A novel technique for C1-C2 posterior screw insertion using patient-specific guides created by CT-based 3D printing.

C1-C2 fixation has been developed for the rigid fusion of atlantoaxial instability. C1 lateral mass screw (C1 LMS)-C2 pedicle screw fixation is used more frequently due to its rigid fixation and high bone fusion rate. However, C1 screw placement is relatively unsafe even with recently developed image-based navigation systems. Patient-specific screw guide templates (PSGT) were developed to improve the accuracy and safety of C1 screw placement. Herein, we investigated the outcomes of the C1-C2 posterior fixation technique using PSGT. This was a retrospective study of six patients who underwent posterior cervical spinal fusion using the PSGT between January 2022 and April 2023. Operative time, estimated blood loss, intraoperative radiation dose, surgical cost, and screw placement accuracy were evaluated and compared with those achieved with preoperative CT-based navigation (navigation group, n = 15). Screw accuracy was assessed using Neo's classification. PSGT showed good results, although the differences were not statistically significant (operation time: 104.3 ± 9.7 min vs 116.4 ± 20.8 min; estimated blood loss: 56.7 ± 72.4 mL vs 123.2 ± 162.3 mL; and radiation dose: 1.8 ± 1.2 mSv vs 2.6 ± 0.8 mSv, respectively). PSGT was particularly better in terms of the accuracy of C1 LMS (PSGT: 100%, navigation: 83.3%). The deviation at the entry point was minimal, and the difference between the sagittal and transversal angles from the preoperative plan was small. We investigated the clinical efficacy of using the PSGT for C1-C2 posterior fixation. PSGT improved the accuracy of C1 LMS insertion.

Bow Hunter's Syndrome with Rotational Atlantoaxial Instability: A Rare Association.

Bow Hunter's syndrome (BHS) is a very rare condition in which there is rotational vertebral artery (VA) insufficiency. The association of BHS with rotational atlantoaxial instability is extremely rare. We are reporting a case of pediatric BHS who presented with features of VA insufficiency on neck rotation. Careful evaluation revealed rotational C1-C2 instability. Provocative digital subtraction angiography and dynamic neck computed tomography were the mainstay of our diagnostic armamentarium. Our case emphasizes the fact that VA abnormalities need special consideration in young patients with craniovertebral junction instability and a high degree of suspicion is necessary in most instances for accurate diagnosis.

Anatomical description of a new ligamentous supporting structure of the canine cranial cervical spinal cord.

The cranial cervical vertebral column carries a unique range of mobility with the addition of dorsal and ventral flexion and rotation. The denticulate ligaments provides support and protection of the spinal cord, but little is known of the adaption of this apparatus at the cranial cervical portion of the spinal cord. We present in this publication a new pair of ligaments in dogs that supports the spinal cord inside the vertebral canal at the level of the C1-C2 spinal segments.

Transverse interlaminar ultrasound-guided C1-C2 puncture for the intrathecal administration of nusinersen in patients with spinal muscular atrophy.

INTRODUCTION/AIMS: Severe spinal deformities and previous spinal orthopedic instrumentation may result in substantial technical challenges for nusinersen delivery through lumbar puncture in patients with spinal muscular atrophy (SMA). The aim of this paper was to review our experience with ultrasound-guided cervical puncture as an alternative approach for the intrathecal administration of nusinersen. METHODS: This was a retrospective medical record review of transverse interlaminar ultrasound-guided C1-C2 puncture for nusinersen delivery in SMA patients. The details of puncture, complications, and success rate of the procedure were summarized. RESULTS: There were four patients who received a total of 13 cervical punctures for nusinersen delivery. All procedures were technically successful with no major complications. Full doses of nusinersen were delivered intrathecally. DISCUSSION: Transverse interlaminar ultrasound-guided C1-C2 puncture is an alternative approach for administering nusinersen if lumbar puncture fails. The success of the technique requires a thorough preprocedural evaluation of cervical spine imaging, sound knowledge of the cervical sonoanatomy and careful manipulation of the needle.

Physiotherapeutic Approach Towards Sensory and Motor Recovery in a Patient With Lateral Mass Fixation: A Report of a Rare Case.

Atlantoaxial dislocations (AAD) are a diverse set of C1-C2 rotatory subluxations that include the inferior and superior axial facet articulations. C1-C2 segments are both covered by cranial-cervical ligaments, indicating that AAD would damage both joints. Whenever the posterior elements are missing or impaired, lateral mass screw fixation has replaced alternative posterior cervical fixation procedures as the preferred treatment for securing the sub-axial cervical spine. An increase in muscle tone, hyperreflexia, pathological reflexes, digit/hand clumsiness, and gait deviations caused by spinal cord compression at the cervical level are the most common clinical features. A 23-year-old female patient came with the chief complaint of weakness, tingling sensation, and numbness in both upper and lower limbs along with imbalance while walking. She had a history of falls which was managed conservatively. As the symptoms progressed, an MRI, a CT scan, and an X-ray of the neck were done to rule out the level of injury which revealed AAD, and the patient was operated on for C1-C2 lateral mass fixation. Post-operatively, the patient was referred to the physiotherapy department for further management. The patient's quality of life and daily functioning were positively affected after undergoing early intervention as measured by the Functional Independence Measure, Neck Disability Index, Berg Balance Scale, and Dynamic Gait Index.

Augmented Reality in Spine Surgery: A Case Study of Atlantoaxial Instrumentation in Os Odontoideum.

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.

Short-term and long-term results of odontoid screw fixation in patients with Type II and rostral Type III dens fractures.

OBJECTIVES: To evaluate both the short-term and long-term outcomes of odontoid screw fixation (OSF), identifying potential risk factors for implant-related complications in patients with odontoid fractures. METHODS: This is a retrospective observational cohort study. Inclusion criteria were as follows: 1) Type II fractures and rostral Type III fractures, according to the Anderson and D'Alonzo classification; 2) patients older than 15 years. Exclusion criteria were: 1) other Type III injuries; 2) osteoporosis confirmed by densitometry or a CT bone density score below 100 Hounsfield units; 3) odontoid fractures related to tumors or aneurysmal bone cysts. RESULTS: In total, 56 patients were considered for the analysis of short-term results, and 26 patients were evaluated for long-term outcomes. No significant differences were observed in the preoperative imaging data and intraoperative features of OSF between patients with Type II and rostral Type III fractures. The mean operative duration was 63.9 ± 20.9 min, and the mean intraoperative blood loss was 22.1 ± 22.9 ml. Screw cut-out was identified in four patients with rostral Type III fractures (p = 0.04). The rate of screw cut-out was found to correlate with the degree of dens fragment displacement. The bone fusion rate was 95.7%. CT scans identified stable pseudarthrosis in two cases. We observed C2-C3 ankylosis in all cases following partial disc resection. One third of patients with screws placed through the anterior lip of C2 showed no C2-C3 ankylosis. A strong trend towards lateral joint ankylosis formation in patients with a median lateral mass dislocation of 11.9 mm was observed. Most SF-36 scores either matched or exceeded the corresponding normal median values in the published reference database. CONCLUSIONS: OSF is a reliable treatment method of Type II and rostral Type III odontoid fractures with fragment displacement of 4 mm or less. The minimally invasive OSF through the anterior-inferior lip of C2, using monocortical screw placement and cannulated instruments, without rigid intraoperative head immobilization, is sufficient to achieve favorable clinical and fusion results. This technique reduces the risk of ankylosis in the C2-C3 segment. OSF restore the quality of life for patients with odontoid fractures to levels comparable to those of the general population norm.

Immediate postoperative resolution of syrinx post-C1/C2 fixation in an operated case of foramen magnum decompression for Chiari malformation: Is Goel's procedure a rescue surgery or a gold standard?

Chiari malformation (CM) is a common neurological disorder with foramen magnum decompression (FMD) as a commonly accepted treatment. The authors present a case of CM-1 wherein there was no radiological instability preoperatively and FMD was done as a treatment, after which the patient improved transiently only to deteriorate further. Atlantoaxial fixation was done as a second-stage procedure, after which the patient improved clinically and radiologically. The knowledge of this case and surgical entity should be borne in mind before the formulation of a treatment plan. It is important that the solution is to identify and treat the underlying pathology rather than to decompress and directly manipulate the tonsils.

Evaluation of Craniometric Parameters and Efficacy of Posterior Surgical Intervention Types in Basilar Invagination Patients.

OBJECTIVE: Basilar invagination is one of the most frequently observed abnormalities at the craniovertebral junction, in which the odontoid process of C2 prolapses into the foramen magnum. METHODS: The current study included 27 patients who underwent surgery for basilar invagination between October 2013 and January 2023. The study group was divided into 2 groups according to basilar invagination types; type I (the presence of type A atlantoaxial instability and instability is the main pathology) and type II (the presence of type B and C atlantoaxial instability and skull base dysgenesis is the main pathology). Craniometric parameters included in the study were atlantodental interval, posterior atlantodental interval, Chamberlain's line violation, clivus-canal angle, Welcher's basal angle, and Boogaard angle. RESULTS: The mean age of the patients was 24.30 ± 14.36 years (5-57 years). Fourteen patients (51.9%) were female, and 13 patients (48.1%) were male. Ten patients (37%) had type I basilar invagination, and 17 patients (63%) had type II basilar invagination. Preoperative and postoperative atlantodental interval and Boogaard angle were significantly higher in type I basilar invagination, as preoperative and postoperative posterior atlantodental interval and clivus-canal angle were significantly higher in type II basilar invagination. There was a positive strong correlation between Chamberlain's line violation and Boogaard angle. Postoperative Chamberlain's line violation was significantly higher in occipitocervical fixation (P = 0.035). C1 lateral mass screw fixation was found more successful in Chamberlain's line violation correction than occipital plates. Occipitocervical fixation was found to be associated with higher postoperative Nurick scores (P = 0.015) and complication rates (P = 0.020). Cages applied to the C1-C2 joint space were found to be associated with higher fusion rates (P = 0.023) and lower complication rates (P = 0.024). CONCLUSIONS: In the present study, it was found that C1-C2 fixation was more successful in correcting craniometric parameters and had lower complication rates than occipitocervical fixation. In appropriate patients, it was determined that cage application increased the success rates of the operations.

Atlantoaxial facet fixation using cervical facet cage: technical case report and review of the literature.

In 1994, the use of interfacet spacer placement was for joint distraction, reduction, and fusion to supplement atlantoaxial or occipitocervical fixation. Here, we present a unique case of bilateral atlantoaxial interfacet fixation using cervical facet cages (CFC) in a pediatric patient with basilar invagination. In addition, we review the literature on atlantoaxial facet fixation. We present a 12-year-old boy with Wiedemann-Steiner syndrome who presented with multiple episodes of sudden neck jerking, described as in response to a sensation of being shocked, and guarding against neck motion, found to have basilar invagination with cervicomedullary compression. He underwent an occiput to C3 fusion with C1-C2 CFC fixation. We also conducted a literature review identifying all publications using the following keywords: "C1" AND "C2" OR "atlantoaxial" AND "facet spacer" OR "DTRAX." The patient demonstrated postoperative radiographic reduction of his basilar invagination from 6.4 to 4.1 mm of superior displacement above the McRae line. There was a 4.5 mm decrease in the atlantodental interval secondary to decreased dens retroflexion. His postoperative course was complicated by worsening of his existing dysphagia but was otherwise unremarkable. His neck symptoms completely resolved. We illustrate the safe use of CFC for atlantoaxial facet distraction, reduction, and instrumented fixation in a pediatric patient with basilar invagination. Review of the literature demonstrates that numerous materials can be safely placed as a C1-C2 interfacet spacer including bone grafts, titanium spacers, and anterior cervical discectomy and fusion cages. We argue that CFC may be included in this arsenal even in pediatric patients.

"Letter to the editor: traumatic atlantoaxial rotatory fixation in adults: a systematic review of published cases".

This critique evaluates a recent study on adult traumatic atlantoaxial rotatory fixation (AARF), focusing on its strengths, weaknesses, and suggestions for future research. The study provides a comprehensive examination of the anatomical and biomechanical complexities of the C1-C2 articulation, shedding light on the rare nature of adult traumatic AARF and common injury mechanisms. It categorizes AARF based on the atlanto-dental interval (ADI) and dislocation severity, aiding clinicians in assessing injury severity and treatment planning. Furthermore, the study explores conservative and surgical management approaches, offering valuable insights into treatment decision-making and outcomes. However, limitations such as its retrospective nature, reliance on reported cases, lack of standardized protocols, and limited sample size may constrain the generalizability of findings. Future research should prioritize prospective, multicenter studies with standardized protocols, collaborative efforts among institutions, and innovative techniques to advance our understanding and management of adult traumatic AARF.

Combined Anterior Odontoid Screw Fixation and C1-C2 Jefferson Fracture Anterior Fixation: A Step-by-Step Technical Note.

BACKGROUND: Combined triple atlas (C1)-axis (C2) fixation has been described in previous literature as a safe, effective, and minimally invasive procedure for complex atlas and odontoid fractures that allows for a greater range of motion compared with posterior approaches and atlanto-occipital fusion. However, it is rarely performed due to the occipital-cervical diastasis resulting from often-fractured C1 joint masses. No evidence-based consensus has been reached regarding the treatment of complex atlantoaxial fractures, and the choice of surgical strategy is based only on clinical experience. METHODS: We report the combined triple C1-C2 fixation technique with manual reduction of the joint masses during patient positioning on the operating table, which allowed for effective stabilization during a single surgical session. We describe our experience in the management of a 75-year-old patient presenting with an acute complex type II fracture of C1, which also involved 1 lateral mass, combined with a type II odontoid fracture and occipital-cervical diastasis. RESULTS: We provide a step-by-step guide for combined triple C1-C2 anterior fixation with manual fracture reduction and describe the clinical case of an acute complex type II fracture of C1, which also involved 1 lateral mass, combined with a type II odontoid fracture and occipital-cervical diastasis. CONCLUSIONS: Combined triple C1-C2 fixation represents a safe and efficient minimally invasive anterior approach for complex type II fractures of C1 with type II odontoid fractures. Manual reduction of the joint masses during patient positioning allows for effective stabilization in a single surgical session.

A Rare Case of Grisel's Syndrome in A 6-Year-Old Child.

Introduction: C1-2 rotatory subluxation is more commonly seen in children compared to in adults. It often has a history of respiratory tract infection, cervical trauma, and recent history of surgery of the head or neck. Case Report: A 6-year-old boy presented to us with complaints of insidious onset of progressive deformity of the neck since the past 3 months. On examination, the patient had a classic "cock robin" deformity with his left head tilt and right-sided chin rotation. There was tenderness and spasm of the left sternocleidomastoid muscle. Radiologically, the child had unilateral C1-C2 facetal dislocation. There were associated abnormalities consisting of unilateral occiputoatlantal fusion and C2-C3 fusion. Magnetic resonance imaging (MRI) showed C1-C2 subluxation with kyphotic deformity the apex of which was impinging on the brainstem. The patient was put on skull traction with Crutchfield Tongs with progressively increasing weights for 1 week and serial X-rays were taken. Computed tomography (CT) scan was repeated at the end of 1 week which showed no improvement. C1-C2 open reduction and fusion was done. Post-operative period was uneventful. He improved on serial follow-ups. At follow-up at 18 months, the child remains comfortable, is going to school and doing all indoor and outdoor activities. His posture continues to be balanced. Radiologically, C1-C2 joint shows signs of a solid fusion. Conclusion: A thorough history taking and a meticulous clinical examination if important for evaluation of torticollis in a child. Proper imaging helps in confirming the diagnosis and grading the severity. Prompt treatment is necessary for getting a good outcome.

Lesson learned in endoscopic endonasal dens resection for C1-C2 spinal cord decompression.

PURPOSE: Endoscopic endonasal approach (EEA) is the safest and most effective technique for odontoidectomy. Nevertheless, this kind of approach is yet not largely widespread. The aim of this study is to share with the scientific community some tips and tricks with our ten-year-old learned experience in endoscopic endonasal odontoidectomy (EEO), which remains a challenging surgical approach. MATERIAL AND METHODS: Our case series consists of twenty-one (10 males, 11 females; age range of 34-84 years) retrospectively analyzed patients with ventral spinal cord compression for non-reducible CVJ malformation, treated with EEA from July 2011 to March 2019. RESULTS: The results have recently been reported in a previous paper. The only intraoperative complication observed was intraoperative cerebrospinal fluid (CSF) leak (9.5%), without any sign of post-operative CSF leak. CONCLUSIONS: Considering our experience, EEO represents a valid and safe technique to decompress neural cervical structures. Despite its technical complexity, mainly due to the use of endoscope and the challenging surgical area, with this study we encourage the use of EEO displaying our experience-based surgical tips and tricks.

C1-C2 intraarticular distraction with anterior cervical cages for basilar invagination realignment: Operative technique nuances and review of literature.

Neurosurgical management of basilar invagination (BI) has traditionally been aimed at direct cervicomedullary decompression through transoral dens resection or suboccipital decompression with supplemental instrumented fixation. Dr. Goel introduced chronic atlantoaxial dislocation (AAD) as the etiology in most cases of BI and described a technique for distracting the C1-C2 joint with interfacet spacers to achieve reduction and anatomic realignment. We present our modification to Goel's surgical technique, in which we utilize anterior cervical discectomy (ACD) cages as C1-C2 interfacet implants. A young adult male presented to our institution with BI, cervicomedullary compression, occipitalization of C1, and Chiari 1 malformation. There was AAD of C1 over the C2 lateral masses. This reduced some with preoperative traction. He underwent successful C1-C2 interfacet joint reduction and arthrodesis with anterior cervical discectomy (ACD) cages and concomittant occiput to C2 instrumented fusion. BI can be effectively treated through reduction of AAD and by utilizing ACD cages as interfacet spacers.

Nuance in Craniovertebral Junction Surgical Approach for Posterior C1-C2 Harms Stabilization: "Window Transposition" of the External Vertebral Venous Plexus for Bloodless C1 Lateral Mass Screw Insertion: Anatomical Aspects and Technical Notes.

Atlas and axis instrumentation may be necessary in cases of several craniocervical junction pathologies. According to the Harms technique, C1-C2 polyaxial screws are inserted respectively in the C1 lateral masses and in C2 pedicles. C1 lateral mass screw insertion requires the careful subperiosteal dissection of the posterior elements of C1, the identification of the screw entry point by the downward distraction of C2 nerve root, and the cautious sparing of the overlying posterior external vertebral venous plexus (peVVP), whose bleeding, obstructing the surgical field, is sometimes barely controlled by hemostatic agents and swabbing. The authors describe in detail the anatomical aspects of an alternative surgical technique developed for the microsurgical transposition of the C1-C2 interposed external vertebral venous plexus in the case of Harms C1-C2 screw stabilization. The longitudinal median incision of the atlantoaxial membrane, followed by bilateral subperiosteal dissection and microsurgical section respectively at the inferior borders of the C1 laminae and at the superior borders of the C2 laminae, allows, as a "window opening," the symmetrical mediolateral transposition of the peVVP. This procedure provides a faster and cleaner anatomical exposition of the posterior surface of the C1 lateral mass and the C2 isthmus, preventing troublesome intraoperative venous bleeding that hinders C1 lateral mass screw insertion.

C2 Odontoid Fracture Associated with C1-C2 Rotatory Dislocation: A Retrospective Analysis of 2 Surgical Techniques.

BACKGROUND: Odontoid fractures in association with a C1-C2 rotatory luxation reports are seldom found in the literature. The fusion between the lateral mass of C1 and C2 could be of interest to ensure adequate treatment in these particular cases. We report 23 cases where there was coexistence of an odontoid fracture and rotatory subluxation, which were treated surgically using cages between C1 and C2 or just traditional Goel-Harms technique. We evaluated the radiologic fusion rate, reoperation rate, and complications. METHODS: This was a single-center, retrospective, cohort study of patients with C2 fractures (mixed type and C1-C2 rotatory luxation according to the Fielding classification) who were treated surgically. Radiologic computed tomography scans were used to assess fusion (presence of bridging trabecular bone end plate or pseudoarthrosis) between 6 months and 1.5 years after the surgery. RESULTS: Twenty-three patients were diagnosed with C2 fractures and C1-C2 rotatory luxation that were treated surgically and were suitable for the analysis; 11 patients underwent C1-C2 fusion with intra-articular cages, and 12 underwent a classical Goel-Harms technique. The fusion rate at the C1-C2 joint was higher in the cages group. Only 12 patients exhibited fusion at the level of the odontoid fracture. CONCLUSIONS: C2 fractures associated with C1-C2 rotatory dislocation are rare. The fusion rate at the level of the odontoid in these patients appears to be lower than that reported in patients without rotatory dislocation. It may be of special interest to obtain a clear fusion at the C1-C2 joint, where this type of implant seems to offer an advantage.

Comparison of intraoperative CT- and cone beam CT-based spinal navigation for the treatment of atlantoaxial instability.

BACKGROUND CONTEXT: Due to the complexity of neurovascular structures in the atlantoaxial region, spinal navigation for posterior C1-C2 instrumentation is nowadays a helpful tool to increase accuracy of surgery and safety of patients. Many available intraoperative navigation devices have proven their reliability in this part of the spine. Two main imaging techniques are used: intraoperative CT (iCT) and cone beam computed tomography (CBCT). PURPOSE: Comparison of iCT- and CBCT-based technologies for navigated posterior instrumentation in C1-C2 instability. STUDY DESIGN: Retrospective study. PATIENT SAMPLE: A total of 81 consecutive patients from July 2014 to April 2020. OUTCOME MEASURES: Screw accuracy and operating time. METHODS: Patients with C1-C2 instability received posterior instrumentation using C2 pedicle screws, C1 lateral mass or pedicle screws. All screws were inserted using intraoperative imaging either using iCT or CBCT systems and spinal navigation with autoregistration technology. Following navigated screw insertion, a second intraoperative scan was performed to assess the accuracy of screw placement. Accuracy was defined as the percentage of correctly placed screws or with minor cortical breach (<2 mm) as graded by an independent observer compared to misplaced screws. RESULTS: A total of 81 patients with C1-C2 instability were retrospectively analyzed. Of these, 34 patients were operated with the use of iCT and 47 with CBCT. No significant demographic difference was found between groups. In the iCT group, 97.7% of the C1-C2 screws were correctly inserted; 2.3% showed a minor cortical breach (<2 mm); no misplacement (>2 mm). In the CBCT group, 98.9% of screws were correctly inserted; no minor pedicle breach; 1.1% showed misplacement >2 mm. Accuracy of screw placement demonstrated no significant difference between groups. Both technologies allowed sufficient identification of screw misplacement intraoperatively leading to two screw revisions in the iCT and three in the CBCT group. Median time of surgery was significantly shorter using CBCT technology (166.5 minutes [iCT] vs 122 minutes [CBCT]; p<.01). CONCLUSIONS: Spinal navigation using either iCT- or CBCT-based systems with autoregistration allows safe and reliable screw placement and intraoperative assessment of screw positioning. Using the herein presented procedural protocols, CBCT systems allow shorter operating time.

C1-C2 subluxation in enthesitis-related arthritis: two case reports and literature review of ten cases.

BACKGROUND: C1-C2 subluxation is a rare complication of enthesitis-related arthritis (ERA). If left untreated, it may lead to functional impairment or cervical spinal cord compression. This study aims to highlight key points regarding the management of C1-C2 subluxation in ERA. CASE PRESENTATION: We present two cases of C1-C2 subluxation: an 8-year-old boy with ERA and 16-year-old boy with ERA with bilateral sacroiliitis. Ten cases of ERA in the literature were reviewed. The diagnosis of C1-C2 subluxation is mostly based on radiographs and cervical spine computed tomography. All patients were treated with non-steroidal anti-inflammatory drugs. Six ERA patients were treated surgically for cervical fusion. Most ERA patients with sacroiliitis had cervical collar protection. Neurologic abnormalities after treatment were not reported. Despite the use of cervical collar, cervical fusion and persisting ankylosis were found in two ERA patients with sacroiliitis without surgical treatment. CONCLUSIONS: Cervical spine protection and ruling out spinal cord compression should be prioritized, in addition to controlling the underlying inflammation in ERA. Cervical halter traction may be applied after severe cervical inflammation is excluded. To reduce the risk of complications, early recognition and appropriate treatments of C1-C2 subluxation in ERA are essential.

Advances in surgical treatment for atlantoaxial instability focusing on rheumatoid arthritis: Analysis of a series of 67 patients.

AIM: An estimated 88% of rheumatoid arthritis (RA) patients experience various degrees of cervical spine involvement. The excessive movement of the atlantoaxial joint, which connects the occiput to the upper cervical spine, results in atlantoaxial instability (AAI). AAI stabilization is usually achieved by C1 lateral mass-to-C2 pedicle screw-rod fixation (LC1-PC2 fixation), which is technically challenging in RA patients who often show destructive changes in anatomical structures. This study aimed to analyze the clinical results and operative experiences of C1-C2 surgery, with emphasis on the advancement of image-guided surgery and augmented reality (AR) assisted navigation. METHODS: We presented our two decades of experience in the surgical management of AAI from April 2004 to November 2022. RESULTS: We have performed surgery on 67 patients with AAI, including 21 traumatic odontoid fractures, 20 degenerative osteoarthritis, 11 inflammatory diseases of RA, 5 congenital anomalies of the os odontoideum, 2 unknown etiologies, 2 movement disorders, 2 previous implant failures, 2 osteomyelitis, 1 ankylosing spondylitis, and 1 tumor. Beginning in 2007, we performed LC1-PC2 fixation under C-arm fluoroscopy. As part of the progress in spinal surgery, since 2011 we used surgical navigation from presurgical planning to intraoperative navigation, using the preoperative computed tomography (CT) -based image-guided BrainLab navigation system. In 2021, we began using intraoperative CT scan and microscope-based AR navigation. CONCLUSION: The technical complexities of C1-C2 surgery can be mitigated by CT-based image-guided surgery and microscope-based AR navigation, to improve accuracy in screw placement and overall clinical outcomes, particularly in RA patients with AAI.