| BACKGROUND:Basilar invagination (BI) is a congenital abnormality of the cranio-cervical anatomical structure, which is characterized by telescoping of the odontoid process into the foramen magnum.The pathogenesis of BI are mostly relevant to the flat skull base, occipital-cervical fusion, and Kleip-Feil malformation during embryonic development. The main pathological changes are the bone structure around foramen magnum (odontoidectomy, basal part of occipital bone, occipital condyles and squama) rose to cranial cavity, which led to volume reduction of the cranio-cervical junction (CJ). These changes cause symptoms of neural damages as the spinal cord oppression. Moreover, in these areas exist respiratory and circulatory center, sustained oppression can lead to serious disability, even dead.Management of patients with BI can be challenging because of complex and variable anatomy of the upper cervical spine. BI can be treated by the excision of the odontoid process,which is easy to damage the spinal cord and cause dural tear.However, direct transoral decompression and followed by posterior instrumentation has been accepted as a standard procedure during the past three decades. Despite the fact that such an approach provides a good clinical efficacy, it presents obvious disadvantage. It entails a combinative anterior-posterior approach management, which will increase surgical injuries.Recently, the indication for anterior decompressions has been questioned by Goel et al. who emphasized that ventral compressions by the odontoid could be reduced by posterior distraction of the Cl/2 joints alone and advocated C1/2 fusions sparing the occiput. However, whether a pure reduction of the invagination and fusion is sufficient therapy or additional anterior and posterior bony decompressions and duraplasties should be performed as well is still not clearly defined. And major BI patients has taken the posterior foramen magnum decompression surgery with poor effects, and need renovation surgery. However, occipitocervical and atlantoaxial fixation can’t be effective as the missing bone structure. Coupled with deformity of BI patients, there are many patients are not suitable for the posterior fixed fusion surgery as the vertebral artery high across, atlantoaxial pedicle narrow, and occipital hypoplasia. Therefore, the posterior reduction and fusion can only be used for the BI patients with reversible atlanto-axial dislocation, and not for the patients with irreducible and irreducible dislocation.For the deficiency in the BI treatment, we have innovatively use the transoral odontoid process down operation, this procedure was followed by a complex transoral atlantoaxial dislocation in our hospital for many years using the transoral atlantoaxial reduction plate (TARP). There were two unique features with this operation. The first is the use of TARP instrument’s longitudinal push open mechanism to move down the dens outside the foramen magnum. The second is the use the plate screw technique to fix the atlanto-occipital complex and the axis.The advantages of this procedures were using odontoid process down technology to retain the odontoid process structure to avoid serious complications of odontoid process resection. By raising the anterior skull base can effectively correct the spinal medulla oblongata. By anterior decompression and internal fixation in one single operation could avoid the operation trauma of posterior internal fixation surgery, and solve the problems with posterior fixation. After systematic anatomic study and clinical application we has confirmed that the procedure can achieve the odontoid process down and fixation at the same time through the anterior operation.Compared with other treatments, the anterior tranoral odontoid process down operation in the treatment of BI greatly decrease the incidence of complications. However, we have found that there are still obvious shortage in the clinical application. In some cases, there are poor neural function recovery after operation. The imaging study found that these patients had bad postoperative gear position. About two-thirds patients had bulbar and spinal oppression as the insufficient odontoid process down, whereas about one-thirds patients with excessive odontoid process down.Through in-depth analysis, we found two potebtial reasons that led to these problems with poor odontoid process down. A. The accurate target value of the odontoid process down can’t be determined before the operation, because of the shortage of quantitative data about the relation between the volume changes of cranio-cervical junction and the odontoid process down. B. During the operation the location of odontoid process can’t be clearly observed as the bone structures of cranio-cervical junction are all irregular and overlapped.The fundamental reason for these problems is lack of quantitative data about the relation between the volume changes of cranio-cervical junction and the odontoid process down. And conventional methods are difficult to calculate the volume due to the irregular anatomy of cranio-cervical junction. These are the core issues affecting the clinical effects. In our current study, we try to use the recently Digital Orthopaedics to investigate the cranio-cervical junction. Digital orthopaedic technology is a new developmental technology of this century, with accuracy, digital design and operation. This new technology combines computer aided design and Rapid prototype technologies, and can reconstruct the three-dimensional model of the anatomy of cranio-cervical junction region from the CT profile data.By this means, the physicians can observe the lesions from any direction, which will greatly improve the cognitive ability of orthopaedic surgeons for complex lesions. This can also provide a great deal of help for complex spinal operation. Furthermore, by using this new technology, we prepare the surgical planning on a computer, and achieve personal and accurate operation. We propose that focused on defining the measurement method and measurement range through three-dimensional reconstruction. We establish the quantitative relations between the odontoid progress down and the volume of cranio-cervical junction to guide surgical planning.Objective:In the present study we use the digital orthopaedic technology to get the primary data of the patients with basilar invagination by the thin slice CT scanning of cervical vertebra. And then we rebuild the three dimensional model of craniocervical junction based on SnapMC algorithm. By this mean, we calculate the vertebral canal volume, and measure the odontoid process displacement. We investigate the efficacy of the TRAP treatment in patients with BI by retrospective analysis. We also found the quantitative relations among the odontoid process descension distances, craniocervical volumes, and outcome of the operation, which can be used to guide surgical planning.Methods:1. Testing the accuracy of the volume measurement by rebuilding the irregular three dimensional models based on SnapMC algorithm.We got CT images of nine quite irregular small stone by CT thin layer chromatographic scanning. The data was imported to Yorktal Bone CT Image Processing Software to rebuild three dimensional simulation model, and then using voxel method to measure its volume. Finally we compared with the actual volume to verify the accuracy of the reconstruction and measurement method.2. Retrospective analysis of transoral atlantoaxial reduction plate in the treatment of basilar invagination53 patients with basilar invagination with atlantoaxial dislocation and 10 patients with basilar invagination with Klippel-Feil syndrome who underwent transoral atlantoaxial reduction plate (TARP) reduction and fixation from 2009 to 2012 were reviewed. The clinical assessment and the measurements of the images were performed preopera-tively, postoperatively and at most recent follow-up.3. Quantitative study on the volume of the cranial cervical junction and clinical effect.This study enrolled 20 patients with basilar invagination who underwent TARP procedures. Axial, sagittal and coronal craniocervical computed tomography (CT) images were processed, and a three-dimensional reconstruction of the craniocervical junction was performed. Craniocervical volumes and odontoid process descension distances were measured pre- and post-operatively. Patient neurological function was evaluated according to the Japanese Orthopedic Association (JOA) score signed for cervical disorders. Pearson correlation analysis was applied for statistical comparisonsResult:1.In the present study we have used Yorktal Bone CT Image Processing Software to quickly and accurately rebuild the irregular three dimensional model based on SnapMC algorithm. This model is very similar to solid geometry, and can be used to precisely measure the size.2. All operations were successfully completed, the operation time were 115-205min (mean ± sd=130±30min), bleeding volume were 35-95 (mean ± sd=50±15). There was no complications of neurological damage, dural crack, and vascular injury. There was no difficulty in swallowing or choking, etc. Postoperative CT scan showed that the nail road was accurate, and no deviation. There was one patient appeared postoperative pulmonary infection within 3 days. And there was two patient with wound infection, who was treated with occipital cervical fusion after removing the steel.Clinical efficacyAll the 51 patients were followed up for average 43.17 months (ranging from 25 to 64 months). The average preoperative and 3 months postoperative JOA scores were 9.24 (n= 51) and 13.95 (n= 51), respectively, indicating 60.7% improvement. The average of the most recently follow up was 14.88, indicating 72.68% improvement versus the preoperative scores, and 11.98%versus the 3 months postoperative scores.48patients (94.12%) had shown symptoms of clinical remission to varying degrees. Clinical symptoms of one patient didn’t improve, with preoperative and postoperative JO A scores all being three points. There were two patients symptoms shown improved after one month operation, whose preoperative JO A score was 8, and 9 points, postoperative JO A scores 10, and 11 points. However, after one month these two patients symptoms gradually worsened as several times fall during the ambulation exercise. And in the most recent follow-up the JOA score were the same before surgery. All the 51 patients graft had been fused within 3-6 months after operation.Image assessmentThe BAI decreased from an average(mean ± standard deviation) of 18.4±5.5mm (n= 51) before surgery to 10.2±4.3mm (n= 51) after surgery. The BDI increased from an average(mean ± standard deviation) of-4.2±5.2mm (n=51) before surgery to 5.9±3.3mm (n=51) after surgery. The CCA increased from an average(mean ± standard deviation) of 120±16°(n=51) before surgery to 149±11°(n=51) after surgery, and CL from-9.4±4.2mm to 0.4±2.9mm, WL from-6.5±4.5mm to 2.2±3.9mm, ML from-3.1±4.2mm to 5.4±2.7mm.3. Pre-and post-operative measurement data were completed.Surgical efficacy (JOA%) was significantly associated with the improvement rate of craniocervical volume (V%),the odontoid descension distance,and the absolute value of craniocervical volume changes (V) (P<0.01), with the correlation coefficient (r) being 0.83,0.80, and 0.61 respectively. Nevertheless, no significant correlation was noted between the surgical efficacy (JOA%) and age,symptom duration, preoperative JOA score,odontoidante displacements clivus-odontoid angle change (P>0.05).Craniocervical volume improvement rate (V%) is significantly associated with odontoid descension distance (r=0.8; P<0.01), but not associated with the odontoidante displacement or the clivus-odontoid angle change (P>0.05).Conclusion:1.We have successfully applied the Yorktal Bone CT Image Processing Software to rebuild the irregular three dimensional model. We have achieved the accurate measurement of volume, which will be useful for the further clinical validation and application.2.The TARP operation is a effective and safe method of treatment for patients with basilar invagination with atlantoaxial dislocation.The mid-term clinical result was satisfactory.3.The odontoid descending distance can predict the craniocervical volume improvement rate in basilar invagination patients following TARP operations, and both of them can serve as predictors of surgical efficacy. We speculate that a deliberate strategy planning the odontoid descending distance preoperatively may be helpful to improve the efficacy of TARP operations in basilar invagination patients. |
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