reduced ROMs to 0.4° in flexion, 0.4° in extension,1.0° in lateral bending and 0.7° in axial rotation, which indicate the same ROMs in all directions as the posterior atlantooccipital fixation status (P>0.05). There was no significantly difference in NZs in all direction between the above two fixation methods (P>0.05). Compared with the intact state or the injury status, the anterior atlantooccipital transarticular screw fixation status or the posterior atlantooccipital fixation status decreased the ROM or NZ significantly in all directions (P<0.05).Conclusion1. The clival reconstruction plate system was developed, which optimized the clival screw placement and supported the anchoring points at C1, function as the tension effect of the plate and the axial support of the titanium cage. The biomchaincal test shows the clival reconstruction plate system was more stable than the commonly used fashioned titanium mesh cage. This fixation system provides a specific fixation devices and optimal surgical methods to reconstruct the ventral defect of the occipitocervical region.2. The clival fixation plate was developed, which showed the same stability as the posterior occipitocervical fixation in the flexion, extension and lateral bending, and weaker in axial rotation. This study indicated that the clival fixation plate could provide a reliable anterior fixation method to restore the stability of the occipitocevical region.3. This study indicated that the TO approach was not available for the trans-clivus occipitocervical fixation; It was successfully performed on 71% of specimes with TOP approach,86% with TOHP approach and 100% with MO approach. However, the MLO approach is absolutely required to the patients with small mouth crack or mouth opening limited, the flat skull base or basilar imagination, lower cervical spine exposing and fixation, to achieve the clival plate fixation for the occipitocervical region.4. The anterior atlantooccipital transarticular screw fixation was feasible and safe anatomically, with the ideal posterior inclination angle of 41.7° on the sagittal plane, ideal diverge angle of 11.6° on the coronal plane, and the ideal screw length 30.4 mm. The anterior atlantooccipital transarticular screw fixation had the same stability as the posterior atlantooccipital fixation method. This study incdicated that the anterior atlantooccipital transarticular screw fixation could be a reliable fixation method to restore the stability of the atlanto-occipital joint. |
PDF Full Text Request