OBJECTIVE: The study aimed to evaluate the safety, feasibility, effect on fusion, and clinical efficacy of atlas lateral mass and C2-3 transfacet screw fixation technique, serves as an alternative method to traditional posterior atlantoaxial fixation.
METHODS: Patients with atlantoaxial instability who underwent atlas lateral mass and C2-3 transfacet fixation surgery were included. The duration of the surgery and the quantity of blood lost during the operation were recorded. Patients were monitored via X-ray and computed tomography scans to evaluate the degree of fusion at the one-month and 12-month follow-up. The Neck Visual Analogue Scale(VAS) and Neck Disability Index(NDI) were evaluated preoperatively, in the postoperative first week, and at the 12-month follow-up for clinical follow-up.
RESULTS: A total of eight patients with atlantoaxial instability due to odontoid fracture or Arnold- Chiari malformation accompanied by bony or vascular abnormalities were included in the study between 2017 and 2024. All eight patients underwent successful atlas lateral mass and C2-3 transfacet screw fixation, with no neurovascular injury noted during surgery. All patients with fracture exhibited fusion at the 12-month mark, and both the Neck VAS and NDI scores demonstrated significant improvement at both the one-week and 12-month postoperative periods(p<0.05).
CONCLUSIONS: The atlas lateral mass and C2-3 transfacet screw fixation technique, an alternative to conventional posterior fixation, has been demonstrated tobe an efficacious method for providing adequate stabilization and fusion in patients with atlantoaxial instability, even in the cases of thin C2 pedicle, high-riding vertebral artery, previous failed surgeries or reoperation.

BACKGROUND: Upper cervical complex fractures are associated with high rates of neurological damage and mortality. The Dickman\'s classification is widely used in the diagnosis of upper cervical complex fractures. However, it falls short of covering the full spectrum of complex fractures. This limitation hinders effective diagnosis and treatment of these injuries.
OBJECTIVE: To address the diagnostic gap in upper cervical complex fractures, the study introduces a novel classification system for these injuries, assessing its reliability and usability.
METHODS: Proposal of a new classification system for upper cervical complex fractures.
METHODS: The study comprised the clinical data of 242 patients with upper cervical complex fractures, including 32 patients treated at our hospital, along with an additional 210 cases from the literature.
METHODS: The inter-observer and intra-observer reliability (kappa coefficient, κ) of this classification system were investigated by 3 spine surgeons. The 3 researchers independently re-evaluated the upper cervical complex fracture classification system 3 months later.
METHODS: The proposed classification categorizes upper cervical complex fractures into 3 main types: Type I combines odontoid and Hangman\'s fractures into 2 subtypes; Type II merges C1 with odontoid/Hangman\'s fractures into 3 subtypes; and Type III encompasses a combination of C1, odontoid, and Hangman\'s fractures, divided into 2 subtypes. Meanwhile, a questionnaire was administered in 15 assessors to evaluate the system\'s ease of use and clinical applicability.
RESULTS: A total of 45 cases (18.6%) unclassifiable by Dickman\'s classification were successfully categorized using our system. The mean κ value of inter-observer reliability was 0.783, indicating substantial reliability. The mean κ value of intra-observer reliability was 0.862, indicating almost perfect reliability. Meanwhile, thirteen assessors (87.7%) stated that the classification system is easy to remember, easy to apply, and they expressed intentions to apply it in clinical practice in the future.
CONCLUSIONS: This system not only offers high confidence and reproducibility but also serves as a precise guide for clinicians in formulating treatment plans. Future prospective applications are warranted to further evaluate this classification system.

UNASSIGNED: To identify clinical and MR predictors of retro-odontoid pseudotumor (ROP) regression after posterior fixation in patients with atlantoaxial instability.
UNASSIGNED: We included patients who had undergone posterior fixation for atlantoaxial instability and preoperative and postoperative MR imaging. Patients were classified into two groups according to the degree of ROP regression after posterior fixation: regression (≥ 10% reduction) and no regression (< 10% reduction). Mann-Whitney and Fisher\'s exact tests were performed to identify the clinical (age and sex) and MR predictors (preoperative ROP thickness, ROP type, MR signal homogeneity of the ROP, spinal cord signal change, spinal cord atrophy, ossified posterior longitudinal ligament, os odontoideum, and atlantodental interval) associated with ROP regression.
UNASSIGNED: We retrospectively assessed 11 consecutive patients (7 female; median age, 66 years [range, 31-84 years]). Posterior fixation induced ROP regression in eight (72.7%) patients. Older age and greater preoperative ROP thickness significantly correlated with ROP regression (p = 0.024 and 0.012, respectively). All patients with preoperative ROP thickness > 5 mm exhibited ROP regression. The other variables were not significantly associated with ROP regression.
UNASSIGNED: Older age and thicker preoperative ROP are associated with ROP regression after posterior fixation in patients with atlantoaxial instability.
UNASSIGNED: 치상돌기 후방부 가성 종양(retro-odontoid pseudotumor; 이하 ROP)이 있는 환자 중, 경추 후방 유합술 후 가성 종양의 퇴행에 대한 임상 및 MR 예측 인자를 조사한다.
UNASSIGNED: 2016년 3월부터 2021년 12월까지 경추 후방 유합술을 받은 만성 환축추 불안정성 환자 중, 수술 전후의 MRI가 모두 있는 환자를 대상으로 하였다. 수술 후 ROP 두께가 감소한 정도에 따라, 10% 이상 감소한 그룹과, 10% 미만으로 감소한 그룹으로 분류한 후 ROP의 퇴행과 관련된 임상 특성(나이 및 성별) 및 MR 영상 소견을 분석하여 통계 분석하였다.
UNASSIGNED: 조건을 만족하는 11명의 환자 중 수술 후 8명의 환자에서 ROP 두께가 감소하였으며 (72.7%), 가성 종양의 퇴행에 환자의 나이(p = 0.024)와 수술 전 ROP의 두께(p = 0.012)가 유의하게 연관되었다. 성별, ROP의 유형, ROP의 MR signal 균일성, 척수 신호 변화, 척수 위축, 후종인대골화증, 치상돌기골, 그리고 환추상돌기간격은 ROP의 퇴행과 유의한 연관이 없었다.
UNASSIGNED: 만성 환축추 불안정성 환자 중, 연령이 높고, 수술 전 ROP의 두께가 더 두꺼울수록 경추 후방 유합술 후 ROP 퇴행이 더 많이 진행되었다.

Chiari malformations, characterized by the herniation of cerebellar tonsils through the foramen magnum, are complex neurosurgical conditions that pose significant diagnostic and therapeutic challenges.1 Traditional interventions, such as foramen magnum decompression, have been the mainstay of treatment but are not universally effective, especially in cases with underlying atlantoaxial instability. However, recent studies highlight the importance of atlantoaxial instability in their pathogenesis, shifting the therapeutic focus towards atlantoaxial fixation.2 Research shows that atlantoaxial fixation can effectively address the underlying instability, leading to better symptomatic relief and neurological outcomes compared to traditional decompression methods.3,4-17 The findings from these studies consistently demonstrate that atlantoaxial instability is a critical factor in the development of Chiari malformations. Atlantoaxial fixation not only resolves the mechanical instability but also leads to significant symptomatic relief and improved neurological outcomes. Comparative analysis indicates superior efficacy of atlantoaxial fixation over traditional decompression techniques, especially in patients with concurrent basilar invagination and syringomyelia. This surgical Video 1 illustrates a case of a 20-year-old male patient with tonsillar herniation, syringomyelia, atlantooccipital assimilation, atlantoaxial instability, basilar invagination and dorsolumbar scoliosis, who was successfully managed with cervical fixation using a bilateral C1 lateral mass and C2 transpedicular screw construct. This surgery was able to achieve clinical and radiologic improvement without the need for a foramen magnum decompression. The patient consented to the procedure and to the publication of his images.

Background: Atlantoaxial instability is the most common cervical instability in patients with rheumatoid arthritis (RA). Its course may differ in different patients and may have different degrees of severity and symptoms. Methods: There are a number of studies on systemic factors associated with the development of this instability, but there are few publications in the scientific literature on the influence of biomechanical factors on the development of cervical instability. One of the areas that allows the study of biomechanical factors influencing spine pathologies is the analysis of sagittal balance using radiological parameters. The study of radiological parameters of sagittal balance has contributed to understanding the pathology of selected spine diseases and is currently an indispensable tool in planning surgical treatment. Results: The presented study, conducted on a group of RA patients with cervical instability, was performed to look for a relationship between C1-C2 instability and sagittal balance parameters. Conclusions: Among the examined selected parameters, a statistically relationship between C1-C2 instability and the Cobb angle C1-C7 and OD-HA parameters has been found. This confirms the need for further in-depth research on this areas.

OBJECTIVE: Surgical stabilization of the Atlas vertebrae is indicated for severe atlantoaxial instability (AAI) in patients with Down syndrome (DS). This study aims to evaluate the morphological characteristics of the Atlas lateral mass (ALM) in patients with DS with regard to safe instrumentation for surgical stabilization and to compare them with non-syndromic group.
METHODS: This multicenter, retrospective, case-control study included age- and sex-matched patients with and without DS aged > 7 years with a cervical computed tomography (CT) scan. After three-dimensional CT reconstruction, nine parameters were evaluated for both groups. All included measurements were performed by a neuroradiologist who was blinded to clinical data.
RESULTS: Forty-three of 3,275 patients with DS were included in this study. Matching number of consecutive patients without DS were identified (mean age: 16 years). Patients with DS were significantly shorter than those without DS. Seven of nine parameters related to ALM were significantly lower in patients with DS than in those in the control group, including anterior wall height (AH), posterior wall height (PH), their ratio, and arch-ALM angle. On adjusting data for patient height, patients with DS had a smaller PH, lower PH/AH ratio, and steeper arch-ALM angle than the control group.
CONCLUSIONS: Patients with DS had a smaller posterior ALM wall and a steeper arch-ALM angle than the control group without DS. This information is important for surgical planning of safe posterior ALM exposure and safe instrumentation for surgical stabilization in patients with DS.

OBJECTIVE: The present study described a modified technique of atlantoaxial arthrodesis in patients with atlantoaxial instability (AAI) along with the postoperative clinical and radiological results.
METHODS: Five patients underwent this method for their AAI concurrent with C1 arch hypoplasia and/or the development of odontoid pannus causing myelopathy. After thorough exposure of the posterior surface of the C1-2 complex, the bilateral C2 nerve roots were sectioned to allow for easier access to the C1/2 facet joints. To prepare a suitable grafting bed, the C1/2 facet capsule was opened, and then the articular cartilaginous and synovial tissues were thoroughly removed. After being properly fashioned to match the gap between the C1/2 facet joint spaces, the structural bone grafts from the iliac crest were directly inserted into the facet joint spaces. To alleviate cord compression caused by concomitant odontoid pannus and/or hypoplastic C1 arch, C1 laminectomy was necessitated in all cases. Subsequently, posterior screw-rod instrumental fixation was conducted.
RESULTS: All 5 patients underwent this procedure successfully. Clinical and radiological follow-up data of all patients indicated favorable relief of clinical symptoms and early rigid C1-2 stability. The sequelae of C2 nerve resection were not remarkable. No other neural or vascular damage associated with this technique was observed.
CONCLUSIONS: Modified atlantoaxial arthrodesis via intraarticular autografting using the structural iliac bone combined with posterior instrumentation appears to be an efficient alternative treatment method for AAI patients with concurrent pathologies, even when the C1-2 posterior arches are unavailable for the grafting bed.

An 8-month-old, 3.4 kg, castrated male Toy Poodle was referred for progressive tetraparesis and respiratory disorder without a history of trauma. Repeated computed tomography (CT) and magnetic resonance imaging (MRI) with different positions of the neck revealed concurrent atlanto-occipital dislocation (AOD) and atlantoaxial instability (AAI) with spinal cord compression. This case was unique due to its congenital nature and the absence of trauma. The surgical treatment involved precise removal of the C1 vertebra\'s ventral articular facet, which was compressing on the spinal cord, attributed to its fixed and malaligned position within the atlantooccipital joint. Following facetectomy, the stabilization of the occipital bone to the C2 vertebra was achieved by screws, wire, and polymethyl methacrylate. Two days after surgery, the dog recovered ambulation and showed gradual improvement in gait, despite mild residual ataxia. Postoperative CT and radiographs showed successful decompression of the spinal cord. The screw loosening was confirmed at 114 days, which was managed successfully by extracting the affected screws. Through the 21-month monitoring period, the dog showed a normal gait with a wide-based stance of the pelvic limbs when standing and experienced no pain. This case represents the first report of concurrent congenital AOD and AAI treated with a ventral surgical approach, contributing new insights to the understanding and management of such complex cranio-cervical junction disorders in veterinary neurosurgery.

Despite advancement in surgical innovation, C1-C2 fixation remains challenging due to risks of screw malposition and vertebral artery (VA) injuries. Traditional image-based navigation, while useful, often demands that surgeons frequently shift their attention to external monitors, potentially causing distractions. In this article, we introduce a microscope-based augmented reality (AR) navigation system that projects both anatomical information and real-time navigation images directly onto the surgical field. In the present case report, we discuss a 37-year-old female who suffered from os odontoideum with C1-C2 subluxation. Employing AR-assisted navigation, the patient underwent the successful posterior instrumentation of C1-C2. The integrated AR system offers direct visualization, potentially minimizing surgical distractions. In our opinion, as AR technology advances, its adoption in surgical practices and education is anticipated to expand.

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