|Year : 2022 | Volume
| Issue : 1 | Page : 6-9
Posterior one is not the only approach: Ventral odontoid decompression in the spectrum of complex irreducible atlantoaxial dislocation with basilar invagination-When and why?
Department of Neurosurgery, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
|Date of Submission||26-Dec-2021|
|Date of Acceptance||26-Dec-2021|
|Date of Web Publication||9-Mar-2022|
(M.Ch.), Associate Professor, Department of Neurosurgery, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Sardhara J. Posterior one is not the only approach: Ventral odontoid decompression in the spectrum of complex irreducible atlantoaxial dislocation with basilar invagination-When and why?. J Spinal Surg 2022;9:6-9
|How to cite this URL:|
Sardhara J. Posterior one is not the only approach: Ventral odontoid decompression in the spectrum of complex irreducible atlantoaxial dislocation with basilar invagination-When and why?. J Spinal Surg [serial online] 2022 [cited 2022 May 27];9:6-9. Available from: http://www.jossworld.org/text.asp?2022/9/1/6/339276
Indeed, in the recent era, the tremendous paradigm shift of surgical algorithm from combined anterior approach to posterior only approach for most craniovertebral junction (CVJ) anomalies patients is appreciable and remains successful.,,,,,, However, sticking to a single approach for every case in the broad spectrum of CVJ anomalies sometimes remains disastrous. I still do not believe in the extinction of ventral decompression as a surgical approach, although it can be very beneficial for a specific subset of complex CVJ anomalies, which I would like to emphasize here.
The majority of the neurospinal surgeons must have encountered the list of nightmares of experience in patients with CVJ anomalies, which do not improve or even may worsen after exhaustive trial of realignment by posterior C1/C2 distraction. Usually, failure for complete reduction or incomplete reduction of C1/C2 dislocation in such cases is the reason for suboptimal clinical outcomes in those patients. The reasoning behind the high surgical complexity of the developmental CVJ anomalies patients lies in their bony variation in the facet joint complex.,,, Clinical studies have demonstrated that the contraction of anterior muscles, ligaments, and capsules of the atlanto-axial joint, especially the osteophytes and scar tissue inside the atlanto-dens interspace, prevent the complete reduction in irreducible atlantoaxial dislocation (AAD) and basilar invagination (BI)., BI with flat and symmetrical facet joints usually reduces with the standard surgical maneuvers by opening and manipulating facet joints by the posterior approach. A subset of patients with BI having significant ventral compression due to high craniocervical kyphosis is sometimes seen due to clival segmentation anomalies or severe retroversion of the dens in KlippelFeil syndrome. Very high BI with asymmetric facet joints or retroverted odontoid process (due to hyperlordotic cervical spine) can coexist rotational C1/C2 dislocation and coronal tilt. Such a patient's facet joints are extremely difficult to reduce and align in the normal position by joint manipulation or distraction. Besides, over-distraction of C1/C2 facet joints to achieve that reduction could be detrimental due to stretching of already compromised neural tissue behind the joint. In such patient's bony decompression through anterior approach either with the transoral route or endoscopic endonasal route can be used and is safe. The endoscopic endonasal approach has gradually become popular nowadays. In computed tomography (CT) or magnetic resonance imaging, the line joining the caudal border of the nasal process to the posterior tip of the hard palate is drawn; if C2 body is lying above this line in such cases, it would be tough to decompress from transoral approach; therefore, the endonasal approach would be the better alternative. The minimally invasive access and faster recovery associated with this technique make it a valid option compared to routinely practicing conventional transoral decompression of the odontoid.
Indications of ventral decompression in a specific subset of patients are mentioned here.
| Very High Basilar Invagination|| |
A very high BI is called when the odontoid tip intersects the “P-IOP line” in the mid-sagittal image of the CT CVJ. P-IOP line is the novel universal diagnostic index for all types of BIs. It is the line joining between the posterior tip of the hard palate palate (P) and internal occipital protuberance (IOP). The distance from the tip of the odontoid process to the P-IOP line is measured; if it is <9 mm, it is diagnosed with BI; if it intersects or crosses the P-IOP line, it is called very high BI). Platybasia with a very high BI with vertical asymmetrical joints frequently led to insufficient distraction of the odontoid from the foramen magnum due to great difficulty in joint manipulation [Figure 1]a and [Figure 1]b. Moreover, forceful over-distraction may induce significant spinal cord damage, and the patient may have severe postoperative complications such as ventilator dependency and/or quadriparesis. Direct transoral or endonasal ventral odontoid decompression can be a safe and straightforward approach in such patients with a better outcome.
|Figure 1: Some case examples (a and b) of patients with atlantoaxial dislocation and very high basilar invagination (BI), which seem very difficult to reduce by only posterior C1/C2 distraction methods. A very high BI is called when the odontoid tip intersects (a) or crosses (b) “the P-IOP line” (red line) (P-IOP line is a line joining between the posterior tip of the hard palate and internal occipital protuberance). The distance from the tip of the odontoid process to the P-IOP line is measured; if it is <9 mm, then it is diagnosed as BI; if it intersects or crosses the line, it is very high BI|
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| Basilar Invagination + Atlantoaxial Dislocation + Rotational Dislocation + Coronal Tilt|| |
In our previous research, we evaluated 154 congenital AAD patients, and all the C1/C2 joints were assessed to see the axis of C1/C2 dislocation in all the planes. We have found that there are six types of combinations of C1-2 dislocations in all three different axes. The most common among all is the combined type, a combination of AAD, BI, Coronal tilt, and rotational dislocation. With BI, each patient of irreducible AAD should be looked for co-existed rotational dislocation and coronal tilt or gross facet joints asymmetry. The alignment in all the planes is the key to completely reducing AAD and BI and optimal surgical outcomes.
Very high BI with asymmetrical vertical facet joints [Figure 2]a and [Figure 2]b is a very challenging to reduce by the posterior C1/C2 distraction method. One has to look carefully for both the sagittal and coronal orientation of facet joints; if one side is vertical and the opposite side it is oblique or flat joints; in this scenario, putting a spacer in between two joints on both side rather lead to more compromise in the cervical canal as the tip of the odontoid goes backward; and compress the canal further; this is the most common reason for the failure of complete reduction of AAD and BI result in failure of improvement or even worsening of neurological status. We prefer either in situ posterior fusion or ventral decompression followed by posterior fusion in such cases.
|Figure 2: Depicts the computed tomography coronal view of C1/C2 joints orientation. Very high basilar invagination with such kind of asymmetrical vertical facet joints (a and b) is very challenging to reduce by posterior C1/C2 distraction method|
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| Irreducible Os Odontoideum|| |
Os odontoideum is of two varieties, reducible and irreducible. Important etiological factors for irreducibility are the abnormal impactation of the tip of odontoid between the body of the C2 process and transverse ligament, sometimes fused abnormally and prevented from complete reduction [Figure 3]. Sometimes, hypertrophy of C1 anterior arch with anomalous Os bone in dysplastic Os odontoideum causing significant ventral compression cannot be reduced by the posterior approach only. Most of the irreducible AAD could become reducible after anterior release without odontoid resection followed by stabilization by the anterior or posterior approach.
|Figure 3: Computed tomography sagittal view showing the orthotopic variety of Os odontoideum with irreducible atlantoaxial dislocation. Irreducibility is due to the abnormal impactation of the tip of odontoid between the body of the C2 process and transverse ligament, fused abnormally and preventing it from complete reduction|
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| Syndromic Atlantoaxial Dislocation|| |
Various kinds of 84 different known syndromes are described in the literature, co-existing with CVJ anomalies. They ranged from asymptomatic presentation to severe cervical myelopathy, which warrants ventral decompression sometimes [Figure 4]. Patients with Morquio syndrome usually presented with reducible AAD due to C1/C2 instability; infrequently, the patient may present with significant ventral compression due to retro-odontoid deposition of mucopolysaccharides, which require transoral decompression. Congenital fusion of multiple level cervical vertebrae in the patients with Klippel Feil (KF) syndrome is compensated by gradually progressing cervical hyperlordosis and then retroversion of odontoid. High BI in KF syndrome is frequently associated with platybasia and retroverted odontoid, which poses significant ventral compression, and there is very less possibility of complete reduction by posterior only approach due to co-existed coronal facet joint asymmetry. Retro-odontoid deposition composed of a dense fibrocollagenous tissue in Larson syndrome due to persistent microinstability poses significant ventral compression in the background of sub-axial cervical kyphosis can be better managed with a combined approach including ventral decompression [Figure 5].
|Figure 4: MRI and computed tomography-craniovertebral junction (CVJ) was suggestive of complex cervical deformity with scoliosis towards the left and exaggerated cervical lordosis with C2-C3 retrolisthesis. Significant spinal canal narrowing (7.5 mm) was present at C2, causing spinal cord 12 compression (a and b). This case is diagnosed with caudal regression syndrome with CVJ anomalies due to associated occult spina bifida with sacral agenesis 13 and tethered cord syndrome and operated by transoral decompression of C2 and C3 vertebral body followed by posterior Occiput to C3 fusion|
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|Figure 5: Patient with Larson syndrome, showing retro-odontoid with deposition of a dense fibrocollagenous tissue due to persistent micro instability. Significant ventral compression in the background of sub-axial cervical kyphosis can better managed with combined approach including ventral decompression.|
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| Re-Surgery for Persistent Myelopathy (Failed Posterior C1/C2 Distraction)|| |
In one of the surgical series of 414 patients, 55 patients needed re-surgery. Out of all patients, we concluded that around 15 (18.3%) patients required re-surgery due to persistent odontoid compression by lack of complete reduction after first surgery despite C1/C2 distraction. The factors responsible for irreducibility were high, and retroverted BI, gross facet joint asymmetry, and associated server coronal tilt and rotational dislocation hindered AAD and BI's complete reduction and subsequently underwent second stage transoral decompression for optimal outcome. Moreover, due to fibrous adhesion and pseudoarthrosis around the facet joints and C1 arch, re-exposure and joint manipulation are extremely difficult with a high risk of CSF leak and VA injury. In such cases, fresh ventral approaches are a safe alternative.
| Issues With Over Distraction of C1/C2 Joints And Joint Drilling|| |
C1/C2 joint manipulation by drilling from the posterior approach to manage the reduction of joints are one of the popular technique in the recent period. Some part of facet joints drilling in order to reduce the C1/C2 vertical dislocation is feasible. However, extensive drilling of joints, especially in anomalous vertical asymmetrical joints in high BI patients, has a high risk of subsidence of the cage into the lateral mass of the C1, keeping in view that the strong cortical surface is rendered weak by drilling. In addition, drilling of the C2 facet may endanger the VA injury in the high arching vertebral artery groove in some C2 lateral mass atrophy cases. The pathological consequences of over distraction of C1/C2 joint beyond the 7–8 mm height and its impact on the already compromised spinal cord is highly detrimental as a safe physiological limit for degree of distraction of the C1/C2 joint is still unknown.
| Conclusion|| |
The ventral decompression technique in the case of irreducible AAD and BI is still not obsolete. Very high BI with retroverted odontoid, gross facet joint asymetry, rotational dislocation with coronal tilt, syndromic AAD with significant ventral compression, patients with re- surgery after failed C1/C2 distraction and irreducible odontoideum are the group of subset in which ventral route can be highly effective and safe.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]