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CASE REPORT
Year : 2017  |  Volume : 65  |  Issue : 5  |  Page : 1068-1075

Simultaneous odontoid excision with bilateral posterior C1-2 distraction and stabilization utilizing bilateral posterolateral corridors and a single posterior midline incision


Department of Neurosurgery, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India

Date of Web Publication6-Sep-2017

Correspondence Address:
Arun K Srivastava
Department of Neurosurgery, Sanjay Gandhi Postgraduate Institute of Medical Sciences, Lucknow, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/neuroindia.NI_819_17

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 » Abstract 

A simultaneous odontoid decompression and bilateral posterior atlanto-axial facetal distraction, C1-2 joint spacer/bone graft placement and stabilization may be performed utilizing the ‘posterior-only’ approach. This procedure may be performed utilizing a single posterior midline incision, a bilateral posterior approach to the C1-2 facet joints and a bilateral posterolateral approach to the odontoid process and C2 body. It may be carried out in situations where a C1-2 non-reduction/partial reduction using a ‘posterior alone’ procedure is anticipated due to the complex bony/soft tissue configuration anterior at the thecal sac existing at the cervicomedullary junction. In the four cases described in this report, the procedure led to a successful circumferential decompression at the level of foramen magnum along with posterior C1-2 facetal distraction and stabilization in various complex craniovertebral junction anomalies (atlantoaxial dislocation [AAD] and/or a high basilar invagination [BI] associated with a significantly retroverted dens, along with a rotatory component, due to grossly asymmetrical facet joints). This technique may also be utilized in those diseases that result in an anterior osteoligamentous mass at the CVJ associated with C1-2 instability.


Keywords: Atlantoaxial dislocation, craniovertebral instability, craniovertebral junction, posterior atlantoaxial distraction, posterior stabilization, surgery
Key Message:
Odontoid decompression along with bilateral posterior atlanto-axial facetal distraction, C1-2 joint spacer placement and stabilization may be performed utilizing the ′posterior-only′ approach through a single posterior midline incision. This has the potential to relieve both anterior and posterior thecal compression at the C1-2 level as well as to achieve stabilization in the case of a complex craniovertebral junction anomaly; and, in lesions at the CVJ that result in an extensive anterior osteoligamentous mass with C1-2 instability.


How to cite this article:
Srivastava AK, Behari S, Sardhara J, Das KK. Simultaneous odontoid excision with bilateral posterior C1-2 distraction and stabilization utilizing bilateral posterolateral corridors and a single posterior midline incision. Neurol India 2017;65:1068-75

How to cite this URL:
Srivastava AK, Behari S, Sardhara J, Das KK. Simultaneous odontoid excision with bilateral posterior C1-2 distraction and stabilization utilizing bilateral posterolateral corridors and a single posterior midline incision. Neurol India [serial online] 2017 [cited 2021 Apr 15];65:1068-75. Available from: https://www.neurologyindia.com/text.asp?2017/65/5/1068/214090


The C1-2 joint manipulation [1],[2],[3] based upon the Cartesian coordinates,[4],[5] the utilization of three-dimensional computed tomograms [4] and three-dimensional imaging and printer models [6],[7] has led to the addressal of atlantoaxial dislocation with or without basilar invagination utilizing the ‘posterior only approach’ to the craniovertebral junction (CVJ). There still are certain clinical situations [8],[9] where a transoral approach is required, and in these situations, the transoral excision of the odontoid is either performed under the same anaesthesia, utilizing the initial supine position followed by a posterior stabilization and fusion in prone position;[10] or, the transoral surgery is performed subsequently as a salvage procedure to alleviate the persistent anterior neuraxial compression, if there is lack of clinical improvement after the posterior distraction and stabilization surgery.[4],[8] However, both these techniques involve two procedures; subjecting these often poorly nourished patients with advanced myelopathy and extremely compromised respiratory reserve to two surgeries in the same or in a subsequent setting, definitely adds to the morbidity of the procedure.[8],[10] The transoral surgery is through a potentially infected oral cavity, and often leads to pharyngeal wound dehiscence and velopharygeal insufficiency. The vertebral artery is not visualised but is always in potential danger, especially if a simultaneous torticollis due to coexisting cervical scoliosis is also present.[10],[11]

We describe a surgical technique wherein a simultaneous odontoid decompression and bilateral posterior atlanto-axial facetal distraction, C1-2 joint spacer/bone graft placement and stabilization may be performed utilizing the ‘posterior-only’ approach, using a single posterior midline incision, a bilateral posterior approach to the C1-2 facet joints, and a bilateral posterolateral approach to the odontoid process and C2 body, under the same anesthesia. This is performed in situ ations where a C1-2 non-reduction/partial reduction using a ‘posterior alone’ procedure is anticipated due to a complex bony and/or soft tissue configuration present anterior at the thecal sac at the cervicomedullary junction.


 » Surgery Top


Anatomical principles

The junction between the odontoid process and the C2 vertebra is defined by the upper border of the pedicles of the axis vertebra. Following the C1-2 facetal manipulation on both sides of the axis vertebra,[1],[2] if the upper border of the C2 pedicle is traced along both the sides, lateral exposure of the surface of the odontoid process is obtained. The odontoid process may then be drilled utilizing a high speed drill (with a diamond burr) from both the sides, connecting the two corridors in the midline, at the C1-2 level, while keeping the posterior cortical surface of C2 vertebra-anterior cervicomedullary dural interface directly in view [Figure 1]a, [Figure 1]b and [Figure 2].
Figure 1: (a) Oblique view of the C1 and C-2 vertebrae from the posterolateral aspect demonstrating that the possibility of odontoid exposure (blue shaded area) is further increased by performing the C-1/C-2 joint distraction, and by removal of the posterior arch of the  Atlas More Details (shaded area) to a point just short of the medial aspect of the vertebral artery groove on its superior border. The green arrow demonstrates the trajectory of approach for drilling the odontoid process from the posterolateral aspect. (b) Both the orange arrows mark the bilateral approach to drilling the odontoid and the contiguous C2 body (shaded area). ‘S’ represents the superior facetal surface of the same side as the surgeon's position, while ‘O’ represents the superior facetal surface of the opposite side. Thus, a bilateral trajectory is adopted coursing along the superior surface of the pedicle of axis on both the sides

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Figure 2: Three dimensional CT scan of the CVJ with vertebral artery angiogram showing co-dominant vertebral artery (horizontal white arrows) with a bifid posterior arch of atlas. The pars interarticularis of the axis (*) is thin on both the sides. In this case, while drilling the bifid atlas, one should stop short of the superior margin of its posterior arch to avoid encountering the horizontal segment of the vertebral artery stationed there; and, the vertical portion of the third segment of the vertebral artery is also seen just beyond the lateral margin of the C1-2 facet joints (#). The posterolateral trajectory ((oblique black arrows on both sides) to the odontoid (o) is along the superior surface of the C2 pedicles (^) and is facilitated by removal of the middle two-thirds of the posterior arch of atlas

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Surgical steps

The patient is intubated utilizing a flexo-metallic endotracheal tube intubation and placed prone on chest and pelvic bolsters. The head of the patient is placed on a horse-shoe head rest in neutral position, taking care that there is no compression on both the eyes. The patient's torso is adequately supported by cushioned metallic side-supports fixed on the table to facilitate the tilting of the table during surgery without displacing the patient's position. A cervical traction is applied with the traction weight being 7-10% of body weight utilizing Gardner-Wells tongs, maintaining the neck in the neutral position.[12]

A midline vertical skin incision from the inion to the C 3 - C4 spinous process is made. The fascia is opened in a ‘Y’ shaped fashion, leaving an inverted triangular- shaped fascia (∇) attached to the occipital bone to facilitate a better closure at the end of surgery. The midline avascular ligamentum nuchae is divided. Successive layers of muscles over the occipital bone are separated utilizing a subperiosteal dissection. The posterior rim of foramen magnum with the occipitalised C1 (or the free C1 posterior arch) as well as the lamina of C2 are exposed until the C1-2 facet joints on either side. Care is taken to ensure that the subperiosteal dissection of the posterior elements of atlas and axis extends until, but not beyond, the lateral masses of C1 and C2 vertebrae, and that the lateral half of the upper margin of the C1 posterior arch is not exposed to avoid injuring the third part of the vertebral artery present at these locations.[11],[13] Incurving posterior rim of the foramen magnum (if present, along with the occipitalised atlas) may be drilled at this stage. Following the medial border of pars interarticularis of C2 leads to the C1/C2 joint space. The C2 nerve roots should be sectioned to expose bilateral joint spaces. The pedicle of the axis on either side is exposed by a sharp dissection of the periosteum. The C1/C2 joint capsule is opened and denuded, the joint space is distracted, and either a spacer or a wedge bone graft is placed within the joint space [Figure 3]a. The distraction and manipulation of C1/C2 articular masses is carried out to achieve the realignment of the atlas and axis vertebrae to their desired positions but the screws and rods are not placed as they would interfere with the operative trajectory required for the odontoid excision. If acceptable reduction or realignment is not achieved with the posterior C1-2 distraction, and the thecal sac is still tented posteriorly due to anterior compression, then the operative approach is suitably extended to include excision of the odontoid. The operating table, with the patient's torso securely stabilised utilizing cushioned side supports, is tilted towards the opposite side by 15-20 degrees. Dissecting the soft tissue brings the entire height of the lateral surface of the odontoid process in view. Gentle drilling of the odontoid process is carried out with the help of a diamond drill of 3mm diameter mounted on a long and narrow, and slightly oblique handle [Figure 3]b. If required, the part of the cortical bone at the postero-superior aspect may also be cut with the help of a fine chisel and hammer. The same procedure is repeated on the opposite side until the odontoid is completely removed. The posterolateral part of the remnant apical part of the odontoid process often remains retracted by the apical and alar ligaments, and this last remnant may have to be gently pulled down to divide the soft tissue structures [Figure 3]c. The posterior cortical margin of the odontoid may be made paper-thin using the high-speed drill but not actually breached initially. Using dissectors, it may then be lifted off the dura. This ensures dural protection and prevents its non-uniform bulging into the operative field that may make the bulged out-pouches of the dura from cortical bone vulnerable to breech. Once the odontoid is completely drilled out from both the sides [Figure 3]d, either a C1/C2 or an occipito-cervical stabilization is performed in the same stage. Screws are placed in the lateral mass of C1 and in the pars interarticularis/pedicle of C2 and connected with rods on both the sides. If the occipital bone is included in the fusion, the rods extend to a plate fixed on the midline occipital squama utilizing occipital screws. Onlay bone grafts harvested from the iliac crest are placed over the decorticated posterior surfaces of the C1-2 facet joints, the squama of the occipital bone and the posterior C1 arch and lamina of C2. The traction weight is removed immediately following the distraction and fusion procedure. Closure of the surgical wound is performed in layers. A hard cervical collar is placed to stabilize the neck for a period of three months.
Figure 3: Intraoperative images showing (a) spacer placement in the right C1-2 facet joint space; (b) Drilling of the odontoid process from the posterolateral approach after removal of the middle part of the C1 arch; (c) Removal of the apical remnant of the drilled odontoid process using biopsy forceps; and, (d) The black curved arrow shows the trajectory of the unilateral drilling along the superior surface of the C2 pedicle lateral to the dural sac

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 » Case Reports Top


Case 1

A 16-year old male patient presented with progressive spastic quadriparesis with difficulty in walking. His preoperative Japanese Orthopedic Association Scale score modified to the Indian settings [modified JOAS score][6] was 6. His preoperative dynamic lateral radiographic images of the CVJ in flexion and extension showed an irreducible AAD with os odontoideum [Figure 4]a. The AAD did not reduce despite optimum C1/C2 joint distraction due to the presence of a small bony ossicle insinuated between the antero-inferior margin of the medial aspect of the C1 facet and the dislocated anterior arch of atlas, and the facet and body of axis. The three-dimensional (3-D) multiplanar computed tomographic (CT) images of the CVJ showing the bony ossicle situated between the anterior margin of C1 and C2 facet surfaces, extending into the space between the inferior margin of the dislocated anterior arch of atlas and the body of axis [Figure 4]b. The AAD and the presence of the bony ossicle between C1-2 were confirmed during the intraoperative C-arm imaging. He underwent a posterior C1-2 distraction and spacer placement followed by an posterolateral approach to the anteroinferior part of the C1-2 facet joint on the right side. The bony spicule was removed under direct vision after drilling of the small overlying anteroinferior margin of the right facet joint and the inferior border of the anterior arch of atlas. Screws were placed in the lateral mass of atlas and the pars interarticularis of axis. Following the tightening of ini over the rod placed in the screw head, the C1-2 facet as well as the C1-2 vertebrae retained their proper alignment, ensuring reduction of AAD. Onlay bone grafts harvested from the iliac crest were placed over the decorticated posterior surfaces of the C1-2 facet joints, the squama of the occipital bone and the posterior C1 arch and lamina of C2 [Figure 4]c. There was a small dural breech on the lateral surface of the dura that could be overcome with sutures and a fascial patch graft. The postoperative CT axial image of the CVJ showed an adequate reduction of AAD. He retained his postoperative power but developed a small pressure sore in the neck at the site of the margin of the hard cervical collar that was continually worn for 3 months. At a follow up visit after 3 months, his modified JOAS score had improved to 8 and he had considerable improvement in his spasticity. His follow up plain radiographs of the CVJ showed a stable C1-2 union with no AAD and an adequate spinal canal at the upper cervical spine.
Figure 4: Patient 1 (a) The preoperative lateral fluoroscopy of the CVJ showing an irreducible AAD with os odontoideum (black horizontal arrow). The AAD was not reducing despite C1/C2 joint distraction due to the presence of a small bony ossicle (blue vertical arrow) insinuated between the antero-inferior margin of the medial aspect of the C1 facet along with the dislocated anterior arch of atlas, and the facet and body of axis; (b) Three dimensional CT scan of the CVJ showing the bony ossicle between anterior margin of C1 and C2 facets (curved red arrow) reaching up to the space between the inferior margin of the dislocated anterior arch of atlas and the body of axis; and, (c) Postoperative CT axial image of the CVJ showing that once the bony ossicle was removed utilizing the posterolateral approach, from between the anterior C1-2 facet margins and from between the C1 anterior arch and the body of axis, an adequate reduction of AAD and posterior C1-2 stabilization was possible using screws placed in lateral mass of C1 and body of axis and connected by rods

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Case 2

A 32-year old male patient presented with progressive spastic quadriparesis for 5 years with a mild neck torticollis. His preoperative modified JOAS score was 8. His CT-CVJ sagittal dynamic images were suggestive of non-reducible AAD associated with a rotational component with a retroverted odontoid that was also resulting a mild BI [Figure 5]a. The coronal CT images showing asymmetrical articular masses with joint asymmetry and vertical joint orientation [Figure 5]b. The axial image at the level of the CVJ showed an increased atlanto-dental interval [Figure 5]c. The successful performance of bilateral C1-2 joint distraction, spacer placement, odontoid drilling from both the sides and posterior C1-2 stabilization was carried out. A small dural breech occurred during the drilling process close to the origin of the C2 nerve root that could be repaired with sutures and a muscle-fascial patch. The postoperative parasagittal CT images [Figure 5]d and [Figure 5]e showed spacers between the C1–C2 joints on either side with C1 lateral mass screw and C2 pars interarticularis screw placement. The postoperative CT axial [Figure 5]f and sagittal [Figure 5]g images showed the adequately drilled odontoid process using the posterolateral approach. The postoperative period was uneventful and at a follow up period of three months, the internal orthosis appeared stable on radiological evaluation. The patient had improved to a modified JOAS score of 10.
Figure 5: Patient 2 (a) CT-CVJ sagittal images is suggestive of non-reducible AAD associated with a rotational component with a retroverted odontoid that is causing mild basilar invagination. (b) Coronal images showing asymmetrical articular masses with joint asymmetry and vertical C1-2 facet joint orientation; (c) Axial image showing an increased atlanto-dental interval; (d and e) Parasagittal images showing spacers between the C1–C2 joints on either side with C1 lateral mass screw and C2 pars interarticularis screw placement. (f) Axial; and, (g) Sagittal images showing the drilled odontoid process using the posterolateral approach

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Case 3

A 32-year old male patient presented with a 12-year history of progressive spastic quadriparesis and respiratory difficulty for the past one month, due to which he had difficulty in walking. He had a short neck and torticollis since birth. His modified JOAS score was 9. His CT-CVJ sagittal image was suggestive of a retroverted odontoid with a mild basilar invagination [Figure 6]a. The axial images showed a significant increase in the atlanto-dental interval with coexisting C1-2 rotational component [Figure 6]b. He underwent bilateral C1-2 joint distraction, spacer placement, odontoid drilling from both the sides and posterior C1-2 stabilization. The postoperative sagittal [Figure 6]c, axial [Figure 6]d and coronal CT images [Figure 6]e showed the drilled odontoid with spacers within the C1-2 facet joint space, and the vertebral screws well-placed in the C1 and C2 lateral masses. The lateral dural breech during the drilling could be well-repaired. There was an immediate postoperative improvement in his tightness and weakness, and his respiratory difficulty and torticollis also showed improvement. At a follow up visit after 6 months, his modified JOAS score had improved to 12 and there was considerable improvement in his walking difficulty although the power and spasticity had not completely normalised.
Figure 6: Patient 3 (a) CT-CVJ sagittal image suggestive of an occipitalised atlas, a retroverted odontoid with a mild basilar invagination causing canal compromise; (b) Axial images showing the significant atlanto-dental interval with coexisting C1-2 rotational component. (c) Sagittal; (d) Axial; and (e) Coronal images undertaken in the postoperative period showing the drilled odontoid with spacers within the C1-2 facet joint space and screws placed in the C1 and C2 lateral masses

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Case 4

This 18-year old male patient had significant spasticity, weakness and urinary incontinence for the past two years. He was unable to walk even with full support. His modified JOAS score was 8. His T2-weighted sagittal magnetic resonance (MR) image was suggestive of significant reduction in the effective canal diameter due to a retroverted odontoid [Figure 7]a; His CT sagittal [Figure 7]b and, axial images [Figure 7]c showed platybasia along with AAD and occipitalised atlas. During bilateral C1-2 joint distraction, spacer placement, odontoid drilling from both the sides and posterior C1-2 stabilization, there was considerable difficulty in drilling the odontoid, especially its posterosuperior portion. A small remnant of the apical tip of the odontoid could not be removed but was left in situ as it was very close to the dura and was not causing any canal impingement. He required a postoperative tracheostomy and prolonged ventilatory support and remained on clean intermittent catheterization due to his urinary incontinence. At follow up after three months, there was no significant improvement in his neurological status and he retained his modified JOAS score of 8. His sagittal [Figure 7]d, coronal [Figure 7]e, parasagittal [Figure 7]f and axial [Figure 7]g postoperative CT images showed the drilled odontoid with the C1-2 joint distraction, bone graft placement within the facet joint, and C1 lateral mass and C2 pars interarticularis stabilization. A small apical segment of the odontoid remnant located on the postero-supero-lateral position of the cavilty created by drilling the odontoid, was still seen but was not causing any bony impingement on the thecal sac.
Figure 7: (a) T2 weighted MR image, sagittal view suggestive of significant reduction in effective canal diameter due to a retroverted odontoid; (b) CT sagittal; and, (c) axial image showing platybasia along with AAD and occipitalised atlas; (d) Sagittal; (e) Coronal; (f) Parasagittal; and, (g) Axial follow up images showed the drilled odontoid with a simultaneous performed C1-2 joint distraction, bone graft placement and C1 lateral mass and C2 par-interarticularis stabilization. A small apical segment of the odontoid remnant arising from its postero-supero-lateral portion (white arrow) is still seen following the odontoid decompression but is not causing any bony impingement

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 » Discussion Top


The surgical management of CVJ anomalies is persistently evolving, especially after the unique concept of ‘anterior anomalies being addressed utilizing the anterior approach’ propounded by Dr. Arnold Menezes,[1] followed by the "C1/C2 joint distraction and stabilization’ by a ‘posterior only approach’ described by Dr. Atul Goel.[2] The posterior C1-2 facetal manipulation and stabilization in atlanto-axial dislocation (AAD), basilar invagination and rotatory AAD [1],[2],[4],[14],[15] has significantly reduced the need for an anterior decompression in this subset of cases.

Clinical situations where anterior decompression may still be warranted along with posterior C1-2 stabilization

The requirement of anterior decompression of the odontoid may still be needed in the case of an irreducible os odontoideum that is well-dislocated anterior to the body of axis, and is prevented from attaining its reduced position due to the fibrous or bony adhesions, or an additional bony remnant between the os odontoideum and the body of axis, as seen in one of our cases. In a very oblique and retroverted odontoid in the presence of AAD, or a very high BI that is causing a significant thecal compression, even maximal C1-2 facet distraction will still be unable to bring about complete C1-2 reduction as well as odontoid descent from its invaginated position within the foramen magnum, and achieve an adequate spinal decompression.[4],[8] In patients with gross rotatory C1-2 dislocation associated with AAD and C1-2 facetal locking, an asymmetrical thecal compression (especially in the situations where grossly asymmetrical and vertical joints coexist that may also mandate facetal drilling)[16] may be observed and even the maximal joint manipulation may not be enough to bring about relief from the bony compression and a proper bony alignment. Following surgery for stabilization of the reducible AAD utilizing the C1-2 facet posterior distraction and stabilization, if the C1-2 vertebrae remain in a persistently dislocated position relative to one another, then an additional anterior decompressive surgery will be required [4],[8],[10] If this situation may be anticipated during surgery, immediately following the posterior distraction and stabilization (by simultaneously checking the operative situation using C-arm, O-arm or neuronavigational images), an odontoid decompression may be simultaneously carried out utilizing the posterolateral approach described in this article. In type B basilar invagination with  Chiari malformation More Details and an associated small posterior fossa, the entire anterior and posterior margin of the foramen magnum is insinuated into the foramen magnum causing foramen magnum stenosis.[17] This condition is often associated with a fused occipital condyle-C1 lateral mass complex that may be atrophic, grossly asymmetrical and oblique.[17] A C1-2 distraction procedure is, therefore, often not possible to the extent required and a simultaneous odontoid excision utilizing the posterolateral approach may be mandated. The presence of a large anterior pannus/osteoligamentous/retroodontoid mass in a patient with rheumatoid [18] or tuberculous AAD,[19] Morquio syndrome (mucopolysaccharidosis),[9] or even congential AAD (where the retroodontoid mass occurs due to a persisting instability)[20] may require the simultaneous anterior excision of the compressing mass along with the bilateral C1-2 posterior stabilization procedure under the same anaesthesia, utilizing the same posterior midline incision, C1-2 distraction, manipulation and spacer placement within bilateral facet joints, and an anterior decompression utilizing the posterolateral approach.

Surgical considerations and areas of caution

There are certain important surgical principles that are common to the technique of bilateral posterior C1-2 facet distraction, spacer placement and stabilization procedure as well as to its additional bilateral extension to perform the odontoid excision from the posterolateral corridor. A subperiosteal dissection along the bony surfaces of the C1-2 bones helps in avoiding venous bleeding from the paravertebral venous plexus in the region. The key to reaching the C1-2 facet joints on both the sides is to follow the medial border of pars interarticularis of the axis and to avoid performing soft tissue dissection along the lateral half of the superior border of posterior arch of atlas and lateral to the facets of axis, to avoid injuring the vertebral artery in that location.[11],[13] It is possible that due to anomalies like the congenital absence of foramen transversarium of the atlas, persistence of intersegmental artery or a low lying posterior inferior cerebellar artery below the foramen magnum, the vertebral artery may cross the posterior surface of the C1-2 facet joint either on one side or bilaterally, and may be more prone to injury during the posterior approach to this region. Thus, a comprehensive information regarding variations and the course of the vertebral artery utilizing a preoperatively performed multiplanar computed tomographic angiography with three dimensional reconstruction images is mandatory [Figure 2].[11] Its variable dominance, especially when associated with other coexisting CVJ anomalies, should be assiduously looked for, and on that side, the surgical dissection and stabilization should be undertaken with extra care. Bilateral C2 nerve roots need to be divided in order to obtain a lateral access to the C1-2 facet joints, and further to access the odontoid process situated in the midline from either side. This has not led to any disabling hypoaesthesia of the suboccipital region or an increase in the incidence of pressure sore in the suboccipital region, while the patients were being nursed in a supine position following their surgery.

There are certain unique considerations while the posterior approach is being extended to drill the odontoid process from either side. Excision of the C1 posterior arch and an approach along the upper surface of pedicle of axis after the tilting of table toward the opposite side (with the torso of the patient supported by the preoperative application of side supports arising as extensions from the operating table) helps in acquiring a posterolateral trajectory to the odontoid process. The narrow working corridor between the posterior pharyngeal wall and the vertebral column, that is, the prevertebral space, especially at the level of the posteriorly dislocated or a high-placed odontoid is addressed by performing the C-1-2 facet joint distraction and spacer/bone graft placement within the joint space prior to the odontoid drilling. However, the C1-2 screws and the rods are not placed prior to the odontoid drilling as they would restrict the posterolateral trajectory to the odontoid. The C1-2 facet joint distraction and C1-2 joint spacer/bone graft placement maintain the reduced position of the odontoid and change its curvature from a posteriorly directed one to a more vertical one. This change in the orientation of the odontoid to a more vertical one automatically creates more space between the odontoid-C2 body and the dura, and permits the passage of instruments and the drill handle to carry out the odontoid removal from both the sides [Figure 1] and [Figure 3]. This sequence of steps also helps to stabilize the C1-2 complex while the osteoligamentous decompression is taking place, and prevents the causation of recurrent compression of the thecal sac during surgical manipulation.

In our initial experience, dural breech often occurred while using the drill due to the infolding of the dura and its prolapsing into the cavity created by the drilled odontoid. The presence of rotatory C1-2 dislocation coupled with translational AAD makes drilling of the odontoid process easier from one side than the other. In addition, the consequent asymmetrical compression on the thecal sac makes the dura more vulnerable to be breeched on the side of greater compromise during the operative drilling of the odontoid from the lateral aspect.[14],[15] This complication could be reduced by protecting the dura and preventing its forward prolapse utilizing a curved dissector like the Penfield number 3 dissector to guard the dura during the odontoid drilling from the lateral aspect on both the sides. A uniform drilling made the posterior cortical margin of the odontoid paper-thin and its subsequent removal by elevating it from the underlying dura using a dissector also helped us in minimizing this complication in our subsequent patients. The dural breech occurred most frequently at the junction of the C2 nerve root with the lateral dural margin and required either a muscle-fascial patch kept adherent to the dura utilizing either fibrin glue, or sutures. The supero-medial obliquity of the approach, as is experienced in the anterior retropharyngeal approach,[21],[22],[23] made the superior and posterior part of the odontoid the most difficult part to drill, and the drilling posed further difficulty in the presence of BI with platybasia. The apex of the odontoid process is often attached to the clivus with apical and alar ligaments, and the retracted odontoid apical remnant attached to the apical ligament may have to be pulled down utilizing a biopsy forceps, along with the excision of the tethering ligament. In one of our patients, this resulted in a small remnant of the apical part of odontoid being left in situ as a vigorous attempt at its retrieval might have resulted in neuraxial compromise [Figure 7]. A 30-degree endoscope has been utilized to facilitate drilling of the anterior portion of the odontoid and C2 body through the narrow corridor between the nasopharynx and the vertebral column. The main limiting factor was the frequent fogging of the endoscope due to the blood and bone dust.[24] Angled drills and instruments that enable access across the midline in the prevertebral region will further facilitate the endoscopic-assisted removal of the impinging odontoid on the thecal sac. Utility of SSEP (somato-sensory evoked potential) and MEP (motor evoked potential) monitoring helps in minimizing the risk of inadvertent injury to the cervicomedullary junction and upper cervical cord during the C1-2 joint manipulation as well as odontoid drilling.

The advantages and the pitfalls of the approach

This approach provides a one-stage simultaneous odontoid excision from both the sides and bilateral posterior C1-2 facet joint distraction, C1-2 spacer placement and stabilization. Thus, it permits a more radical approach to complex configurations, pathology and anomalies of the CVJ that provides a 360 degree circumferential excision and stabilization from a posterior approach that is much more familiar to the surgeon. It bypasses the potentially infected oral cavity. Therefore, there is also the prospect of performing the bone and metal plate stabilization from an anterior aspect.[24] It is possible to perform decompression from both the sides. Therefore, if there is any bony or soft tissue anomaly or pathology that is preventing the access to the surgical field from one direction then the opposite direction may be adopted. The approach facilitates a good control of the bleeding from the pre- and paravertebral venous plexus.

Drilling the odontoid relieves the thecal compression; preserving the anterior arch of the atlas simultaneously helps in maintaining anatomical landmarks that may be helpful during a subsequent readiological evaluation. Thus, on intra- and postoperative lateral radiological imaging of the CVJ, it is possible to observe the relative positions of the anterior arch of atlas and the remnant C2 body, as well as the relative mobility between them on dynamic images to assess for persisting thecal compression, extent of odontoid excision and the stability of the posterior construct. Contrary to the transoral approach, where the surgeon's approach is limited by the anatomical structures hidden from direct view like the facet joints and the vertebral artery;[10] and, the extreme obliquity of the unidirectional retropharyngeal approach, that prevents the contralateral part of the C2 body and the C1-2 facet joint from being accessed,[21],[22],[23],[24] this bilateral approach helps in accessing the odontoid from both the sides until it is completely drilled off and the complete midline corridor may be accessed. It also helps in facilitating a bilateral C1-2 facet stabilization utilizing the most physiological technique.

It facilitates a close visualization of the dural-bone interface from a lateral aspect; therefore, an intraoperative dural breech can be better managed utilizing a suture, patch graft or a pedicled muscle overlay graft that is maintained in its position by the fibrin glue. Thus, postoperative complications like a cerebrospinal fluid leak or a pseudomeningocoele formation, are minimized.

It also permits unilateral vertebral artery mobilization (including its mobilization from the foramen transversarium of the atlas and axis) that can further increase the repertoire of the technique and its indications and also expands the surgical corridor, as it would facilitate a more radical drilling of the odontoid and C2 body from a more lateral aspect.

It is also possible to carry out a salvage odontoid excision utilizing the same surgical incision and corridor in a subsequent stage after the initial posterior C1-2 distraction and stabilization, in case there is persistent thecal compression due to a partially reduced AAD or persistent BI.[8]

The pitfalls include the obliquity of approach which makes the posterosuperior part of the apical segment of the odontoid most difficult to access; the lack of adequate space in the surgical corridor to the region; and, the need to frequently change the position of the patient. The commonly encountered variations in the facet joints, and the mutual rotatory movements between the atlas and axis that may lead to an asymmetrical drilling of the odontoid; and, the variations in the course and dominance of the vertebral artery that may often interfere with the adoption of a proper trajectory to the medially located odontoid process also add to the difficulty. All of them may lead to an incomplete decompression of the odontoid process leading to persisting anterior compression. However, the most important issue in the utilization of this approach is the decision-making regarding the actual situation in which it will be needed. The decision to adopt this additional bilateral odontoid removal may either be based on visualizing the complexity of the C1-2 configuration on the preoperative radiological imaging; or, during the intraoperative C1-2 manipulation, where the lack of adequate C1-2 reduction may prompt the utilization of this technique. However, the possibility always remains that a more radical C1-2 distraction, drilling and manipulation during surgery may often lead to an adequate C1-2 reduction, obviating the need for this additional procedure.


 » Conclusions Top


A simultaneous odontoid decompression and bilateral posterior atlanto-axial facetal distraction, C1-2 joint spacer placement and stabilization may be performed utilizing the ‘posterior-only’ approach through a single posterior midline incision, a bilateral posterior approach to the C1-2 facet joints and a bilateral posterolateral approach to the odontoid process and C2 body. This has the potential to work in the case of those complex lesions at the CVJ, where the facetal distraction and posterior stabilization technique alone fails to relieve the anterior thecal compression.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]



 

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