Direct osteosynthesis in the treatment of atlas burst fractures: a systematic review.

PURPOSE: The treatment of unstable atlas fractures remains a controversial topic. The study aims at assessing the prognosis and efficacy of osteosynthesis for unstable atlas fractures through a review of the current literature and additionally aims to compare outcomes between the transoral and posterior approaches. METHODS: A systematic review of databases including PubMed, EMBASE, Cochrane, Web of Science, CNKI, and Wanfang was conducted. Titles and abstracts were screened by two reviewers to identify studies meeting pre-defined inclusion criteria for comprehensive analysis. RESULTS: The systematic review included 28 articles, 19 employing the posterior approach and 9 utilizing the transoral approach. It covered osteosynthesis in 297 patients with unstable atlas fractures, comprising 169 treated via the posterior approach and 128 via the transoral approach. Analysis revealed high healing rates and clinical improvement in both approaches, evidenced by improvements in the visual analog scale, range of motion, atlantodens interval, and lateral displacement distance post-surgery. CONCLUSION: Osteosynthesis offers effective treatment for unstable atlas fractures. Both transoral and posterior approaches can achieve good clinical outcomes for fracture, and biomechanical studies have confirmed that osteosynthesis can maintain the stability of the occipitocervical region, preserve the motor function of the atlantoaxial and occipito-atlantoaxial joints, and greatly improve the quality of life of patients. However, variations exist in the indications and surgical risks associated with each method, necessitating their selection based on a thorough clinical evaluation of the patient's condition.

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.

Management of Unstable C1 Fractures Involving the Lateral Mass: Posterior C1-C2 Screw-Rod Fixation and Fusion.

BACKGROUND Although most unstable C1 fractures can be effectively treated either by conservative treatment with external immobilization or by surgical procedure of C1-ring osteosynthesis, those fractures involving the lateral mass are likely to lead to traumatic arthritis and persistent neck pain. Specific reports of treatment of unstable C1 fractures involving the lateral mass are still scarce. We therefore present this report to evaluate the effectiveness of posterior C1-C2 screw-rod fixation and fusion for unstable C1 fractures involving the lateral mass. MATERIAL AND METHODS From June 2009 to June 2016 in our hospital, 16 cases were diagnosed with C1 fractures involving the lateral mass and treated by posterior C1-C2 screw-rod fixation and fusion from June 2009 to June 2016. The patients' clinical data were retrospectively analyzed. Preoperative and postoperative images were taken to evaluate cervical sequence, location of screws, and bone fusion. Neurological status and neck pain levels were evaluated clinically on follow-up. RESULTS All patients underwent surgery successfully. The mean follow-up duration was 15.3±4.9 months (range 9-24 months). All patients obtained satisfying clinical outcomes with good neck pain alleviation, appropriate screw placement, and reliable bone fusion. None of the patients developed vascular or neurological complications during the operation or follow-up. CONCLUSIONS Posterior C1-C2 screw-rod fixation and fusion is an effective management for unstable C1 fractures involving the lateral mass. This operation can provide reliable stabilization and satisfactory bone fusion.

Radiologic Features of Atlas Occipitalization and Its Clinical Implications.

STUDY DESIGN: Retrospective radiographic analysis. OBJECTIVES: Evaluation of the anatomic features of the craniovertebral junction in patients with occipitalization with and without atlantoaxial dislocation (AAD). SUMMARY OF BACKGROUND DATA: Atlas occipitalization is a common feature of congenital AAD and usually requires surgical intervention. However, not all instances of occipitalization necessarily lead to AAD. No study has specifically examined and compared the craniovertebral bony morphology in occipitalization with, and without, AAD. MATERIALS AND METHOD: We reviewed computed tomography (CT) scans of 2500 adult outpatients. Occipitalization cases without AAD (ON) were selected. Meanwhile, a series of 20 inpatient occipitalization cases with AAD (OD) were obtained in parallel. Another 20 control cases without occipitalization were also included. Multi-directional reconstructed CT images of all cases were analyzed. RESULTS: A total of 18 adults with ON were found in all 2500 outpatients (0.7%). Both anterior height and posterior height of C1 lateral mass in the control group were significantly larger than those in both the ON and OD groups, whereas posterior height in the OD group was significantly less than that in the ON group. Three morphologic types of the occipitalized atlas posterior arch were identified: Type I, bilateral sides were unfused with opisthion; Type II, unilateral side was unfused with opisthion, whereas the other side was fused; and Type III, bilateral sides were fused with opisthion. In the ON group, three cases were type I (17%), six cases were type II (33%), and nine cases were type III (50%). In the OD group, all 20 cases were type III (100%). CONCLUSIONS: Atlas occipitalization with, and without, AAD results from a distinctly different bony morphology at the craniovertebral junction. The novel classification system based on reconstructed CT images may be useful in prognosticating AAD in the setting of atlas occipitalization.

Posterior osteosynthesis with a new self-designed lateral mass screw-plate system for unstable atlas burst fractures.

BACKGROUND: In the treatment of unstable atlas fractures using the combined anterior-posterior approach or the posterior monoaxial screw-rod system, factors such as severe trauma or complex surgical procedures still need to be improved despite the favourable reduction effect. This research described and evaluated a new technique for the treatment of unstable atlas fracture using a self-designed lateral mass screw-plate system. METHODS: A total of 10 patients with unstable atlas fractures using this new screw-plate system from January 2019 to December 2021 were retrospectively reviewed. All patients underwent posterior open reduction and internal fixation (ORIF) with a self-designed screw-plate system. The medical records and radiographs before and after surgery were noted. Preoperative and postoperative CT scans were used to determine the type of fracture and evaluate the reduction of fracture. RESULTS: All 10 patients were successfully operated with this new system, with an average follow-up of 16.7 ± 9.6 months. A total of 10 plates were placed, and all 20 screws were inserted into the atlas lateral masses. The mean operating time was 108.7 ± 20.1 min and the average estimated blood loss was 98.0 ± 41.3 ml. The lateral mass displacement (LMD) averaged 7.1 ± 1.9 mm before surgery and almost achieved satisfactory reduction after surgery. All the fractures achieved bony healing without reduction loss or implant failure. No complications (vertebral artery injury, neurologic deficit, or wound infection) occurred in these 10 patients. At the final follow-up, the anterior atlantodens interval (AADI) was 2.3 ± 0.8 mm and the visual analog scale (VAS) was 0.6 ± 0.7 on average. All patients preserved almost full range of motion of the upper cervical spine and achieved a good clinical outcome at the last follow-up. CONCLUSIONS: Posterior osteosynthesis with this new screw-plate system can provide a new therapeutic strategy for unstable atlas fractures with simple and almost satisfactory reduction.

Paracondylar process combined with persistent first intersegmental vertebral artery: an anatomic case report and literature review.

The paracondylar process (PCP) and the persistent first intersegmental vertebral artery (PFIA) are both rare variations at the craniovertebral junction. We report the above two variations coexisting in one cadaveric head during the training of far lateral approach in our skull base lab. The specimen simultaneously had a left occipitalized atlas associated with a PFIA and a right PCP. The previous reports, the embryogenesis, and the clinical implications of the two variations were also reviewed. Preoperative recognition of the rare variations is essential to a safe far lateral approach.

Morphometric Anatomy of the Posterior Aspect of the Atlas and the Vertebral Artery Groove in Relation to Lateral Mass Screw Placement.

BACKGROUND: Atlantoaxial instability is an important disorder that causes serious symptoms such as difficulties in walking, limited neck mobility, sensory deficits, etc. Atlantal lateral mass screw fixation is a surgical technique that has gained important recognition and popularity. Because accurate drilling area for screw placement is of utmost importance for a successful surgery, we aimed to investigate morphometry of especially the posterior part of C1. METHODS: One hundred and fifty-eight human adult C1 dried vertebrae were obtained. Measurements were performed directly on dry atlas vertebrae, and all parameters were measured by using a digital caliper accurate to 0.01 mm for linear measurements. RESULTS: The mean distance between the tip of the posterior arch and the medial inner edge of the groove was found to be 10.59 ± 2.26 and 10.49 ± 2.20 mm on the right and left, respectively. The mean distance between the tip of the posterior arch and the anterolateral outer edge of the groove was 21.27 ± 2.28 mm (right: 20.96 ± 2.22 mm; left: 21.32 ± 2.27 mm). The mean height of the screw entry zone on the right and left sides, respectively, were 3.86 ± 0.81 and 3.84 ± 0.77 mm. The mean width of the screw entry zone on both sides was 13.15 ± 1.17 and 13.25 ± 1.3 mm. CONCLUSION: Our result provided the literature with a detailed database for the morphometry of C1, especially in relation to the vertebral artery groove. We believe that the data in the present study can help surgeons to adopt a more accurate approach in terms of accurate lateral mass screw placement in atlantoaxial instability.

Posterior arch reconstruction in cervical surgery to restore the global biomechanics of the Atlas: a technical note.

The posterior arch of the atlas is usually not considered one of the main stabilizers of the cranio-cervical junction, allowing surgeons to its removal when needed with a relative certainty to preserve the stability of the atlo-axial segment. However, these considerations do not reflect the importance to examine the integrity of the posterior arch in the whole biomechanics of the atlas. Authors like Gebauer and Panjabi revealed, respectively in experimental and clinical conditions, how the atlas responds to an axial loading force, proving that the whole atlas is involved into horizontal conversion of axial forces and providing evidence supporting the preservation of the posterior arch. Other authors evaluated the risk for anterior arch fracture following C1 laminectomy. In this technical note three different techniques of posterior atlas arch reconstruction after surgical iatrogenic disruption are presented, considering both neoplastic and degenerative disease.

Evaluation of Dural Parameters at C1 Level in Patients with Chiari 1 Malformation Following Foramen Magnum and C1 Posterior Arch Removal: Introduction of a Novel Concept to Decompress without Affecting Stability.

Background: Chiari 1 malformation has crowding at craniovertebral junction (CVJ), treated by Foramen magnum decompression (FMD) but is associated with high failure rates, which is explained by recently introduced concept of central instability. So, we propose a new concept of relieving this crowding without affecting stability. Objective: To derive a threshold for coring out of internal surface of C1 posterior arch instead of complete laminectomy accompanying FMD. Methods and Material: We prospectively included nine patients with a mean age of 25.33 ± 7.97 years, diagnosed with ACM-1 without AAD, who were operated with FMD and lax duraplasty and C1 laminectomy. The preoperative dural diameter and area covered under the dura at the level of C1 were measured and compared with the postoperative state. Results were analyzed to derive a cut-off threshold which could be drilled from the inner aspect of C1 arch. Results: The postoperative AP diameter of the dura increased statistically significantly from pre-op; however, the AP extension was less than the preoperative diameter with posterior arch included. Likewise, the area spanned by the dura increased statistically significantly from pre-op but was less than the cumulative area of dura with C1 arch included in pre-op. Analyzing all, a mean cut-off of 50.58% was achieved. Conclusion: The authors suggest FMD with partial coring (~50%) of the inner part of arch of C1, instead of full-thickness laminectomy with a wider length of coring as the target, and this will serve the purpose intended, without increasing mobility.

Atlas (C1) lateral mass screw placement using the intersection between lateral mass and inferomedial edge of the posterior arch: a cadaveric study.

PURPOSE: To compare the Atlas (C1) lateral mass screw placement between screw trajectories of 0° and 15° medial angulation while using the intersection between lateral mass and inferomedial edge of the posterior arch. METHODS: Forty-eight Atlas lateral masses were prepared and divided into 2 groups: Group 1; screws inserted at 3 mm lateral to the reference point with screw trajectory of 0° angulation(N = 24) and Group 2; those inserted with screw trajectory of 15° medial angulation(N = 24). We evaluated the atlas anatomy, screw purchase and the presence of any breaches using CT scan. RESULTS: The radiographic parameters for Groups 1 and 2 were found statistically different (p-value < 0.05): bilateral intraosseous screw lengths (17.92 ± 1.47 mm. vs. 20.71 ± 2.4 mm.), bilateral screw length (29.92 ± 1.72 mm. vs. 33.13 ± 1.78 mm.), left screw medial angulation (x°) (0.67° ± 0.78° vs.14.17° ± 3.51°), right screw medial angulation (y°) (0.83° ± 1.03° vs.14.25° ± 2.53°) and bilateral screw medial angulation (0.75° ± 0.9° vs. 14.21° ± 2.99°). Twenty-two screws (91.67%) using the 0° medial angulation and nineteen screws (79.17%) using the 15° medial angulation had no cortical violations (Grade 0). However, two screws (8.33%) with 0° medial angulation and five screws (20.83%) with 15° medial angulation had breach less than 2 mm (Grade 1). There were no screws with breach between 2 and 4 mm (Grade 2) or greater than 4 mm. (Grade 3). CONCLUSION: A starting point of 3-mm lateral to the intersection between lateral mass and inferomedial edge of the Atlas posterior arch can be safely and effectively used to insert C1 lateral mass using both 0° and 15° medial angulation.

Torticollis, Facial Asymmetry, Local Pain, and Barré-Liéou Syndrome in Connection with One-Sided Ponticulus Posticus: A Case Report and Review of the Literature.

BACKGROUND: Ponticulus posticus (PP) occurs frequently and may cause symptom series, including vertebrobasilar insufficiency, migraine, hearing loss, and Barré-Liéou syndrome. However, few studies to date have described surgical treatment of PP. We report a rare case of a patient who suffered from torticollis, facial asymmetry, localized pain, and Barré-Liéou syndrome in connection with PP. We also review the pertinent literature, focusing on surgical treatment for symptoms due to PP. CASE PRESENTATION: A 23-year-old male presented with the chief complaint of continuous significant dizziness to the point of losing consciousness while rotating his head to the right. Plain radiographs and computed tomography (CT) scans of the cervical spine showed a С1 anomaly with the formation of complete PP on the left (dominant) side, with acute-angled, С-shaped kinking of the vertebral artery. Resection of PP via the posterior midline was performed successfully. The patient had satisfactory postoperative relief from localized pain and Barré-Liéou syndrome, but there were no obvious changes in the torticollis and facial asymmetry observed during the 3-month follow-up period. CONCLUSIONS: This case is a rare presentation of torticollis, facial asymmetry, localized pain, and Barré-Liéou syndrome in connection with one-sided complete PP. This tetrad indicates that PP may affect the patient earlier than expected. In such situations, early diagnosis and timely surgical treatment may significantly improve patients' quality of life and avoid the development of torticollis and face asymmetry.

Direct Internal Fixation for Unstable Atlas Fractures.

PURPOSE: To investigate the radiologic and clinical outcomes of direct internal fixation for unstable atlas fractures. MATERIALS AND METHODS: This retrospective study included 12 patients with unstable atlas fractures surgically treated using C1 lateral mass screws, rods, and transverse connector constructs. Nine lateral mass fractures with transverse atlantal ligament (TAL) avulsion injury and three 4-part fractures with TAL injury (two avulsion injuries, one TAL substance tear) were treated. Radiologic outcomes included the anterior atlantodental interval (AADI) in flexion and extension cervical spine lateral radiographs at 6 months and 1 year after treatment. CT was also performed to visualize bony healing of the atlas at 6 months and 1 year. Visual Analog Scale (VAS) scores for neck pain, Neck Disability Index (NDI) values, and cervical range of motion (flexion, extension, and rotation) were recorded at 6 months after surgery. RESULTS: The mean postoperative extension and flexion AADIs were 3.79±1.56 (mean±SD) and 3.13±1.01 mm, respectively. Then mean AADI was 3.42±1.34 and 3.33±1.24 mm at 6 months and 1 year after surgery, respectively. At 1 year after surgery, 11 patients showed bony healing of the atlas on CT images. Only one patient underwent revision surgery 8 months after primary surgery due to nonunion and instability findings. The mean VAS score for neck pain was 0.92±0.99, and the mean NDI value was 8.08±5.70. CONCLUSION: C1 motion-preserving direct internal fixation technique results in good reduction and stabilization of unstable atlas fractures. This technique allows for the preservation of craniocervical and atlantoaxial motion.

Suitability of 3.5-mm screw for the atlas in children: a retrospective computed tomography analysis.

BACKGROUND: The growth and development of the atlas in children has not been studied to date using a large sample size. OBJECTIVE: To study whether a 3.5-mm screw is suitable for the atlas in children, to explore the anatomical size and development of the atlas in 0-14-year-old children, and to provide morphological basis for lateral mass screw internal fixation. METHODS: A Computed Tomography (CT) morphometric analysis was performed on 420 pediatric atlases. In the atlas, D1, D2, D3, D4, and α of the atlas lateral mass were measured. Statistical analysis was performed using one-way ANOVA and Students' t test. The least square method was used for the regression analysis of the change trend in anatomical structure. The curve with the greatest goodness of fit was used as the anatomic trend regression curve. RESULTS: D1, D2, D3, and D4 generally showed an increasing trend with age. The ranges of averages of D1, D2, D3, D4, and α in 0-14 year-old children were as follows: 4.576-9.202 mm, 9.560-25.100 mm, 3.414-10.554 mm, 11.150-27.895, and 12.41°-20.97°, respectively. The trends of the fitting curves of L1 and L3 were power functions, and those of L2 and L4 were logarithmic curves. CONCLUSIONS: CT examination could help in preoperative decision-making, and 3.5-mm screw was found to be suitable for lateral mass screw internal fixation in children aging 2 years and older. D1-D4 increased with age. This provided a certain reference to perform posterior atlantoaxial fusion in children and is of great significance to design posterior atlantoaxial screw in children.

Upper Cervical Trauma.

Craniocervical injuries (CCJs) account for 10% to 30% of all cervical spine trauma. An increasing number of patients are surviving these injuries due to advancements in automobile technology, resuscitation techniques, and diagnostic modalities. The leading injury mechanisms are motor vehicle crashes, falls from height, and sports-related events. Current treatment with urgent rigid posterior fixation of the occiput to the cervical spine has resulted in a substantial reduction in management delays expedites treatment of CCJ injuries. Within CCJ injuries, there is a spectrum of instability, ranging from isolated nondisplaced occipital condyle fractures treated nonoperatively to highly unstable injuries with severely distracted craniocervical dissociation. Despite the evolution of understanding and improvement in the management of cases regarding catastrophic failure to diagnose, subsequent neurologic deterioration still occurs even in experienced trauma centers. The purpose of this article is to review the injuries that occur at the CCJ with the accompanying anatomy, presentation, imaging, classification, management, and outcomes.

Anterior reduction and C1-ring osteosynthesis with Jefferson-fracture reduction plate (JeRP) via transoral approach for unstable atlas fractures.

BACKGROUND: To introduce a novel transoral instrumentation in the treatment of unstable fractures of the atlas. METHODS: From January 2008 to May 2018, 22 patients with unstable C1 fractures who received Jefferson-fracture reduction plate (JeRP) via transoral approach were retrospectively analyzed. The case history and the radiographs before and after surgery were noted. The type of fracture, the reduction of the fracture, and position of the internal fixation were assessed through preoperative and postoperative CT scans. RESULTS: All 22 patients successfully underwent anterior C1-ring osteosynthesis using the JeRP system, with a follow-up of 26.84 ± 9.23 months. Among them, 9 patients had transverse atlantal ligament (TAL) injury, including 3 in Dickman type I and 6 in type II. The preoperative lateral mass displacement (LMD) decreased from 7.13 ± 1.46 mm to 1.02 ± 0.65 mm after the operation. Bone union was achieved in all patients without implant failure or loss of reduction. There were no surgery-related complications, such as wound infection, neurological deficit, or vertebral artery injury. However, atlantoaxial dislocation occurred in 3 patients with Dickman type I TAL injury 3 months postoperatively without any neurological symptoms or neck pain. CONCLUSIONS: Transoral C1-ring osteosynthesis with JeRP is an effective surgical strategy to treat unstable atlas fractures with a safe, direct, and satisfactory reduction. The primary indication for the JeRP system is an unstable fracture (Gehweiler type I/III) or/ and TAL injury (Dickman type II).

Three-dimensional anatomic analysis and navigation templates for C1 pedicle screw placement perpendicular to the coronal plane: a retrospective study.

OBJECTIVE: To explore the corridor for atlas pedicle screw placement perpendicular to the coronal plane and to develop patient-specific navigation templates for pedicle screw placement. METHODS: This study is a retrospective analysis. A total of 71 patients (41 males and 30 females) were involved in this study from June 2016 to June 2018, and they were divided into a template group (39 patients) and a conventional group (32 patients). The CT-based 3D reconstruction models were analyzed in the template group. From the perspective of the 3D atlas in a coronal view, the pedicle corridor was obtained. Taking the center of the tangential circle of the pedicle as the entry point, we simulated screw placement perpendicular to the coronal plane. Then, the individual navigation template was designed and used in surgery. In the conventional group, free-hand pedicle screw placement was performed perpendicular to the coronal plane. The diameter of the maximum tangential circle and screw length of the pedicle corridor were measured in the template group. The surgical time, radiation exposure time, screw grading criteria and so on were evaluated and compared between the two groups after surgery. RESULTS: ;The diameter of the maximum tangential circle and the distance between the entry point and posterior tubercle were significantly greater in males than in females. The operation was successfully completed in all patients, without aggravation of nerve injury, and the follow-up was 12-20 months, with an average of 15.6 months. A total of 78 screws were inserted in the template group, and 64 screws were inserted in the conventional group. The surgical times in the template group and conventional group were 76.47±24.44 min and 125.63±36.41 min, respectively. The radiation exposure times in the template group and conventional group were 3.51±1.77 and 10.15±4.95, respectively, and there was a significant difference between the two groups. In the template group, the deviation in the screw entry point and screw angle were 1.92±1.67 mm and 2.08±1.98°, respectively. The medial angle deviation between the left and right sides was 2.71±1.88° in the template group, which was significantly less than the deviation of 3.76±2.22° in the conventional group. CONCLUSION: A pedicle screw trajectory perpendicular to the coronal plane can be quickly obtained based on the perspective of 3D models. The technique of screw placement perpendicular to the coronal plane assisted by navigation templates has a shorter operative time, lessintraoperative fluoroscopy and a higher safety of screw placement than traditional surgery.

Anterior Atlas Fracture After C1 Laminectomy Which Was Successfully Treated by Brace Therapy: A Case Report.

CASE: We report a case of a 67-year-old male patient who underwent a C1 laminectomy with laminoplasty at C2-3 because of cervical ossification of the posterior longitudinal ligament. At 6 weeks after surgery, neck pain occurred after minor trauma without neurological deterioration. Computed tomography (CT) demonstrated C1 anterior atlas fracture with a 3-mm gap. After a 3-month brace therapy using a Philadelphia collar, the patient's neck pain disappeared with complete bone union according to the CT. CONCLUSION: Among 14 cases that were reported previously, none of the adult patients achieved bone union by brace therapy. Therefore, this is the only case report in which bone union could be achieved by brace therapy.

Surgically Treated C1 Fractures: A Population-Based Study.

OBJECTIVE: To characterize surgical treatment and outcomes of C1 fractures in a population-based setup. METHODS: Patients with C1 fracture treated at Kuopio University Hospital Neurosurgery were retrospectively identified from January 1996 to June 2017. C1 fractures were classified according to the AO Spine Upper Cervical and Gehweiler classification systems. Patients were divided into 4 groups based on their treatment: group 1 (underwent C1 surgery as a primary option), group 2 (underwent C1 surgery as a secondary option after initial nonoperative treatment), group 3 (underwent surgery involving the C1 level with main indication being a concomitant cervical spine fracture), and group 4 (C1 fracture treatment was nonoperative). RESULTS: We identified 47 patients with C1 fracture (mean age, 60.3 ± 18.2 years; 83.0% men; American Society of Anesthesiologists score, 2.3 ± 0.8). Concomitant cervical spine fractures were present in 89.4% of cases, most commonly in the C2 vertebra (75.4%). In group 2, 3 of 5 fractures changed from AO Spine type A to B in control imaging after nonoperative treatment, indicating fracture instability and requiring secondary surgery. Good C1 fracture alignment was achieved for 10 of 10 followed-up patients in groups 1 and 2, and for 10 of 11 followed-up patients in group 3. Residual neck pain and stiffness were present in all groups. Neurologic symptoms were rare and mild. CONCLUSIONS: For unstable C1 fractures, surgery is safe treatment with good outcomes. Fractures initially determined as stable may require surgery if alignment is worsened in follow-up imaging. Magnetic resonance imaging is recommended to better detect unstable C1 fractures in diagnostic imaging.

Role of Atlas Assimilation in the Context of Craniocervical Junction Anomalies.

Atlas assimilation (AA) may be associated with atlantoaxial dislocation, Chiari malformation (CM), and basilar invagination. The importance of AA in the context of craniocervical junction (CVJ) anomalies is unclear. Considering this context, this study's objective is to discuss the role of AA in the management of CVJ anomalies, especially in CM. A comprehensive literature review was performed. In addition, some illustrative cases were discussed on the basis of our review. Finally, we propose a theoretic algorithm to evaluate patients with AA and CM. AA is a proatlas segmentation anomaly that may be complete or incomplete. It may be totally asymptomatic or symptomatic as the result of transferred shifted forces onto the C1-2 joints, leading to clear instability (atlantoaxial dislocation) or mild C1-2 instability. Cautious surgical planning may be required due to associated vertebral artery anomalies. AA with concomitant C2-C3 segmentation failure is highly associated with late C1-C2 instability. CVJ decompression failure was reported in patients with CM and a low clivus canal angle (<130-135 degrees). Patients with assimilated anterior C1 arches usually have evident AAD. CM patients with AA generally have type 1 BI or type 2 BI and are reported with higher rates of CVJ instabilities when compared with those "pure" CM. Dynamic examinations may provide additional evidence of atlantoaxial instability. Although AA per se is not considered an unstable configuration, further and detailed evaluations of patients with CM associated with AA are necessary. Some associated unstable configurations required concomitant CVJ fixation.

3D-Printed Screw-Rod Auxiliary System for Unstable Atlas Fractures: A Retrospective Analysis.

OBJECTIVE: To develop and validate the efficacy of a 3D-printed screw-rod auxiliary system for unstable atlas fractures. METHODS: This research is a retrospective analysis, and a total of 14 patients, including 11 males and three females, were enrolled in our hospital from January 2017 to March 2019 who underwent occipitocervical fusion assisted by the 3D-printed screw-rod auxiliary system were reviewed, and with an average age of 53.21 ± 14.81 years, an average body mass index (BMI) of 23.61 ± 1.93 kg/m2 . The operation time, blood loss and radiation times during the operation were recorded. The maximum fracture displacement values of pre- and post-operation were measured based on CT imaging. All screw grades were evaluated after surgery. The occipital-cervical 2 (O-C2 ) angle and occipitocervical inclination (OCI) angle of pre-operation, post-operation and the last following-up were measured. The dysphagia scale 3 months after surgery and at the last follow-up, the Neck Disability Index (NDI) 3 months after surgery and at the last follow-up were assessed. RESULTS: All patients were completed the surgery successfully. There was no patient with severe dysphagia or aggravation of nerve injury. The follow-up was from 12 to 14 months, and with an average of 12.5 months. The average surgery time, average blood loss and average radiation times for the 14 patients were 112.14 min, 171.43 mL and 5.07 times, respectively. There was a significant difference in maximum fracture displacement between pre- and post-operation values (P < 0.05). A total of 56 screws were inserted in 14 patients, among them, three screws were classified as grade 1, and the other screws were classified as grade 0. There was a significant difference in the O-C2 between pre-operation and 3 days after operation (P = 0.002); There was a significant difference in OCI angles between pre-operation and 3 days after operation (P < 0.05); there was no significant difference in the O-C2 or OCI angle between 3 days after the operation and the last follow-up (P = 0.079; P = 0.201). The dysphagia scales of two patients were assessed as mild at 3 months after surgery, and the others were assessed as normal at 3 months after surgery. All patients' dysphagia scores returned to normal at the last follow-up. The average NDI and average neck Visual Analogue Scale (VAS) scores at the last follow-up were 2.53 and 8.41, respectively. CONCLUSION: It can objectively restore the OCI to normal with few post-operative complications under the assistance of a screw-rod auxiliary system to perform occipitocervical fusion for unstable atlas fractures and atlantooccipital joint instability.