Redefining Congenital Atlantoaxial Dislocation: Objective Assessment in Each Plane Before and After Operation

The role of clivus and atlanto-occipital lateral mass height in basilar invagination with or without atlas occipitalization

Basilar invagination (BI) is a common deformity. This study aimed to quantitatively evaluate the height of clivus and atlanto-occipital lateral mass (LM) in patients with BI with or without atlas occipitalization (AOZ). We evaluated 166 images of patients with BI and of controls. Seventy-one participants were control subjects (group A), 68 had BI with AOZ (group B), and 27 had BI without AOZ (group C). Parameters were defined and measured for comparisons across the groups. Multiple linear regression analysis was used to test the relationship between Chamberlain's line violation (CLV) and the clivus height ratio or atlanto-occipital LM height. Based on the degree of AOZ, the lateral masses in group B were classified as follows: segmentation, incomplete AOZ, complete AOZ. From groups A to C, there was a decreasing trend in the clivus height and clivus height ratio. There was a linear negative correlation between the clivus height ratio and CLV in the three groups. Generally, the atlanto-occipital LM height followed the order of group B < group C < group A. The atlanto-occipital LM height was included only in the equations of groups B. There were no cases of atlantoaxial dislocation (AAD) in group C. There was a decreasing trend in LM height from the segmentation type to the complete AOZ type in group B. BI can be divided into three categories: AOZ causes LM height loss; Clivus height loss; Both clivus and LM height loss. The clivus height ratio was found to play a decisive role in both controls and BI group, while the atlanto-occipital LM height loss caused by AOZ could be a secondary factor in patients with BI and AOZ. AOZ may be a necessary factor for AAD in patients with congenital BI. The degree of AOZ is associated with LM height in group B.

Database Review of 514 Patients with Os Odontoideum. Detailed Analysis of 258 Surgically Treated (1978-2019)

OBJECTIVE

Database review (1978-2019) is to identify the cause of os odontoideum, its presentation, associated abnormalities, and management recommendations.

METHODS AND MATERIALS

Review of referral database of 514 patients and 258 surgically treated patients ages 4-64 years. Detailed history of early childhood trauma and initial encounter record retrieval were made. Patients had dynamic motion radiographs, dynamic motion MRI and also CT to identify pathology and reducibility of craniocervical instability. Preoperative crown halo traction was made before the year 2000 except in children. Intraoperative traction with O-arm/CT documentation was made since 2001. Reducible and partially reducible cases underwent halo traction under general anesthesia distraction, dorsal stabilization, and rib graft augmentation for fusion. Later semi-rigid instrumentation and subsequently rigid instrumentation was made. Irreducible compression of cervicomedullary junction was treated with ventral decompression. The follow up was 3-20 years.

RESULTS

Database; acute worsening after trauma 262, insidious neurological deficit 252. Minimal/normal motion with neurological deficit was present in 18, previous C1-C2 fusion with worsening in 18. 28 patients of 64 without treatment worsened in 4 years. An intact odontoid process was seen in 52 children of 156 who had early craniovertebral junction trauma and later developed os odontoideum.

SURGICAL EXPERIENCE

There were 174 patients with reducible lesions and partially reducible were 22. Irreducible lesions were 62. Of the reducible, 50 underwent transarticular C1-C2 fusion, 26 C1 lateral mass, and C2 pars screw fixation. 182 had occipitocervical fusion (19 had extension of previous C1-C2 fusion and 43 after transoral decompression). 62 with irreducible ventral compression of the cervicomedullary junction underwent transoral decompression; 43 had a trapped transverse ligament between the os and C2 body and 19 previous C1-C2 fusions. Compression was by the axis body, os odontoideum, and the posterior C2 arch. Syndromic and skeletal/connective tissue abnormalities were found in 86 (36%).

COMPLICATIONS

2 patients worsened, age 10 and 62, due to failure of semi-rigid construct.

CONCLUSIONS

The etiology of os odontoideum is multifactorial considering the associated abnormalities, reports of congenital-familiar occurrence, and early childhood craniovertebral trauma which also plays a role in the etiology. Patients with reducible lesions require stabilization. Asymptomatic patients are at risk for later instability. Patients who underwent childhood C1-C2 fusion must be followed for later problems. The irreducibility was seen due to trapped transverse ligament, pannus, or previous dorsal C1-C2 fusion.

Facet-occiput slope angle: A novel predictor of cage placement feasibility during surgery in basilar invagination patients

Background and aim

Direct posterior reduction and manipulation of the C1-2 joints, accompanied by placement of spacers, is the state-of-the-art technique for treating basilar invagination (BI) and atlantoaxial dislocation (AAD). The hindrance of occiput to reaching up to the true atlantoaxial facets (AAF) during the surgery remains challenging for cage placement. The aim of this study was to explore an objective and precise method of measuring the effect of the hindrance of occiput to reaching up to the true AAF and cage placement during surgery.

Method

We collected the clinico-imaging data of 58 patients with BI and AAD (Group A) who underwent surgery in our hospital, and 78 control cohorts (Group B) were retrieved retrospectively. We measured facet-occiput slope angle (FOSA) in midsagittal CT. Patients were positioned prone for surgery based on preoperative flexion O-C2a, and access to the true AAF was observed intraoperatively. The cut-off value of FOSA for the feasibility of cage placement in BI and AAD patients was appointed when access to the true AAF was impossible due to the hindrance of occiput during surgery.

Results

The cut-off value of FOSA for the feasibility of cage placement was 34o with an area under the curve AUC of 0.800 (95 % CI: 0.672-0.928, P < 0.001) and the Youden index of 0.607. In patients with FOSA >34o, reaching up to the true AAF and 3D-printed cage placement was impossible. FOSA was negative in Group A and positive in Group B, significantly larger in females compared to males in both groups and significantly larger postoperatively in Group A.

Conclusion

FOSA can objectively measure the feasibility of cage placement when the patient is positioned prone per preoperative flexion O-C2a. A FOSA >34o is contraindication for cage placement.

The clinical validity of atlantoaxial joint inclination angle and reduction index for atlantoaxial dislocation

Objective

Atlantoaxial dislocation patients with neurological defects require surgery. Sometimes, release surgery is necessary for irreducible atlantoaxial dislocation to further achieve reduction. Whether release surgery is essential relies on the surgeon's experience and lacks objective reference criteria. To evaluate the value of atlantoaxial joint inclination angle (AAJI) in sagittal and coronal planes and reduction index (RI) in the surgical approach selection for atlantoaxial dislocation.

Methods

Retrospectively analyzed 87 cases (42 males and 45 females, 9-89 years) of atlantoaxial dislocation from January 2011 to November 2020. In addition, 40 individuals without atlantoaxial dislocation were selected as the control group. Imaging parameters were compared between the two groups. According to surgical methods, the experiment group was divided into two groups including Group A(release surgery group) and Group B (conventional operation group). The parameters were measured based on CT and x-ray. The relevant imaging parameters and clinical scores, including the AAJI in sagittal and coronal planes, the atlas-dens interval (ADI) before and after traction, the RI, and JOA scores were measured and analyzed.

Results

The sagittal and coronal atlantoaxial joint inclination angles(SAAJI and CAAJI) in the control group were 7.91 ± 0.42(L), 7.99 ± 0.39°(R), 12.92 ± 0.41°(L), 12.97 ± 0.37°(R), in A were 28.94 ± 1.46°(L), 28.57 ± 1.55°(R), 27.41 ± 1.29°(L), 27.84 ± 1.55°(R), and in B were 16.16 ± 0.95°(L), 16.80 ± 1.00°(R), 24.60 ± 0.84°(L), 24.92 ± 0.93°(R) respectively. Statistical analysis showed that there was a statistical difference in the SAAJI between the control group and the experiment group (P < 0.01), as well as between groups A and B (P < 0.01). The RI in groups A and B was 27.78 ± 1.46% and 48.60 ± 1.22% respectively, and there was also a significant difference between the two groups (P < 0.01). There was negative correlation between SAAJI and RI.

Conclusions

The SAAJI and RI can be used as objective imaging indexes to evaluate the reducibility of atlantoaxial dislocation. And these parameters could further guide the selection of surgery methods. When the RI is smaller than 48.60% and SAAJI is bigger than 28.94°, anterior release may be required.

Three-dimensional reduction method with a modified C2 isthmus screw in irreducible atlantoaxial dislocation: a technical note

BACKGROUND

Three-dimensional reduction plays a vital role in surgical reduction of irreversible atlantoaxial dislocation (IAAD). However, the most commonly used combination of C1 pedicle screw (PS) or lateral mass screw (LMS) and C2 PS or isthmus screw often fails to achieve satisfactory reduction at one time. The difficulty is usually caused by short anteroposterior and vertical distance between heads of C1 and C2 screws, which lack enough space for reduction operation. The objective of this study is to describe a three-dimensional reduction method with a modified C2 isthmus screw and to illustrate its advantage and effectiveness for IAAD.

METHODS

Twelve patients with IAAD underwent reduction and fixation with modified C2 isthmus screw combined with C1 PS or LMS, fusion with autologous bone graft. The insertion point was lateral to the intersection of caudal edge of C2 lamina and lateral mass, with a trajectory towards C2 isthmus, via lateral mass. The three-dimensional reduction was achieved through pulling and distracting. Radiographic evaluation included anteroposterior and direct distance between different insertion points, the occipitoaxial angle (O-C2A), clivus-canal angle (CCA) and cervicomedullary angle (CMA). Clinical outcomes evaluation included the Japanese Orthopaedic Association (JOA) score, Visual analog scale (VAS) and Neck Disability Index (NDI).

RESULTS

All the patients maintained effective reduction during the follow-up. The anteroposterior and direct distance was significantly higher in modified C2 isthmus screw than C2 PS whether combined with C1 PS or LMS (P < 0.05). The degree of O-C2A, CCA and CMA, JOA score, NDI, and VAS were significantly improved after the surgery (P < 0.05).

CONCLUSIONS

Three-dimensional reduction method with a modified C2 isthmus screw is effective and safe in managing IAAD. It can increase the anteroposterior and vertical distance between the heads of C1 and C2 screws, which is benefit for the three-dimensional reduction operation of IAAD.

A Safe and Effective Posterior Intra-Articular Distraction Technique to Treat Congenital Atlantoaxial Dislocation Associated With Basilar Invagination: Case Series and Technical Nuances

BACKGROUND

The management of atlantoaxial dislocation (AAD) associated with basilar invagination (BI) is challenging, and traditional posterior-only approaches lack the ability to release the anterior soft tissue resulting in unsatisfactory reduction. Furthermore, vertebral artery anomalies and deformed anatomy increase surgical risks.

OBJECTIVE

To introduce a safe and efficient technique to reduce congenital AAD and BI through a single-stage posterior-only approach.

METHODS

A total of 65 patients with AAD and concomitant BI who had congenital osseous abnormalities were retrospectively analyzed. All patients had anterior soft tissue released through a posterior-only approach, followed by intra-facet cages implantation, cantilever correction, and instrumentation. Clinical results were measured using the Japanese Orthopedic Association (JOA) scale, and radiographic measurements included the atlanto-dental interval, the distance of odontoid tip above Chamberlain's line, clivus-canal angle (CCA), and syrinx length. Paired t-tests were used to compare preoperative and postoperative measurements.

RESULTS

The mean JOA score increased from 10.98 to 14.40 at 1-yr follow-up. Complete reduction of AAD and BI was achieved in 48 patients (73.8%). The mean CCA improved from 115° preoperatively to 129° postoperatively. Reduction of syrinx size was observed in 14 patients at 1 wk and in 35 patients 1 yr after surgery. All patients achieved bony fusion.

CONCLUSION

Posterior intra-articular distraction followed by cage implantation and cantilever correction can achieve complete reduction in most cases of congenitally anomalous AAD associated with BI.

Morphometric Analysis of the Lateral Atlantoaxial Joints in Patients with an Old Type II Odontoid Fracture and Atlantoaxial Dislocation: A Study Based on CT Analysis

MINI

The morphological features of the lateral atlantoaxial joints (LAJs) in patients with old type II odontoid fractures and atlantoaxial dislocation have not been fully analyzed. Our study found the changes in morphological features of the LAJs in some patients, and revealed the causes and consequences of the changes in morphological features of the LAJs.

Displaced odontoid synchondrosis fracture with C1-2 dysjunction in an 18-month-old child: challenges and solutions

BACKGROUND

Odontoid synchondral fractures in very young children with displacement/angulation are highly unstable and require surgical intervention. Soft and small bones with poor pull-out strengths make instrumentation and manipulation difficult.

CASE REPORT

We report an 18-month-old child with such a fracture where minimal traction made C1-2 dysjunction apparent with neurological worsening. The C1-2 facets were fixed with a short plate and facetal screws. The child had a good outcome.

CONCLUSION

Traction should be applied cautiously to avoid distraction injuries. Careful intraoperative manipulation should be planned to avoid any pull outs/fractures while realigning the spine and fixing it.

Anesthetic management for cesarean delivery in a woman with congenital atlantoaxial dislocation and Chiari type I anomaly: a case report and literature review

Background

The preferable choice of anesthesia for the patients with congenital atlantoaxial dislocation (CAAD) and type I Arnold Chiari malformations (ACM-I) has been a very confusing issue in clinical practice. We describe the successful administration of combined spinal-epidural anesthesia for a woman with CAAD and ACM-1 accompanied by syringomyelia.

Case presentation

Our case report presents the successful management of a challenging obstetric patient with CAAD and ACM-1 accompanied by syringomyelia. She had high risks of difficult airway and aspiration. The injection of bolus drugs through the spinal or epidural needle may worsen the previous neurological complications. The patient was well evaluated with a multidisciplinary technique before surgery and the anesthesia was provided by a skilled anesthesiologist with slow spinal injection.

Conclusions

An interdisciplinary team approach is needed to weigh risks and benefits for patients with CAAD and ACM-1 undergoing cesarean delivery. Therefore, an individual anesthetic plan should be made basing on the available anesthetic equipments and physicians’ clinical experience on anesthetic techniques.

Fiberoptic bronchoscopy versus video laryngoscopy guided intubation in patients with craniovertebral junction instability: A cinefluroscopic comparison

Background:

Manipulation during endotracheal intubation in patients with craniovertebral junction (CVJ) anomalies may cause neurological deterioration due to underlying instability. Fiberoptic-bronchoscopy (FOB) is better than video laryngoscope (VL) for minimizing cervical spine movement during intubation. However, evidence suggesting superiority of FOB in patients with CVJ instability is lacking. We prospectively compared dynamic movements of the upper cervical spine during intubation using FOB with VL in patients with CVJ anomalies.

Methods:

A prospective, randomized, and clinical trial was conducted in 62 patients of American Society of Anaesthesiologist Grade I-II aged between 12 and 65 years with CVJ anomalies. Patients were randomized for intubation under general anesthesia with either VL or FOB. The intubation process was done with application of skeletal traction and recorded cinefluroscopically. The dynamic interrelationship of bony landmarks (horizontal, vertical, and diagonal distances between fixed points on posterior C1 and C2) was analyzed to indirectly calculate alteration of the upper cervical spinal canal diameter (at CVJ). Atlanto-dental interval (ADI) was calculated wherever possible.

Results:

The alteration in canal diameter (using bony landmarks) at CVJ during intubation was not significant with the use of either VL or FOB (P > 0.05). In 41 patients, where ADI could be measured, ADI was reduced (increased spinal canal diameter) in a greater number of patients in VL group when compared to FOB group (P < 0.05).

Conclusion:

Using rigid skull traction, intubation under general anesthesia with VL offers similar advantage as FOB in terms of the spinal kinematics in patients with CVJ anomalies/instability. Nevertheless, greater number of patients intubated with VL may have an advantage of increased cervical spinal canal diameter when compared to FOB.

Outcome of Surgery for Congenital Craniovertebral Junction Anomalies with Atlantoaxial Dislocation/Basilar Invagination: A Retrospective Study of 94 Patients

OBJECTIVE

To evaluate the results of surgery for congenital craniovertebral junction (CVJ) anomalies with atlantoaxial dislocation (AAD)/basilar invagination (BI) and compare the results of transoral odontoidectomy and posterior fusion (TOO+PF) with only posterior fusion (PF) in patients with irreducible AAD/BI.

METHODS AND RESULTS

All 94 patients with congenital CVJ anomalies with AAD/BI operated on during the 3-year study period (June 2013-May 2016) were included. Of these patients, 55 had irreducible AAD/BI and the remaining 39 had reducible AAD/BI. TOO+PF was restricted to patients (34/94; 36.2%) with irreducible AAD/BI when reduction and realignment by intraoperative C1-C2 facet joint manipulation were considered technically difficult and risky. The remaining patients with irreducible AAD/BI and all the patients with reducible AAD/BI (60/94; 63.8%) were managed with only posterior fusion. Poor preoperative Nurick grade, preoperative dyspnea/lower cranial nerve deficits, and syringomyelia were associated with significantly higher incidence of postoperative pulmonary complications. Follow-up ≥3 months (final follow-up) was available for 87 patients. Good outcome (Nurick grade 0-3) at final follow-up was noted in 90% (45/50) of the patients with irreducible AAD/BI and 91.9% (34/37) of the patients with reducible AAD/BI. Preoperative poor Nurick grade (4-5) was the only factor associated with poor outcome. No significant difference in perioperative complications, outcome, and fusion was noted between patients who underwent TOO+PF or only PF for irreducible AAD/BI.

CONCLUSIONS

Many of the patients with congenital AAD/BI showed remarkable recovery after surgery. Preoperative poor Nurick grade (4-5) is associated with poor outcome. TOO+PF is a safe alternative treatment option for irreducible AAD/BI when only PF techniques are technically difficult/risky.

Classification of the facets of lateral atlantoaxial joints in patients with congenital atlantoaxial dislocation

PURPOSE

To investigate the morphological characteristics and para-positions of the facets of lateral atlantoaxial joints (FLAJs) in patients with congenital atlantoaxial dislocation (CAAD) and to propose a classification system for the FLAJs.

METHODS

A total of 93 cases of CAAD were included in this retrospective study. The obliquity and slippage of the FLAJs in the sagittal and coronal planes were measured and observed in the CT images of all of the cases. The obliquity and slippage of the FLAJs represented the morphological characteristics and the para-positions, respectively, and were used as classification parameters. Accordingly, a classification system for the FLAJs was established. We additionally investigated the correlation between the classifications of the FLAJs and various types of CAAD. The classifications of the FLAJs in 34 patients with irreducible AAD (IAAD) were also investigated.

RESULTS

One hundred eighty-six FLAJs in 93 patients were classified into 6 types (namely, A, B1, B2, C, D1, and D2) for obliquity and 3 types (namely, S₀, S₁, and S₂) for slippage. Among the 186 FLAJs, type B1 and type S₀ were the most common obliquity and slippage types, respectively. There were 11 combination types for obliquity and 5 combination types for slippage of bilateral FLAJ in 93 patients. Most of the patients (69.7%, 47/70) with anteroposterior AAD had accompanying slippage and anteversion of the FLAJ in the sagittal plane. Rotational AAD was found in 10 patients with asymmetrical slippage in both FLAJs in the sagittal plane. Lateral translational AAD was found in 6 patients with an S₁-type FLAJ in the coronal plane. In 5 patients with lateral angular AAD, FLAJs of types D1 and S₂ were observed on one side. Among the 34 patients with IAAD, 31 patients had both obliquity and slippage in the FLAJs on one or both sides.

CONCLUSION

The morphological characteristics and para-positions of the FLAJs on both sides largely determine the types of AAD in patients with CAAD. The types of obliquity and slippage of the FLAJ are related to the reducibility of AAD.

The Value and Limitation of Cervical Traction in the Evaluation of the Reducibility of Atlantoaxial Dislocation and Basilar Invagination Using the Intraoperative O-Arm

OBJECTIVE

To assess the value and limitation of cervical traction in the evaluation of the reducibility of atlantoaxial dislocation (AAD) and basilar invagination (BI) using the intraoperative O-arm.

METHODS

A total of 22 patients with hyperextensive, irreducible AAD were included. The cervical traction test under general anesthesia was performed, and the degree of reduction was evaluated using the O-arm before the operation started. The traction effects both vertically and horizontally were evaluated. All cases then underwent modified direct posterior reduction and fixation. Clinical outcomes were evaluated using the Japanese Orthopaedic Association (JOA) scale. Radiologic measurements included the anterior atlantodental interval, the distance of odontoid tip above Chamberlain line, and the clivus-canal angle. Magnetic resonance imaging signal changes, size of syringomyelia, and the space ventral to medulla also were used to evaluate the postoperative reduction result.

RESULTS

After the cervical traction test, 7 patients achieved incomplete reduction, 5 achieved only vertical reduction, 6 achieved only horizontal reduction, and 4 achieved complete reduction in both horizontal and vertical orientations as assessed by the O-arm. All patients underwent a direct reduction technique. The mean JOA score increased from 11.1 to 14.5. Complete reduction of AAD and BI were achieved in 19 patients (86.4%), with partial reduction achieved in 3 (13.6%). Sufficient cerebrospinal fluid space anterior to the medulla with improved JOA score was achieved in the 3 partially reduced patients.

CONCLUSIONS

With the innovations of direct posterior reduction techniques, cervical traction under anesthesia may not sufficiently predict the reducibility of BI and AAD. Cervical traction still plays an important role during the direct posterior reduction procedure.

Foramen magnum decompression without bone removal: C1-C2 posterior fixation for Chiari with congenital atlantoaxial dislocation/basilar invagination

Background:

Atlantoaxial dislocation (AAD) and basilar invagination (BI) may coexist with Chiari malformations (CM) and a small posterior fossa volume. These are typically treated with craniovertebral junction fusion and foramen magnum decompression (FMD). Here, we evaluated whether C1–C2 posterior reduction and fixation (which possibly opens up the ventral foramen magnum) would effectively treat AAD and CM without additionally performing FMD.

Methods:

This is a retrospective analysis of 38 patients with BI, AAD, and CM who underwent C1–C2 posterior reduction and fusion without FMD. Baseline and follow-up clinical, demographic, and radiological data were evaluated.

Results:

The vast majority of patients (91.9%) improved both clinically and radiographically following C1–C2 fixation alone; none later required direct FMD. Notably, AAD was irreducible in 25 (65.8%) patients. Preoperatively, syringomyelia was present in 28 (73.7%) patients and showed resolution. In 3 (8.1%) patients, resolution of syrinxes did not translate into clinical improvement. Of interest, 5 patients who sustained inadvertent dural lacerations exhibited transient postoperative neurological worsening.

Conclusions:

Posterior C1–C2 distraction and fusion alone effectively treated AAD, BI, accompanied by CM. The procedure sufficiently distracted the dens, reversed dural tenting, and restored the posterior fossa volume while relieving ventral brainstem compression making FMD unnecessary. Surgeons should, however, be aware that inadvertent dural lacerations might contribute to unwanted neurological deterioration.

Irreducible Posterior C1-2 Dislocation with Retrolisthesis of Dens: Hindsight from 10 Cases

OBJECTIVE

Posterior C1-2 dislocation secondary to fracture of the dens or os odontoideum is uncommon. Little is known about posterior dislocations in which close reduction fails, requiring intraoperative maneuvers. The objective of this retrospective study was to analyze clinical presentations, factors causing irreducibility, and nuances in the achievement of intraoperative reduction.

METHODS

The clinicoradiological features of 10 patients with irreducible posterior C1-2 dislocation were studied. Six were posttraumatic, with odontoid fractures, and 4 had os odontoideum. The radiologic images were studied to analyze the cause of irreducibility, and the operative management of these cases was discussed.

RESULTS

The patients with traumatic dislocation had persistent neck pain (n = 6) and early onset (n = 1) or delayed onset (n = 4) myelopathy. The fracture line was oblique, extending anterosuperiorly to posteroinferiorly in all except 1 patient, with fracture fragments distracted in 4 and interlocked in 2. There was associated lateral translation in 2. All patients had facet locking. Intraoperative reduction was achieved in all by unlocking the facets, intrafracture reduction, or both. All 4 patients with congenital posterior dislocations had retrolisthesis of dens with lateral translation. They presented with neck tilt (n = 4) and severe myelopathy (n = 3). They were easier to reduce intraoperatively, but the improvement lesser in comparison with the traumatic fractures.

CONCLUSIONS

The posterior C1-2 dislocation associated with fracture of the dens or os-odontoideum is a distinct entity. Lateral translation is often seen with retrolisthesis of the os odontoideum and occasionally in traumatic posterior dislocations. It is necessary to address the cause of irreducibility and achieve multiplanar realignment for a good outcome.

Anomalous V3 Segment Aneurysm Associated with Congenital Atlantoaxial Dislocation: Case Report and Discussing the Challenges in Management

BACKGROUND

An anomalous vertebral artery is not a deterrent for posterior C1-C2 joint manipulation and reduction of atlantoaxial dislocation (AAD). However, presence of an incidental aneurysm in the aberrant segment of artery with concurrent AAD adds to the surgical challenge.

CASE DESCRIPTION

A 30-year-old woman presented with neck pain and spastic quadriparesis. Her imaging revealed atlantoaxial dislocation and bony segmentation defects. Three-dimensional computed tomography angiography showed bilateral anomalous vertebral arteries (V3 segment) and an incidental aneurysm on the arterial segment that crossed the right C1-C2 joint posteriorly. Because the artery bearing the aneurysm was nondominant, it was ligated and successful C1-C2 posterior reduction and fusion could be performed.

CONCLUSION

The association of an incidental aneurysm with an anomalous vertebral artery in congenital AAD is unusual. The etiology could be an underlying collagen defect or repeated shearing trauma to the vessel wall due to C1-C2 instability. It would be less risky to proceed with endovascular embolization followed by occipitocervical fusion without opening the joints in case the aneurysm is present on the dominant aberrant V3 segment. Ventral decompression can be supplemented for irreducible AAD. On the contrary, if the aneurysm is present on the nondominant aberrant V3 segment, the C1-2 joint can be opened and manipulated following an initial endovascular treatment of the aneurysm. If the circumstances demand, the nondominant artery can be ligated and sacrificed, although there is a small risk of formation of stump aneurysm.

"Suspended Posterior Tubercle of Atlas" with Atlantoaxial Dislocation

INTRODUCTION

Congenital anomaly of the C1 posterior arch is a well-known entity and is often associated with atlantoaxial dislocation. However, a well-formed C1 posterior tubercle with absence of the remaining posterior arch is rare. Such unusual anomalies pose a surgical challenge as trying to delineate the arch early in the course of surgery could be potentially dangerous. We discuss here a similar case of C1 posterior arch defect with atlantoaxial dislocation and its management.

CASE REPORT

A 17-year-old female presented with progressive spastic quadriparesis and neck pain. Evaluation revealed atlantoaxial dislocation with the presence of a well-formed posterior C1 tubercle in the absence of the rest of the posterior arch. C1-C2 joints were opened, and lateral masses were fused in reduced position. Intraoperatively, a posterior C1 tubercle was found suspended from the lateral masses by fibrous bands. The surgical nuances have been discussed.

CONCLUSION

Presence of posterior tubercle alone with aplasia of the posterior arch results from a persistent posterior ossification center with nonextension of lateral ossification centers. In the presence of the C1 posterior fibrous arch, the joint spaces must be exposed first before attempting to delineate the posterior arch. This will prevent inadvertent injury to the vertebral artery and dura.

Delineate, Yet not Dread: Anomalous Vertebral Artery in Pediatric Congenital Atlantoaxial Dislocation and Basilar Invagination

Introduction:

The deformed joints seen in congenital atlantoaxial dislocation (CAAD) are often associated with vascular anomalies. It is important to identify these vascular anomalies and address them appropriately without compromising the manipulation and fusion of C1–C2 joints. The small bones in pediatric age group pose an additional challenge.

Materials and Methods:

Data of fifty-six children with CAAD operated in the last 4 years was analyzed. A computed tomography angiogram was obtained preoperatively to assess for the course of the third segment of vertebral artery (VA). The anomalous VA was dissected and safeguarded during drilling and manipulation of the C1–C2 joints.

Results:

Of the 112 VAs, 5 were aplastic, 21 crossed the joint posteriorly. Only one patient with reducible atlantoaxial dislocation (AAD) had anomalous VA crossing the joint posteriorly, the remaining VA anomalies were seen with irreducible AAD. Anomalous VA was seen on both sides in 2 patients. The most common anomaly was an inverted VA seen in seven sides. In all patients, the anomalous VA could be dissected and safeguarded without compromising the C1–C2 dissection and manipulation and fusion. In children, even the normal VA may occasionally pose difficulties while manipulation of joints. Challenges while addressing the anomalous and normal VA in pediatric age group have been described. Techniques to overcome these have been discussed.

Conclusion:

It is important to delineate the anomalous VA. However, the presence of such an artery is not a deterrent to the manipulation of C1–C2 joint, essential for best results. Special attention needs to be paid to the extent of distraction, medial C2 transverse foramen, and dissection/drilling of the area superior to the anomalous VA in the pediatric age group.

"Soft that molds the hard:" Geometric morphometry of lateral atlantoaxial joints focusing on the role of cartilage in changing the contour of bony articular surfaces

Purpose:

The existing literature on lateral atlantoaxial joints is predominantly on bony facets and is unable to explain various C1-2 motions observed. Geometric morphometry of facets would help us in understanding the role of cartilages in C1-2 biomechanics/kinematics.

Objective:

Anthropometric measurements (bone and cartilage) of the atlantoaxial joint and to assess the role of cartilages in joint biomechanics.

Materials and Methods:

The authors studied 10 cadaveric atlantoaxial lateral joints with the articular cartilage in situ and after removing it, using three-dimensional laser scanner. The data were compared using geometric morphometry with emphasis on surface contours of articulating surfaces.

Results:

The bony inferior articular facet of atlas is concave in both sagittal and coronal plane. The bony superior articular facet of axis is convex in sagittal plane and is concave (laterally) and convex medially in the coronal plane. The bony articulating surfaces were nonconcordant. The articular cartilages of both C1 and C2 are biconvex in both planes and are thicker than the concavities of bony articulating surfaces.

Conclusion:

The biconvex structure of cartilage converts the surface morphology of C1-C2 bony facets from concave on concavo-convex to convex on convex. This reduces the contact point making the six degrees of freedom of motion possible and also makes the joint gyroscopic.