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. Follow-up 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%) or group B (≥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.
Keywords: Basilar invagination; Decompression; Internal fixation; Transoral.
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