The C2 isthmus screw provided sufficient biomechanical stability in the setting of atlantoaxial dislocation-a finite element study.

BACKGROUND: The emerging of the C2 isthmus screw fixation technique is gaining popularity in the setting of atlantoaxial dislocation or other conditions requiring fixation of C2. However, the biomechanical stability of this fixation is poorly understood. PURPOSE: To compare and elucidate the biomechanical stability of C2 pedicle screw (C2PS), C2 isthmus screw (C2IS) and C2 short isthmus screw (C2SIS) fixation techniques in atlantoaxial dislocation (AAD). METHOD: A three-dimensional finite element model (FEM) from occiput to C3 was established and validated from a healthy male volunteer. Three FEMs, C1 pedicle screw (PS)-C2PS, C1PS-C2IS, C1PS-C2SIS were also constructed. The range of motion (ROM) and the maximum von Mises stress under flexion, extension, lateral bending and axial rotation loading were analyzed and compared. The pullout strength of the three fixations for C2 was also evaluated. RESULT: C1PS-C2IS model showed the greatest decrease in ROM with flexion, extension, lateral bending and axial rotation. C1PS-C2PS model showed the least ROM reduction under all loading conditions than both C2IS and C2SIS. The C1PS-C2PS model had the largest von Mises stress on the screw under all directions followed by C1PS-C2SIS, and lastly the C1PS-C2IS. Under axial rotation and lateral bending loading, the three models showed the maximum and minimum von Mises stress on the screw respectively. The stress of the three models was mainly located in the connection of the screw and rod. Overall, the maximum screw pullout strength for C2PS, C2IS and C2SIS were 729.41N, 816.62N, 640.54N respectively. CONCLUSION: In patients with atlantoaxial dislocations, the C2IS fixation provided comparable stability, with no significant stress concentration. Furthermore, the C2IS had sufficient pullout strength when compared with C2PS and C2SIS. C2 isthmus screw fixation may be a biomechanically favourable option in cases with AAD. However, future clinical trials are necessary for the evaluation of the clinical outcomes of this technique.

Successful recovery from cardiac arrest due to atlantoaxial subluxation in Down syndrome: a case report.

INTRODUCTION: Down syndrome is the most common chromosomal abnormality associated with intellectual impairments. Unexpected deaths are common with this disease. There are certain difficulties in clarifying the cause of death because the manifestations may be quite diverse and involve many organ systems. Atlantoaxial subluxation is a dangerous complication of Down syndrome, as it may lead to cervical cord-medullary compression. CASE PRESENTATION: Herein, we present a case of Down syndrome in a patient who completely recovered from cardiac arrest due to atlantoaxial subluxation. The neck was immobilized during post-cardiac arrest care, and the patient underwent surgery after 14 days. The patient could walk independently and was discharged 3 months later. At the last follow-up 5 years after surgery, the patient's general condition was good. DISCUSSION: Physicians should be aware that atlantoaxial instability can cause cardiac arrest in patients with genetic syndromes.

A new etiology of nontraumatic C0-C1-C2-Complex instability - abnormality of musculus rectus capitis posterior minor: a case report.

PURPOSE: This study presents an abnormality of the musculus rectus capitis posterior minor (RCPmi) as a new etiological factor for nontraumatic sagittal plane instability in the C0-C1-C2-complex, with a focus on identifying the absence or atrophy of RCPmi on both sides. METHODS: A 36-year-old male patient presented with recurring neck pain (VAS 8/10) and tingling paresthesia in the entire left hand over a six-month period, without significant neurological deficits. Radiated arm pain was not reported. Imaging examinations revealed sagittal plane instability in the C0-C1-C2-complex, spinal canal stenosis (SCS), and myelopathy at the C1 level. Subsequently, a dorsal C0-1 reposition and fusion with laminectomy were performed. RESULTS: The congenital absence or atrophy of RCPmi, leading to the lack of cephalad-rearward traction on the C1-tuberculum-posterius, induced a developmental failure of the C1 posterior arch. Consequently, the oblate-shaped C1 posterior arch lost support from the underlying C2 posterior arch and the necessary cephalad-rearward traction throughout the patient's 36-year life. This gradual loss of support and traction caused the C1 posterior arch to shift gradually to the anterior side of the C2 posterior arch, resulting in a rotational subluxation centered on the C0/1 joints in the sagittal plane. Ultimately, this led to SCS and myelopathy. Traumatic factors were ruled out from birth to the present, and typical degenerative changes were not found in the upper cervical spine, neck muscles, and ligaments. CONCLUSION: In this case, we not only report the atrophy or absence of RCPmi as a new etiological factor for nontraumatic sagittal plane instability in the C0-C1-C2-complex but also discovered a new function of RCPmi. The cephalad-rearward traction exerted by RCPmi on the C1 posterior arch is essential for the development of a normal C1 anterior-posterior diameter.

Unilateral Biplanar Screw-Rod Fixation Technique for the Treatment of Odontoid Fractures in Patients with Atlantoaxial Bone or Vascular Abnormalities.

OBJETIVE: This study aims to introduce the unilateral biplanar screw-rod fixation (UBSF) technique (a hybrid fixation technique: 2 sets of atlantoaxial screws were placed on the same side), which serves as a salvage method for traditional posterior atlantoaxial fixation. To summarize the indications of this technique and to assess its safety, feasibility, and clinical effectiveness in the treatment of odontoid fractures. METHODS: Patients with odontoid fractures were enrolled according to special criteria. Surgical duration and intraoperative blood loss were documented. Patients were followed up for a minimum of 12 months. X-ray and computerized tomography scans were conducted and reviewed at 1 day, and patients were asked to return for computerized tomography reviews at 3, 6, 9, and 12 months after surgery until fracture union. Recorded and compared the Neck Visual Analog Scale and Neck Disability Index presurgery and at 1 week and 12 months postsurgery. RESULTS: Between January 2016 and December 2022, our study enrolled 7 patients who were diagnosed with odontoid fractures accompanied by atlantoaxial bone or vascular abnormalities. All 7 patients underwent successful UBSF surgery, and no neurovascular injuries were recorded during surgery. Fracture union was observed in all patients, and the Neck Visual Analog Scale and Neck Disability Index scores improved significantly at 1 week and 12 months postoperative (P < 0.01). CONCLUSIONS: The UBSF technique has been demonstrated to be safe, feasible, and effective in treating odontoid fractures. In cases where the atlantoaxial bone or vascular structure exhibits abnormalities, it can function as a supplementary or alternative approach to the conventional posterior C1-2 fixation.

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.

"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.

Dens Growth After Surgical Fixation in Children with Morquio-Brailsford Disease.

Mucopolysaccharidosis type IVA is a lysosomal storage disorder caused by a deficiency of the enzyme N-acetyl-galactosamine-6-sulphate sulphatase. Mucopolysaccharidosis type IVA is multisystemic disease with significant spinal involvement and atlantoaxial instability leading to neural compression and significant morbidity. Dens hypoplasia is a common feature of this condition. In this study we demonstrate that after spinal fixation, there is new growth of dens in significant proportion of patients, suggesting atlantoaxial instability as one of the major driving forces of lack of development of dens in this condition.

Design of a novel lateral mass screw-plate system for the treatment of unstable atlas fractures: a finite element analysis.

BACKGROUND: Osteosynthesis of unstable atlas fractures preserves joint motion and therefore has a distinct advantage over a range of treatment procedures. To prevent the potential disadvantages associated with osteosynthesis, a new atlas lateral mass screw-plate (LMSP) system has been designed. However, the biomechanical role of using the LMSP system in atlas internal fixation is not known. The aim of this study was to compare the biomechanical stability of a new LMSP with traditional posterior screw and rod (PSR) fixation techniques on the occipitocervical junction (C0-C2) through finite element analysis. METHODS: A nonlinear C0-C2 finite element model of the intact upper cervical spine was developed and validated. The unstable model using the PSR system was then compared with the model using the LMSP system for fixation. A vertical load of 40 N was applied to the C0 to simulate head weight, while a torque of 1.5 Nm was applied to the C0 to simulate flexion, extension, lateral bending, and axial rotation. RESULTS: The range of motion of both systems was close to the intact model. Compared with the LMSP system model, the PSR system model increased flexion, extension, lateral bending, and axial rotation by 4.9%, 3.0%, 5.0%, and 29.5% in the C0-C1 segments, and 4.9%, 2.7%, 2.4%, and 22.6% in the C1-C2, respectively. In flexion, extension, and lateral bending motion, the LMSP system model exhibited similar stress to the PSR system model, while in axial rotation, the PSR system model exhibited higher stress. CONCLUSIONS: The findings of our study indicate that the two tested system models provide comparable stability. However, better stability was achieved during axial rotation with the LMSP system, and in this system, the maximum von Mises stress was less than that of the PSR one. As the atlantoaxial joint functions primarily as a rotational joint, the use of the LMSP system may provide a more stable environment for the joint that has become unstable due to fracture.

Atlantoaxial rotatory subluxation following surgical treatment of a cervical teratoma in a child: a case report.

Atlantoaxial rotatory subluxation (AARS), which is characterised by an abnormal alignment of the atlantoaxial joint, is rarely reported after oral and maxillofacial surgery. A four-year-old girl developed AARS after neck surgery. The child initially had treatment for one month in a timely manner. Follow ups revealed reduced symptoms of neck pain and the previous tilt disappeared after serial treatment. This case aimed to increase awareness of AARS and provide a reference for oral and maxillofacialsurgeons.

[Advances in the technology of surgical treatment for atlantoaxial dislocation].

The etiology and pathological morphology of atlantoaxial dislocation (AAD) are complex. Based on the pathological anatomical characteristics of AAD, combined with clinical techniques, it is essential to formulate reasonable classification criteria and develop corresponding treatment strategies for different types of AAD. The satisfactory outcome of surgical treatment for AAD can only be achieved through the comprehensive application of various atlantoaxial reduction techniques, tension band releasing techniques, internal fixation and fusion techniques. This article discusses the latest advancements in surgical treatment techniques for AAD, thoroughly explores treatment strategies based on different types of AAD, and analyzes the practicality and effectiveness of clinical classification and treatment strategies. The posterior atlantoaxial facet releasing and distraction compression reduction technique may pose challenges to traditional treatment strategies in the future. In the development of surgical treatment techniques for AAD, microspinal surgical techniques may play a significant role in improving surgical methods and enhancing treatment outcomes.

Anatomy of the craniocervical junction - A review.

An in-depth understanding of the anatomy of the craniocervical junction (CCJ) is indispensable in skull base neurosurgery. In this paper, we discuss the osteology of the occipital bone, the atlas (C1) and axis (C2), the ligaments and the muscle anatomy of the CCJ region and their relationships with the vertebral artery. We will also discuss the trajectory of the vertebral artery and review the anatomy of the jugular foramen and lower cranial nerves (IX to XII). The most important surgical approaches to the CCJ, including the far lateral approach, the anterolateral approach of Bernard George and the endoscopic endonasal approach, will be discussed to review the surgical anatomy.

Early Outcomes of Bone Autografting in the Bilateral Atlantoaxial Joints Applied in Posterior Fusion Surgery.

OBJECTIVE: Cable-dragged reduction and cantilever beam internal fixation can provide promising results in the treatment of atlantoaxial dislocation or instability. However, bilateral atlantoaxial joints bone autografting has not been conducted in this technique. We aim to evaluate the safety and effectiveness of bilateral atlantoaxial joints bone autografting in posterior cable-dragged reduction and cantilever-beam internal fixation. METHODS: In this retrospective study, we included 14 patients with a minimum 24-month follow-up from December 2019 to September 2020. The granular bone harvested from the iliac crest was packed into the bilateral atlantoaxial joints of 14 patients in posterior cable-dragged reduction and cantilever-beam internal fixation. X-ray imaging and cervical computed tomography (CT) were performed during follow-up. The time required for bone fusion was recorded. The clinical outcomes were evaluated using the JOA scores, NDI, and VAS scores. Mann-Whitney U test, the chi-squared test, or the Fisher exact test were used to compare the two groups regarding patient characteristics, clinical outcomes, bone fusion rates, and cervical sagittal alignment. RESULTS: The operations were successfully performed in all patients without any intraoperative complications. The mean operation time was (169.64 ± 20.91) minutes, and the intraoperative blood loss was (130.71 ± 33.62) mL. All patients received satisfactory reductions and firm bony fusion at the final follow-up. The fusion rates were 64.29% in the atlantoaxial joints and 21.43% in post bone graft area at 3 months postoperatively, and a significant difference was observed (p = 0.022). Besides, the cervical sagittal alignment in all patients was well maintained in the last follow-up compared to preoperatively. Importantly, a complete bony fusion in the atlantoaxial joints was observed in all patients. Moreover, the JOA, NDI, and VAS scores had improved significantly at the last follow-up. CONCLUSION: Bone autografting of the bilateral atlantoaxial joints is a safe and effective technique to increase bone fusion rates, shorten bone fusion time, and reduce complication rates when the cable-dragged reduction and cantilever beam internal fixation approach is used. Therefore, it is a cost-effective surgical procedure for treating patients with atlantoaxial dislocation or instability.

Retrospective analysis of atlantoaxial rotatory fixation describing age distribution and gender ratio in children and adolescents: A preliminary report.

INTRODUCTION: Atlantoaxial rotatory fixation (AARF) in children presents with an acute onset of neck pain. Almost all cases heal within a few days of onset and are treated conservatively. Because few cases of AARF have been reported, the age distribution or gender ratio of AARF in the child population have not been described enough. In Japan, the social insurance system covers all citizens. Thus, we used insurance claims data to investigate the features of AARF. The aim of this study is to examine the age distribution, compare gender ratio and determine the recurrence proportion of AARF. METHODS: We used the JMDC database to search for claims data submitted between January 2005 and June 2017 for cases of AARF in patients aged <20 years. RESULTS: We identified 1949 patients with AARF, of which 1102 (56.5%) were male. The mean age was 98.3 ± 42.2 months and 91.6 ± 38.4 months in males and females, respectively, and males with AARF were significantly older at onset than females with AARF (p < 0.001). In both sexes, the highest frequency of AARF occurred when the patient was 6 years old. There were 121 (6.2%) cases of recurrent AARF (male: 61, 5.5%; female: 60, 7.1%), but the age differences between the sexes in these cases were not statistically significant. CONCLUSIONS: This is the first report to describe the characteristics of the study population of AARF. Males were more likely to suffer from AARF than females. Furthermore, age (in months) at AARF onset was significantly higher in males than in females. Recurrence rate was not significant in both sexes.

Myelopathy resulting from degenerative atlantoaxial subluxation.

PURPOSE: To present the clinical features and treatment strategy of degenerative atlantoaxial subluxation (DAAS). METHODS: Patients with DAAS treated in our institution from 2003 to 2020 were retrospectively reviewed. We utilized the Japanese Orthopedic Association (JOA) scale to evaluate the neurologic status and distance of Ranawat et al. (DOR) to measure vertical migration. RESULTS: We recruited 40 patients with > 2 years of follow-up and an average age of 62.3 ± 7.7 years. All the patients had myelopathy; only one patient had moderate trauma before exacerbation of symptoms, and the duration of symptoms was 34 ± 36 months. The most frequent radiological features were vertical migration of C1 (100%), sclerosis (100%), and narrowing of the atlantoaxial lateral mass articulations (100%). Two patients underwent transoral release combined with posterior reduction and fusion, and 38 patients underwent posterior reduction and fusion with C1 lateral mass screws-C2 pedicle screws and plate systems only. Forty cases (100%) achieved a solid atlantoaxial fusion, and 38 cases (95%) achieved anatomic atlantoaxial reduction. The JOA score increased from 9.3 ± 2.6 to 14.8 ± 2.1 (P < 0.01). DOR increased from 14.5 ± 2.5 to 17.8 ± 2.2 mm at the final follow-up (P < 0.01). Loosening of the locking caps was detected in one case, bony fusion was achieved, and harvest-site pain was reported in five patients. CONCLUSION: DAAS differs from other types of AAS and presents with anterior subluxation combined with vertical subluxation arising from degenerative changes in the atlantoaxial joints. We recommend anatomic reduction as an optimal strategy for DAAS.

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.

Craniocervical fusion in the paediatric population - case series of 21 patients.

PURPOSE: Craniocervical junction instability in a paediatric population presents a formidable challenge to the neurosurgeon. With a variety of anatomical variations, diminutive bony and ligamentous structures, possible superimposed syndromic abnormalities, the craniocervical junction is a technically challenging region to operate within. We aimed to review our series of patients to identify the common pathologies necessitating craniocervical fusion along with the use of intraoperative image guidance. METHODS: We performed a retrospective review of twenty-one patients, with a mean age of 8.1 years, undergoing craniocervical fixations, involving either occipitocervical fusion or atlantoaxial fixation, from a single institution over a twelve-year period. The presentation, preoperative investigations, indication for surgery, surgical procedure, use of intraoperative navigation and clinical and radiological results were examined. RESULTS: Twelve patients underwent primary C1-2 fixation, with the remaining 9 undergoing occipitocervical fusion. Five patients underwent surgery for traumatic instability, seven for os odontoideum, six for congenital anomalies and three for post-infectious instability. Follow up for 20 patients averaged 34 months (range 2-93 months). Five patients had Trisomy 21 and all underwent C1-2 fixation. Frameless stereotactic image guidance was utilised in five patients. No patients suffered immediate complications resulting from craniocervical junction fusion. Patients were observed to either neurologically improve (n = 6), or arrest their neurological deterioration following surgical intervention (n = 14), with concomitant radiological evidence of osseous fusion at follow up in 18 of 20 patients (90%). Two patients (10%) had radiological evidence of screw lucency, but neither required intervention because of being asymptomatic. CONCLUSIONS: Craniocervical fixation in a paediatric population is a viable and safe treatment modality for the management of disorders requiring stabilisation at the craniocervical junction. Our experience of utilising frameless stereotaxy in the setting of grossly distorted anatomical landmarks is also reported.

Athrodesis of the lateral atlanto-axial joint for the relief of neck pain and cervicogenic headache.

BACKGROUND: Osteoarthrosis of the lateral atlanto-axial joint (LAAJ) may be a cause of upper neck pain and headache. Intra-articular injection of steroids may provide only short-lasting relief. For intractable pain, arthrodesis of the joint might be considered. OBJECTIVE: To determine the success rates of arthrodesis of the lateral atlanto-axial joint for relieving neck pain and disability. DESIGN: Practice audit. SETTING: Private practice of senior author. SUBJECTS: Prospective series of 23 consecutive patients. METHODS: Outcomes were measured using a numerical rating scale for neck pain, and the Neck Disability Index for disability. Success rates were calculated for various degrees of improvement of neck pain at long-term follow-up (8-40 months), and for achieving various combinations of improvement of both neck pain and disability. RESULTS: Complete relief of pain was achieved in 40% of patients, with a further 40% achieving at least 50% relief. At long-term follow-up, 30% of patients had no neck pain and no disability, and a further 25% had only minimal pain, minimal disability, or both. CONCLUSIONS: The present study did not corroborate earlier studies that claimed outstanding outcomes for arthrodesis of the LAAJ, but its outcomes are consonant with more recent studies that provided transparent outcome data. These studies provide Pain Physicians with empirical data on success rates and outcomes, upon which they can base their consideration of referral for arthrodesis.