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REVIEW ARTICLE
Year : 2018  |  Volume : 66  |  Issue : 4  |  Page : 1003-1015

Controversies in the surgical management of congenital craniocervical junction disorders – A critical review


1 Department of Neurology, Neurosurgery Division, University of Campinas (UNICAMP), Campinas-SP, Brazil
2 Department of Neurosurgery, All India Institute of Medical Sciences (AIIMS), New Delhi, India

Date of Web Publication18-Jul-2018

Correspondence Address:
Dr. P Sarat Chandra
Department of Neurosurgery, All India Institute of Medical Sciences (AIIMS), New Delhi
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0028-3886.237025

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 » Abstract 


Introduction: Congenital disorders of the craniovertebral junction (CVJ) include a wide range of conditions, such as Chiari malformation (CM), basilar Invagination (BI), and atlantoaxial dislocation (AAD). The objective of this paper is to critically review the literature related to the management of congenital CVJ disorders focusing on: the significant developments in the past (from anterior open ventral decompression to modern CVJ realignment); the diagnosis of CVJ instability; the role of atlantoaxial fixation without posterior fossa decompression in patients with tonsillar herniation and no evidence of CVJ instability; use of C1-2 inter-articular spacers and use of C1-2 interarticular spacers with intra-operative manipulations to correct BI with AAD along with its deformity.
Materials and Methods: We performed a review of articles showing up on PubMed database without time restriction. Articles were included according to the purpose of our review and selected by two authors (AFJ and PSC).
Results: CVJ instability may be inferred when there is atlantoaxial abnormal motion seen on dynamic studies, facet joint subluxation or severe symptomatic CVJ kyphosis; routine fixation of patients with CM without clear CCJ instability, while based on an interesting hypothesis, still requires further studies; use of C1-2 inter-articular spacers for re-establishing CVJ alignment is probably the most effective surgery for posterior CVJ realignment and reduction of AAD and BI, potentially avoiding the need for an open or endoscopic anterior odontoidectomy (AO); current development of deformity correcting surgeries and the measurement of joint indices to plan surgery have provided new strategies for treatment.
Conclusion: We present a critical review of important new concepts involved in the surgical treatment of CVJ congenital disease.


Keywords: Atlanto-axial dislocation, basilar invagination, Chiari malformation, concepts, craniovertebral junction, surgery, treatment
Key Message: A critical review of important concepts involved in the surgical treatment of craniovertebral congenital disease is being discussed. These include significant developments in the past, newer parameters in the diagnosis of craniovertebral instability, the effectiveness of atlantoaxial fixation without posterior fossa decompression in patients with tonsillar herniation without evident craniovertebral junction (CVJ) instability, the role of C1‑2 inter-articular spacers for treating basilar invagination with atlantoaxial dislocation, and the role of anterior approaches to the CVJ for both re‑aligning and fixation.


How to cite this article:
Joaquim AF, Tedeschi H, Chandra P S. Controversies in the surgical management of congenital craniocervical junction disorders – A critical review. Neurol India 2018;66:1003-15

How to cite this URL:
Joaquim AF, Tedeschi H, Chandra P S. Controversies in the surgical management of congenital craniocervical junction disorders – A critical review. Neurol India [serial online] 2018 [cited 2018 Nov 20];66:1003-15. Available from: http://www.neurologyindia.com/text.asp?2018/66/4/1003/237025




Congenital craniovertebral junction (CVJ) disorders include a wide range of conditions, such as  Atlas More Details assimilation, segmentation defects of the CVJ, Chiari I malformation (CM), and basilar invagination (BI).[1],[2],[3],[4],[5] They can be found alone or associated with other syndromes, such as achondroplasia, Morquio, Larson, Marshall, or Down syndrome, generally associated with a reducible atlantoaxial dislocation (AAD).[1],[2],[3],[4],[5],[6] The neural components of congenital CVJ disorders are tonsillar herniation and syringomyelia, commonly found associated with bony anomalies.[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16],[17] Surgical treatment is well accepted in the setting of symptomatic CVJ disorders and may also be considered to be an option in patients with a high risk of clinical deterioration.[2],[3],[4],[5],[8],[9],[11]

CM is characterized by caudally displaced cerebellar tonsils below the level of the foramen magnum.[12],[13] The estimated incidence of CM in the general population, considering also asymptomatic patients, is about 0.1 to 0.5%.[7],[14] The radiological diagnosis of CM is generally accepted when the tonsils are 5 mm below the level of the foramen magnum, although clinical symptoms can be found even in patients who have only an obliteration of the retrocerebellar cerebrospinal fluid spaces.[7]

The diagnosis of BI is classically established in cases when the tip of the odontoid is above the Chamberlain's line (a line drawn from the posterior tip of the hard palate to the tip of the opisthion).[4],[5],[17],[18],[19] It is generally accepted that the limit for the diagnosis is when the tip of the dens is located more than 5 mm above the Chamberlain's line, although 2 mm and 2.5 mm are also found in the literature as diagnostic thresholds.[5],[19] More recently, BI has been considered to be a part of the spectrum of broad range of normality as it has been found in many asymptomatic patients, and is characterized by a vertical dislocation of the upper cervical spine into the foramen magnum, with or without vertical dislocation of the axis within the atlas (C2 body telescoping into the C1 ring), which is generally secondary to the acute coronal inclination of the C1-2 facets.[20],[21],[22],[23],[24]

In the last decade, new concepts involving the surgical management of congenital CVJ were proposed, such as a single-stage posterior approach for treating severe BI with AAD, along with CVJ realignment, avoiding the need for an open or an endoscopic anterior odontoidectomy.[2],[19],[20],[21],[22],[23],[24],[25],[26],[27],[28],[29],[30],[31],[32],[33],[34],[35],[36],[37] Following the shift of attention to the use of spacers and performing realignment of the C1-2 joints, it became important to understand the orientation, morphology, and anatomical characteristics of the joints that often have a variable morphology.[2],[19],[20],[21],[22],[23],[24],[34],[35],[36],[37],[38],[39],[40] Interestingly, some surgeons chose to undertake an anterior approach to not only reduce the dens but also perform anterior screw/plate fixation either through the trans-oral route or through the anterior cervical approach.[41],[42],[43],[44]

In this article, we have performed a critical review of these controversial topics, discussing the current trends in CVJ surgery based on the most recent medical evidence and have also reviewed the various important developments that have taken place in the past.


 » Materials and Methods Top


We performed a broad narrative review of the literature related to congenital CVJ disorders in the PubMed database without time restriction until December 1st 2017. The following key-words were used for searching, either in an isolated or a combined manner: “craniovertebral junction,” “ Chiari malformation More Details,” “atlantoaxial dislocation,” “anomalies,” and “basilar invagination.” Cross-referenced articles were also included when related to our objective. Articles were selected by two authors (AFJ and PSC), and grouped according to one of the following main topics:

  1. The significant developments in the past
  2. The diagnosis of CVJ instability
  3. The value of routine CVJ fixation in patients with CM without evident CCJ instability
  4. The use of C1-2 interarticular spacer for treating BI with AAD, and the use of C1-2 interarticular spacers with intraoperative manipulations to correct BI with AAD along with its deformity
  5. Role of anterior approaches to perform reduction along with fixation. Here, we briefly reviewed the role of the use of anterior trans-articular screws, use of screw/plate constructs and also methods to reduce and re-align the CV junction
  6. The development of surgical strategies for CVJ anomalies in the future has also been summarised. Here, we briefly describe the possibility of development of artificial joints for CVJ.


Finally, we provide a summary of the strategies that may be adopted to manage CVJ anomalies.


 » Results Top


The significant developments in the past

The developments in the management of CVJ anomalies have occurred slowly but steadily over the past 5 decades resulting in a dramatic change of concepts and paradigms. Wadia et al., way back in 1967 in a classic paper, described in 28 cases, 4 types of clinical presentations that mainly included some form of progressive myelopathy.[45] He also noted that most of the patients, presenting with severe myelopathy, also have bladder symptoms.

In the United States, Arnold Menezes has made tremendous contributions to the advancement of factors influencing the treatment of CVJ diseases.[7],[15] He had suggested that the treatment plan should consider the reducibility of the lesion (if the anatomic alignment could be restored with traction), the direction and the mechanics of the compression, the etiology of the compression (such as a solid bone versus a soft pannus, for instance) and the presence of ossification centers.[7],[15],[46] His large experience with the ventral approach for CVJ was published in many papers and was extremely useful for patients with fixed or irreducible anterior brainstem compression.[46]

Considering the developments in video assisted anterior surgery of the CVJ, endoscopic assessment of anterior CVJ compression was popularized in the last decade, being an extremely elegant procedure. It served as an alternative to the open transoral resection, potentially avoiding the soft palate injury and with a better visualization of the upper cervical spine structures.[47],[48]

In Germany, a large series of patients with CVJ anomalies were reported by Klekamp. This was probably one of the largest experiences in Europe in the surgical treatment of patients with CVJ anomalies.[49],[50] He proposed that patients without ventral compression, even with BI, could be treated successfully with posterior approaches (decompression of the foramen magnum alone) and posterior CVJ realignment would decrease ventral compression in the majority of the cases. Thus, he reserved anterior decompression for patients with severe anterior compression.[49],[50] Similar treatment strategies were reported by authors in South America and China.[5],[34]

Indian surgeons, too, have provided many new insights in the treatment of CVJ anomalies, probably due to the higher prevalence of the anomaly in India.[51],[52],[53],[54],[55],[56] Jain et al., reported in 1993, the technique of occipital axis wiring fusion for AAD associated with occipitalization of the atlas. This was a very effective strategy in patients with AAD who have an atlas assimilation.[57] After making a groove in the occipital squama, 1 cm posterior to the foramen magnum, they recreated the posterior arch of the atlas (that was assimilated with the posterior occipital squama). Once the “artificial atlas” was created, a standard sublaminar wiring fixation was performed.[58]

Goel, in 2004, proposed atlantoaxial joint distraction with direct lateral mass fixation (the technique of lateral mass screw placement was also described by him) that permitted CVJ realignment without the need of anterior decompression in some selected cases.[35] This contribution revolutionised the treatment of BI with AAD, as many patients no longer needed an anterior approach, with an indirect ventral decompression being performed. Although this technique had a tremendous impact on the treatment of patients with BI, further Indian studies reported failure in some cases that had C1-2 distraction, requiring additional procedures for ventral decompression. There were also wound related problems.[59] Additionally, some anatomical variations preclude the use of C1 lateral mass or C2 pars/pedicles screws for all patients with AAD. In this setting, another Indian surgeon, Sarat Chandra reported a new technique of occipito-cervical fusion with CVJ distraction, compression, extension and reduction (DCER). This new technique allows CVJ realignment in patients with severe atlantoaxial instability, considering the joint morphology in a unique perspective.[24],[25],[26],[27]

More recently, there has been a resurgence of interest in re-aligning and fixing CVJ from the anterior approach. Patkar reported a craniovertebral fixation using custom made rods fixed anteriorly in the mid-cervical vertebrae, with the rods contoured to reach the safe paraspinal corridor and then connected with connectors to the occipital plate.[43]

The diagnosis of CVJ instability

The definition of CVJ instability may be extrapolated from the White and Panjabi concept of spinal instability, i.e., any CVJ anomaly that may lead to neurological deficits, progressive deformity, or structural pain may be considered as unstable.[60] Although theoretically simple, this definition includes a multitude of clinical and radiological presentations where a specific diagnosis may be challenging to establish, especially in this complex region.[2],[61],[62] In addition, instability can be acute and evident, such as in AAD, or late, secondary to chronic, and progressive changes that will result in deformity and pain.

Considering instability in BI, Goel proposed, in 2009, a classification that categorizes patients into two main groups according to the presence or absence of instability:[4] Group A – patients with CVJ instability (presence of AAD) and Group B – patients without CVJ instability (associated with clivus hypoplasia).[4] In both the groups, patients had the tip of the odontoid at least 2 mm above the Chamberlain's line; however, in Group A, the dens is above the McRae line (a radiographic line drawn from the basion to the opisthion) and above the Wackenheim's clival line (a radiographic line along the clivus and extending inferiorly into the upper spinal canal), with AAD. Treatment in this group would include craniocervical realignment and fixation. Of note, decompression of the foramen magnum was questionable once neural release was generally obtained with craniocervical realignment.[62],[63],[64] On the other hand, Group B patients had a normal alignment of the clivus and the odontoid process, with the dens below both the Wackenheim's clival line and the McRae's line. At that time, he had proposed that there was no mechanical instability in group B and the cause of BI was a clivus hypoplasia, with a normal atlantoaxial relationship. For this group, the author had proposed at that time that surgical treatment should consist of foramen magnum decompression without craniocervical fixation.[4] Of note, the role of the clivus canal angle (CCA) and the consequent craniocervical kyphosis as a potential cause of instability in patients with clivus hypoplasia was not considered.

In this context, some authors have emphasized that the CCA may play a role in the management of CVJ disorders. The normal CCA ranges from 150° to 180°.[37] It can be influenced by dynamic changes, with the angle decreasing by approximately 30° when a craniovertebral flexion is performed.[37] A low CCA may result in biomechanical neuraxial stress on the brainstem, leading to clinical deterioration due to ventral brain stem compression (VBSC).[65]

Bollo et al., reported the results of a retrospective review of 101 pediatric patients with CM who underwent posterior decompression.[66] A total of 19 patients underwent fusion for CVJ stabilization as an initial procedure or after failure of isolated foramen magnum decompression. They identified some risk factors for CVJ fusion in their cohort such as: BI (hazard ratio[HR] 9.8, 95% confidence interval[CI] 2.2–44.2) and a CCA of less than 125° (HR 3.9, 95% CI 1.2–12.6). The study addresses the importance of the CCA as a potential cause of CVJ instability.

Although the CCA may be important, it only takes into account osseous structures, potentially underestimating the soft tissue compression by the retro-odontoid tissue. As an alternative, Grabb et al., proposed a measurement to quantify ventral brain stem compression (VBSC), also known as the B-C2 index.[67] This index was obtained based on a line drawn between the basion (B) and the posteroinferior aspect of the C2 body (C2), and on another line perpendicular to this line that was drawn through the odontoid tip to the ventral dura. The distance representing the amount of ventral canal encroachment was then measured. In 40 patients with CM who had a posterior fossa decompression, those who had the B-C2 index of less than 9 mm, were treated successfully with posterior fossa decompression alone, whereas those patients with the index of 9 mm or more required reduction of the VBSC before posterior fossa decompression. They have concluded that patients with a B-C2 index of more than 9 mm should receive reduction of VBSC prior to posterior fossa decompression.

Recently, Chandra et al., reported three new indices for evaluating the severity of BI and AAD in 70 patients, namely, the sagittal joint inclination (SJI), the coronal joint inclination (CJI), and the craniocervical tilt (CCT). These newly described indices correlated with the severity of BI and AAD. Potentially, they can be used for planning the surgical strategy and also to predict the clinical outcome.[2],[27] Finally, the authors have postulated that the degree of joint obliquity was an important factor in affecting the stability of the joint. Increasing angulations of SJI and CJI may increase the risk of BI and AAD. This risk is likely to increase with the person assuming a bipedal posture. This could be one of the reasons why most of the congenital CVJ disorders are found between the first and third decade and why some patients with clivus hypoplasia deteriorate even after posterior fossa decompression.[61]

An additional index (the vertical atlantoaxial index - VAAI) was proposed by Kulkarni et al., to measure the vertical instability using mid-sagittal CT scan films. This index assesses the relationship of the atlas and the axis.[68] Components of lateral bending and lateral angular dislocation were also reported as components of the broad range of CVJ instability in patients with congenital dislocations in the lateral plane.[69],[70],[71]

Specifically addressing AAD, it would be of importance to state that the concept of “reducible” vs. “irreducible” is fast disappearing. Earlier, a considerable degree of surgical strategy would depend on finding whether the AAD would reduce on dynamic radiological studies or even after a trial of preoperative traction. It is now becoming clear that most of the “irreducible” AADs may also be reduced by opening up the C1-2 joints intraoperatively.[58],[61],[72]

Fenoy et al., proposed that the evaluation of CVJ instability preoperatively must include a complete computed tomography (CT) scan and magnetic resonance imaging (MRI) of the CVJ, including a three-dimensional reconstruction of the CVJ using a CT scan for better clarification of the bone anatomy.[3] Moreover, dynamic MR imaging in flexion and extension views may be extremely useful to evaluate the extent of ventral and dorsal cervicomedullary compression and the possibility of reduction. They proposed some criteria of CVJ instability, such as the predental space being greater than 3 mm in adults, a gap being present between the occipital condyles and the atlas facet joints, the vertical clivus-odontoid translation being greater than 2 mm, and an abnormal motion seen on dynamic radiological evaluation.[3] Menezes et al., and Klekamp et al., have described that in patients with CM, with anomalies of segmentation (such as C2-3 fusion and atlas assimilation) in the CVJ were at a high risk of postoperative instability after posterior fossa decompression even without preoperative instability.[6],[15],[73] Finally, instability can also be secondary to musculo-ligamentous weakness. Risk factors responsible for this instability may include congenital syndromes such as Ehler–Danlos and Down's syndrome. Acquired muscular weakness may be caused by muscle retraction and fibrotic changes due to repeated operations, inadequate closure at surgery, loss of innervation of the musculature because of the presence of a high cervical syringomyelia, or a summation of all of these factors.[3],[35],[73],[74] Thus, all these factors should also be considered in patients with recurrent CVJ symptoms even after an adequate decompression [Table 1].
Table 1: Summary of the main craniovertebral junction indices found in the literature

Click here to view


Summary of the recommendations for diagnosing CVJ instability

Evaluation of instability should include a CT scan with reconstruction and an MRI. Dynamic imaging is recommended if instability cannot be ruled out with static examinations.

Clear CVJ instability may be inferred when

  1. There are facet joint dislocations documented on static examinations, such as atlantoaxial subluxation, with anterior or posterior dislocation of the atlas/assimilated atlas over the axis. The loss of normal congruence between the facet joints may be a clear evidence of instability;
  2. Radiological abnormal dislocation is documented on dynamic examinations that presents as abnormal movements of the facet joints with (sub) luxation, and a progressive increase in the atlanto-dens interval.


Potential CVJ instability may be inferred

  1. In the setting of severe craniocervical kyphosis, even when there is normal facet joints congruence. Craniocervical kyphosis may be inferred with a CCA of less than 125°, a pB-C2 index of greater than 9 mm or a high CCT [Table 1].


The value of routine CVJ fixation of patients with CM without evident CCJ instability

Recently, Goel reported a case series of 65 patients with CM treated with atlanto-axial fixation without foramen magnum decompression.[75] Clinical evaluation was based on five clinical grades that depended on the functional capabilities of patients, and the patients were classified according to their atlantoaxial facet alignment into three types, based on their CT scanning with the head in flexion and extension, CT angiography and MRI: 1) Type I dislocation (17 patients), wherein the facet of the atlas was dislocated anterior to the facet of the axis; 2) Type II dislocation (31 patients), wherein the facet of the atlas was dislocated posterior to the facet of the axis; and, 3) Type III dislocation (17 patients), wherein there was absence of demonstrable facetal misalignment.

A total of 55 (84.6%) patients also had syringomyelia, 46 (70.7%) patients had BI and 37 patients had both (56.9%). BI was diagnosed when the dens was up to 2.5 mm above the Chamberlain's line. Three patients had previously undergone a foramen magnum decompression and duraplasty. The follow-up ranged from 3 to 48 months (mean 18 months).

The author reported that 63 patients (96.9%) had some sustained clinical improvement, one patient had persistent symptoms and one died due to vertebral artery injury.[75] He concluded that atlantoaxial stabilization without bone decompression and without duroplasty is the main treatment form for symptomatic tonsillar herniation, whether or not the condition is associated with BI or syringomyelia. According to the author's new theory, patients with BI in Group B had instability even when it was not demonstrated by dynamic changes. The same theory was applied to CM: all patients had atlantoaxial instability. They have postulated that syringomyelia in CM is primarily because of the C1-2 instability, either subtle or apparent. The resultant tonsillar herniation is the result of a compensatory protective phenomenon, acting as natural “air-bags” that protect the spinal cord from the effects of the atlantoaxial instability.

Type I facetal dislocation was most commonly found in patients with BI of the Group A, being the most severe instability. Type II dislocation was more frequently associated with BI of Group B, whereas Type III dislocation, present in 17 cases, did not have any evidence of facetal misalignment on dynamic or plain imaging. However, the author claimed that in all these cases, he was able to discern instability intra-operatively.

Finally, it was reported that CM with or without BI is always associated with atlantoaxial instability even when it is not demonstrable on radiological imaging and that foramen magnum decompression was unnecessary and actually harmful.

On the other hand, Jea has emphasized that dissecting the anomalous vertebral artery for C1 lateral mass fixation is completely unnecessary since there is atlas assimilation in the majority of cases of BI; therefore, an occipital fixation to C2 would be biomechanically similar and technically easier, with a much lower risk of vertebral artery injury. It would also be more suitable to maintain a good craniocervical alignment in patients with BI of group A.[76] Finally, he has stated that the mortality rate in the study by Goel was high (one death due to vertebral artery injury) compared to other large series of patients who have treated CM. Additionally, some authors have pointed out that atlantoaxial instability due to other causes (such as rheumatoid arthritis) is not associated with tonsillar herniation or syringomyelia. Fixation of the atlantoaxial complex may result in restriction of the cervical rotation and morbidity. Furthermore, this new theory cannot explain the clinical improvement seen in patients in the previously reported series, who underwent posterior fossa decompression alone for treating CM, even though Goel et al., emphasize that the improvement which occurs is due to release of compression by the “air bags-tonsils.” Thus, the neurological improvement that occcurs following posterior fossa decompression is a transient improvement as it does not tackle the primary cause, which is instability at the C1-C2 joints. The hypothesis suggested by Goel et al., is interesting but does require randomized as well as carefully conducted studies to prove its value. It is also limited by significant ethical issues, such as not performing a foramen magnum decompression and/or duroplasty in patients in the presence of a symptomatic tonsillar herniation.

Yin et al., has also questioned the idea that atlantoaxial instability is present in all cases of CM.[77] They argued that CM has a very complex pathogenesis and that decreased volume of the posterior fossa is the main reason for the development of CM without ventral compression.[77] Rahman, 2015, pointed out that the tonsils are not “air-bags” since they cause more compression of the neural structures than CSF, suggesting that AAD is not the cause of symptoms in CM.[78] As has also been stated by many other authors, he also suggested that a congenital shallow posterior fossa is well documented in CM and is the most accepted pathogenic phenomenon for explaining the symptoms in CM.[7],[64],[66] However, the issues raised by Goel do need to be considered very carefully as they have opened up the possibility of a new window to understand this complex pathology.

Summary of the recommendations for atlantoaxial fixation without posterior fossa decompression in patients with tonsillar herniation and no evident CVJ instability

Routine atlantoaxial fixation without posterior fossa decompression for patients with tonsillar herniation, with or without syringomyelia, and no evident CVJ instability may not be recommended until further evidence is available. However, the approach should merit a more careful study in centers where an ethical clearance may be obtained to undertake such a study.

Use of C1-2 inter-articular spacers for treating basilar invagination with atlantoaxial dislocation

Posterior approaches for reducing BI without using C1-C2 inter-articular spacers were based on the preoperative traction, with reduction of BI followed by OC fusion, indirectly reducing the anterior compression and improving the neurological status.[3],[4] However, many patients with BI and AAD may have a “fixed” AAD when submitted to skeletal traction. In this context, some authors proposed a direct intraoperative posterior occipito-C2 screw reduction as an alternative to preoperative skeletal traction.[31],[59] The technique consists of decompressing the posterior margin of the foramen magnum (including the fused posterior arch of C1) followed by insertion of bilateral C2 pedicle screws, with longitudinal rod distraction. The odontoid process is dragged downward and anteriorly facilitating the reduction of AAD and the occipital screw is then finally tightened.[72],[78] This technique is a good alternative for treating AAD, especially in patients with assimilation of the atlas. However, the main shortcoming of this technique is the absence of anterior column support, which may lead to cranial settling and excessive postoperative craniocervical kyphosis, with consequent downward displacement of the horizontal gaze of the patient.[79],[80]

The concept of using spacers that help in facilitating distraction, and hence, in reducing the BI and in causing re-alignment of the CVJ was first introduced by Goel et al.[35],[36],[62] This technique is very effective, especially if the atlas is not fused to C2 [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]. The procedure consists of inserting C1 lateral mass screws and C2 pedicle screws, followed by opening of the facet joints of C1-2, decortication and insertion of a spacer (bone graft or metal spacers) inside the joints for distraction. This technique is potentially more powerful in correcting the craniocervical alignment than the reduction of the AAD without using a spacer. An osteotome is used to distract and manipulate the joint and realign atlantoaxial joints in all planes.[62] Of note, the surgical technique is challenging and requires a long learning curve because this particular group of patients has vertebral artery anomalies and smaller lateral masses compared to normal subjects, as well as atlas assimilation in the majority of the cases. In addition, the technique may become more difficult or nearly impossible to perform when the joints are vertically oriented.
Figure 1: A 7-year old boy developed quadriparesis after sustaining a fall while running. CT scan (a) showed atlanto-axial dislocation with listhesis of C1 over C2 along with mild BI. CT scan through the joints (b) shows some degree of subsidence between C1-C2. MRI (c) showed cervico-medullary compression with significant cord changes. 3-D CT with angiogram (d and e) showed evidence of normally placed vertebral artery along with bifid C1 spine. The patient underwent a C1-2 screw placement along with spacers (f and g). Spacers were placed to correct the subsidence. Reduction was adequate and the listhesis was corrected (f)

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Figure 2: A 21-year old male patient presented with progressive quadriparesis. CT can (a) showed mild to moderate BI with canal compression. CT scan with 3D reconstruction (b) and through the joints (c) showed a sagittal inclination of 100 degrees. A DCER was performed with spacer placement and a short fixation between the occiput and C2 laminae was also done (d and e). Postoperative CT scan revealed a good reduction and re-alignment (f)

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Figure 3: Unlike the case presented in Figure 2, this patient had a very severe BI and AAD leading to severe cord compression (a). CT scan through the joints (b) showed joints, which were completely vertical (arrow head). However, this led to development of a pseudo-articulation between the upper surface of C2 lamina and the occiput (right arrow,b). This allowed the placement of a spacer in this space (extra articular distraction, c). Since the BI and AAD were very severe, an additional purchase of C3, C4, C5 lateral masses were taken. Following DCER, realignment was attained and the compression was completely relieved (d)

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Figure 4: Another example of severe BI with AAD (a) with vertical joints (b) and severe cord compression (c). The patient underwent extra-articular distraction followed by DCER, which allowed for a complete relief of cord compression and correction of deformity (d-f)

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Figure 5: A 8 year old boy had an os-odontoideum which developed a pathological cartilaginous fracture leading to displacement of the segment along with AAD and cord compression (a and b). 3-D CT scan (c) clearly shows the displaced fragment (arrow head) and the body of dens (arrow). DCER and fixation between the occiput and C2 laminae led to complete reduction (d and e). Figure f shows the spacer in situ

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The use of C1-2 interarticular spacers with intraoperative manipulations to correct basilar invagination with atlantoaxial dislocation along with its deformity

In 2013, Chandra et al., reported their results on a novel pilot technique named DCER (distraction, compression, extension, and reduction) to reduce BI with AAD through a single-stage posterior approach.[28] This novel method avoids the use of an anterior transoral procedure and consists of not only distracting the C1-2 joints using an interarticular spacer but also includes the performance of horizontal occipito-cervical manipulations that may correct the CVJ deformity secondary to the AAD. This technique is applied in cases where the C1 is fused with the occiput. Here, the patients are placed in prone position on a U-shaped headrest with the head fixed, with a skull traction applied just enough to provide optimal stabilization (with about 2-3 kg of weight). Then, a subperiostal exposure of the occipital squama as well as posterior C1 and C2 vertebrae is performed, followed by 3 steps: (1) removal of the posterior margin of the foramen magnum for posterior decompression, (2) distraction of the occipito/C1-C2 joints for vertical reduction of BI using a interarticular spacer, and, (3) compression and extension of occipito-C1 on C2 over the fulcrum created by the placement of the spacer. The techniques of compression and extension may be performed by customized reducers placed between the occipital temporary screw and C2 spine or by placing a screw on the occipital bone and progressively tightening a stainless steel braided wire between the occipital screw and the C2 lamina. This technique initially leads to compression of the spacers followed by extension at the occipital-C1 and C2 joints leading to reduction of both the AAD and BI [28] [Figure 6] and [Figure 7].
Figure 6: The following figures shows sagittal sections through various congenital cranio-vertebral junction anomalies with vertical facet joints to demonstrate the “pseudo joints”. T= true joint, P= pseudo joint. Figures a and b illustrate the mechanism of formation of a pseudo-joint, when the facet joint becomes vertical. Figures c-f show the CT images of true vs pseudo joints in various patients with vertical occipito-C1 and C2 facet joints

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Figure 7: Schematic diagram showing the fundamental principle of DCER. (a) CT image of severe BI with AAD. (c) Once the spacer is added, the BI gets corrected but not the AAD. (b) Correction achieved once DCER is performed. (d) The same procedure explained schematically. Once compression between the occiput-C1 and C2 is provided, this results in extension of the occipito-C1 and C2 joint leading to reduction in both AAD and also residual BI

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This technique was initially published as a pilot study conducted in 35 patients.[28] A larger series of 79 patients with BI and AAD treated using the DCER technique along with two new modifications, has been published more recently.[25],[26],[27] The two new modifications have included joint remodeling and extra-articular distraction. In the cases, where the sagittal joint inclination was moderately severe (SJI: 100–160°), joint re-modeling was performed by “horizontalizing” the facet using a diamond drill. In cases of vertical joints (SJI: >160°), utilizing the technique of “extra-articular” distraction has beeen suggested, where the spacer is placed between a “pseudo joint” created between the upper surface of the C2 and the occiput.[70] This “pseudo joint” is formed due to the settling of occiput over the superior surface of the proximal pars and now transmits the weight of the head (as the true joint cannot do the same due to its vertical orientation). Thus, these pseudo joints are more superficially located than the true joints, and in some cases are even characterized by presence of “synovial membrane” and “synovial fluid.” The spacer once placed within the pseudo joint is then used as a fulcrum to reduce both AAD and BI as well, thus correcting the deformity. The authors have also suggested that an additional purchase may be obtained by incorporating the C3 and C4 lateral masses. These surgical techniques focus on deformity correction and provides different surgical strategies based on the measurement of joint indices previously described by the authors.[2],[42]

Using the same rationale, Salunke et al., reported their surgical results of C1-2 facet comprehensive drilling in 19 cases with BI, achieving direct posterior reduction in patients with irreducible AAD.[81] They reported that all patients had clinical improvement and 17 had total reduction and fusion with extensive drilling of the atlantoaxial joints surface. Of note, careful attention must be made of the anomalous vertebral arteries (VA) that are often present.[82],[83] A preoperative three-dimensional CT angiography is highly recommended before joints manipulations.[84],[85],[86],[87] The normal site of VA should be preferentially treated first because it facilitates opening of the abnormal site, potentially decreasing VA injury. C2 nerve root is encountered before the anomalous VA, which can be useful for surgical orientation.

A final remark is that fixation of the occipital squama has been questioned by some authors, as the majority of CVJ instability is in the atlantoaxial joint.[85] Inclusion of lateral masses of atlas in the construct may increase the rigidity of construction, avoiding the deleterious effects of craniocervical fixation in the subaxial spine, such as misalignment and disc degeneration. However, most of the patients with BI may have atlas assimilation and, in this scenario, further studies addressing the clinical differences between fixation of the occipital squama or only the assimilated lateral masses of the atlas are necessary [Table 2].
Table 2: Summary of current strategies in the surgical management of CVJ - Suggestions of the authors based on literature review

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Summary of the recommendations for using C1-2 interarticular spacers for treating basilar invagination and for intraoperative manipulations with deformity correcting surgeries

The use of C1-2 interarticular spacers is a valid surgical option for re-establishing craniocervical alignment in specific BI cases, probably being the most effective and powerful procedure to reduce BI and AAD, correct the deformity, and also avoid the need for an anterior odontoidectomy (AO). Apart from producing just distraction, spacers may be used as a fulcrum to produce a horizontal motion that may help correct BI, AAD, and the deformity. While the results have been good in the hands of few, the steep learning curve has to be taken into consideration, especially the complications associated with the handling of vertebral artery and the blood loss from the venous plexus. Additionally, in the setting of clinical deterioration after a posterior surgery with CVJ realignment, an additional anterior approach for brainstem decompression may be necessary. Chandra is also in the process of developing an universal CVJ reduction device which would allow the surgeon to not only perform extension at the occipital-C1/C2 joint but also would provide a sagittal translational movement, allowing for an optimal re-alignment (US patent 14/897,156). He is of the opinion that such a device would allow even surgeons of lesser experience to reduce and re-align the CVJ and thus achieve an optimal fixation.

Future questions regarding the long-term follow-up of DCER techniques and its influence in the final alignment and degeneration of subaxial cervical spine remain to be studied

The role of anterior approaches to the CVJ for both re-aligning and fixation

Yin et al., reported the results of five cases of AAD treated by one stage transoral atlantoaxial reduction and plate fixation.[88] This novel approach consisted of a transoral decompression, with resection of the dens and anterior atlantal arch, decortication of the C1-2 articular capsules and cartilaginous surface, followed by placement of a transoral reduction plate (TARP) system – a “butterfly-shaped” plate made of titanium. Four screws were used, two for the lateral masses of atlas and two for the body of the axis. An iliac crest graft was then inserted in the joints and the midline wound was closed. Of note, the majority of cases treated were old type II odontoid fractures. Patients required a tracheotomy prior to surgery. They reported that this procedure was also effective for irreducible AAD with ventral cord compression. Other authors have also reported small case series of transoral reduction of AAD with plate fixation, recommending this technique for well selected cases.[89],[90]

Future of surgical treatment of CVJ anomalies

The treatment of CVJ anomalies demands specific management in referral centers, where the highest level of surgical expertise is available. Currently, with a multitude of clinical and radiological presentations and with many surgical options being available, surgeons who manage diseases at the CVJ should be able to perform all the different procedures, from an anterior endoscopic decompression to the posterior craniocervical fixation with joint remodelling and re-alignment. An understanding of the nuances of each approach as well as the benefits and risks of different treatment modalities are mandatory to improve patient outcome and decrease morbidity. Future perspectives included the development of artificial atlantoaxial joints, similar to cervical arthroplasty. Salunke has proposed a design for artificial C1-2 joints that can mimic natural atlantoaxial movements, which may be used in clinical practice in the near future. Improvements in screws and plate designs, as well as in reduction tools for CVJ realignment, would also result in better clinical outcomes and safer procedures.[91]

Pearls and pitfalls

  1. The technique of addressing various anomalies in the area of CVJ with BI/AAD is undergoing rapid changes with a lot of innovations coming up and many surgeons proposing their own techniques. Thus, in this era of change, the whole paradigm of management is in a state of flux
  2. Pre-operative traction has been practically given up although it does result in a significant reduction.[7],[10],[34] The only indications for a pre-operative traction could be


    1. Completely reducible AAD with the patient presenting to the emergency in a deteriorating state with progressive quadriparesis. Usually, most of these patients can be immobilized on a hard Philadelphia collar and should be admitted and operated upon, as soon as possible
    2. Traumatic AAD, (note that traumatic atlanto-occipital dislocation is a contraindication for traction).
    3. Trans-oral surgery is also being given up progressively. The only indications would be:[41],[42]


    1. Infective pathologies like tuberculosis with significant compression
    2. Clival segmentation anomalies where the clivus is fused or pseudo-articulates with the dens causing ventral compression
    3. Learning curve of the surgeon is not adequate to perform solely the posterior procedure.


  3. It is important to ascertain the position of the vertebral artery in congenital anomalies. Hence, a CT angiogram with three dimensional reconstruction is mandatory.[84] Presence of a VA anomaly may be a relative contraindication for performing a spacer distraction technique, but Chandra et al., have suggested VA mobilization.[24],[27] In this situation, the surgeon should have adequate expertise to repair the rent in the VA, if it occurs, or should have a vascular surgeon available during surgery. It is important to place the construct screws on the side of non-dominant VA first.
  4. Alternate fixation strategies should always be available and planned e.g., laminar screws, C2 pedicle screws, wiring, etc
  5. In the sub-axial spine, it is important not to expose the joints of spaces where fixation is not being contemplated, e.g., if C3 fixation is being contemplated, then the C4 level should not be exposed, to prevent any undue exposure of the facet joints, leading to their instability
  6. Finally, it is important to remember that the metallic implants are bound to fail over time, hence adequate bone and osteogenic material should be made available to allow for an optimal bone fusion.



 » Conclusion Top


Surgical treatment of patients with CVJ anomalies is challenging even for experienced surgeons. Specific criteria for CVJ instability have been proposed. The use of C1-2 spacers for treating AAD associated with BI has been discussed in detail. In addition, new surgical procedures such as DCER, joint remodeling, and extra-articular distraction have also been presented. These techniques bring in a new era of surgical procedures, which apart from relieving spinal cord compression, also correct the deformity.

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]
 
 
    Tables

  [Table 1], [Table 2]



 

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