Revision surgery for basilar invagination associated with atlas-axis dislocation after failed magnum foramen decompression

English Keywords:Basilar invagination  Atlas-axis dislocation  Magnum foramen decompression  Transoral anterior reduction plate

English Abstract:

  【Abstract】 Objectives: To investigate the revision surgery for basilar invagination associated with atlas-axis dislocation after failed magnum foramen decompression. Methods: From February 2006 to October 2010, 9 cases suffering from basilar invagination associated with atlas-axis dislocation were included in this series. All cases underwent posterior magnum foramen decompression in other hospitals prior to admission into our institute, and all had neurofunction deteriorated. All patients presented with difficulty in standing or walking and limb numb or weakness. The preoperative JOA score was 7-11(average, 7.8±2.1). Bone defect due to decompression around the magnum foramen was evidenced in the image, and all cases had atlas-axis dislocation with the brain stem compressed by the odontoid process of axis. The brain stem- medulla oblongata angle was 105°-138°(average, 125±11°). Revision surgery of transoral anterior reduction and fixation with transoral anterior reduction plate（TARP） was performed. The JOA score was used to evaluate the neurofucntion, and the brain stem-spinal angle was measured for evaluating the decompression. Results： All cases underwent the revision surgery successfully with no complication such as dura rupture, infection et al, and all 9 cases were followed up for 10-26 months(mean, 14 months) and all had neurofunction improved with different extent. The JOA scores improved from 7.8±2.1 to 13.7±1.8 three months after revision surgery with the improvement rate of 64.1%. The stem-spinal angles improved from 125°±11° to 148°±15° three months after revision surgery. At final follow-up, the average JOA score was 14.4±2.1 with improvement rate of 71.7%, and the brain stem-medulla oblongata angle maintained well. 8 cases had bony union in CT scan 6 months after revision surgery. 1 patient was subjected to the second revision due to instrument failure after an injury to the head,and got bony fusion 10 months later. Conclusions: Posterior magnum foramen decompression can not decompress the ventral side of brain stem， which cannot be used for basilar invagination complicated with atlas-axis dislocation, while anterior transoral reduction and instrumentation can manage this effectively and can be used as a salvation to the failed posterior magnum foramen decompression.