title: The importance of atlantoaxial fixation after odontoidectomy.
abstract: OBJECT Although anterior odontoidectomy has been widely accepted as a procedure for decompression of the craniovertebral junction (CVJ), postoperative biomechanical instability has not been well addressed. There is a paucity of data on the necessity for and choice of fixation. METHODS The authors conducted a retrospective review of consecutively treated patients with basilar invagination who underwent anterior odontoidectomy and various types of posterior fixation. Posterior fixation included 1 of 3 kinds of constructs: occipitocervical (OC) fusion with atlantoaxial (AA) fixation, OC fusion without AA fixation, or AA-only (without OC) fixation. On the basis of the use or nonuse of AA fixation, these patients were assigned to either the AA group, in which the posterior fixation surgery involved both the atlas and axis simultaneously, regardless of whether the patient underwent OC fusion, or the non-AA group, in which the OC fusion construct spared the atlas, axis, or both. Clinical outcomes and neurological function were compared. Radiological results at each time point (i.e., before and after odontoidectomy and after fixation) were assessed by calculating the triangular area causing ventral indentation of the brainstem in the CVJ. RESULTS Data obtained in 14 consecutively treated patients with basilar invagination were analyzed in this series; the mean follow-up time was 5.75 years. The mean age was 53.58 years; there were 7 males and 7 females. The AA and non-AA groups consisted of 7 patients each. The demographic data of both groups were similar. Overall, there was significant improvement in neurological function after the operation (p = 0.03), and there were no differences in the postoperative Nurick grades between the 2 groups (p = 1.00). According to radiological measurements, significant decompression of the ventral brainstem was achieved stepwise in both groups by anterior odontoidectomy and posterior fixation; the mean ventral triangular area improved from 3.00 ± 0.86 cm2to 2.08 ± 0.51 cm2to 1.68 ± 0.59 cm2(before and after odontoidectomy and after fixation, respectively; p < 0.05). The decompression gained by odontoidectomy (i.e., reduction of the ventral triangular area) was similar in the AA and non-AA groups (0.66 ± 0.42 cm2vs 1.17 ± 1.42 cm2, respectively; p = 0.38). However, the decompression achieved by posterior fixation was significantly greater in the AA group than in the non-AA group (0.64 ± 0.39 cm2vs 0.17 ± 0.16 cm2, respectively; p = 0.01). CONCLUSIONS Anterior odontoidectomy alone provides significant decompression at the CVJ. Adjuvant posterior fixation further enhances the extent of decompression after the odontoidectomy. Moreover, posterior fixation that involves AA fixation yields significantly more decompression of the ventral brainstem than OC fusion that spares AA fixation.
authors.affiliation: Department of Neurosurgery, Neurological Institute, and.|School of Medicine and.
authors.forename: Peng-Yuan
authors.initials: PY
authors.lastname: Chang
authors.affiliation: Department of Neurosurgery, Neurological Institute, and.|School of Medicine and.
authors.forename: Yu-Shu
authors.initials: YS
authors.lastname: Yen
authors.affiliation: Department of Neurosurgery, Neurological Institute, and.|School of Medicine and.
authors.forename: Jau-Ching
authors.initials: JC
authors.lastname: Wu
authors.affiliation: Department of Neurosurgery, Neurological Institute, and.|School of Medicine and.
authors.forename: Hsuan-Kan
authors.initials: HK
authors.lastname: Chang
authors.affiliation: Department of Neurosurgery, Neurological Institute, and.|School of Medicine and.|Institute of Pharmacology, National Yang-Ming University; and.
authors.forename: Li-Yu
authors.initials: LY
authors.lastname: Fay
authors.affiliation: Department of Neurosurgery, Neurological Institute, and.|School of Medicine and.|Molecular Medicine Program, Taiwan International Graduate Program, Academia Sinica, Taipei, Taiwan.
authors.forename: Tsung-Hsi
authors.initials: TH
authors.lastname: Tu
authors.affiliation: Department of Radiology, Taipei Veterans General Hospital.|School of Medicine and.
authors.forename: Ching-Lan
authors.initials: CL
authors.lastname: Wu
authors.affiliation: Department of Neurosurgery, Neurological Institute, and.|School of Medicine and.
authors.forename: Wen-Cheng
authors.initials: WC
authors.lastname: Huang
authors.affiliation: Department of Neurosurgery, Neurological Institute, and.|Department of Radiology, Taipei Veterans General Hospital.|School of Medicine and.
authors.forename: Henrich
authors.initials: H
authors.lastname: Cheng
keywords: AA = atlantoaxial; BI = basilar invagination; CVJ = craniovertebral junction; OC = occipitocervical; atlantoaxial fixation; cervical; craniovertebral junction; occipitocervical fixation; odontoidectomy