Occipitocervical fusion with relief of odontoid in

Authors: Tetsuya Yoshizumi Hidetoshi Murata Yuriko Ikenishi Mitsuru Sato Hajime Takase Kensuke Tateishi Satoshi Nakanowatari Jun Suenaga Nobutaka Kawahara

Publish Date: 2014/02/20

Volume: 37, Issue: 3, Pages: 519-525

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Abstract

A 65yearold woman presented with basilar invagination manifesting as neck pain dysesthesia around the lips and truncal ataxia The radiological findings demonstrated invagination of the odontoid process into the medulla oblongata and vertical atlantoaxial subluxation with C1 assimilation The clivoaxial angle was 88° and the cervicomedullary angle was 115° indicating severe basilar invagination We planned occipitocervical fusion with atlantoaxial distraction using a cylindrical titanium cage C2 pedicle screws were inserted and the atlantoaxial joint was opened to translocate the odontoid process downward A cylindrical titanium cage packed with local bone graft was inserted into the opened facet joint space OccipitalC2 fusion was completed by fastening the occipital bone plates with pedicle screws using titanium rods Postoperatively the apex of the odontoid process descended by 7 mm and the clivoaxial and cervicomedullary angles opened to 112° and 125° respectively Invagination of the odontoid process into the medulla oblongata was relieved The preoperative symptoms improved and she remained symptomfree without requiring anterior decompression over 2 years Bone fusion of the atlantoaxial joints was completed with sustained facet distraction 12 months after the surgery and adequate relief of the basilar invagination was maintained The atlantoaxial distraction method using a cylindrical titanium cage can be a useful option in posterior fusion surgery for basilar invaginationBasilar invagination is a manifestation of ‘vertical’ atlantoaxial instability 12 Incompetence of the muscles of the nape of the neck secondary to trauma or poor muscle nutrition may be the pathogenetic cause Listhesis of the facet of atlas over the facet of axis results in superior and posterior migration of the odontoid process in relationship to the arch of atlas resulting in basilar invagination and atlantoxial dislocation 14 The atlantoaxial dislocation in such cases is not freely mobile and reducible and was earlier referred to as ‘fixed’ atlantoaxial dislocation 7 The most defining feature that probably revolutionised the treatment of ‘basilar invagination’ was the identification of the fact that atlantoaxial joints in such cases are not fixed but are functional and mobile and more importantly are reducible 1 5 9 Instability of the atlantoaxial joint and microtrauma inflicted to critical neural structures by repeated abnormal movements of the odontoid process are the cause of neurological deficits and are more important than structural malformation or deformation that it results 9 The subtleness and longstanding nature of process of listhesis result in remarkable natural readjustments that lead to a host of musculoskeletal and neural alterations all aimed at reducing the impact of instability and in reducing the neural compromise Torticollis short neck platybasia bone fusions and several similar morphological alterations that are frequently observed in cases with basilar invagination are all potentially reversible following surgical procedure that stabilizes the atlantoaxial joint 9Opening of the atlantoaxial joint denuding of the articular cartilage stuffing of bone graft within the confines of the atlantoaxial joint and subsequent plate/rod and screw fixation of C1 and C2 pars/pedicle/facets form the basis of our fixation technique 6 8 The description of feasibility and safety of sectioning of the C2 ganglion whenever necessary to obtain wide exposure of the region to complete all the steps of the fixation technique is another crucial step in the advancement of surgery in the craniovertebral region 4 The exposure of the atlantoaxial joint in cases with basilar invagination is significantly more difficult when compared to normally located joints The joints are rostrally located and dissection in the region amidst large venous complexes can be tedious Sectioning of C2 ganglion particularly in such cases can assist in providing a panoramic view to the joint and facets so that the entire surgical procedure can be done under direct surgical visionDistraction of facets of the spine by employing metal spacers is emerging to be a robust technique for provision of stability and realignment 10 11 Impaction of metal spacer within the atlantoaxial joint provides significant stability to the region 2 Distraction of the facets by the spacers at the site of fulcrum of craniovertebral movements results in reduction of basilar invagination and restoration of craniovertebral and spinal alignment 4 13 However as our experience in the treatment of basilar invagination in increasing we have realised that it is more important to obtain stability of the atlantoaxial region than to aim at morphological reduction in basilar invagination With that aim in mind introduction of bone graft within the confines of the joint and in the appropriately prepared suboccipital region is crucially importantThe authors in the present manuscript have resorted to inclusion of the occipital bone in the fusion construct The use of short plates/rods and segmental fixation at the point of fulcrum of movements as is done for atlantoaxial fixation is biomechanically far superior when compared to the use of long plates/rods necessary for occipitocervical fixation The use of long length screws as is possible in the strong and largely cortical bone facets of atlas and axis is much more robust when compared to the use of multiple short screws in the suboccipital squama Inclusion of the occipital bone and subaxial spinal segment not only is unnecessary but can significantly reduce the strength of the implant and adversely affect the neck movements and neck growth 3 Manipulation of the facets that is the point of pathogenesis of basilar invagination is far more effective than remote manipulation of the occipital bone Although the technique of exposure of the atlantoaxial joint is relatively difficult and tedious if learnt appropriately and performed adequately it can lead to gratifying surgical results in this relatively complex and daunting clinical situation

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