A study on a CT imaging classification of congenital atlantoaxial dislocation and its clinical significance

English Keywords:Congenital atlantoaixal dislocation  Atlantoaxial dislocation CT image classification  Surgery strategy  Transoral osteotomy, remodelling, releasing, reduction and fixation with plate

English Abstract:

  【Abstract】 Objectives: To develop a classification method of congential atlantoaxial dislocation(CAAD) based on CT imaging features, and to investigate its guiding values for determining atlantoaxial surgery strategies. Methods: From January 2020 to December 2022， 61 patients with CAAD were included in the study，consisting of 26 males and 35 females, aged 32±12 years(6-61 years). And the patients were divided into three types based on the extent of deformity observed in atlantoaxial lateral mass joint and atlanto-odontoid joint: Type A(23 cases, mild deformity in the lateral mass joint without concurrent atlanto-odontoid joint deformity); Type B(20 cases, moderate deformity in the lateral mass joint without concurrent atlanto-odontoid joint deformity); Type C(18 cases, severe deformity in the lateral mass joint or concurrent deformity of atlanto-odontoid joint). Different surgical strategies were employed according to the distinctive classification: Type A or Type B patients underwent posterior reduction and fixation with instrumentation only with general anesthesia, after which, additional posterior atlantoaxial facet joint release was performed for patients with unsatisfactory reduction; Type C patients received transoral osteotomy, remodelling, releasing, reduction and fixation with plate(TORP). The operative time and blood loss were recorded and compared between different types of patients. The follow-up period extended from 10 to 18 months. Cervical spine CT and MRI examinations were performed at postoperative 1 week to observe and measure the reduction indicators of atlantoaxial dislocation, and overall reduction rates were calculated. At 3 months after operation, Japanese Orthopaedic Association(JOA) score was used to evalute the recovery of spinal cord function, bone fusion status was assessed through CT examinations. Results: 22 cases underwent posterior reduction and fixation with instrumentation only under general anesthesia(type A 20 cases, type B 2 cases). 21 cases received posterior reduction by release of lateral mass joint and fixation with posterior instrument(type A 3 cases，type B 18 cases). 18 cases(type C) underwent TORP operation. Postoperative CT and MRI images taken one week after the procedure exhibited well-aligned atlantoaxial joints, indicating the release of spinal cord compression in all 61 patients. During follow-up, all the patients demonstrated diverse levels of improvement in spinal cord function. For type A cases, the JOA score improved from a preoperative value of 9.8±2.7 to 13.9±2.8 at three months postoperatively(P<0.05). Type B cases exhibited an improvement in JOA score from 9.5±2.4 preoperatively to 13.7±3.1 at three months postoperatively(P<0.05). Type C cases showed an improvement from 9.1±2.9 to 13.3±2.5 over the same period(P<0.05). At preoperation and 1 week after operation, for type A, the atlas-dens interval(ADI) was 5.8±2.5mm and 0.8±0.4mm, vertical distance from dens to Chamberlain line(VDI) was 5.7±3.6mm and 1.0±0.8mm, cervical medullary angle(CMA) was 138.4°±12.4° and 156.5°±13.3°, and clivus axis angle(CAA) was 131.6°±11.5° and 149.5°±14.4°; For type B, ADI was 6.9±3.8mm and 1.1±0.9mm, VDI was 5.9±4.3mm and 1.1±1.0mm, CMA was 135.1°±15.2° and 157.3°± 13.2°, and CAA was 128.4°±13.5° and 152.5°±13.4°; For type C, ADI was 7.2±3.9mm and 1.2±1.5mm, VDI was 8.8±5.1mm and 1.5±1.8mm, CMA was 132.7°±10.9° and 158.2°±15.3°, and CAA was 124.5°±17.8° and 153.8°±11.2°; And the ADI, VDI, CMA and CAA of the three types after operation all improved significantly(P<0.05). The overall reduction rates were 84.30% for type A, 82.68% for type B, and 81.53% for type C(P>0.05). With the exception of one case of type A, which experienced screw loosening due to poor bone fusion and subsequently underwent revision surgery via the transoral approach, the remaining 60 patients all achieved stable bony fusion within 10 to 12 months postoperatively. Conclusions: The CT imaging classification method for CAAD can provide accurate and reliable guidance in the selection of surgical methods for atlantoaxial dislocation.