Treatment of basilar invagination associated with atlantoaxial dislocation through distracting and reducing the atlas-axis facet joint and implanting struct allograft bone by transoral approach

English Keywords:Basilar invagination  Atlantoaxial dislocation  Transoral approach  Reduction  Fusion  Internal fixation

English Abstract:

  【Abstract】 Objectives: To investigate the clinical value for treatment of basilar invagination(assocaitaed with atlantoaxial dislocation) through distracting the atlas-axis facet joint and implanting struct allograft bone by transoral approach. Methods: From December 2009 to December 2011, 33 patients diagnosed with basilar invagination associated with atlantoaxial dislocation were treated by distracting the atlas-axis facet joint and implanting struct allograft bone through transoral approach. All patients had symptoms of spinal medulla compression. The atlas-dens index(ADI), distance from tip of dens to Chamberlain line(DCL), vertical atlantoaxial index(VAAI) and cervicomedullary angle(CMA) were measured on the radiography or CT image before and after operation to evaluate the reduction of atlantoaxial dislocation and the decompression of medulla. The function of spine was evaluated by the JOA score. The ADI, DCL, VAAI, CMA was 3.8-12.1mm(7.9±3.9mm), 3.0-15.6mm（9.3±6.2mm）, 0.35-0.51(0.46±0.07) and 112°-145°(127°±13°) respectively before operation, and the spine function ranged from 7 to 10 before surgery. All cases received operations through distracting the atlas-axis facet joint and implanting struct allograft bone and TARP plate by transoral approach. Operation time and blood loss were recorded, and complications were observed after operation. All patients were followed up for 8-23 months(mean 11.5 months), the reduction of atlas-axis facet joint dislocation and improvement of spinal cord compression were evaluated by images, the bone fusion and screw placement route were evaluated with CT reconstruction image. Results: The mean operation time was 110-185min(145±35min), and the average blood loose was 35-85ml(58±18ml). There were total 66 atlas lateral mass screws, 41 reverse axis pedicle screws and 25 axis vertebrae body screws. Among them, there were 2 reverse axis pedicle screws violated into the vertebral artery foramen, leading to cerebellum thrombosis, and the other screws were all in right place. 1 patient showed soft tissue infection after operation and then the TARP plate was taken off and changed into posterior instructation. Postoperative CT image showed the dens of axis could be pulled down form the magnum foramen to gain reduction ideally, the compressions were resolved effectively. The ADI changed to 0.2-4.5mm(2.3±2.1mm), the VAAI changed to 0.60-0.84(0.74±0.08), the CMA changed to 140°-178°(157°±15°). There were statistical differences between post and pre- operation(P<0.01), and the sypmptoms of limbs numbness and weakness improved more greatly than preoperation. The JOA scores changed to 13-16(15.2±0.9) in the third month after operation, and reached to 13-17（15.3±0.8） at the final follow-up, which all showed statistical differences compared with the preopeation(P<0.01). Conclusions: It is an effecitve operation for treatment of basilar invagination associated with atlantoaxial through distracting and reducing the atlas-axis facet joint and implanting struct allograft bone by transoral approach, however with some risk and difficulty of surgery, which should only be carried out under stricted indications and with perioperative cares. 【Key words】 Basilar invagination; Atlantoaxial dislocation; Transoral approach; Reduction; Fusion; Internal fixation