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Study Design: Multicenter case-control study., Objective: To identify imaging characteristics of the cervical spine in patients with retro-odontoid pseudotumor (ROP) without rheumatoid arthritis (RA) and determine the pathogenesis of ROP., Background: ROP results from proliferative changes in the soft tissue of the atlantoaxial junction surrounding the region of the transverse ligament, and is commonly seen in RA patients. However, the pathogenesis of ROP caused by mechanical instability of the upper cervical spine in patients without RA is yet to be explained., Materials and Methods: We collected imaging data [preoperative radiographs, magnetic resonance imaging (MRI), and computed tomography (CT)] of patients who underwent surgery between April 2011 and March 2022 at the three university hospitals for ROP (cases) and cervical spondylotic myelopathy (as age, sex, and institution matched controls). The two groups were compared for different parameters on cervical dynamic radiographs, MRI, and CT., Results: The ROP group consisted of 42 patients, and the control group comprised 168 patients. C2-C7 range of motion was significantly smaller in the ROP group (25.8 ± 2.6°) compared with the control group (33.0 ± 1.0°). C2-C7 sagittal vertical axis was significantly larger in the ROP group than the control group (39.3 ± 3.6 vs. 32.2 ± 1.3 mm). MRI and CT assessment showed progressive degeneration at all intervertebral levels in the ROP group. A significant positive correlation was observed between the thickness of the soft tissue posterior to the dental process and the atlantodental interval in the flexion position ( r = 0.501)., Conclusions: The development of ROP was associated with degeneration of facet joints and intervertebral disks in the middle and lower cervical spine. Our findings suggest that decreased mobility of the middle and lower cervical spine may cause instability in the upper cervical spine, leading to the formation of ROP., Competing Interests: The authors report no conflicts of interest., (Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc.)

Study Design: Retrospective study., Objective: To classify surgical failures following atlantoaxial dislocation, present strategies for revisions, and evaluate the clinical results of revision surgery., Summary of Background Data: With the increase in atlantoaxial dislocation surgery, the number of surgical failures has gradually risen. However, current reports on atlantoaxial surgical revision are limited in scope. There remains a lack of summary regarding the causes of surgical failure, a detailed classification system, and no proposed strategy for revision surgery., Materials and Methods: A total of 109 cases of failed surgery following atlantoaxial dislocation were classified according to the reduction immediately after surgery and the fusion status before revision. The reduction, decompression, fusion status, and outcomes following revision surgery were evaluated by x-ray, computed tomography, magnetic resonance imaging, and the Japanese Orthopaedic Association score. The data were analyzed statistically with a paired-samples t test and multivariable logistic regression analysis., Results: The 109 patients were classified into three categories of failure: nonreduction with nonfusion (NR-NF, 73 cases), nonreduction with fusion (NR-F, 19 cases), and reduction with nonfusion (R-NF, 17 cases). Sixty-four patients underwent anterior revision, 21 posterior revision, and 24 anteroposterior revision. Postoperative complications were the primary cause of early revisions. After revision, complete decompression was achieved in all cases, anatomical reduction in 89 cases, significant improvement of Japanese Orthopaedic Association score in 77 cases, and fusion achieved in 86 cases. Twelve cases experienced surgical complications and three underwent a second revision., Conclusions: The authors found that NR-NF was the most common type of failure following surgery for atlantoaxial dislocation. Revision strategies can be guided according to the descriptive classification of failure, and revision surgery should focus on achieving adequate reduction, appropriate fixation, and reliable fusion to optimize postsurgical outcomes., Competing Interests: The authors report no conflicts of interest., (Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.)

Study Design: Retrospective cohort study., Objective: To verify the clinical efficacy of a novel transoral stepwise release technique (TSRT) for the treatment of irreducible atlantoaxial dislocations (IAAD)., Summary of Background Data: Anterior release for IAAD remains challenging, with a 3.2 times higher complication rate than posterior release. However, there are some patients who cannot achieve successful reduction from a posterior approach and require the higher-risk anterior release. Our work presents a novel anterior release technique that aims to minimize iatrogenic injury and associated complications from an anterior release., Materials and Methods: IAAD cases who were treated with TSRT were retrospectively studied. Primary outcomes included fusion rate, complications, and neurological function over the course of a minimum 1-year follow-up. Radiographic differences between preoperative and postoperative imaging were also considered. A preoperative prediction model for the actual release grade was developed using multivariate logistic regression based on demographic factors and the craniovertebral abnormalities identified on preoperative images, evaluating the need for higher-grade TSRT release., Results: We included 201 IAAD cases, with 42% (84/201) demonstrating degeneration of the atlantoaxial joint or anterior-hook-like dens. The reduction was achieved in all cases, with 80% (160/201) of cases only requiring relatively low-grade or grade I types TSRT release. Degeneration of the atlantoaxial joint was significantly associated with the need for higher-grade TSRT release (odds ratio:16.68, CI: 2.91-94.54, P = 0.002). The overall complication rate was 4.5% (9/201). Over the course of follow-up, the fusion rate reached 98.5%, and the American Spinal Injury Association and Japanese Orthopedic Association scores were significantly improved to 97.28 and 16.25 ( P < 0.01 and P < 0.01), respectively., Conclusion: This study demonstrated that our novel TSRT anterior release technique demonstrated complication rates similar to those published in the literature for posterior release. TSRT can be used as an alternative to posterior release techniques for refractory cases or when a posterior approach is not considered viable., Competing Interests: The authors report no conflicts of interest., (Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.)

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., Competing Interests: The authors report no conflicts of interest., (Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.)

Study Design: Observational and morphological study with three-dimensional (3D) computed tomography (CT) analysis., Objective: To discover the morphology and configuration deformities of craniovertebral junction (CVJ) and upper cervical spine in children with unilateral hemifacial microsomia (HFM). To determine whether there are specific HFM patients who are at higher risk of certain cervical vertebral anomaly., Summary of Background Data: The evaluation for cervical vertebrae anomaly in HFM children, especially in CVJ region, is underreported., Methods: Eighty-eight unilateral HFM children (64 males, 24 females) with four Pruzansky-Kaban types (I, Ila, Ilb, and III) underwent cranial and cervical CT scanning from skull to C5 in neutral position. The 3D morphology and configuration of the occipital condyle, atlas, and axis, etc. were evaluated on the presence of deformed detailed structures of CVJ region., Results: No C1 deformation was found in type I group. Six (14.3%) type Ila cases, seven (33.3%) type IIb cases, and six (37.5%) type Ill cases had lateral masses asymmetry of C1 (P  < 0.05). Five (55.6%) type I cases, 17 (40.5%) type Ila cases, 12 (57.1%) type Ilb cases, and 10 (62.5%) type Ill cases had C2 anomaly (P > 0.05). The incidence rate of C1-C2 instability for four groups were 33.3% (type I), 33.3% (type IIa), 33.3% (type IIb), and 31.3% (type Ill), respectively (P > 0.05)., Conclusion: For HFM children, the incidence of C1 deformation increased from type I to type Ill. The probability of C2 anomaly and C1-C2 instability in children with different types of HFM is nearly the same. The craniovertebral junction of every HFM child must be monitored carefully for C1-C2 instability before any surgical procedure to avoid atlantoaxial dislocation and spinal cord injury.Level of Evidence: N/A., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

Study Design: A retrospective cohort study., Objective: To examine factors related to severe aggravation of preexisting cervical lesions in patients with rheumatoid arthritis (RA) under current pharmacologic treatments with biologics., Summary of Background Data: Advanced RA cervical lesions carry a risk of irreversible damage to the spinal cord; however, risk factors for aggravation are unclear after the use of biologics became more popular., Methods: Of 166 patients with preexisting cervical lesions at baseline, 87 who had cervical X-ray images taken at baseline and at the final visit (with an interval of more than 1 yr) were evaluated retrospectively. Aggravated instabilities determined at the final visit, were defined as follows: atlantoaxial subluxation (AAS) = atlantodental interval ≧ 10 mm; vertebral subluxation (VS) = a Ranawat value < 10 mm; and subaxial subluxation (SAS) = an anterior vertebral slip ≧ 4 mm or a multilevel slip ≧ 2 mm. Patients were divided into two groups based on the radiographic results: severe aggravation and non-severe aggravation. Explanatory variables were gender, age of RA onset, duration of disease, average observation period, Disease Activity Score 28 based on C-reactive protein (DAS28-CRP) at baseline, drug treatment history, presence of mutilating deformities in the hands, presence of RA-related joint surgery, and the prevalence of each cervical lesion at baseline., Results: The severe group comprised 14 patients (16.1%). There was no significant difference between the two groups with respect to demographic data. Multivariate logistic regression analysis revealed that preexisting SAS lesions (odds ratio: 7.59, 95% confidence interval: 1.16-49.6) and no history of biologic treatment (odds ratio, 0.10; 95% confidence interval, 0.17-0.58) were associated with aggravation., Conclusion: Preexisting SAS lesions were associated with aggravation. Meanwhile, biologics may be effective at preventing aggravation.Level of Evidence: 3., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

Study Design: Biomechanical study using cadaveric cervical spines., Objective: To evaluate joint mobility and stiffness at the craniovertebral junction., Summary of Background Data: Data on the intersegmental kinematics of the craniovertebral joints are available in the literature with a widespread range of values. The effect that alar ligament injuries have on intersegmental kinematics remains unclear and requires further biomechanical investigation., Methods: Ten occipito-atlanto-axial (C0-C1-C2) human specimens were articulated to flexion, extension, bilateral lateral bending, and bilateral axial rotation. The moment-rotation response was continuously tracked through the entire range of motion before and after unilateral alar ligament transection of the right side., Results: The intersegmental (C0-C1/C1-C2) moment-rotation response was continuously quantified in full flexion (7.2 ± 6.6°/12.1 ± 5.8°), extension (11.1 ± 6.4°/3.0 ± 2.8°), lateral bending to the right (3.1 ± 2.2°/1.6 ± 1.2°) and left sides (3.3 ± 1.6°/2.1 ± 1.5°), and axial rotation to the right (1.2 ± 3.5°/32.3 ± 9.3°) and left sides (2.7 ± 2.6°/25.3 ± 8.3°). Unilateral alar ligament transection increased the range of motion of C0-C2 in the three planes of movement; however, intersegmental motion alterations were not always observed., Conclusion: Increases in the range of extension and lateral bending at C0-C1, which had not been reported previously, were observed. Further, the range of rotation on the right and left sides increased, in conjunction with the increased ranges at C0-C1 and C1-C2.Level of Evidence: N/A., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

Mini: The morphological features of the lateral atlantoaxial joints (LAJs) in patients with old type II odontoid fractures and atlantoaxial dislocation have not been fully analyzed. Our study found the changes in morphological features of the LAJs in some patients, and revealed the causes and consequences of the changes in morphological features of the LAJs., (Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.)

Study Design: Clinical case series., Objective: To present a surgical technique and results of posterior direct reduction of lateral atlantoaxial joints for rigid pediatric atlantoaxial subluxation (AAS) using a fulcrum lever technique., Summary of Background Data: The surgical treatment of pediatric rigid AAS is still technically challenging. Several factors contribute to the surgical difficulty, such as small vertebrae, incomplete bone formation, dysplasia, the difficulty of reduction and external fixation are considered as a surgical daunting challenge. Herein, the surgical technique of posterior direct reduction of lateral atlantoaxial joints for rigid pediatric AAS using a fulcrum lever technique is presented., Methods: This retrospective study included 10 pediatric patients with rigid AAS who underwent posterior direct reduction of bilateral C1/2 facet joints via a fulcrum lever technique. The indication for surgery was the presence of neurological symptoms and spinal cord atrophy with an intramedullary high signal at the C1 level on T2-weighted magnetic resonance (MR) images. The surgical procedure consisted of three steps: (1) opening and distraction of the C1/2 facet joints and placement of tricortical bone as a spacer and fulcrum; (2) placement of C1 and C2 screws; and finally, (3) compression between the C1 posterior arch and C2 lamina and constructing C1/2 fusion. All patients underwent the neurological and radiological evaluations before and after surgery., Results: Eight of 10 patients demonstrated genetic disorders, either Down syndrome or chondrodysplasia punctate. Besides, all cases documented congenital anomaly of the odontoid process. Bilateral C1 lateral mass screws were successfully placed in all cases. No evidence of postoperative neurovascular complications. Radiological evaluation showed the corrections and bony fusions of C1/2 facet joint in all cases., Conclusion: The fulcrum lever technique for rigid pediatric AAS can be one of the effective surgical solutions to this challenging pediatric spinal disorder., Level of Evidence: 4.

Study Design: A retrospective case series study with at least 10 years of follow-up data., Objective: To validate the reliability of bilateral C1-2 transarticular screws and C1 laminar hooks and a bone autograft for acute pediatric atlantoaxial instability., Summary of Background Data: The reliability of initial posterior atlantoaxial fusion in pediatric patients is still controversial. To date, however, only a few published articles with short-term follow-up data are available to help spinal surgeons understand the effects of posterior atlantoaxial fusion in the skeletally immature spine., Methods: Five pediatric patients with acute atlantoaxial instability underwent atlantoaxial fusion using the above technique over a 3-year period. During a minimum 10-year follow-up period, not only outcomes and complications were investigated, but the vertical growth of the constructed spine in relation to the growth of the entire cervical spine, overall cervical spinal alignment, and adjacent-segment instability were evaluated., Results: The clinical follow-up indicated solid fusion and complete clinical relief from symptoms. No neural or vascular impairment was observed. The radiological evaluation showed that all patients had growth within the fusion construct reaching a mean 35.4% of the entire cervical spine. There were no radiological indicators of subaxial instability, even when cervical sagittal alignments became straight with a mean C2-7 angle of 6.4°., Conclusion: The results showed that initial posterior atlantoaxial fusion accomplished with bilateral C1-2 transarticular screws, C1 laminar hooks fixation, and bony autograft is a reliable surgical technique for treating acute pediatric atlantoaxial instability without negative effects on vertical growth at the fused level or the stability of the subaxial spine., Level of Evidence: 3.

Study Design: A retrospective clinical study., Objective: The aim of this study was to evaluate the efficacy and safety of fluoroscopy-guided atlantoaxial pedicle screw fixation in patients younger than 12 years., Summary of Background Data: C1-C2 pedicle screw fixation is a widely accepted treatment method for atlantoaxial dislocation (AAD). However, data regarding its use for atlantoaxial fusion (AAF) in children are limited., Methods: Thirty-six consecutive patients younger than 12 years underwent C1-C2 pedicle screw fixation for AAD between 2007 and 2017. Anatomical parameters of the C1 pedicle were measured on preoperative computed tomography (CT). Accuracy of pedicle screw fixation was assessed on postoperative CT using the following definitions: Type I, screw threads completely within the bone; Type II, less than half the diameter of the screw violating the surrounding cortex; and Type III, clear violation of the transverse foramen or spinal canal. Demographic, surgical, radiation dose, and clinical data were recorded., Results: Patients underwent 144 screw fixations (67 C1 pedicle screws, 68 C2 pedicle screws, 5 C1 lateral mass screws, and 4 C-2 laminar screws) for a variety of pediatric AADs, with 36.5 ± 8.5 months of follow-up. Among the 135 pedicle screws, 96.3% were deemed "safe" (Type I or II) and 80.7% (109/135) of the screws were rated as being ideal (Type I); five screws (3.7%) were identified as unacceptable (Type III). Average estimated blood loss (EBL) was 92 mL, and the average total radiation exposure during the operation was 6.2 mGy (in the final 26 cases). There were no neurovascular injuries. All patients showed radiographic stability and symptom resolution., Conclusion: C1-C2 pedicle screw fixation under fluoroscopy is safe and effective for the treatment of AAD in children younger than 12 years. However, it may be technically challenging owing to the special anatomical features of children and should be performed by experienced surgeons., Level of Evidence: 3.

Study Design: Retrospective review., Objective: Evaluate radiographic and clinical outcomes for infants and children, who underwent rigid occipito-cervical fixation for traumatic craniocervical dissociation (tCCD)., Summary of Background Data: Traumatic craniocervical dissociation is devastating. Children are at high risk but make up a large number of survivors. Non-rigid fixation has traditionally been favored over screw and rod constructs due to inherent challenges involved with instrumenting the pediatric craniocervical junction. Therefore, outcomes for rigid occipito-cervical instrumentation in infants and young children with tCCD remain uncertain., Methods: Retrospective review of children who survived tCCD between 2006 and 2016 and underwent rigid occipito-cervical fixation., Results: Fifteen children, from 8 months to 8 years old (mean, 3.8 yr), were either a passenger (n = 11) or a pedestrian (n = 4) in a motor vehicle accident. Seven patients had weakness: five with quadriplegia, one with hemiparesis, and one with bilateral upper extremity paresis. Ten patients had concurrent C1-2 instability. At last follow-up, four patients had improved motor function: one with bilateral upper extremity paresis and one with hemiparesis regained full strength, one with quadriplegia regained function on one side while another regained function in bilateral upper extremities. All underwent rigid posterior occipito-cervical fixation, with two patients requiring additional anterior and posterior fixation at non-contiguous levels. Fourteen patients were stable on flexion-extension x-rays at a mean follow-up of 31 months (9-1 yr or longer, 7-2 yr or longer). There were no cases of deformity, growth disturbance, or subaxial instability., Conclusion: Children who survive tCCD may regain function after stabilization. Rigid internal rod and screw fixation in infants and young children safely provided long-term stability. We advocate using C2 translaminar screws to exploit the favorable anatomy of pediatric lamina to minimize the risks of occipitocervical (OC) instrumentation., Level of Evidence: 4.

Study Design: Retrospective comparative study., Objective: To compare the outcomes of C1-C2 transarticular screw combined with C1 laminar hook (TAS+C1H) and C1-C2 transarticular screw combined with modified Gallie technique (TAS+G) for treating reducible atlantoaxial dislocation (AAD)., Summary of Background Data: Both TAS+C1H and TAS+G fixation were 3-point fixation techniques for AAD. TAS+C1H technique was comparable to TAS+G technique in biomechanics. However, it is unknown whether it can achieve same outcomes as TAS+G technique., Methods: Data of the 63 patients who underwent TAS+C1H or TAS+G fixation and fusion because of AAD were retrospectively reviewed. Bone fusion time was recorded. The outcomes evaluated by visual analog scale score for neck pain (VASSNP), Nurick scale, neck stiffness (none/mild/severe), patient satisfaction, and Neck Disability Index (NDI) were compared between two groups., Results: At the final follow-up, bone graft fusion rates were 100% in both groups (P > 0.05). Nurick scales were significantly improved in both groups (P < 0.05), but with no significant differences between groups (P > 0.05). There were no significant differences between two groups in VASSNP, neck stiffness, patient satisfaction, or NDI (all P > 0.05). There were no complications related to the surgical approach and instrumentation in either group., Conclusion: Both TAS+C1H and TAS+G fixation were effective in the treatment of reducible AAD. TAS+C1H was safer than TAS+G because it could potentially reduce the risk of spinal cord and venous plexus injury associated with sublaminar cables., Level of Evidence: 3.

Study Design: Finite element analysis., Objective: To compare the biomechanical stability imparted to the C1 and C2 vertebrae by the transarticular (TA), C1 lateral mass (LM)-C2 pedicle (PS), C1LM-C2 pars, and C1LM-C2 translaminar (TL) screw fixation techniques., Summary of Background Data: Cadaveric biomechanical studies of several atlantoaxial posterior fixation techniques have been performed, showing significant heterogeneity in biomechanical properties among the studies., Methods: From computed tomography images, a nonlinear intact three-dimensional C1-2 finite element model was developed and validated. Four finite element models were reconstructed from different C1-2 fixation techniques. The range of motion (ROM) and maximum von Misses stresses for the four screw techniques were compared under flexion, extension, lateral bending, and axial rotation., Results: C1LM-C2PS showed the greatest decrease in ROM with flexion/extension and lateral bending. C1-2TA and C1LM-C2 pars showed less ROM reduction than the other techniques, in flexion/extension. C1LM-C2TL showed the least decrease in ROM during axial rotation. For C1-2TA, the maximum stress was in the C1-2 joint region. In the C1LM-C2PS, the C1 rod head, C2 pars screw, and C2TL screw were stressed at the C2 rod head. The maximal von Mises stress on the C1-2TA at the C1-2 joint site was the highest at flexion/extension, whereas the C1LM-C2PS had the lowest stress on the screw at flexion/extension and lateral bending. The C1LM-C2TL showed the highest stress in axial rotation and lateral bending., Conclusion: In this study, C1LM-C2PS fixation was the most stable technique. If surgeons have to use other fixation methods besides the C2 pedicle screw, they need to be aware that additional fixation or postoperative immobilization may be required to achieve ROM restriction. Careful observation at the maximum stress site on the screw including screw loosening, screw-bone interface disruption or screw fracture will be necessary during follow-up imaging examinations (x-ray and computed tomography scan) after atlantoaxial fixation., Level of Evidence: N/A.

Study Design: A prospective study of 20 multimorbid patients older than 65 years undergoing minimally invasive surgical treatment for odontoid fracture., Objective: To analyze the results of percutaneous transarticular atlantoaxial screw fixation as a new minimally invasive treatment modality in this high risk group of patients., Summary of Background Data: Odontoid fractures are a common injury pattern in the elderly. These fractures typically present significant challenges as geriatric patients often have multiple comorbidities that may adversely affect fracture management. Despite numerous publications on this subject, with a trend toward primary operative stabilization, the appropriate treatment for this frequent and potentially life threatening injury remains controversial., Methods: Between January 2013 and December 2015, 20 consecutive patients underwent posterior percutaneous transarticular atlantoaxial screw fixation for odontoid fracture type II. The two main inclusion criteria were age 65 years or older and ASA score of III or IV. The screws were inserted percutaneously with the help of two fluoroscopy devices. Clinical and radiological examinations were regularly performed for a minimum of 18 months postoperatively., Results: The mean age was 81 years, all of them with multiple comorbidities. Reduction of the fracture and screw insertion was possible in all cases. The mean operative time was 51.75 minutes and mean blood loss was 41.7 mL. Three patients died in the first 3 months after surgery. Healing of the fracture occurred in 15 patients (88.2%). Revision surgery was not necessary in any of the patients. Mean visual analogue scale (VAS) at the final follow-up was 2.4, and mean patient satisfaction score was 7.1., Conclusion: Percutaneous transarticular atlantoaxial fixation in elderly patients offers a good minimally invasive operative treatment in this multimorbid group of patients. This new technique with short operative time is well tolerated by the geriatric patients leading to a healing rate up to 88%., Level of Evidence: 4.

Study Design: Case report., Objective: We report here on an 18-month-old boy with brachytelephalangic chondrodysplasia punctata (BCDP), whose atlantoaxial instability was successfully managed with occipitocervical instrumented fusion (OCF) using screw and rod instrumentations., Summary of Background Data: Recently, there have been a number of reports on BCDP with early onset of cervical myelopathy. Surgical OCF is a vital intervention to salvage affected individuals from the life-threatening morbidity. Despite recent advancement of instrumentation techniques, however, rigid OCF is technically demanding in very young children with small and fragile osseous elements. To our best knowledge, this is the first report on application of the instrumentation technique to a toddler patient with BCDP., Methods: A 16-month-old boy with BCDP presented with tetraplegia and swallow obstacle. Hypoplasia of the odontoid process and atlantoaxial instability were present in lateral radiographs. T2-weighted magnetic resonance (MR) images revealed a high signal region in the spinal cord at the C1-2 and C7-T1 levels. Cervical computed tomography (CT) showed that the pedicles and lateral masses in the cervical spine were small and immature, but the laminae were comparatively thick., Results: One week before surgery, the patient was fitted with a Halo-body jacket. We performed plate-rod placement with occipital cortical screws and C2/C3 interlaminar screws, and added an autogenous bone graft using the right 8 and 9 ribs. Rigid fixation of the occipito-cervical spine was completed successfully without major complications. Postoperative halo-body jacket immobilization was continued for 3 months, after which Aspen collar was fitted. CT confirmed occipitocervical bone fusion at 6 months after surgery. Mild clinical improvements in motor power of the affected muscles and swallowing were witnessed at 1 year postoperatively., Conclusion: Rigid fixation using screw, rod, and occipital plate instrumentation was successful in an 18-month-old toddler with BCDP and atlantoaxial instability. Bone fusion was achieved at postoperative 6 months., Level of Evidence: 5.

Study Design: Retrospective comparative study., Objective: To compare the outcomes of C1-C2 transarticular screw with C1 laminar hook (TAS + C1H) fixation and C1 trans-arch lateral mass screw with C2 pedicle screw (C1TLMS + C2PS) fixation in the treatment of reducible atlantoaxial dislocation (AAD)., Summary of Background Data: TAS + C1H is comparable to TAS with posterior wiring techniques and superior to C1 lateral mass screw combined with C2 pedicle screw (C1LMS + C2PS) in biomechanics. There were, however, few studies analyzing the differences in outcomes between TAS + C1H technique and modified C1LMS + C2PS technique (C1TLMS + C2PS) for treating AAD., Methods: Data of 30 patients with reducible AAD treated by TAS + C1H fixation and another 30 cases treated by C1TLMS + C2PS fixation were retrospectively analyzed. Bone fusion time was recorded. The outcomes evaluated by American Spinal Injury Association impairment scale, visual analog scale score for neck pain, neck stiffness (none/mild/severe), patient satisfaction, and Neck Disability Index (NDI) were compared between two groups., Results: There were no complications related to the surgical approach and instrumentation in either group. At the final follow-up, bone graft fusion rates were 100% in both the TAS + C1H fixation group and the C1TLMS + C2PS fixation group (P > 0.05). The neurological status evaluated by American Spinal Injury Association impairment scale were greatly improved in both screw-hook group (P < 0.001) and screw-rod group (P < 0.001), but with no significant differences between groups (P > 0.05). There were no significant differences between two groups in visual analog scale score for neck pain, neck stiffness, patient satisfaction, or Neck Disability Index (all P > 0.05)., Conclusion: C1TLMS + C2PS fixation was comparable to TAS + C1H fixation in fusion rate and functional outcomes for treating reducible AAD. To reduce the risk of vertebral artery injury, computed tomography scan, and reconstruction should be done to analyze vertebral artery course and C1-C2 anatomic structures before operation., Level of Evidence: 3.

Study Design: A prospective multicenter cohort study for more than 10 years of outpatients with rheumatoid arthritis (RA)., Objective: To identify predictive risk factors of cervical spine instabilities, which may induce compression myelopathy in patients with RA., Summary of Background Data: Many reports described the natural course of cervical spine involvement in RA. Only a few studies, however, conducted comprehensive evaluation of its prognostic factors., Methods: Cervical spine instability was radiographically defined as atlantoaxial subluxation with the atlantodental interval greater than 3 mm, vertical subluxation (VS) with the Ranawat value less than 13 mm, and subaxial subluxation with irreducible translation of 2 mm or higher. The "severe" category of instability was defined as atlantoaxial subluxation with the atlantodental interval of 10 mm or lower, vertical subluxation with the Ranawat value of 10 mm or higher, and subaxial subluxation with translation of 4 mm or higher or at multiple levels. Of 503 "definite" or "classical" patients with RA without baseline "severe" instability, 143 were prospectively followed throughout for more than 10 years. The Cox proportional hazards regression analysis was performed to determine predictors for the development of "severe" instabilities. To exclude biases from the low follow-up rate, similar assessments were performed in 223 patients followed for more than 5 years from baseline., Results: The incidence of cervical spine instabilities and "severe" instabilities significantly increased during more than 10 years in both 143 and 223 cohorts (all P < 0.01). Multivariable Cox proportional hazards models found that baseline mutilating changes (hazard ratio [HR]=19.15, 95% confidence interval [95% CI] = 3.96-92.58, P < 0.01), corticosteroid administration (HR = 4.00, 95% CI = 1.76-9.11, P < 0.01), and previous joint surgery (HR = 1.99, 95% CI = 1.01-3.93, P = 0.048) correlated with the progression to "severe" instability in 143 cases and also in 223 cases (HR = 8.12, 95% CI = 2.22-29.64, P < 0.01; HR = 3.31, 95% CI = 1.68-6.53, P < 0.01; and HR = 2.07, 95% CI = 1.16-3.69, P = 0.014, respectively)., Conclusion: Established mutilating changes, concomitant corticosteroid treatment, and previous joint surgery are relatively robust indicators for a poor prognosis of the cervical spine in patients with RA, based on the consistency in more than 10-year analysis of two different settings., Level of Evidence: 3.

Study Design: Retrospective study., Objective: To investigate whether clivodens angle (CDA) could diagnose basilar invagination (BI) at computed tomography (CT)., Summary of Background Data: Over the years, multiple craniometric methods such as Chamberlain line, McGregor line, McRae line, Wackenheim clivus baseline, and Welcher basal angle have been described for evaluation of craniovertebral junction anomalies, initially with radiography and later with CT. However, such a variety of measurements in turn reflects the difficulty in making a definite diagnosis of BI and there is a certain disadvantage in all of these criteria because the anatomic landmarks vary within a normal range., Methods: CDA, described an angle formed at the intersetion of a line that runs along the long axis of the clivus and one that runs along the long axis of the dens, was measured on mid-sagittal reconstructed CT images from 63 BI patients and 100 control participants to compare the two groups by using independent-sample t test. Interobserver reliability was evaluated with Kendall correlation coefficient. For evaluating the diagnostic performance and determining the cutoff value of CDA, receiver operating characteristic curve was utilized., Results: The measurement of CDA showed good interobserver agreement (KCC = 0.891). Compared with control participants whose mean value was 135.8 degrees ± 9.2 (range, 118-156°), BI patients had a significantly smaller one (P < 0.001), 110.4 degrees ± 15.8 (range, 55-140°). The area under receiver operating characteristic curve was 0.937 (95% confidence interval: 0.901, 0.973), and the cutoff value of 125 degrees had the largest Youden index (J), 0.715., Conclusion: Having a better diagnostic performance than clivoaxial angle, CDA can be utilized for diagnosing BI., Level of Evidence: 3.

Study Design: Retrospective case series of atlantoaxial rotatory fixed dislocation (AARFD)., Objective: To describe clinical features and the surgical treatment of AARFD., Summary of Background Data: The classification and treatment strategy for atlantoaxial rotatory fixation (AARF) were previously described and remained controversial. AARF concomitant with atlantoaxial dislocation has different clinical features and treatment strategy with the most AARF. Due to deficiency of the transverse ligament or odontoid, the atlantoaxial remains unstable even after the torticollis relieved or cured. Because of the rarity, treatment strategy for this special condition has not been specialized and fully explored in the literatures., Methods: Thirty-two children with AARFD (sustained torticollis more than 6 weeks and atlanto-dental internal more than 5 mm) were retrospectively reviewed. Treatment methodology, pearls, and pitfalls of the treatment were discussed., Results: Thirty-two cases had sustained torticollis for an average of 5.7 months. ADI of them ranged from 8 to 22 mm, with a mean of 11.3 mm. Eight cases presented with signs and symptoms of spinal cord dysfunction. All 32 cases underwent surgery and had no spinal cord or vertebral artery injury. The surgery included posterior reduction and fusion (reducible dislocation and torticollis, 16 cases), and transoral release followed by posterior reduction and fusion (irreducible dislocation and torticollis, 16 cases). The average follow-up time was 42 months. Solid fusion and torticollis healing were achieved in 31 patients (96.9%) as detected radiologically. Two cases (6.3%, 2/32) suffered complications (cerebrospinal fluid leakage and recurred torticollis followed by revision)., Conclusion: AARFD had distinct clinical features relative to common presentations of AARF. Because of deficiency of the transverse ligament or odontoid and subsequent atlantoaxial dislocation, surgical treatments are applied for this condition, including transoral release and posterior C1-2 reduction and fusion. AARFD cases were successfully managed surgically without preoperative traction, with few complications seen., Level of Evidence: 4.

Study Design: A retrospective comparative study., Objective: The aim of this study was to compare the outcomes of anterior screw fixation and posterior temporary-fixation in the treatment of Anderson-D'Alonzo type II odontoid fractures., Summary of Background Data: Posterior C1-C2 temporary-fixation can spare the motion of C1-C2 in the treatment of odontoid fractures. However, it is unknown whether it can achieve the same outcomes as anterior screw fixation., Methods: Data of 20 patients who underwent posterior temporary-fixation due to Anderson-D'Alonzo type II odontoid fractures with intact transverse ligament were retrospectively reviewed. Another 20 patients undergoing anterior screw fixation were randomly selected as the control group. The range of motion (ROM) in rotation of C1-C2 measured on functional computed tomography (CT) scan and outcomes evaluated by the visual analog scale (VAS) for neck pain, neck stiffness, patient satisfaction, and neck disability index (NDI) were compared between two groups at the final follow-up., Results: At the final follow-up, 19 cases in each groups achieved facture healing. Total C1-C2 ROM in rotation on both sides in the posterior temporary-fixation group was 32.4 ± 12.5°, smaller than 40.0 ± 13.0 in the anterior fixation group. However, there was no statistical difference between two groups. And there was no significant difference between two groups in functional outcomes evaluated by VAS for neck pain, neck stiffness, patient satisfaction, and NDI., Conclusion: Posterior temporary-fixation can spare the motion of C1-C2 and achieve same good clinical outcomes as anterior screw fixation in the treatment of Anderson-D'Alonzo type II odontoid fractures. It was an ideal alternative strategy to anterior screw fixation., Level of Evidence: 3.

Study Design: A CT-based study of pediatric atlas., Objective: The aim of this study was to identify morphometric patterns and dimensions of the pediatric C1 posterior arch to establish guidelines for the posterior arch crossing screw (PACS) fixation., Summary of Background Data: The PACS fixation is an alternative or supplement to the C1 lateral mass screw or pedicle screw constructs. However, the anatomic feasibility of this technique has not been well documented in the pediatric population., Methods: A total of 123 pediatric patients were assigned into 6 groups based on age at an interval of 3 years. The C1 posterior arch unsuited to PACS fixation was classified as type 1 with synchondrosis, and type 2 without synchondrosis. Three subtypes of type 2 were included: the underdeveloped tubercle, the flat arch, and the undersized tubercle (height < 7 mm or width < 3.5 mm), respectively. The C1 posterior tubercle height and arch width, the projected PACS length and angle were measured, respectively., Results: There were 19 patients of type 1 and 68 patients of type 2. Type 1 was mostly found in patients under age 3 years, whereas type 2 was largely observed in patients older than 4 years. The tubercle size was the most limiting variable for successful PACS placement. The PACS fixation was feasible for 42% patients over age 7 years and only 5% patients under age 6 years. The posterior tubercle height increased with age, whereas the tubercle width, the PACS length, and axial-plane angle increased with age up to 12 years. The PACS length was between 16 and 18 mm with the angle between 18° and 23° for patients over age 7 years., Conclusion: The PACS fixation was anatomically feasible in patients over age 7 years, but contraindicated in patients under age 6 years. Pediatric patients for the PACS fixation should be assessed before surgery., Level of Evidence: 4.

Study Design: Case report., Objective: We report on a case with a retro-odontoid synovial cyst, and the immediate reduction of the cyst was confirmed after lateral atlantoaxial joint puncture and arthrography., Summary of Background Data: Retro-odontoid synovial cysts are rare diseases located posteriorly to a dense axis. Because most reports have focused on surgical treatment, only a few have examined nonsurgical treatment. However, several months are required after nonsurgical treatment until cyst regression., Methods: A 52-year-old female presented with atlantoaxial instability. She complained of neck pain and numbness in her hands. Magnetic resonance imaging revealed a retro-odontoid synovial cyst. Lateral atlantoaxial joint puncture and arthrography were performed., Results: Two days after treatment, the patient showed significant improvement in the numbness of her hands, and a follow-up magnetic resonance imaging revealed an immediate reduction in the cyst. During a 4.5-year follow-up period, no recurrence of the clinical symptoms occurred., Conclusion: Lateral atlantoaxial joint puncture may immediately reduce retro-odontoid synovial cysts, and the lateral atlantoaxial joint has a communication channel with the retro-odontoid synovial cyst via the atlantodental joint. Once disappearance of the cyst is confirmed, an acceptable long-term outcome can be achieved with nonsurgical treatment even in cases with atlantoaxial instability., Level of Evidence: N/A.

Study Design: A retrospective case series., Objective: To describe a novel intraoperative reduction technique applying C1 transposterior arch lateral mass screw combined with C2 pedicle screw and rod system for pediatric acute atlantoaxial rotatory subluxation with injury of transverse ligament and evaluate outcomes of this technique., Summary of Background Data: For atlantoaxial rotatory subluxation with disruption of transverse ligament or recurrent cases, initial posterior atlantoaxial fusion is a preference. It is an important prerequisite for successful surgery to achieve satisfactory reduction of atlantoaxial articulation after preoperative cranial traction. However, the placement of cranial tractor and persistent traction may be challenging due to a pediatric patient's noncompliance and unsuitable anatomic structure. Therefore, an intraoperative way to achieve reduction and to keep solid stability with only a single procedure is needed., Methods: The consecutive patients with atlantoaxial rotatory subluxation with injury of transverse ligament, including 4 males and 1 female, underwent intraoperative reduction and fixation applying C1 posterior arch lateral mass screw combined with C2 pedicle screw and rod system during a 2-year period. The surgical technique and procedure of treatment were intensively reviewed; the clinical outcomes were retrospectively investigated in the aspects of clinical symptoms and imaging appearance., Results: Clinical follow-ups were obtained for an average of 29.4 (range, 24-30 mo) months. The clinical and radiological follow-up indicated a complete clinical relief and satisfactory reduction, stable arthrodesis of atlantoaxial articulation. No neural and vascular impairment related to this technique were observed., Conclusion: The primary outcome showed under sufficient preoperative imaging measurements, C1 transposterior arch lateral mass screw combined with C2 pedicle screw and rod system that obviated preoperative cranial traction provided reliable reduction and stability of atlantoaxial articulation for atlantoaxial rotatory subluxation with injury of transverse ligament., Level of Evidence: 4.

Study Design: A retrospective case-control study., Objective: To assess the usefulness and reproducibility of 2 novel safe and simple radiographical measurements for atlantoaxial instability in children with Down syndrome., Summary of Background Data: In pediatric atlantoaxial instability, early diagnosis is important for improved outcomes because of poor postoperative recovery in progressed neurological symptoms. Conventional dynamic radiography of the cervical spine is associated with a potential risk of worsening neurological symptoms., Methods: We retrospectively reviewed the medical records of 50 patients (24 boys and 26 girls) with atlantoaxial instability associated with Down syndrome. Of the 50 children, 11 had undergone and 4 had been scheduled for surgery (surgical group). In this investigation, in addition to the atlas-dens interval (ADI) and space available for spinal cord (SAC), we measured C1 inclination angle and C1/4 SAC ratio on lateral radiographs of the cervical spine in the neutral position. To assess the diagnostic abilities of these indices to determine indication for surgery, receiver operating characteristic analysis of each index was performed, and their diagnostic abilities were compared using the area under the receiver operating characteristic curve. Moreover, we assessed reproducibility of our 2 proposed indices., Results: The discriminatory abilities of C1/4 SAC ratio (area under the receiver operating characteristic curve, 1.00) and C1 inclination angle (0.91) were comparable with those of ADI (0.98) and SAC (0.95). For the interobserver and intraobserver reliability of the novel indices, the correlation coefficients were in the range from 0.88 to 0.99. Correlation was observed between the ADI and C1/4 SAC ratio (r = 0.507, P < 0.01) and between the ADI and C1 inclination angle (r = 0.407, P < 0.01)., Conclusion: The diagnostic abilities of the 2 novel radiographical measurements were comparable with those of ADI and SAC. Moreover, these novel measurements can be obtained safely on lateral radiographs of the cervical spine in the neutral position., Level of Evidence: 4.

Study Design: Retrospective study of 146 patients with the diagnosis of occipitalization, atlantoaxial dislocation (AAD) and basilar invagination, using a novel surgical treatment strategy., Objective: To introduce a novel fixation and reduction technique., Summary of Background Data: Atlas occipitalization associated with basilar invagination often result in fixed AAD that need reduction and occipitocervical fixation. The widely used occipitocervical fixation with suboccipital screws has several limitations such as the poor screw purchase in maldevelopment of the occipital bone, limited area available for implants in previous suboccipital craniectomy. The placement of occipitalized C1 lateral mass screw is an alternative option., Methods: From June 2007 to June 2013, 146 patients of occipitalized atlas with fixed AAD and basilar invagination, underwent fixation and reduction via C1 lateral mass and C2 pars/pedicle screw., Results: A total of 143 patients achieved the follow-up in the range from 6 months to 4 years (average, 30 mo). Neurological improvement was seen in all the 143 patients, with the averaged Japanese Orthopedic Association scores increasing from 11.6 to 15.5. Radiographical evaluation showed that solid bony fusion was achieved in all patients, and complete reduction was attained in 95 patients, and partial reduction (>60%) in 40 patients, and no effective reduction in 8 patients who had additional transoral decompression. Magnetic resonance imaging demonstrated that the ventral cervicomedullary compression was relieved in all patients., Conclusion: Although technically demanding, the C1 lateral mass placement in occipitalization is very useful in the rescue situation where more conventional stabilization alternatives are not technically possible, or as routine occipitocervical stabilization. It provides firm stabilization offering an optimum situation for bony fusion, and meanwhile the effective reduction of fixed AAD and basilar invagination. An extremely high fusion rate can be expected with minimal complications and minimal postoperative immobilization with this technique.

Study Design: Retrospective cohort analysis., Objective: To clarify the effect of biological agents (BAs) on the development and progression of cervical lesions in patients with rheumatoid arthritis (RA) and to identify biomarkers that accurately predict disease progression., Summary of Background Data: The introduction of BAs changed the paradigm of RA treatment. However, their effects on cervical lesions in patients with RA have not been studied., Methods: Ninety-one subjects who had received BAs for 2 years or more were enrolled. Mean radiographical interval was 3.9 years. Disease activity was evaluated by disease activity score-C-reactive protein levels, and matrix metalloproteinase-3 levels. Cervical lesions were defined as an atlantodental interval more than 3 mm for atlantoaxial subluxation (AAS), Ranawat value less than 13 mm for vertical subluxation (VS), and anterior or posterior listhesis more than 2 mm for subaxial subluxation. Disease progression was defined radiographically as an increase in the atlantodental interval more than 2 mm for AAS, a decrease in both Ranawat and Redlund-Johnell values more than 2 mm for VS, and an increase in listhesis more than 2 mm for subaxial subluxation. We used multivariate regression techniques to assess predictors of disease progression., Results: Baseline radiographical evaluation showed no pre-existing cervical lesion in 44 patients, AAS in 29, and VS in 18. Radiological progression occurred in 7% patients without baseline lesions, 79% in the AAS group, and 72% in the VS group. The incidence of progression was significantly lower in patients without lesions at baseline. Multivariate regression analysis demonstrated pre-existing cervical lesions, disease activity score-C-reactive protein levels at baseline and metalloproteinase-3 levels at final visit as good predictors of RA progression., Conclusion: BAs prevented de novo cervical lesions in patients with RA but failed to control progression in patients with pre-existing cervical lesions. Disease activity score-C-reactive protein levels at baseline were related to pre-existing joint destruction, and metalloproteinase-3 levels accurately predicted ongoing bone destruction during BA treatment., Level of Evidence: 3.

Study Design: Anatomical measurements and in vitro biomechanical testing were performed to evaluate a new method for posterior C1 fixation., Objective: This study sought to assess C1 posterior arch crossing screw fixation for posterior C1-C2 fixation, using anatomical measurements and biomechanical testing with traditional C1 pedicle screws (PS) in a cadaveric model., Summary of Background Data: Atlantoaxial instability often requires surgery, and the current methods for atlas fixation incur some risk to the vascular and neurological tissues. Thus, new, effective, and safe methods are needed for salvage operations., Methods: Morphometric analysis of the C1 posterior arch was performed using 3-dimensional computed tomography. Six fresh ligamentous human cervical spines (C0-C4) were evaluated for their biomechanics. The specimens were tested in their intact condition and after stabilization (C1-C2 PS, C1 posterior arch screws [PAS] with C2 PS) and injury due to 1.5 N·m of pure moment in flexion, extension, lateral bending, and axial rotation. During testing, 3-dimensional angular motion was measured with a motion capture platform (Vicon Nexus). Data for all scenarios were recorded, and statistical analysis was performed., Results: Anatomical assessment indicated that 91.51% of C1 posterior tubercles exceeded 7 mm in thickness, 93.40% had a width of the posterior arch of greater than 3.5 mm, and 65.57% had a unilateral screw length of greater than 15 mm, indicating that the posterior arch fixation could be achieved by two 3.5 × 15-mm screws placed in a crossed manner. Twenty-two cases (11%) were not suitable for crossing screw placement because the posterior arch was flat and the entry point was present on the same side. Biomechanical testing showed that the PS and PAS rod-screw systems significantly reduced flexibility in flexion, extension, and rotation compared with the intact position. For lateral bending, there was a trend for the C1 PS and PAS systems toward decreased flexibility in comparison with the intact position. At the same time, C1 PAS decreased C1-C2 movement by 33.0% in left bending (P = 0.171) and 24.4% in right bending (P = 0.095); however, no significant difference was observed for left bending with C1 PAS compared with C1 PS, and the C1 PS and PAS systems significantly reduced the flexibility more than destabilization., Conclusion: Crossing screw fixation of the C1 posterior arch is straightforward and imposes little risk of injury to the neural and vascular structures as long as the implants remain intraosseous. According to the results of our anatomical and biomechanical study, C1 posterior arch crossing screw fixation may constitute an alternative method for posterior atlantoaxial fixation., Level of Evidence: 3.

Study Design: Case report of a patient with atlantoaxial subluxation who underwent posterior cervical fixation., Objective: To describe a novel approach for the efficient use of a full-scale, 3-dimensional model for preoperative planning and surgery., Summary of Background Data: Instrumented fusion of the cervical spine with screws and rods is indicated for atlantoaxial subluxation. Fatal complications, such as vertebral artery and spinal cord injuries, may occur during screw insertion. Making appropriate connecting rods, after screw insertion, is often time consuming. Therefore, precise preoperative planning and careful intraoperative procedures are required., Methods: A 73-year-old male with atlantoaxial subluxation presented with progressive quadriplegia and gait disturbance. Surgery involving a C1 laminectomy and posterior cervical fixation was planned; and a 3D model, allowing visualization of the vertebral artery, was developed. Bilateral C1 and C4 lateral mass screws and C2 pars screws were experimentally inserted into the model. Rods with appropriate curvature were created to obtain rigid screw fixation, and were used during the surgery. Moreover, radiography and computed tomographic images of the instrumented model were analyzed to ensure the proper orientation of the screws., Results: During surgery, screw insertion was performed, under fluoroscopic guidance, and compared with the 3D model and its preoperative radiographs. According to the preoperative analysis of the model-computed tomographic images, the direction of the C1 lateral mass screws was changed laterally, and the lengths of the C2 pars screws were shortened to avoid complications. The sterile, prebent rods could be elegantly adapted to the screws without additional bending. The postoperative course was uneventful, and postoperative computed tomographic images showed proper screw positioning., Conclusion: Three-dimensional models that allow (1) visualization of the vertebral artery, (2) evaluation of radiological images after screw insertion, and (3) the use of prebent rods during surgery contribute to the safety of the cervical posterior fixation., Level of Evidence: N/A.

Study Design: Retrospective study of 904 patients with a diagnosis of atlantoaxial dislocation (AAD), using a novel surgical classification and treatment strategy., Objective: To describe a novel surgical classification and treatment strategy for AADs., Summary of Background Data: AADs can result from a variety of etiologies, yet no comprehensive classification has been accepted that guides treatment. Because of the rarity of the cases, however, the treatment strategy has also been debated., Methods: During a period of 12 years, a total of 904 patients with a diagnosis of AAD were recruited from a single academic institution. According to the treatment algorithm that included preoperative evaluation using dynamic radiograph, reconstructive computed tomography, and skeletal traction test, the cases were classified into 4 types: I to IV. Types I and II were fused in the reduced position from a posterior approach. Type III, which were irreducible dislocations, were converted to reducible dislocations using a transoral atlantoaxial release, followed by a posterior fusion. Type IV presented with bony dislocations and required transoral osseous decompressions prior to posterior fusion., Results: Four hundred seventy-two cases were classified as type I, 160 as type II, 268 as type III, and 4 cases as type IV. Follow-up was in the range of 2 to 12 years (average: 60.5 mo). Eight hundred and ninety-nine cases (99.4%) achieved a solid atlantoaxial fusion. Anatomic atlantoaxial reduction was achieved in 892 cases (98.7%), whereas 12 cases had a partial reduction. Neurological improvement was seen in 84.1% (512/609) of the patients with myelopathy. The overall complication rate was 9.1% (82/949)., Conclusion: Our surgical classification and treatment strategy for AADs was applied in those 904 cases and associated with excellent clinical results with a minimal risk of complications., Level of Evidence: 4.

Study Design: A cross-sectional study., Objective: The purpose of this study was to investigate the effect of reduction of anterior atlantoaxial subluxation (AAS) on the oropharyngeal airway space., Summary of Background Data: Our previous studies have shown that reduction of the occipito-C2 angle (O-C2A) makes the mandible shift posteriorly, resulting in oropharyngeal airway stenosis, which occasionally causes postoperative dysphagia after occipitocervical fusion. Based on this background, we hypothesized that reduction of AAS would also cause oropharyngeal airway stenosis independent of the O-C2A, because it also shifts the mandible posteriorly. To our knowledge, there are no data demonstrating an association between reduction of AAS and the oropharyngeal airway space., Methods: The authors prospectively evaluated 64 patients with rheumatoid arthritis. We analyzed lateral cervical plain radiographs of 5 different positions (neutral, flexion, extension, retraction, and protrusion), and measured the O-C2A, C2-C6 angle, anterior atlantodental interval, anteroposterior distance of the narrowest oropharyngeal airway space (nPAS), and so on. The subjects were classified into 2 groups: group R comprised patients with a "reducible AAS" in dynamic cervical movement, and group N comprised "patients without AAS" patients., Results: In the multiple regression analysis, the change in the O-C2A was the only significant independent variable related to the percentage change in the nPAS from the neutral position in group N. On the contrary, the change in the anterior atlantodental interval and change in the O-C2A were significantly related to the percentage change in the nPAS in group R. No cases in group N and 7 cases (28%) in group R showed a paradoxical decrease in the nPAS in extension, in which the O-C2A is largest and reduction of AAS is obtained., Conclusion: Reduction of AAS has a negative effect on the oropharyngeal airway space. Therefore, reduction of AAS during occipitocervical fusion may cause postoperative dysphagia despite maintenance of the O-C2A.

Study Design: Prospective case series and radiographical analysis., Objective: This study aimed to characterize the changes in subaxial alignment after surgical correction of occipitoaxial kyphosis, establish normal parameters, and report on clinical outcomes in a population of patients with chronic atlantoaxial dislocation patients presenting with swan neck deformities., Summary of Background Data: Swan neck deformity of the cervical spine is a term used to describe the simultaneous development of both abnormal kyphosis and hyperlordosis malalignments. Currently, there are no published series that discuss their outcomes after treatment and, more specifically, the subsequent changes that occur in the subaxial spine after the correction of the primary deformity in cases of chronic hyperkyphosis at the occipitoaxial segment., Methods: This was a prospective clinical and radiographical study in a population of patients with chronic atlantoaxial dislocation presenting with swan neck deformities. C0-C2 and C2-C7 angles were measured using plain radiographs pre- and postsurgery. The relationship between the alignment of the occipitoaxial joint and the subaxial cervical spine was evaluated. Japanese Orthopaedic Society scores were used to assess functional outcomes., Results: C0-C2 improved from a mean of -14.4° (SD, 9.5°) preoperatively to a mean of 7.8° (SD, 1.0°) postoperatively (P = 0.02). C2-C7 changed from a mean of 43° (SD, 2.8°) to a mean of 18.6° (SD, 11.2°) postoperatively (P = 0.02). A significant correlation was detected between the changes that occurred in the upper and lower cervical alignments (R = 0.133; P < 0.01). Clinically, the Japanese Orthopaedic Society preoperative scores improved significantly to postoperative (P < 0.01)., Conclusion: This study reports the novel auto-correction of subaxial abnormalities after treatment of the primary upper cervical deformity and delineates the relationship between these 2 occurrences, thus demonstrating the reversibility of such complex abnormalities. Furthermore, the clinical outcomes after surgical treatment of swan neck deformities secondary to atlantoaxial dislocation are favorable and associated with a low complication rate.

Study Design: This is a clinical case report with a review of relevant literature., Objective: To describe a case of Larsen syndrome with C3-C4 spondyloptosis and atlantoaxial dislocation in a middle-aged female patient and to discuss management strategies., Summary of Background Data: Spondyloptosis of the cervical spine is relatively rare and is caused by trauma, destruction of the vertebral bodies by tumors, or tuberculosis. Such gross vertebral displacement is usually associated with significant neurological deficits. Larsen syndrome is characterized by multiple joint displacements and can, very rarely, be associated with nontraumatic spondyloptosis of the cervical vertebra. A single case report of C1-C2 joint laxity causing atlantoaxial dislocation in a patient with Larsen syndrome is available in literature. No reports of any patient (with Larsen syndrome or nonsyndromic) who had both cervical spondyloptosis and atlantoaxial dislocation are available in literature., Methods: A 36-year-old female presented with chronic neck pain, bilateral hand deformity, and mild spasticity involving all 4 limbs. Cervical radiograph, computed tomographic scan, and magnetic resonance image revealed C3-C4 spondyloptosis and atlantoaxial dislocation., Results: A combined ventral decompression of subaxial spine and instrumentation from C2 to C5, followed by posterior C1-C2 distraction arthroplasty and lateral mass stabilization of the subaxial spine up to C6, was done. The cervical deformity was corrected, and the patient remains symptom free., Conclusion: Patients with spondyloptosis of the cervical spine can rarely present with chronic neck pain and minimal neurological deficits. An additional pathology, such as atlantoaxial dislocation, can add to the complexity. Circumferential stabilization and fusion would be required in such cases to achieve a good outcome. Larsen syndrome is a rare cause of nontraumatic cervical displacements.

Study Design: Consecutive case series and literature review., Objective: To describe the utility of 3-dimensional computed tomographic angiography (3D CTA) for evaluating vertebral artery (VA) anomalies before surgery., Summary of Background Data: Recent advances in instrumentation surgery at the craniovertebral junction (CVJ) enable us to perform rigid internal fixation. However, the risk of VA injury as a complication of the surgery has become a major problem. Thus, the importance of preoperative evaluation of the VA course has been emphasized., Methods: Cases of 100 consecutive patients who underwent CVJ instrumentation surgery since July 1998 were analyzed. Occipitocervical/thoracic or C1-C2 posterior fusion was performed for atlantoaxial subluxation (AAS) in 59 patients and cervical fixation including C2 was required for middle-to-lower cervical lesions in 41 patients. Twenty-seven patients with AAS had a congenital skeletal anomaly (CSA) at the CVJ including os odontoideum and occipitalization of C1 (AAS-CSA[+] group). Anomalous VAs at the extra- and intraosseous regions were evaluated by 3D CTA., Results: No neurovascular injury occurred during surgery. Abnormal courses of the VA at the extraosseous region were detected in 10 cases: 2 had fenestration and 8 had a persistent first intersegmental artery. All 10 cases were in the AAS-CSA(+) group. A high-riding VA was detected in 31 cases. Fourteen out of the 31 cases were in the AAS-CSA(+) group, indicating 51.9% of the AAS-CSA(+) group had high-riding VA. In the AAS-CSA(+) group, a C1-C2 transarticular screw and C2 pedicle screw were actually inserted in 58% and 31% of the planned insertions, respectively., Conclusion: The present findings suggest that the frequency of an abnormal VA at the extra- and intraosseous regions is increased when patients have AAS and CSA at the CVJ. Using preoperative 3D CTA, we can precisely identify anomalous VAs and thereby reduce the risk of their intraoperative injury.

Study Design: Retrospective case series of chronic atlantoaxial rotatory fixation (AARF) treated by a novel closed reduction method (remodeling therapy) and review of the literature., Objective: To describe clinical features of chronic AARF and the rationale of the remodeling therapy., Summary of Background Data: Treatment strategy for chronic recurrent AARF remains controversial. Posterior C1-C2 arthrodesis has been widely used for recurrent unstable AARFs after the closed reduction, and a variety of posterior fusion techniques have been advocated. In contrast, several investigators reported a chronic AARF case treated by a simple traction or closed reduction followed by cervical immobilization. Previously, we have found that a deformity of the superior C2 facet joint (C2 facet deformity) on three dimensional computed tomography (3D CT) reconstructions is a risk factor for recurrent subluxation. In addition, the remodeling of this C2 facet deformity by careful closed manipulation followed by halo fixation (remodeling therapy) could prevent the recurrence of subluxation., Methods: Twelve children with chronic AARF who sustained torticollis for an average of 4.4 months after the onset were referred to our clinic. The mean age at the initial visit was 7.8 years. All patients underwent the remodeling therapy as reported previously. Radiographic findings and clinical courses were retrospectively reviewed. Treatment methodology, pearls, and pitfalls of the remodeling therapy were discussed with review of the literature., Results: 3D CT images before reduction revealed persistent atlantoaxial subluxation and the C2 facet deformity in the dislocated side in all cases. Follow-up 3D CT scans demonstrated the remodeling of the C2 facet deformity at an average of 2.4 months after successful reduction of subluxation. Neither recurrence of symptoms nor subluxation was observed at a mean follow-up of 42 months in any case. The cervical range of motion was 73.9° at the dislocated and 83.5° at the contra-dislocated side from the midline., Conclusion: Chronic irreducible and recurrent unstable AARF should be initially managed by remodeling therapy using the facet deformity sign as a clinical index, if the C1 and C2 have not been osseously fused.

Study Design: Observational and quantitative study with 3-dimensional (3D) computerized tomographic (CT) analysis., Objective: To establish the 3D configuration and morphometric data of obliquity of the lateral atlantoaxial articulations (LAA) in congenital anomaly with occipitalization., Summary of Background Data: Plane radiographs and normal CT scans cannot clearly demonstrate the configuration of LAA as the hindrance of circumambient bony structures. The morphology of anomalous LAA with occipitalization is underreported., Methods: A series of 63 cases with occipitalization and 20 control subjects underwent thin-slice CT scanning. The 3D configuration of LAA were analyzed and categorized based on the degree of olisthy and inclination orientation of the atlantoaxial articular facets (AAF). The obliquity of the AAF was measured in reconstructed sagittal and coronal planes, respectively., Results: Four types of configuration of LAA with occipitalization were found: type I, characterized by slight anteversion of LAA without olisthy of the inferior and superior facets (16% of 126 sides); type II, characterized by partial olisthy of the 2 facets and evident anteversion of LAA (48%); type III, defined by the separation or complete olisthy of the 2 facets (13%); and type IV, wherein the articular facets sloped dorsally (23%). Forty-eight of 49 cases in the former 3 types wherein AAF sloped ventrally had atlantoaxial dislocation (AAD). All type IV cases wherein AAF sloped dorsally had no AAD. In control subjects, LAA had no evident obliquity of anteversion or retroversion., Conclusion: Instability at the C1-C2 junction in congenital anomaly with occipitalization is likely a direct result of the anteversion of LAA and bony malformation of this region, and it aggratates with the increasing obliquity of anteversion of the AAF. Demonstrating 3D morphological changes of LAA may provide a new means to diagnosis instability in congenital anomaly at craniovertebral junction and a basis for rational surgical treatment.

Study Design: Retrospective case series study of surgical outcome for 21 atlantoaxial subluxation patients treated with a new technique, called cable-dragged reduction/cantilever beam internal fixation. Surgery was performed by a single surgeon., Objective: To describe and evaluate the cable-dragged reduction/cantilever beam internal fixation technique for the treatment for old atlantoaxial subluxation irreducible by traction., Summary of Background Data: Management of old atlantoaxial subluxation has always been a difficult task. A more effective way to achieve surgical reduction is needed., Materials and Methods: Twenty one patients, aged 31.6 ± 13.3 years (range, 11-67 years), 17 men and four women, with atlantoaxial subluxation that failed to be reduced after 10 to 111 days in traction, underwent posterior cable-dragged reduction/cantilever beam internal fixation surgery. Frankel classification of neural function before surgery was the following: Frankel B, four patients; Frankel C, five patients; Frankel D, four patients; and Frankel E, eight patients. Plain radiographs, computed tomographic three-dimensional reconstructive images and magnetic resonance images of the cervical spine were obtained at 3, 6, and 12 months after surgery, and each year thereafter. No patient was lost to follow-up, and the follow-up time ranged from 6 months to 4 years. Rate of reduction and C1∼3 fusion, as well as improvement of neural function, were recorded and analyzed., Results: The average follow-up period was 13.2 months. Radiographic evaluation of the group at follow-up showed 16 complete and five partial reductions, and satisfactory decompression and C1∼3 fusion in all cases. Neural function at the end of the follow-up was Frankel B still in one patient, Frankel C in seven patients, and Frankel E in 13 patients., Conclusion: Cable-dragged reduction/cantilever beam internal fixation is almost as effective for reduction as anterior release but is less invasive and risky. It has similar operative time and blood loss to occipitocervical fusion but avoids arthrodesis of occipitoatlantal joint. It is also suitable for patients with severe myelopathy before surgery. Its major disadvantage is that C3, which is left free in the traditional atlantoaxial fusion surgery, has to be involved in fusion. And it is suitable only for patients with intact posterior arches in C1.

Study Design: Retrospective cohort study., Objective: To determine the influence of age, comorbidities, and treatment type on mortality in elderly patients with acute Type II odontoid fractures., Summary of Background Data: Prior studies have documented increased morbidity and mortality among geriatric patients sustaining odontoid fractures. However, there is limited data regarding the effect of patient age, medical comorbidities, and treatment selection on mortality after Type II odontoid (C2) fractures in the elderly., Methods: An institutional registry was used to identify all Type II odontoid fractures sustained by patients aged 65 and older from 1991 to 2006. Demographic information, date of injury, associated injuries, treatment type, and comorbidities were abstracted from medical records. Mortality was ascertained using the National Death Index. Risks of mortality and their associated 95% confidence intervals (CIs) were calculated at 3 months, 1 year, 2 years, and 3 years. Multivariable Cox proportional hazard regression was used to evaluate independent factors affecting mortality stratified by age (65-74 years, 75-84 years, ≥ 85 years) and treatment type (operative or nonoperative treatment, and halo or collar immobilization)., Results: Of 156 patients identified with Type II odontoid fracture, the average age was 82 years (SD = 7.8; Range: 65-101). One hundred and twelve patients (72%) were treated nonoperatively. At 3 years postinjury, there was a 39% (95% CI: 32-47) mortality rate for the entire cohort. Mortality for the operative group was 11% (95% CI: 2-21) at 3 months and 21% (95% CI: 9-32) at 1 year compared with 25% (95% CI: 17-33) at 3 months and 36% (95% CI: 27-45) at 1 year in the nonoperative group. The Cox regression model showed that the protective effect of surgery was seen in patients aged 65 to 74 years, in whom the hazard ratio associated with surgery for mortality after odontoid fracture was 0.4 (95% CI: 0.1-1.5). Those aged 75 to 84 years had a hazard ratio of 0.8 (95% CI: 0.3-2.3), and patients 85 years or older had a hazard ratio of 1.9 (95% CI: 0.6-6.1; P value for interaction between age and treatment = 0.09) with operative treatment having a protective effect in patients aged 65 to 74 years., Conclusion: In a cohort of elderly patients, Type II odontoid fractures were associated with a high rate of mortality, regardless of intervention.

Study Design: Radiographic analysis using normal patients., Objective: To analyze the relationship between the cervical alignment and the oropharyngeal space., Summary of Background Data: Few clinical studies stress the effect of the occipito-C2 (O-C2) alignment on the oropharyngeal space. A previous study showed dysphagia and/or dyspnea after occipitocervical fusion was caused by oropharyngeal stenosis resulting from O-C2 fixation in a flexed position. Other independent researchers showed that development or improvement of obstructive sleep apnea in rheumatoid arthritis patients was related to the O-C2 alignment. However, there are limited basic data demonstrating the relationship between the O-C2 alignment and the oropharyngeal space., Methods: Plain lateral cervical radiographs in five tested positions--neutral, flexion, extension, protrusion, and retraction--of 40 asymptomatic volunteers were collected. The O-C2 angle, the C2-C6 angle, and the anterior-posterior distance of the narrowest oropharyngeal airway space (nPAS) were measured, and the changes in value from the neutral to the other four positions were calculated for each patient., Results: According to the multiple regression analysis, there was an extremely strong linear correlation of the change in the O-C2 angle with the percentage change in the nPAS. Referring to the multiple regression analysis, a decrease of 10° in the O-C2 angle caused a 37% reduction in the nPAS in the neutral position. In contrast, no significant correlation was found between the change in the C2-C6 angle and the percentage change in the nPAS., Conclusion: Our results show the impact of the O-C2 angle on the oropharyngeal space. This knowledge will be useful for the diagnosis and treatment of the upper cervical lesion combined with the upper airway stenosis, and for the determination of the optimal fixation angle in occipitocervical fusion.

Study Design: A retrospective case series., Objective: To propose a novel treatment strategy for chronic atlantoaxial rotatory fixation (AARF)., Summary of Background Data: Treatment strategy for chronic or recurrent AARF remains controversial. We have previously reported that a deformity of the superior facet of the axis (C2 facet deformity), which is frequently observed in patients with chronic AARFs, is a risk factor for recurrent dislocation. In this article, we report seven consecutive cases of chronic AARF who underwent closed manipulation followed by external halo fixation and maintained good reduction with the remodeling of the C2 facet deformity., Methods: Seven girls with a chronic AARF who sustained torticollis for an average of 4.6 months after the onset were referred to our clinic. Closed manipulation by careful manipulation under general anesthesia followed by external immobilization with a halo vest was performed in all cases. Radiographic findings and clinical courses were retrospectively reviewed with approvals by the institutional review board., Results: Three-dimensional computed tomography images before reduction revealed persistent atlantoaxial subluxation and the C2 facet deformity in the dislocated side in all cases. Follow-up three-dimensional computed tomographic scans demonstrated the remodeling of the C2 facet deformity at an average of 2.8 months after successful reduction of subluxation. Subsequently, the halo vests were removed and gentle neck range of motion exercise was started in all cases. The normal cervical range of motion was obtained 2 weeks after the removal of halo vests in five cases, whereas the range of motion remained limited in two cases. At a mean follow-up of 17.4 months, neither symptoms nor recurrence of subluxation occurred in all cases., Conclusion: Chronic irreducible and recurrent unstable AARF can be managed successfully by careful closed manipulation followed by halo fixation, if the C1 and C2 have not been osseously fused. The remodeling of the C2 facet deformity detected on follow-up CT scans can be a useful radiographic parameter to determine the appropriate period of halo fixation in this new treatment strategy obviating the need for surgical intervention.

Study Design: Retrospective radiographic study of the technique for C1 lateral mass screw (C1LMS) and C2 pedicle screw (C2PS) fixation., Objective: To evaluate (1) the accuracy of the C1LMS and C2PS placement; (2) the fusion rate between C1 and C2; (3) the risk for vertebral artery (VA) injury., Summary of Background Data: C1LMS and C2PS fixation is widely used when treating atlantoaxial instability. Several authors have reported their experience focusing on the technical outcomes, with many reporting fusion rates near 100%. However, most of them are relatively small series, and many have applied only plain postoperative radiographs instead of computed tomography (CT). Thus, we feel that the accuracy of C1LMS and C2PS placement has not been fully analyzed, as well as the anatomic relationship between the VA and the screws., Methods: Between December 2000 and September 2008, the fusion status and accuracy of the screws were evaluated on the postoperative reconstructive CT of 319 patients with atlantoaxial instability. Cases with malpositioned screws underwent CT angiography or magnetic resonance angiography after surgery, to evaluate potential VA injury., Results: C1LMS of 95.5% and C2PS of 92.8% were found to be in a "good" position. After 2007, six cases had malpositioned screws, which were all in the "out" or "down" area of the C2 pedicle. Five cases underwent CT angiography and 1 had magnetic resonance angiography to evaluate potential VA injury. No occlusion, associated aneurysm or fistula of the VA was found. All cases (100%) achieved solid fusion between C1 and C2., Conclusion: C1LMS of 95.5% and C2PS of 92.8% were confirmed to be in good position. None of the screws including the malpositioned caused VA injury, clinically or radiographically. The technique for C1LMS and C2PS fixation appears to be safe and effective.

Study Design: An atlantoaxial fixation using bilateral C1-C2 transarticular screws and C1 laminar hooks was used in 5 pediatric patients, who were then followed up for 12 to 17 months to evaluate the technique., Objective: To describe a modified posterior C1-C2 fixation technique and preliminary clinical and radiographic results in 5 pediatric patients., Summary of Background Data: Conventional posterior atlantoaxial fixations, such as Gallie and Brooks techniques, are frequently associated with high rates of pseudarthrosis and implant failure. The C1-C2 transarticular screw fixation has been shown to be effective in treatment of pediatric atlantoaxial instability, as well as adult atlantoaxial instability; however, this 2-point fixation merely stabilizes the atlantoaxial motion segment laterally. A 3-point fixation, composed with bilateral C1-C2 transarticular screws and C1 laminar hooks, has been developed., Methods: Five patients with atlantoaxial instability, including 4 males and 1 female, aged 6 to 17 (average 10) years, underwent atlantoaxial fixation using bilateral C1-C2 transarticular screws and C1 laminar hooks during a 2-year period. The surgical technique and treatment procedures were intensively reviewed, and clinical symptoms and imaging appearance were retrospectively evaluated., Results: Clinical follow-ups were obtained for an average of 14.4 (range: 12-17) months. The clinical and radiologic follow-up indicated a stable arthrodesis and offered clinical relief from symptoms for all patients. No neural or vascular impairment related to this technique was observed., Conclusion: Fixation of the atlantoaxial articulation using bilateral C1-C2 transarticular screws and C1 laminar hooks appears to be a reliable technique for treatment of pediatric atlantoaxial instability.

Study Design: A case-series study., Objectives: To measure the 3-dimensional (3D) morphology and kinematics of the craniovertebral junction (CVJ) using a 3D computed tomography (CT) model; to reveal abnormal patterns and the relationships between pathology and kinematics., Summary of Background Data: Evaluations using radiography, 2-dimensional (2D) CT and magnetic resonance imaging have limitations because of the complex 3D structure of the CVJ., Methods: Twenty-four rheumatoid arthritis patients (21 females, 3 males) with cervical involvement underwent CT scanning of the cervical spine from the basilar process of the occipital bone to the first thoracic vertebra in neutral and flexed positions. The 3D morphology of the occipital condyle, atlas, and axis were classified based on the type of deformity observed. Periodontoid lesions (continuous bony lesions between the atlas and the odontoid process) were also noted. The 3D kinematics in the atlanto-occipital and atlantoaxial joints were evaluated using the volume merge method., Results: Deformities in the atlanto-occipital joints appeared more frequently than those in the atlantoaxial joints. The most common instability pattern was flexural rotation during flexion at the CVJ. The direction of translational motions during flexion was posterior in the atlanto-occipital joint and anterior and caudal in the atlantoaxial joint., Conclusion: The results suggest that bilateral occipital condyle deformation, unilateral and bilateral mass collapse, and periodontoid lesions may affect flexion/extension rotational instability in the atlantoaxial joint. In addition, unilateral occipital condyle deformation and atlantoaxial joint stability may affect sagittal translational instability to the posterior side in the atlanto-occipital joint. The noninvasive 3D CT imaging technique employed here would be useful for predicting the prognosis of patients with rheumatoid deformities at the CVJ.

Study Design: Applying rotating rod techniques to reduce irreducible atlantoaxial dislocation., Objective: To spare the occipital-C1 motion by the strategy in reduction of before surgery irreducible atlantoaxial dislocation with obvious neurologic symptoms and congenital odontoid aplasia., Summary of Background Data: The treatment of atlantoaxial dislocation (AAD) is a challenging problem for most surgeons. Posterior surgical stabilization of C1 and C2 include C1-C2 transarticular screws, or C1 lateral with C2 pars screws. These constructs, however, are based on preoperative reductions. When preoperative skull reduction fails and myelopathic symptoms coexist, long-segment cervico-occipital fusion and decompression are usually the only practical choice., Methods: The authors explored a different surgical technique to spare the axial occipital joints by rotating rods in polyaxial C1, C3 lateral mass, and C2 pars screws, functioning as a lever analogue. Three before surgery irreducible AAD cases with obvious neurologic symptoms and congenital odontoid aplasia were successfully reduced and fused with this procedure. The authors used intraoperative somatosensory-evoked potential monitoring and intraoperative fluoroscopy. Preoperative skull traction was employed to distract and help extend the atlantoaxial complexes., Results: Three C1-C2 dislocations were reduced completely without any deterioration of neurologic signs. Cervical myelopathic symptoms recovered soon after the operation. No atlantoaxial subluxation recurred. They returned to their normal work and/or activities., Conclusion: The rotating rod strategy is a viable option to reduce and fuse C1-C3 for AAD with odontoid aplasia. It spares the occipital-C1 motion.

Study Design: Retrospective radiographic/imaging study., Objective: To evaluate preoperative and sequential postoperative radiographs following C1-C2 arthrodesis for atlantoaxial subluxation in patients with rheumatoid arthritis (RA) to determine risk factors for the development of subaxial subluxations (SAS)., Summary of Background Data: The development of SAS has often been observed after C1-C2 arthrodesis. However, there have been no previous reports on the correlation between radiographic parameters and the incidence of postoperative SAS., Methods: The study group comprised of 58 patients with RA who underwent C1-C2 arthrodesis due to atlantoaxial subluxation. There were 5 men and 53 women with a mean age of 55.8 years. The mean follow-up period was 137 months. Nineteen patients with a postoperative SAS after C1-C2 arthrodesis were classified as the SAS+ group. Other 39 patients without a postoperative SAS were included in the SAS- group. Clinical outcomes and plain radiographs were reviewed retrospectively and compared between the 2 groups., Results: The difference between pre- and postoperative atlantoaxial (AA) angles in the SAS+ group was significantly greater than those in the SAS- group (P = 0.039). The C2-C7 angles changed significantly between pre- and postoperative periods in the SAS+ group (P = 0.039), but not in the SAS- group (P = 0.897). It was suggested that a large AA angle and a small C2-C7 angle observed at the early postoperative period were the risk factors for the development of SAS. We also demonstrated that a high incidence of the C3-C4 SAS resulted from excessive bone fusion at the C2-C3., Conclusion: Excessive correction of AA angle is likely to cause loss of cervical lordosis, resulting in the development of postoperative SAS. In addition, extensive bony union at C2-C3 following C1-C2 arthrodesis frequently leads to the development of extensive SAS at the C3-C4.

Study Design: A biomechanical testing protocol was used to evaluate atlantoaxial fixation techniques in a human cadaveric model., Objective: To compare in vitro biomechanics of atlantoaxial lateral mass fusion cage combined with C1-C2 pedicle screw technique with those of C1-C2 pedicle screw technique alone and C1-C2 transarticular screws combined with Gallie wires., Summary of Background Data: An atlantoaxial lateral mass fusion cage was designed, knowing that the cage, when rigidly combined with C1-C2 pedicle screws, could offer other fusion spots for atlantoaxial stabilization in cases when the posterior arch of the atlas is absent or removed for decompression and a Gallie fixation is impossible. No comparative in vitro biomechanical test has been conducted previously to evaluate the feasibility of this method., Methods: Anatomic measurements of the atlantoaxial lateral masses were taken using computed tomography in normal human subjects. Six fresh-frozen human cadaveric cervical spines (C0-C4) were used in the biomechanical study. Specimens were tested in their intact condition, after destabilization via transverse-alar-apical ligament disruption, and after implantation of 3 fixation constructs: (1) transarticular screws combined with Gallie wires, (2) C1-C2 pedicle screws, and (3) atlantoaxial lateral mass fusion cage combined with C1-C2 pedicle screws. Pure moment loading up to 1.5 Nm in flexion/extension, right-left lateral bending, and right-left axial rotation was applied to the occiput, and relative intervertebral rotations were determined using stereophotogrammetry. Range of motion for the intact, destabilized, and 3 fixation scenarios were determined., Results: The anatomic data indicated that feasible cage design were in 3 sizes: 11/8, 12/9, and 13/10 mm for length/width, and 3.5, 4, and 4.5 mm for height. The biomechanical data indicated that transverse-alar-apical ligament disruption significantly increased C1-C2 motion for all directions. All the 3 fixation techniques significantly reduced motion compared with the intact and destabilized cases. There were no statistically significant differences among the 3 fixation techniques., Conclusion: The biomechanical study indicated that, contrary to expectation, addition of a cage did not increase the stability compared with C1-C2 pedicle screw alone. However, the C1 + C2 + Cage technique may be a viable alternative for atlantoaxial stabilization when the posterior arch of the atlas is absent or removed for decompression and a Gallie fixation is impossible.

Study Design: Case report and literature review., Objective: To discuss the diagnosis, limitations, and treatment of combined occipital-cervical and atlantoaxial disassociation with normal neurologic function., Summary of Background Data: Injuries to the craniocervical junction can lead to devastating neurologic deficits. Occipital-cervical disassociation is a well-documented injury pattern that can lead to pain, spinal cord injury, and death. Early diagnosis and treatment can preserve neurologic function. Combined injuries to both the occipital-cervical and atlantoaxial segments are less common and, to date, have only been described with severe neurologic injury., Methods: Retrospective review of a case. Literature review was performed through Medline and Pubmed searches., Results: This is the first case to present a combined occipital-cervical and atlantoaxial disassociation with a neurologically intact patient. Initial physical examination was limited, but early imaging revealed evidence of instability. Early diagnosis and early (< 24) surgical stabilization was performed with no complications and neurologic preservation. One-year follow-up visit revealed normal neurologic examination with neck pain VAS = 2/10 and neck disability index = 6., Conclusion: Combined injuries to the occipital-cervical and atlantoaxial can result in upper cervical instability. Despite previous reports, neurologic preservation remains a possibility in this injury pattern. Limitations in physical examination and radiographic imaging persist, but early diagnosis and surgical stabilization may improve neurologic outcomes.

Study Design: A prospective study., Objective: To evaluate a novel technique involving an endoscopically assisted anterior release and reduction through an anterolateral retropharyngeal approach with minimum follow-up interval of 31 months., Summary of Background Data: Irreducible atlantoaxial dislocation is typically a chronic process that requires surgical treatment. However, the current literature does not agree on the single best method of treatment. Previously, the best outcomes have been reported with transoral reduction followed by anterior or posterior fixation. Despite recent innovations, numerous complications remain associated with this approach., Methods: About 21 consecutive irreducible atlantoaxial dislocation patients with mean age of 32 years underwent endoscopically assisted anterior release and reduction through the anterolateral retropharyngeal approach followed by posterior fixation. The primary pathologies included 8 late odontoid fractures, 7 cases of os odontoideum, 5 with laxity of the transverse ligament, and 1 with atlanto-occipital assimilation with a hypoplastic odontoid. Neurologic status was evaluated using the Japanese Orthopedic Association scoring system. Radiographic parameters including the atlantodental interval (ADI) and cervicomedullary angle were also measured. Follow-up data were obtained for a minimum of 31 months., Results: Anatomic reduction was achieved in 20 cases and near-anatomic reduction in 1 case. All patients had an uneventful recovery with significant improvement in neurologic function and radiographic parameters. No complications were seen. The atlantodental interval was corrected from an average 6.3 mm before surgery to 2.7 mm after surgery (P < 0.01). The cervicomedullary angle was also corrected from an average 109 degrees before surgery to 152 degrees after surgery (P < 0.01). Preoperative muscle strength was on average 3.5 (on scale from 1 to 5) and improved after surgery to 4.5 (P < 0.01). The average preoperative and postoperative Japanese Orthopedic Association scores were 9.6 and 15.5, respectively, indicating 82.8% improvement., Conclusion: Endoscopically assisted anterior retropharyngeal release combined with posterior fixation is a safe and effective alternative for the treatment of irreducible atlantoaxial dislocation.