Atlantoaxial Joint Distraction for the Treatment of Basilar Invagination: Clinical Outcomes and Radiographic Evaluation

OBJECTIVE: To investigate the causes of partial remission in patients with basilar invagination (BI) and irreducible atlantoaxial dislocation (IAAD) treated with transoral atlantoaxial reduction plate (TARP) without odontoidectomy and quantify the distance of odontoid descent.METHODS: Between August 2010 and July 2012, 22 consecutive patients with BI with IAAD who underwent TARP surgery were reviewed. The preoperative and postoperative radiographic parameters were evaluated. Followup data and the symptom treatment interval (STI), defined as the interval between the onset of symptoms and surgical treatment, were assessed. Neurological function was evaluated as neurologic improvement, defined as ([Postoperative Japanese Orthopedic Association (JOA) score] - [Preoperative JOA score])/(17 - [Preoperative JOA score]). The patients were assigned to group A (= 50%) based on their level of neurologic improvement.RESULTS: All 22 patients improved clinically to varying degrees. The mean preoperative STI was 105.6 +/- 67.6 months for group A and 45.3 +/- 46.7 months for group B (P < 0.05). There were no significant between-group differences in follow-up (P > 0.05) or with respect to radiographic parameters (P > 0.05). Persistent brainstem compression was observed in 1 patient, whose symptoms were not adequately relieved after revision surgery (transoral odontoidectomy and posterior decompression and fusion). No fixation failure was observed.CONCLUSIONS: Descent of the odontoid process is useful for treating basilar invagination. TARP surgery without odontoidectomy may pull the dens caudally and ventrally to achieve sufficient decompression of the spinal cord. Neurologic improvement may be associated with STI.

目的：探讨未行齿状突切除术的经口寰枢椎复位钢板（TARP）治疗寰枢椎脱位（IAAD）合并颅底凹陷症（BI）患者部分缓解的原因，并量化齿状突下降的距离。 方法：回顾2010年8月至2012年7月连续22例接受TARP手术的IAAD合并BI患者。评估术前和术后的影像学参数。评估随访数据以及症状治疗间隔（STI，定义为症状出现与手术治疗之间的间隔）。神经功能评估为神经功能改善，定义为（[术后日本骨科协会（JOA）评分]-[术前JOA评分]）/（17 - [术前JOA评分]）。根据神经功能改善水平将患者分为A组（≥50%）。 结果：22例患者临床均有不同程度改善。A组平均术前STI为105.6±67.6个月，B组为45.3±46.7个月（P<0.05）。随访（P>0.05）以及影像学参数方面组间无显著差异（P>0.05）。1例患者观察到持续脑干受压，其在翻修手术（经口齿状突切除术及后路减压融合术）后症状未充分缓解。未观察到固定失败。 结论：齿状突下降对治疗颅底凹陷症有益。未行齿状突切除术的TARP手术可将齿状突向尾侧和腹侧牵拉，以实现对脊髓的充分减压。神经功能改善可能与STI相关。